GIFSQ — Global Institute for Food Safety & Quality Principle The volatile reducing substances of a vinegar are distilled over and then characterized by four titrimetric values, which are useful in differentiating the types of vinegar. The oxidation value measures the permanganate consumed; the alkaline oxidation value the oxygen required under alkaline conditions; the iodine […]

GIFSQ — Global Institute for Food Safety & Quality Principle The albuminoid ammonia value — the ammonia liberated by alkaline permanganate oxidation of the organic nitrogen — is high in malt vinegars and negligible in artificial products, so it distinguishes the two. Free ammonia is first distilled off and rejected; the alkaline permanganate distillate is […]

GIFSQ — Global Institute for Food Safety & Quality Principle Brewed vinegars give a definite formol value but artificial products do not. It is useful as a preliminary quick test but is not a specific test to differentiate between brewed and synthetic vinegars. Distilled vinegars do not give any formol value. Apparatus required Stoppered conical […]

GIFSQ — Global Institute for Food Safety & Quality Principle Free mineral acid in vinegar changes the colour of methyl violet indicator to blue or green, which reveals its presence. Reagents a. Methyl violet solution: mix 1 part of methyl violet 2B in 10,000 parts of water. b. Water. Procedure To 5 ml of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Caramel in vinegar is first tested by Fiehe’s reaction — the furfural associated with caramel gives a rose colour with resorcinol in hydrochloric acid. Because any liquor containing furfural gives the reaction, it is not conclusive; a sample suspected of containing furfural is confirmed by […]

GIFSQ — Global Institute for Food Safety & Quality Principle Cider vinegar is distinguished by its malic acid content. A quick lead acetate test shows whether the sample is a cider vinegar at all; the malic acid is then separated as calcium malate, the precipitate is ignited, and its ash is boiled with a measured […]

GIFSQ — Global Institute for Food Safety & Quality Principle The vinegar is evaporated and the residue ashed to bring the phosphorus into a form that can be extracted with hydrochloric acid. The phosphorus in an aliquot of the extract is determined by the phosphorus method, and the result is expressed as phosphoric acid using […]

GIFSQ — Global Institute for Food Safety & Quality Principle The vinegar is concentrated to a syrupy consistency to remove the water and volatile acids, and its nitrogen is then determined by the Kjeldahl method. Brewed vinegars contain appreciable nitrogen from the fermentation, while artificial vinegars contain almost none. Procedure Concentrate 50 to 100 ml […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ash content and the alkalinity of the ash reveal whether a vinegar is brewed or artificial: brewed vinegars leave a substantial alkaline ash, while artificial vinegars leave almost none. The total ash is found by ignition; the alkalinity number of the ash is the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total solids are found gravimetrically: a measured volume of vinegar is evaporated to dryness, the residual acid is removed by repeated evaporation with water, and the residue is dried for 2.5 hr at 100° C. Apparatus required Tared silica dish, 5 cm in diameter […]

GIFSQ — Global Institute for Food Safety & Quality Principle The acids in vinegar are determined by titration with standard sodium hydroxide. The total acidity is titrated directly; the fixed acidity is titrated after the volatile acids have been removed by repeated evaporation with water; and the volatile acidity is the difference between the two, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oil is separated from the dried pickle sample by solvent extraction. In the routine procedure the sample is dried and the oil extracted in a Soxhlet apparatus with petroleum ether; the more accurate procedure extracts with a chloroform–methanol mixture, and the oil so obtained […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total acidity of the pickle or chutney is found by titration of a weighed portion of the composite sample. A second portion is evaporated with water to drive off the volatile acids; the acidity remaining is the fixed acidity, and the difference between total […]

GIFSQ — Global Institute for Food Safety & Quality Principle A representative composite sample is prepared from the pickle container so that all determinations (salt, acidity, oil, solids) are carried out on the same homogeneous material. Sampling and container examination follow the procedure for canned foods, and the product is blended before weighing portions. Apparatus […]

GIFSQ — Global Institute for Food Safety & Quality Principle There is no standard method for measuring rehydration, so the technique of each test must be carefully standardised if comparable data are to be obtained. In the procedure below — the one suggested by the US Department of Agriculture — a weighed portion of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle A representative 50 g portion of the dehydrated material is rehydrated and its surface blemishes are counted visually. The count is doubled to report the number of blemishes per 100 g of sample. Apparatus required No special apparatus is named in the source method. Procedure […]

GIFSQ — Global Institute for Food Safety & Quality Principle If peroxidase has survived dehydration, it oxidises guaiacol in the presence of hydrogen peroxide, and the reconstituted tissue develops a reddish-brown colour. The colour observed after 5 and 10 min shows whether the enzyme is active. For dehydrated beetroot the same reaction is shown with […]

GIFSQ — Global Institute for Food Safety & Quality Principle Residual catalase in the dehydrated vegetable decomposes added hydrogen peroxide and liberates oxygen. Visible evolution of oxygen after the peroxide is added shows that the enzyme is still active — a positive test. Apparatus required Test tube (about 1 inch in diameter and 6 inches […]

GIFSQ — Global Institute for Food Safety & Quality Principle The prepared sample is dried in a vacuum oven at 70 ± 1 °C under reduced pressure while a slow stream of dry air passes through the oven. The loss in weight on drying is reported as the moisture content. Apparatus required Metal dish (6–8 […]

GIFSQ — Global Institute for Food Safety & Quality Principle A representative portion of the dehydrated product is ground to a uniform fineness and thoroughly mixed, so that every analytical portion drawn from it represents the bulk. This ground preparation is not used for the enzyme tests, which are carried out on pieces of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Mineral impurities — sand and alkali-soluble silica — are determined by the AOAC method (1975 — 3.005), the approved procedure of the Codex Alimentarius Commission. The sample is ashed, the ash is treated with hydrochloric acid, and the acid-insoluble residue is separated: the portion insoluble […]

GIFSQ — Global Institute for Food Safety & Quality Principle Where a more precise figure is required, as in the determination of salt-free solids, the modified Volhard method — the official method of the AOAC — is followed. The sample is ashed with sodium carbonate, and the chloride in the ash is precipitated with a […]

GIFSQ — Global Institute for Food Safety & Quality Principle The chloride in the tomato product is titrated directly with standard silver nitrate solution by the Mohr method, using potassium chromate as indicator; the first excess of silver forms red-brown silver chromate at the end point. This is the satisfactory method for routine quality control. […]

GIFSQ — Global Institute for Food Safety & Quality Principle The organic acids of the tomato product are extracted with water, and an aliquot of the filtered extract is titrated with standard sodium hydroxide using phenolphthalein as indicator. The result is expressed as anhydrous citric acid. Apparatus required 250-ml volumetric flask Burette Funnel and filter […]

GIFSQ — Global Institute for Food Safety & Quality Principle Tomato varieties differ in pulpiness: those richer in insoluble solids give the product a different body. The soluble portion is washed away with hot water, and the insoluble residue is collected, dried and weighed. The method is based on the procedure prescribed by the Association […]

GIFSQ — Global Institute for Food Safety & Quality Principle In the standards of identity for tomato puree and paste in force in the USA since January 1970, solids content is reported as “natural soluble tomato solids”, based on the sugar-scale reading of a refractometer at 20°C. The AOAC procedure (1975 — 32.008), approved by […]

GIFSQ — Global Institute for Food Safety & Quality Principle The refractive index of the filtered tomato serum is closely related to its soluble solids content. An Abbe refractometer reading, taken at 25°C and corrected for temperature and for any added salt, is converted to total solids by means of the tomato pulp and paste […]

GIFSQ — Global Institute for Food Safety & Quality Principle Water is removed from the tomato product by drying under controlled conditions, and the residue that remains is the total solids. Drying in vacuo at 70°C is the accurate reference method used by public analysts for control work. Drying at atmospheric pressure at the temperature […]

GIFSQ — Global Institute for Food Safety & Quality Principle The pH of the product is measured directly with a pH meter on a sample diluted with an equal quantity of water. The pH range of these products is normally 3.1–3.2, with extreme values of 3.2–3.4. Apparatus required pH meter Glassware for mixing the sample […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is clarified with neutral lead acetate, the excess lead is removed, and the rotation of the solution is measured in a polarimeter before and after inversion of the sucrose. From the direct and invert readings the sucrose content is calculated. Because invert sugar […]

GIFSQ — Global Institute for Food Safety & Quality Principle The clarified, decolourised solution of the sample is examined in a polarimeter. The rotation is related to the soluble solids content of the sample, and the invert sugar percentage is calculated from the difference between the soluble-solids value and the observed rotary power. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total solids are determined by drying a weighed sample to constant weight under reduced pressure at 70°C. Jellies generally contain no insoluble matter, so their total solids are obtained from the soluble solids determined by refractometer, with the invert-sugar correction applied where necessary. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle The water-insoluble matter of the product is determined gravimetrically. The sample is boiled with water, the insoluble residue is filtered on a weighed filter medium, washed free of soluble matter, dried and weighed. Apparatus required Coarse grade filter paper or a wad of cotton Aluminium […]

GIFSQ — Global Institute for Food Safety & Quality Principle The soluble solids content of the product is estimated from the refractive index of the sample at a standard temperature of 20°C. Where the product is too dark to be read directly, it is diluted with a weighed amount of concentrated sugar solution and the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Brix:acid ratio is the ratio of °Brix to the grams of anhydrous citric acid in 100 g of citrus juice or concentrate. A higher ratio indicates a sweeter product and vice versa: a ratio of 14.0 means that for every 14.0 parts of soluble […]

GIFSQ — Global Institute for Food Safety & Quality Principle Heavy bacterial growth while citrus juice is being concentrated can spoil the flavour of the finished product, through diacetyl (2,3-butanedione) made by acid-tolerant bacteria such as Leuconostoc and Lactobacillus. Measuring diacetyl gives a rapid index of sanitation during processing. The test is a modified Voges-Proskauer […]

GIFSQ — Global Institute for Food Safety & Quality Principle The test is based on the increase in viscosity of a juice containing medium-methoxyl pectin and calcium on incubation — an increase caused by the activity of residual pectinesterase in the juice. Residual enzyme de-esterifies the pectin, and the resulting low-methoxyl pectin forms a calcium […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Stevens accelerated cloud-stability test checks pasteurized citrus concentrates for leftover enzyme (pectinesterase) activity, as a measure of the cloud stability of the product. Added pectin is incubated with the reconstituted juice in the presence of barium chloride (which gels pectin whose methoxyl groups have […]

GIFSQ — Global Institute for Food Safety & Quality Principle The opaque cloud and the viscosity of citrus and other fruit juices come largely from their pectin. Hydrolysis of the ester bonds of pectin by the enzyme pectinesterase (PE) causes clarification and gelation of citrus concentrates. The PE activity is measured as the milli-equivalents of […]

GIFSQ — Global Institute for Food Safety & Quality Principle Caffeine is added to some carbonated beverages, particularly of the cola type; the amount should not exceed 200 ppm. The method determines caffeine by extracting it from the beverage with chloroform after oxidation of interfering substances with permanganate, and measuring its absorbance in the ultraviolet […]

GIFSQ — Global Institute for Food Safety & Quality Principle For beverages containing essential oils, the oil is first removed (acidification, ether extraction, then shaking the combined ether extracts with dilute ammonia and recovering the saccharin into the aqueous phase). The saccharin is then hydrolysed by evaporation with hydrochloric acid to ammonium chloride, and the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Benzoic acid is selectively extracted with diethyl ether at pH 4.0, and then saccharin is extracted by making the liquid strongly acidic. Each residue is titrated with standard sodium hydroxide: benzoic acid against phenol red in 60% acetone, saccharin against bromothymol blue in water. Apparatus […]

GIFSQ — Global Institute for Food Safety & Quality Principle Saccharin is extracted from the beverage with ether after strong acidification, and the residue is identified by the resorcinol test: heating saccharin with resorcinol and sulphuric acid gives a dark-green product that turns fluorescent green on alkalinization. Saccharin is the only synthetic sweetening agent permitted […]

GIFSQ — Global Institute for Food Safety & Quality Principle In fruit-juice beverages, benzoic acid and sulphur dioxide are the two preservatives the book permits. For control purposes total sulphur dioxide may be determined by direct titration: the bound sulphur dioxide is first liberated by alkali treatment, the mixture is acidified, and the freed sulphur […]

GIFSQ — Global Institute for Food Safety & Quality Principle In acid media, hexose sugars break down into hydroxymethylfurfural (HMF), which can polymerize or combine with amino compounds to form brown pigments. HMF reacts with resorcinol in an acid medium to give a reddish-pink colour measured at 540 nm, or with barbituric acid and p-toluidine […]

GIFSQ — Global Institute for Food Safety & Quality Principle Furfural forms from ascorbic acid and pentose sugars; it can polymerize or combine with amino compounds and so drives nonenzymatic browning in stored fruit and vegetable products. Measuring furfural is therefore of value in storage studies. It is measured either by its ultraviolet absorption maximum […]

GIFSQ — Global Institute for Food Safety & Quality Principle The increase in absorbance of a clarified sample extract at 440 nm is taken as the measure of nonenzymatic browning (colour may also be measured at 400 or 420 nm). The extract is prepared in aqueous alcohol to remove turbidity and chlorophyll interference. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle The organic matter of the juice is burned off, leaving the mineral ash, which is weighed. The ash of fruit juices is alkaline (mainly carbonates of the alkali metals); its alkalinity is measured by warming with a known excess of standard hydrochloric acid and back-titrating […]

GIFSQ — Global Institute for Food Safety & Quality Principle The alcohol content of good-quality fruit juices is too small for accurate determination by the distillation procedure used for fermented beverages — it comes only from volatile components present in parts per million. When overripe fruit is used, or fermentation occurs before or after juice […]

GIFSQ — Global Institute for Food Safety & Quality Principle Volatile oil is distilled with water from the sample and collected in the graduated tube of the volatile-oil apparatus (the book’s Figure 28-1), where its volume is read directly and converted to per cent by weight using the oil’s specific gravity. Apparatus required Volatile-oil distillation […]

GIFSQ — Global Institute for Food Safety & Quality Principle Oil recoverable by distillation from orange, tangerine and grapefruit juices is 98% or more d-limonene. This is the official method for peel-oil concentration in all single-strength citrus juices and reconstituted citrus concentrates: the juice is co-distilled with isopropanol, the distillate is acidified, and the oil […]

GIFSQ — Global Institute for Food Safety & Quality Principle Peel oil is co-distilled from the juice with steam and collected in a graduated receiver, where the volume of separated oil is read directly. This is the steam-distillation (CSIRO) method for recoverable oil in citrus juices. Apparatus required 2-litre flask (steam generator) 5-litre flask containing […]

GIFSQ — Global Institute for Food Safety & Quality Principle In highly coloured juices, ascorbic acid is determined by titration with N-bromosuccinimide. The end point is the appearance of the brown colour of liberated iodine in an ether layer, which can be seen even in dark juices. Reductones, reductic acid and iron salts do not […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total flavonoid content of citrus juices is measured by the Davis value test: the flavonoids develop a yellow colour with sodium hydroxide in diethylene glycol, measured at 420 nm. In grapefruit juice the value is an index of the bitterness characteristics (naringin is the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Tannin content, a measure of the astringency of the juice and of the tendency of fresh juice to discolour, is determined by direct titration with potassium permanganate using indigo carmine as indicator. Colouring matter, ascorbic acid and sulphur dioxide interfere, so one portion of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Nitrogen in the juice is determined by the micro-Kjeldahl method: the organic nitrogen is digested with concentrated sulphuric acid to ammonium sulphate, the ammonia is distilled into standard acid, and the excess is back-titrated. The quantity of concentrated sulphuric acid for digestion is adjusted to […]

GIFSQ — Global Institute for Food Safety & Quality Principle Volatile acids are separated from the fixed acids of the juice by steam distillation and then titrated in the distillate. Fruit juices normally contain very little volatile acidity (only a few milli-equivalents per litre from aliphatic fatty acids); it serves mainly as a quality index […]

GIFSQ — Global Institute for Food Safety & Quality Principle The free organic acids in the juice are neutralized by titration with standard sodium hydroxide. For routine work the end point is taken to a faint pink colour with phenolphthalein, or electrometrically to pH 8.1 with a glass electrode for dark-coloured juices of low acidity […]

GIFSQ — Global Institute for Food Safety & Quality Principle pH is the logarithm of the reciprocal of the hydrogen-ion concentration, expressed in grams per litre. It measures active acidity, which influences the flavour and palatability of a product and its processing requirements. The glass-electrode pH meter is the quickest and most reliable method available […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total soluble solids are determined from the refractive index of the juice. The Abbe or hand refractometer gives the reading as refractive index or directly as per cent dry substance (°Brix). Fruit acids, the main non-sugar soluble solids in fruit products, affect the refractometer and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total soluble solids are estimated from the specific gravity of the juice, which is measured with hydrometers. The Brix (Balling) hydrometer reads per cent sucrose by weight directly; fruit juices contain more sugar than any other soluble constituent, so the reading is a useful guide […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total solids content is the residue left after the complete removal of water from the sample. Drying under vacuum at 70 °C drives off the moisture without caramelizing the sugars or decomposing heat-sensitive constituents of the juice. Apparatus required Vacuum oven (capable of holding […]

GIFSQ — Global Institute for Food Safety & Quality Principle Inadequately blanched vegetables develop progressive off-flavours, odours and colours from continued enzyme action; the acetaldehyde content serves as an index of this off-flavour development. The distillate is trapped with excess bisulphite, the remaining bisulphite is consumed with excess iodine, and the leftover iodine is back-titrated […]

GIFSQ — Global Institute for Food Safety & Quality Principle The AOAC procedure for the quantitative estimation of peroxidase is based on the oxidation of ascorbic acid in a coupled reaction: ascorbic acid reduces indophenol, peroxidase combines with hydrogen peroxide, and the peroxide–enzyme complex re-oxidises the reduced indophenol. The decrease in ascorbic acid concentration, measured […]

GIFSQ — Global Institute for Food Safety & Quality Principle Catalase decomposes hydrogen peroxide; the residual peroxide is measured iodometrically (the differences between the blank titre and the sample titres are the iodine solution equivalents of the H₂O₂ present at the respective times). Method A demonstrates the presence or absence of catalase; Method B estimates […]

GIFSQ — Global Institute for Food Safety & Quality Principle Peroxidase is among the most heat-resistant enzymes in vegetables. Its residual activity, shown by the guaiacol–hydrogen peroxide colour reaction, has been found to correlate with the keeping quality of frozen vegetables in frozen storage; the test is applicable to frozen peas, snap beans, asparagus and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Raw or under-blanched vegetables discolour, lose flavour and develop off-odours in frozen storage because of enzyme action. Catalase, one of the most heat-resistant enzymes in vegetables, decomposes hydrogen peroxide into oxygen and water; the volume of oxygen liberated in Thompson’s manometric apparatus gives a qualitative […]

GIFSQ — Global Institute for Food Safety & Quality Principle In a mixture of fruit and dry sugar, the fruit content is calculated from the soluble solids of the mixture and the known soluble solids content of the fruit used: the added dry sugar is taken as 100% solids, and the fruit fraction is obtained […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total soluble solids (TSS) content of quick frozen fruits is determined refractometrically: the thawed sample is blended and filtered, the refractometer reading of the clear serum is corrected to 20°C, and the result is expressed in terms of the International Sucrose Scale. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sand and other inorganic materials are separated from the plant tissue by floatation and sedimentation: being heavier, the sand and earthy particles sink to the bottom of the receptacle, where they are collected, incinerated, weighed and reported as “mineral impurities” — technically the water-insoluble inorganic […]

GIFSQ — Global Institute for Food Safety & Quality Principle Calcium in canned vegetables (applicable to canned lima beans, potatoes and tomatoes) is determined by complexometric titration: the product is ashed, the ash solution is passed through an ion exchange column of high phosphate capacity, and the calcium is titrated with standard EDTA solution using […]

GIFSQ — Global Institute for Food Safety & Quality Principle The maturity of canned peas is related to the alcohol-insoluble solids (AIS) — starch, hemicellulose, fibre and proteins: tender green peas have lower AIS values than mature ones. The sample is boiled with 80% alcohol, the alcohol-insoluble residue is collected on a weighed filter paper, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The soluble solids are found by difference: the insoluble solids determined gravimetrically are subtracted from the total solids. Calculation % Soluble solids = % Total solids − % Insoluble solids References Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd […]

GIFSQ — Global Institute for Food Safety & Quality Principle The soluble matter is washed out of the blended solids with repeated hot-water washings; the insoluble residue is collected on a weighed filter paper, dried at 100 °C and weighed. Apparatus required Buchner funnel Dried and weighed filter paper Hot air oven Desiccator Centrifuge Weighing […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total solids are determined gravimetrically by drying the prepared sample on diatomaceous earth in a vacuum oven at 70 °C; the method is an alternate to minimum drained weight in canned mature processed peas, and the result is converted to total solids as a percentage […]

GIFSQ — Global Institute for Food Safety & Quality Principle The concentration of the covering syrup used in canning is greater than the final cut-out strength: during processing the syrup strength falls, and during storage the total sugar distributes itself evenly between the fruit and the liquor. The initial syrup strength needed to reach a […]

GIFSQ — Global Institute for Food Safety & Quality Principle The chloride in the brine is titrated with standard silver nitrate solution using potassium chromate as indicator; for sauerkraut the acidity is neutralised before the estimation. Apparatus required Titration assembly Reagents a. Standard silver nitrate (AgNO₃) solution. b. Potassium chromate indicator. c. 0.1 N sodium […]

GIFSQ — Global Institute for Food Safety & Quality Principle The cut-out strength of the covering syrup is measured as soluble solids with a refractometer, corrected to the standard temperature of 20 °C; no correction is made for water-insoluble solids, invert sugar or other substances. Apparatus required Refractometer Procedure Observe the colour, clarity and flavour […]

GIFSQ — Global Institute for Food Safety & Quality Principle Thermal death time studies require media for cultivating and sporulating the test organisms, for preparing spore suspensions, and for subculturing after heating. The book gives the composition and preparation of the standard media used in this work. Apparatus required Tubes and bottles with cotton-wool plugs […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sugar-acid ratio is an important criterion of quality from the standpoint of taste appeal, especially in juices. It is the ratio of the sugar value, determined with a refractometer, to the grams of acid content determined by titration. Apparatus required Refractometer Titration assembly for […]

GIFSQ — Global Institute for Food Safety & Quality Principle As green beans mature they become more fibrous, and the fibre contributes to the toughness of the product. In the simplified Kramer procedure the pods are blended with water, the fibrous material is washed free on a standard screen, dried and weighed; the weight of […]

GIFSQ — Global Institute for Food Safety & Quality Principle A dip in copper-sulphate–hydrochloric acid solution makes pinholes visible — the solution attacks the bare tinplate showing through. The simple dip suits flat panels for checking application faults, and stamped parts like can ends. Reagents a. Test solution: combine water, copper sulphate and concentrated HCl […]

GIFSQ — Global Institute for Food Safety & Quality Principle Resistance of lacquer to stains caused by sulphur-containing foods during processing is tested by packing sulphur-containing foods in lacquered cans or with test panels in Kilner jars, processing as specified, and examining for adhesion and staining. Procedure Prepare test panels and place in Kilner jars […]

GIFSQ — Global Institute for Food Safety & Quality Principle A lacquered tinplate panel goes into 5% citric acid in a Kilner jar, is heat-processed, and is checked for softening, blistering and breaks in the film. An inside-lacquered open-top can filled with the acid gets the same treatment. Reagents a. Citric acid solution 5% (w/v) […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sulphide staining hits canned foods rich in sulphur compounds — vegetables and meats — and can follow residual sulphur dioxide. High-temperature processing frees the sulphur as volatile sulphides that react with tin or exposed iron to discolour the metal. Here the stain is driven off […]

GIFSQ — Global Institute for Food Safety & Quality Principle Discontinuities let the steel corrode in a bath where the tin’s slightly anodic behaviour partly protects it — 1.09 N sulphuric acid spiked with hydrogen peroxide and ammonium thiocyanate. A cleaned plate sits in that bath; afterwards the dissolved iron is measured colorimetrically. The micrograms […]

GIFSQ — Global Institute for Food Safety & Quality Principle A piece of steel base or detinned plate goes into 6 N hydrochloric acid at 90°C, and the time until iron starts dissolving — or hydrogen starts evolving — at a steady rate is clocked. That opening stretch of sluggish attack is the induction (pickle […]

GIFSQ — Global Institute for Food Safety & Quality Principle How tinplate resists staining by sulphur-rich foods depends partly on the food and partly on the oxide films the plate carries. Natural foods vary too much for a standard test, so chemical stand-ins are used — the one below has been shown to track the […]

GIFSQ — Global Institute for Food Safety & Quality Principle A porosity count alone says little about how the plate will behave in service. Here cleaned plates hang for 24 hours in a closed vessel over a sulphur-dioxide solution; every discontinuity shows up as a brown rust spot. Because the method needs no fixed sample […]

GIFSQ — Global Institute for Food Safety & Quality Principle The plate sits in a bath of acetic acid, hydrogen peroxide and ammonium thiocyanate; the iron it dissolves out is measured colorimetrically. Where the paper tests count spots, this one yields a number — milligrams of iron per unit area — a direct index of […]

GIFSQ — Global Institute for Food Safety & Quality Principle Pores expose bare steel; the iron ions there react with ferricyanide to form a blue complex — each blue spot marks a pore. Reagents a. Ferricyanide solution: prepare a solution containing 1 g of potassium ferricyanide, K₃Fe(CN)₆, and 0.5 g of sodium chloride in 100 […]

GIFSQ — Global Institute for Food Safety & Quality Principle Free tin and the tin–iron alloy layer are dissolved off the steel base selectively. The weight lost gives the coating weight, after correcting for the iron the alloy layer carries with it. Reagents a. Detinning stock solution: dissolve 20 g of antimony trioxide (Sb₂O₃) or […]

GIFSQ — Global Institute for Food Safety & Quality Principle The chlorine demand of water is the difference between the amount of chlorine applied to a treated supply and the amount of free, combined, or total available residual chlorine remaining at the end of the contact period. Chlorine demand determinations are made to determine the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The chlorotex reagent produces a coloured compound in the presence of chlorine, the colour deepening with increasing chlorine concentration. The colour produced is compared with the tints given on the colour chart supplied with the set. Reagents a. Chlorotex reagent (manufactured by the British Drug […]

GIFSQ — Global Institute for Food Safety & Quality Principle The orthotolidine-arsenite (OTA) method permits the measurement of the relative amounts of free available chlorine, combined available chlorine, and colour due to interfering substances. Orthotolidine produces a yellow-coloured compound in the presence of chlorine, and the colour is compared with the standards. The false colours […]

GIFSQ — Global Institute for Food Safety & Quality Principle Chlorine liberates free iodine from potassium iodide solutions at pH 8 or less. The liberated iodine is titrated with a standard solution of sodium thiosulphate, using starch as the indicator. The reaction is preferably carried out at pH 3 to 4. The iodometric method is […]

GIFSQ — Global Institute for Food Safety & Quality Principle The standard method of measuring pollutional strength is the biochemical oxygen demand (BOD) test. BOD of effluents is due to carbonaceous organic material usable as food by aerobic organisms, and organic nitrogenous compounds which serve as food for specific bacteria. The determination of BOD involves […]

GIFSQ — Global Institute for Food Safety & Quality Principle All waters absorb oxygen to a greater or lesser extent from potassium permanganate in a strongly acidulated medium. While pure water may absorb very little oxygen (0.1 mg/litre), water containing organic matter may absorb several times this amount. Though this is an index of neither […]

GIFSQ — Global Institute for Food Safety & Quality Principle The CO₂ present in water in excess of carbonates and bicarbonates is known as free CO₂. Free CO₂ in water is determined by titration with Na₂CO₃ or NaOH using phenolphthalein as indicator; the CO₂ reacts with NaOH or Na₂CO₃ to form sodium bicarbonate. Reagents a. […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sulphates are precipitated from the sample as barium sulphate by the addition of a known excess of barium chloride. The excess of barium left unprecipitated is back-titrated with standard EDTA solution using Eriochrome Black T as indicator. The alkalinity and the hardness of the sample […]

GIFSQ — Global Institute for Food Safety & Quality Principle Chlorides are determined by Mohr’s method. When water containing chlorides is titrated with silver nitrate using potassium chromate as indicator, silver chloride is quantitatively precipitated, and at the end point red silver chromate is formed. Reagents a. 0.0141 N standard NaCl solution: dissolve 0.8243 g […]

GIFSQ — Global Institute for Food Safety & Quality Principle Albuminoid nitrogen is a measure of proteinaceous nitrogen present in water and indicates organic pollution in a water supply. It is largely derived from animal and plant life which are normal to aquatic environments. After the determination of ammonia nitrogen, if a strong solution of […]

GIFSQ — Global Institute for Food Safety & Quality Principle When a sample of water is made alkaline and distilled, the ammonia nitrogen present in the sample passes over in the distillate. The ammonia nitrogen in the distillate may be estimated by nesslerization (Method I) or the distillate may be collected in boric acid and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Nitrite in water is determined through the formation of a reddish-purple azo dye produced at pH 2 to 2.5 by the coupling of diazotized sulphanilic acid with naphthylamine hydrochloride. The diazotization method is suitable for the visual determination of nitrite nitrogen in the range 0.001–0.025 […]

GIFSQ — Global Institute for Food Safety & Quality Principle The reaction between nitrate and 1,2,4-phenoldisulphonic acid produces 6-nitro-1,2,4-phenoldisulphonic acid, which upon conversion to the alkaline salt yields a yellow colour. This colour is compared with standards similarly prepared. Apparatus required Evaporating dish Nessler tubes Reagents a. 1,2,4-Phenoldisulphonic acid solution. b. Standard nitrate solution (prepared […]

GIFSQ — Global Institute for Food Safety & Quality Principle The reaction between nitrate and brucine yields a sulphur-yellow colour, which is used for the colorimetric estimation of nitrate. The colour system does not obey Beer’s law but gives a smooth curve; it is therefore necessary to develop the colour simultaneously in a series of […]

GIFSQ — Global Institute for Food Safety & Quality Principle The pH is a measure of the relative acidity or alkalinity of water. For control purposes (for example, in the treatment of water from a peaty source), the determination of pH gives reliable information on the potential effect of the supply. The pH may be […]

GIFSQ — Global Institute for Food Safety & Quality Principle The acidity of a water may be caused by the presence of uncombined CO₂, mineral acids, and salts of strong acids and weak bases. The determination is based on the titration of a sample with a standard solution of a strong base in the presence […]

GIFSQ — Global Institute for Food Safety & Quality Principle Alkalinity is usually caused by the carbonates, bicarbonates and hydroxides present in water. It is determined by titration with a standard solution of a strong mineral acid to the successive bicarbonate and carbonic acid equivalence points, using appropriate indicators. Phenolphthalein is satisfactory to determine the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Temporary hardness of water is caused by carbonates and bicarbonates of calcium and magnesium and is determined by titration with standard H₂SO₄ using methyl orange as indicator. Permanent hardness is determined by noting the volume of standard NaOH and sodium carbonate required to precipitate the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The hardness of water is almost entirely due to the salts of calcium and magnesium. Occasionally, zinc and iron present in the form of carbonate or sulphate, the presence of free CO₂, or large quantities of NaCl may add to the hardness. Ethylenediamine tetra-acetic acid […]

GIFSQ — Global Institute for Food Safety & Quality Principle After the estimation of total solids, the residue is ignited and the loss in weight is recorded as organic matter. The loss may also include (i) loss of residual water of hydration, (ii) evolution of CO₂ from carbonates, (iii) oxygen from nitrates, and/or (iv) volatilization […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total solids include water-soluble as well as insoluble matter. A measured volume of the well-shaken sample is evaporated in a tared platinum dish and the residue is dried in an oven and weighed. The temperature at which the sample was dried is stated with the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The maximum limit for any permitted coal-tar colour or mixture of colours added to any fruit product is 0.2 g per kg. To estimate the added dye(s) quantitatively, the colour is removed completely from the product without severe heat treatment or strong acids or alkalies […]

GIFSQ — Global Institute for Food Safety & Quality Principle Each stabilizing gum is confirmed by a specific spot test: gel formation with acid (alginates, deesterified pectins), methylene blue staining of fibres (Irish moss), absence of an alcohol precipitate (methyl cellulose), iodine staining (agar, starch), copper sulphate clotting (carboxymethylcellulose), borax gelation (locust bean gum), ruthenium […]

GIFSQ — Global Institute for Food Safety & Quality Principle Stabilizing gums are identified by a systematic group scheme: Group A separates alginates, deesterified pectin and pectin with calcium chloride, ammonium hydroxide and sodium hydroxide; Group B separates Irish moss, tragacanth, agar, methyl cellulose, starch, locust bean gum and karaya with saturated barium hydroxide; Group […]

GIFSQ — Global Institute for Food Safety & Quality Principle Proteins are removed from the food extract by selective precipitation with tannic acid (precipitates proteins only) or trichloroacetic acid (precipitates proteins and alginic acid); the gums and related polysaccharides are then precipitated from the protein-free filtrate with alcohol, and the precipitation of the mixture with […]

GIFSQ — Global Institute for Food Safety & Quality Principle Tertiary butylhydroquinone is extracted from fats, oils or food products with methanol, and estimated colorimetrically with dimethylamine reagent; the colour developed is measured at 500 nm against a calibration curve prepared from standard TBHQ solutions. Apparatus required 50-ml stoppered conical flasks 250-ml conical flask Soxhlet […]

GIFSQ — Global Institute for Food Safety & Quality Principle BHT reacts with o-dianisidine and nitrite to give a purplish red colour, which is extracted into chloroform and measured at 520 nm. The colour is light sensitive, so the reaction is carried out protected from light. Apparatus required 60-ml separating funnel, covered with aluminium foil […]

GIFSQ — Global Institute for Food Safety & Quality Principle BHA reacts with 2,6-dichloroquinonechlorimide to give a stable blue indophenol that is highly specific for BHA compared with other antioxidants. Note: the book prints the reagent name as “2, 2, 6-dichloroquinonechlorimide”; normalized here. The procedure is based on the estimation of BHA in lard; a […]

GIFSQ — Global Institute for Food Safety & Quality Principle The gallates — propyl (PG), octyl (OG) and dodecyl (DG) — in 95% methanol, when shaken with solid ammonium ferrous sulphate, form a clear and stable blue solution with an absorption maximum at 580 nm. Such solutions obey Beer’s law over the range 0.0 to […]

GIFSQ — Global Institute for Food Safety & Quality Principle Antioxidants are extracted into hexane or chloroform, partitioned into ethanol and acetonitrile (or ethyl acetate), separated by two-dimensional thin layer chromatography, and detected with phosphomolybdic acid and ammonia fumes (BHA blue; BHT blue or grey; guaiacol brownish; NDGA and gallates brownish or green) or with […]

GIFSQ — Global Institute for Food Safety & Quality Principle The antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and the gallates — propyl (PG), octyl (OG) and dodecyl (DG) — are extracted with methanol, separated by ascending paper chromatography on oil-impregnated paper with 65% methanol, and detected as blue spots with phosphomolybdic acid and ammonia […]

GIFSQ — Global Institute for Food Safety & Quality Principle Benzoic acid and sorbic acid are measured by their ultraviolet absorption maxima (benzoic acid: 225 nm, with a characteristic triple peak at 282, 272 and 265 nm; sorbic acid: 250 nm; fumaric acid: 225 nm without the triple peak or a shoulder at 233 nm). […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sorbic acid is distilled from the sample, extracted into chloroform, separated from interfering substances on a silicic acid column, and measured by its absorbance at 254 nm against a standard. Apparatus required Two-neck 500-ml distilling flask with ground-glass joints, with a 125-ml separating funnel fixed […]

GIFSQ — Global Institute for Food Safety & Quality Principle In a saturated NaCl solution of the sample, the benzoic acid present is converted into water-soluble sodium benzoate by addition of NaOH. On acidifying the sodium benzoate solution with excess HCl, water-insoluble benzoic acid is formed, extracted with chloroform, and the residue after evaporation is […]

GIFSQ — Global Institute for Food Safety & Quality Principle SO₂ is distilled from the acidified sample, absorbed in standard iodine solution, and the excess iodine is titrated with standard sodium thiosulphate. The method is rapid enough for control purposes and applies to most foodstuffs, provided sulphides are not present. Apparatus required Distillation apparatus as […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is acidified and the evolved SO₂ is swept with CO₂ or nitrogen into cold hydrogen peroxide, where the sulphurous acid is oxidised to H₂SO₄. The sulphuric acid formed is titrated with standard NaOH. Apparatus required All-glass distillation apparatus with gas inlet tube, 500-ml […]

GIFSQ — Global Institute for Food Safety & Quality Principle Free sulphur dioxide is estimated by direct titration with iodine. For total sulphur dioxide, the combined SO₂ is liberated by treatment with excess alkali at room temperature, acidified to prevent recombination, and titrated with iodine. In each case, the iodine consumed by reducing substances other […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is acidified and the ether-extractable organic preservatives (benzoic acid, p-hydroxybenzoic acid, p-chlorobenzoic acid, the esters of p-hydroxybenzoic acid, sorbic acid, dehydroacetic acid, salicylic acid, cinnamic acid) are extracted with ether, purified, separated by thin layer chromatography, and identified from their Rf values and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sulphur dioxide in the sample is reduced to hydrogen sulphide by zinc and dilute hydrochloric acid. The evolved H₂S blackens lead acetate paper held in the mouth of the flask, indicating sulphites. Apparatus required Conical flask Filter paper Reagents a. Lead acetate solution (for dipping […]

GIFSQ — Global Institute for Food Safety & Quality Principle Formaldehyde gives a light to deep purple colour with chromotropic acid in strong sulphuric acid when heated. Formic acid is first reduced to formaldehyde with magnesium and dilute sulphuric acid, and then detected with the same reagent. Apparatus required Distillation apparatus Test tubes Ice bath […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sweetening agents and ether-extractable organic preservatives (benzoic acid, esters of p-hydroxybenzoic acid, p- or o-chlorobenzoic acid, salicylic acid) are separated from the food matrix by rendering the sample alkaline and filtering; the schematic separation procedure (Fig. 12.3) then divides the extract into ether-extractable and non-extractable […]

GIFSQ — Global Institute for Food Safety & Quality Principle Beet juice or betanin added to tomato products (tomato sauce, puree, ketchup) is distinguished from the normal tomato pigment by solubility: the normal tomato colouring matter is extracted with amyl alcohol, while betanin stays in the aqueous solution and can be dyed on tannin-mordanted cotton, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The “brown phase reaction” characterizes chlorophyll in products when the chlorophyll has not previously been treated with alkalies: a green ether or petroleum ether solution of the colouring matter turns brown on treatment with methanolic KOH and quickly returns to green. Apparatus required Test tube […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colouring matter in annatto is bixin. Filter paper moistened with an alkaline extract of the material shows a straw colour that resists washing; on treatment with stannous chloride and drying, the colour turns purple, confirming annatto. Apparatus required Filter paper Reagents a. Warm 2% […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colouring agent in turmeric is curcumin. Dried filter paper impregnated with the material’s alcoholic extract gives a cherry-red colour with a weak solution of boric acid in the presence of HCl, which changes to bluish green on addition of NaOH or NH₄OH. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle Cochineal’s colouring matter is carminic acid. When an amyl alcohol solution of the material is shaken with dilute ammonia, a purple colour develops in the presence of cochineal. Apparatus required Separating vessel or test tube Reagents a. Amyl alcohol. b. Dilute ammonia. Procedure Shake an […]

GIFSQ — Global Institute for Food Safety & Quality Principle Commercial food colours contain coloured impurities (subsidiary dyes) and uncoloured intermediates from manufacture. The subsidiary dyes are separated from the main dye by paper chromatography or by column chromatography on a filter-aid support, and estimated spectrophotometrically. Apparatus required Paper chromatographic apparatus Spectrophotometer 9 cm Whatman […]

GIFSQ — Global Institute for Food Safety & Quality Principle Indigo carmine is the only permitted blue colour, and its recovery by chromatographic separation is very low (5.29%). It has an absorption maximum at 610 nm, where the absorption of other food colours is insignificant. The indigo carmine content of a dye mixture is therefore […]

GIFSQ — Global Institute for Food Safety & Quality Principle The dyes in a food-colour preparation are separated by paper chromatography, each colour band is cut out and eluted, and the individual dyes are identified and estimated spectrophotometrically at their wavelengths of maximum absorption, using either a calibration curve or the tabulated extinction coefficient (Table […]

GIFSQ — Global Institute for Food Safety & Quality Principle Erythrosine is precipitated from aqueous solution with dilute nitric acid, collected on a tared sintered funnel, washed free of nitrate, dried to constant weight, and weighed. The residue weight, corrected by the tabulated factor, gives the dye content. Apparatus required 500-ml beaker Sintered funnel (porosity […]

GIFSQ — Global Institute for Food Safety & Quality Principle The quantitative estimation of a single food colour is carried out by reduction titration with titanium trichloride. The titanium trichloride is standardized against ferrous ammonium sulphate and potassium dichromate, and the dye content is calculated from the titre and the tabulated dye equivalent (Table 12-4). […]

GIFSQ — Global Institute for Food Safety & Quality Principle Oil-soluble coal-tar dyes are taken into an alcoholic solution from the oil or melted fat, and distinguished from natural colouring matters by their colour response to acid and to stannous chloride (reduction decolourises the coal-tar dyes). Apparatus required Separating vessel or funnel Test tubes Reagents […]

GIFSQ — Global Institute for Food Safety & Quality Principle Fragments of wool dyed with the food colour are treated with concentrated HCl, concentrated H₂SO₄, liquor ammonia and 10% NaOH. The colour changes produced are compared with those of known permitted dyes treated in the same way, as a rapid screen before chromatography. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle Water-soluble coal-tar dyes are separated on silica-gel thin layers containing either EDTA or Tris, developed in the matching solvent system, and identified from their Rf values (Table 12-3). Apparatus required Glass plates (20 × 20 cm) Plate spreader Drying oven (120 °C) Chromatographic chamber Reagents […]

GIFSQ — Global Institute for Food Safety & Quality Principle Food colours are separated on paper by ascending or circular-zone chromatography in twelve standard solvents, and identified from their Rf values (Table 12-2) or by co-chromatography with standard dyes. Identity is confirmed by comparing the spectrophotometric absorption pattern of the eluted dye with that of […]

GIFSQ — Global Institute for Food Safety & Quality Principle Water-soluble coal-tar dyes are taken up from an acidified food solution by white wool, stripped from the wool with dilute ammonia, and redyed onto fresh wool. A distinct colour on the second piece of wool indicates a coal-tar dye; the extract is then concentrated for […]

GIFSQ — Global Institute for Food Safety & Quality Principle With the advent of newer instrumental methods of analysis, U.V. standards have been laid down for some of the essential oils; the gas chromatographic method is used for the separation, identification and/or estimation of the individual components of essential oils, and for the quantitative analysis […]

GIFSQ — Global Institute for Food Safety & Quality Principle Concentrated (terpeneless) essential oils are quality-controlled through physical checks — specific gravity, optical rotation, refractive index and solubility in dilute alcohol — which reveal the extent of terpene, sesquiterpene, wax and resin removal, together with the chemical determinations used for single-fold oils. Procedure The concentration […]

GIFSQ — Global Institute for Food Safety & Quality Principle The essential oil is liberated from the extract with dilute hydrochloric acid and warm water, and separated by centrifuging in a Babcock milk test bottle; the oil volume is read off the graduated neck with a correction for the solubility of the oil, and converted […]

GIFSQ — Global Institute for Food Safety & Quality Principle Washed citrus oils leave too little residue on evaporation; added foreign oils and deterpenated citrus oils reveal themselves through altered optical rotation and refractive index of the first 5 ml distillate from a Ladenburg flask distillation. Apparatus required 4 × 8 cm glass dish Water […]

GIFSQ — Global Institute for Food Safety & Quality Principle Peroxides in the oil oxidize iodide to iodine in an acetic acid–chloroform solvent; the liberated iodine is titrated with standard sodium thiosulphate, giving the peroxide value as millimoles of peroxide per litre. Reagents a. Saturated potassium iodide solution in water — prepare fresh. b. Solvent […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ultraviolet absorption spectrum of the oil in alcohol is recorded from 260 to 400 nm; a base line is drawn tangent to the curve at the absorption minimum and at the inflection point near 365–370 nm, and the CD value (the maximum absorbance above […]

GIFSQ — Global Institute for Food Safety & Quality Principle The esters in the oil are saponified by refluxing with a known excess of alcoholic KOH; the unused alkali is back-titrated with standard HCl, and the alkali consumed is converted to the ester value and to the percentage of esters using the molecular weight of […]

GIFSQ — Global Institute for Food Safety & Quality Principle Aldehydes react with hydroxylamine hydrochloride to liberate acid; the liberated acid is neutralized with standard alcoholic KOH to a permanent alkaline colour of the indicator, the titration being repeated with a slightly larger volume of hydroxylamine solution against the first determination as colour standard, giving […]

GIFSQ — Global Institute for Food Safety & Quality Principle Aldehydes react with hydroxylamine hydrochloride to liberate acid, which is titrated with standard hydrochloric acid using bromophenol blue indicator; the difference between the blank and sample titres is converted to aldehyde content with the factor given for the oil (citral or decanal). Apparatus required Glass-stoppered […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oil is steam-distilled until 100 ml of water collects; the non-volatile residue is recovered from the distillation flask and from the distillation products by chloroform and ether extraction, dried and weighed, giving the residue as a percentage of the sample. Apparatus required Steam distillation […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oil is heated on a boiling water bath for the time specified for that oil; the non-volatile residue remaining is weighed and expressed as a percentage of the oil taken. Apparatus required 100 ml glass evaporating dish Water bath Desiccator Procedure Heat a 100 […]

GIFSQ — Global Institute for Food Safety & Quality Principle Successive volumes of alcohol of defined concentration are added to the oil until a clear solution first appears; the mixture is then diluted further and watched for opalescence or cloudiness, and the behaviour is reported as the number of volumes of alcohol of stated concentration […]

GIFSQ — Global Institute for Food Safety & Quality Principle The refractive index is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when monochromatic sodium light of wavelength 5893 Å passes from air into the material; it is measured at 30 °C with a temperature […]

GIFSQ — Global Institute for Food Safety & Quality Principle Optical rotation is the angle in degrees through which the plane of polarization is turned when plane-polarized sodium light passes through a 100 mm layer of the oil; a high positive rotation generally denotes a high terpene content. Dark oils are read in shorter tubes […]

GIFSQ — Global Institute for Food Safety & Quality Principle The specific gravity is the weight of oil contained in a pycnometer divided by the water equivalent of the same pycnometer at the same temperature, measured in air; a temperature correction is applied when the test temperature differs from the specified temperature, within ±3 °C […]

GIFSQ — Global Institute for Food Safety & Quality Principle Containers of one type and grade of essential oil from the same batch are grouped together, and a defined number of containers is sampled at random; the individual and composite samples are sealed with a small head space and stored cool and protected from light, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colour value of turmeric oleoresin is the E¹%₁cm value at 422 nm; a dilute solution in 95% alcohol is measured spectrophotometrically and the absorbance is multiplied by the appropriate factor for the solution strength used. Apparatus required 100 ml volumetric flasks Spectrophotometer with 1 […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oleoresin is diluted with acetone to a defined concentration and its colour is matched visually against a potassium dichromate–cobaltous chloride blank in Nessler tubes, or its absorbance is measured spectrophotometrically at 458 nm; the colour value is calculated from the dilution used or from […]

GIFSQ — Global Institute for Food Safety & Quality Principle Piperine is determined either by finding the total nitrogen by the Kjeldahl procedure and converting it to piperine, or spectrophotometrically by measuring the absorbance of the oleoresin solution at 341–342 nm against a calibration curve prepared from purified piperine. Apparatus required Kjeldahl digestion and distillation […]

GIFSQ — Global Institute for Food Safety & Quality Principle Dilutions of the oleoresin in sweetened water are tasted by a panel; the Scoville heat value corresponds to the greatest dilution at which a just-perceptible pungent sensation remains, with at least 3 of 5 panel members agreeing. Apparatus required 50 ml volumetric flask Reagents a. […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oleoresin is boiled with water and the volatiles are distilled into a graduated receiver trap; after the water and oil layers separate and cool to room temperature, the percentage of volatile oil is read directly on the graduated portion of the receiver. The recovered […]

GIFSQ — Global Institute for Food Safety & Quality Principle Spice extracts carry the flavouring constituents of the natural spice in a solvent such as propylene glycol or vegetable oil. The original solvent is removed where possible, the oil is liberated into a salt solution and separated by centrifuging in a Babcock milk test bottle; […]

GIFSQ — Global Institute for Food Safety & Quality Principle The floral waste in saffron — yellow filaments, pollens, stamens, part of the ovary and other parts of the flower of Crocus sativus L. — is separated by hand picking from a weighed quantity of the sample and expressed as per cent by weight. Apparatus […]

GIFSQ — Global Institute for Food Safety & Quality Principle Pure saffron gives an immediate blue colour with the sulphuric acid–diphenylamine test solution, which rapidly turns to brown-red; the blue colour persists in the presence of nitrates. Apparatus required Shallow porcelain dish Reagents a. Test solution: dissolve 0.1 g of diphenylamine in 20 ml of […]

GIFSQ — Global Institute for Food Safety & Quality Principle Argemone oil present as an adulterant in mustard oil gives an orange-red precipitate in light flocks in the acid layer when treated with hydrochloric acid and ferric chloride reagent; under the microscope the precipitate appears as needle-like crystals (straight for argemone; curved needles suggest a […]

GIFSQ — Global Institute for Food Safety & Quality Principle The pungent principles are extracted with ethyl alcohol, and serial dilutions of the clear extract in sweetened water are tasted until a distinct pungency in the throat or mouth is just perceptible; the Scoville value is the total dilution factor at that point. Reagents a. […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ginger sample is dry-ashed and the calcium is determined as described in Chapter 6; the potassium permanganate titre is converted to calcium oxide by the factor 2.8. Procedure Weigh accurately 2 to 4 g of the material ↓ Follow the dry ashing procedure, and […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is defatted and the tannins extracted with boiling water; the extract is titrated with standard potassium permanganate using indigo as indicator, and the permanganate consumed (blank minus sample) is converted to quercitannic acid by the factor 0.006235, or to oxygen absorbed by the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The volatile oil is distilled with water from the spice sample and collected in a graduated Clevenger trap of the design suited to the oil’s density; the volume of oil collected, read to 0.02 ml, gives the volatile oil content as per cent volume by […]

GIFSQ — Global Institute for Food Safety & Quality Principle Spices like chilli, allspice and clove contain little or no true starch, for which acid hydrolysis gives unduly high results; the starch is therefore converted to sugars by digestion with malt extract (diastase) at 55 °C, and the resulting glucose is hydrolysed with acid and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Alcohol-insoluble carbohydrates are hydrolysed with hydrochloric acid to reducing sugars, which are estimated by the Lane and Eynon volumetric method and calculated as crude starch. Dark digests that interfere with the Fehling titration are clarified with neutral lead acetate before titration. Apparatus required Funnel with […]

GIFSQ — Global Institute for Food Safety & Quality Principle Cumin, coriander, cloves, chilli and similar spice powders do not contain significant amounts of true starch and therefore do not give a positive starch–iodide test; a positive reaction with iodine solution in such powders indicates added starch, and the finding is followed up by a […]

GIFSQ — Global Institute for Food Safety & Quality Principle The alcohol-soluble matter is extracted by steeping the sample in 95% ethyl alcohol for 16 hr; an aliquot of the filtered extract is evaporated to dryness and the residue weighed, giving the alcohol extract as a percentage of the sample weight. Spices containing more than […]

GIFSQ — Global Institute for Food Safety & Quality Principle Piperine, the pungent principle of pepper, concentrates in the nonvolatile ether extract and contains nitrogen; the extract is therefore digested by the Kjeldahl procedure and the nitrogen found is converted to crude piperine by the factor 20.36. Apparatus required Continuous extraction apparatus Tared 250 ml […]

GIFSQ — Global Institute for Food Safety & Quality Principle The nitrogen in the pepper sample is determined by the Kjeldahl procedure as given in Chapter 1, using 1 g of black or white pepper sample. Apparatus required Kjeldahl digestion and distillation apparatus (as given in Chapter 1) Procedure Weigh 1 g of the black […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ether-free residue remaining after the determination of nonvolatile ether extract is carried through acid and alkali digestion, which removes the digestible matter; the crude fibre remaining is filtered, dried and weighed as given in Chapter 1. Apparatus required Digestion flask Procedure Quantitatively transfer the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The spice is extracted with diethyl ether in a Soxhlet apparatus; after drying the total residue, the portion still soluble in cold ether is removed by decantation, so that the nonvolatile ether extract is found from the difference between the total residue and the ether-insoluble […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ground spice is extracted with anhydrous ether in a Soxhlet apparatus; the dried ether extract is weighed to give the total ether extract. Heating the extract to constant weight drives off the volatile portion, the loss in weight being the volatile ether extract and […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is carbonized and ignited in a muffle furnace until all carbon is removed; the mineral residue remaining after ignition is the total ash. Spices whose ash resists burning white are leached with hot water to remove soluble salts before re-ignition; mustard flour, which […]

GIFSQ — Global Institute for Food Safety & Quality Principle Water is distilled from the sample with an immiscible solvent and collected in a calibrated trap, the volume of water collected giving the moisture content. Spices whose sugars may decompose and form water are distilled with benzene instead of toluene; capsicum, dehydrated onion, garlic and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Gross spice samples from a lot are blended, ground and sieved to the particle size required for analysis, then stored under conditions that prevent change before the determinations are made. Apparatus required Mixer capable of mixing gross spice samples (a double cone blender such as […]

GIFSQ — Global Institute for Food Safety & Quality Principle Extraneous matter in pepper is separated by sifting through a perforated sieve of defined hole size; the sieved material is then hand picked for foreign organic and inorganic matter. Light (immature) berries are separated by floatation in an alcohol–water solution of defined specific gravity, dried […]

GIFSQ — Global Institute for Food Safety & Quality Principle Extraneous matter is removed by hand picking from a weighed quantity of the material and weighed, giving the percentage by weight of extraneous matter. For whole spices, the organic extraneous matter (chaff, stem, straw, etc.) and the inorganic extraneous matter (dust, dirt, stones, lumps of […]

GIFSQ — Global Institute for Food Safety & Quality Principle A spice consignment may come from one lot or from a mixed lot (different varieties, grades or years of production). Samples drawn from a defined number of containers of similar character are combined into a bulk sample, which is divided into portions for analysis, reference […]

GIFSQ — Global Institute for Food Safety & Quality Principle When an oil is used for frying, a progressive deterioration takes place — mainly the build-up of oxidised material — and the oil has to be rejected at some stage. Physical signs of deterioration are colour, increased viscosity, tendency to foam and lowering of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Butter fat, coconut oil and palm kernel oil develop a distinctive odour and taste quite different from those of oxidative rancidity. The taste and odour are due to ketones rather than aldehydes and esters, and arise from the action of moulds, mainly Penicillium and Aspergillus, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The active oxygen method (AOM) measures the time in hours required for a sample of fat or oil to attain a predetermined peroxide value (100 m.e.) under specified conditions of test. Air is passed through the fat maintained at high temperature until the peroxide value […]

GIFSQ — Global Institute for Food Safety & Quality Principle The peroxide value of an oil or fat is the amount of peroxides present, expressed as milli-equivalents of peroxide per 1000 g of sample. The sample is dissolved in a solvent, treated with potassium iodide, and the iodine liberated by the peroxides present in the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The oxidation of fats produces compounds that react with 2-thiobarbituric acid to give red-coloured products. The fat sample is dissolved in an organic solvent such as benzene, chloroform or carbon tetrachloride, and the reactive material is extracted with an acetic acid–thiobarbituric acid–water solution. The aqueous […]

GIFSQ — Global Institute for Food Safety & Quality Principle The test depends upon the formation of a red colour when an oxidised fat is treated with conc HCl and a solution of phloroglucinol in ether. The compound in rancid fats responsible for the colour reaction is epihydrin aldehyde. All oxidised fats respond to the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The methyl esters of the fatty acids, after purification, are separated by gas-liquid chromatography. With a polyester liquid phase on Chromosorb W, the esters appear in order of increasing number of carbon atoms and, for the same number of carbon atoms, of increasing unsaturation. Peak […]

GIFSQ — Global Institute for Food Safety & Quality Principle For examination of the fatty acid composition by gas-liquid chromatography, the fat is converted into methyl esters. The triglycerides are transesterified with methanol under the influence of HCl, sodium methylate or boron trifluoride; alternatively the fatty acids isolated from the triglycerides are treated with methanol […]

GIFSQ — Global Institute for Food Safety & Quality Principle The fat is extracted from the sample at room temperature using a mixture of chloroform and methanol. The extract is diluted with the calculated amount of water so that the two phases separate; the lower chloroform layer, which contains the fat, is separated, washed with […]

GIFSQ — Global Institute for Food Safety & Quality Principle Mineral oil is not saponifiable. When the oil is saponified with alcoholic KOH and diluted with hot water, any mineral oil present produces a distinct turbidity. The method is sensitive when the mineral oil content is 0.5% or more. For quantitative estimation, the method for […]

GIFSQ — Global Institute for Food Safety & Quality Principle Argemone oil is detected by the formation of straight or needle-shaped reddish-brown crystals at the junction of the acid and oil layers when the hydrochloric-acid extract of the oil is treated with ferric chloride solution and heated. When the argemone oil content is less than […]

GIFSQ — Global Institute for Food Safety & Quality Principle Linseed oil is detected by the formation of a precipitate when its chloroform solution, brominated to a deep red colour, is treated with rectified spirit and ether and chilled in ice water. Apparatus required Dry stoppered test tube Ice water bath Reagents a. Chloroform. b. […]

GIFSQ — Global Institute for Food Safety & Quality Principle Cottonseed oil is detected by the red colour that develops when the fat is heated with a solution of sulphur in carbon disulphide and amyl alcohol at 112–115°C. The carbon disulphide is first evaporated off, after which the sustained heating develops the colour. Apparatus required […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sesame oil is detected by the crimson colour formed when the oil is treated with a dilute furfural solution and concentrated hydrochloric acid (the AOAC-adopted modification of the Baudouin test). A confirmatory shake with water distinguishes the sesame reaction, since the colour disappears when sesame […]

GIFSQ — Global Institute for Food Safety & Quality Principle This is a test to verify the presence of groundnut oil. Oils containing arachidic acid give a precipitate when their alcoholic soap solution is treated with dilute acetic acid or HCl. The precipitate forms at a particular temperature which is specific to the oil. For […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Kirschner value is a measure of the steam-volatile, water-soluble fatty acids forming water-soluble silver salts (butyric acid). After the R.M. value determination, the R.M. titrate is treated with silver sulphate, which precipitates the fatty acids forming water-insoluble silver salts; the remaining filtrate is redistilled […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Polenske value differs from the Reichert-Meissl value in that it is a measure of the steam-volatile but water-insoluble fatty acids — like caprylic, capric and lauric acids — present in oils and fats. The insoluble fatty acids retained on the filter paper during the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Reichert-Meissl (R.M.) value is the number of millilitres of 0.1 N NaOH solution required to neutralise the steam-volatile, water-soluble fatty acids distilled from 5 g of an oil or fat under the precise conditions specified in the method. It is a measure of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Unsaponifiable matter is that fraction of the substances in oils and fats which is not saponified by caustic alkali but is soluble in ordinary fat solvents. The material is completely saponified with alcoholic KOH and the unsaponifiable matter extracted with petroleum ether (or ethyl ether, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The acid value is the number of milligrams of KOH required to neutralise the free fatty acids present in one gram of the oil or fat. The sample is dissolved in neutralised alcohol and titrated with standard alkali using phenolphthalein as indicator. If the free […]

GIFSQ — Global Institute for Food Safety & Quality Principle Soluble mineral matter includes minerals combined with fatty acids in the form of soaps and in soluble form, usually present as lime soaps. The combined kerosene filtrate and washings from the insoluble impurity determination are burned off and the ash weighed, giving the soluble mineral […]

GIFSQ — Global Institute for Food Safety & Quality Principle The impurities in fats and oils consist of dirt, meal and other foreign substances insoluble in kerosene and petroleum ether. The fat is dissolved away in hot kerosene and the insoluble residue is collected on a prepared Gooch crucible; the gain in weight of the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Water in fats tends to settle when the fat softens and melts, so the sample is thoroughly mixed to distribute it uniformly before analysis. The moisture and other volatile matter are driven off by drying the sample in an oven at 105°C, and the loss […]

GIFSQ — Global Institute for Food Safety & Quality Principle The Crismer test determines the miscibility of the oil sample with a standard amyl-ethyl alcohol reagent: the temperature at which definite cloudiness appears on cooling (the turbidity temperature) is characteristic, within certain limits, for each kind of oil. The observed value is corrected for the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The thiocyanogen (SCN) value (T.V.) is a measure of the unsaturation of fats and oils, expressed as the equivalent number of centigrams of iodine absorbed per gram of sample (% iodine absorbed). Thiocyanogen does not add to fatty acids such as linoleic and linolenic in […]

GIFSQ — Global Institute for Food Safety & Quality Principle The iodine value (I.V.) is the number of grams of iodine absorbed per 100 g of the oil or fat, when determined using Wijs solution. The material is treated in carbon tetrachloride medium with a known excess of iodine monochloride in glacial acetic acid; the […]

GIFSQ — Global Institute for Food Safety & Quality Principle When a fat is boiled with an excess of alcoholic KOH, the triglycerides hydrolyse and glycerol and soap are formed. The alkali consumed in this hydrolysis, expressed as the number of milligrams of KOH required to saponify completely one gram of the oil or fat, […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colour of an oil or fat is an identity and quality characteristic, measured either by visual matching in a Lovibond Tintometer or spectrophotometrically at the wavelength of maximum absorption against a solvent blank. Apparatus required Lovibond Tintometer with 1 inch or 5.25 inch cell, […]

GIFSQ — Global Institute for Food Safety & Quality Principle Fats are complicated mixtures of a large number of components and do not display a single melting point but a melting range. The fat, conditioned through a prescribed preheating and chilling routine, is observed in capillary tubes while the temperature is raised slowly: the temperatures […]

GIFSQ — Global Institute for Food Safety & Quality Principle The refractive index of an oil or fat, measured at a specified temperature, is an identity characteristic used to distinguish one oil from another and to detect admixture. It is read on an Abbe or Butyro refractometer against a monochromatic light source. Apparatus required Abbe […]

GIFSQ — Global Institute for Food Safety & Quality Principle The specific gravity of an oil or fat is the ratio of the weight of a given volume of the oil at 25°C to the weight of an equal volume of water at 25°C. It is determined gravimetrically with a pycnometer after bringing both the […]

GIFSQ — Global Institute for Food Safety & Quality Principle Total sulphur dioxide in sugar is determined by the distillation procedure (Method I) as given in Chapter 12 of the book, using 100 g of the sample. Apparatus required Distillation assembly as given for Method I in Chapter 12 of the book. Reagents As given […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sugar crystals are graded by sieve analysis: a weighed sample is shaken on a nest of sieves and the fractions retained on each sieve are weighed; the weight of each fraction in grams is the percentage of sugar retained on that sieve. The cumulative percentages […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colouring matter in sugar is measured by its absorption at 420 nm in a spectrophotometer against a distilled-water reference of zero colour. Earlier procedures based on the difference between the spectral absorption curves of colouring matter and turbidity at two wavelengths were not entirely […]

GIFSQ — Global Institute for Food Safety & Quality Principle Lead, copper and arsenic in sugar are determined after sugar-specific sample preparation; the final estimation of each element is carried out by the method given in Chapter 6 of the book. For refined sugar, lead is separated directly from the dissolved sample; for raw or […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sugar sample is dissolved in distilled water and filtered through a tared membrane filter of 5 µm pore size. The membrane retains the insoluble extraneous matter (atmospheric dust, rust from weighing scales, fibre from packing material, etc.); after thorough washing, drying and weighing, the […]

GIFSQ — Global Institute for Food Safety & Quality Principle In raw and/or impure sugars, the percentages of sucrose, reducing sugar, ash and moisture are totalled and the total is subtracted from 100 to give the per cent of organic matter other than sugars. This difference procedure does not suit the routine analysis of refined […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is dried to constant weight in a hot air oven or in a vacuum oven; the loss in weight is reported as moisture. The result obtained may not reflect the true moisture content, because carbohydrates and some other organic compounds are not stable […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is charred with concentrated sulphuric acid, which converts the mineral constituents to their sulphates, and then ashed in a muffle furnace at 550°C. The residue is moistened with dilute sulphuric acid, dried and re-ashed until constant weight; the increase in the weight of […]

GIFSQ — Global Institute for Food Safety & Quality Principle The ash content of refined sugar is too low to be measured by the gravimetric method. The electrical conductivity of an aqueous sucrose solution is almost entirely due to the dissolved ash (solutions of pure sugars are very poor conductors), so the ash content is […]

GIFSQ — Global Institute for Food Safety & Quality Principle The organic matter of the sugar sample is destroyed by charring and ashing in a muffle furnace at 550°C until an almost white ash remains. The ash is moistened, dried and re-ashed to obtain a constant weight; the increase in the weight of the tared […]

GIFSQ — Global Institute for Food Safety & Quality Principle Reducing sugars reduce the copper in Miller’s alkaline copper reagent to cuprous oxide on heating in a boiling water bath. After cooling, acetic acid and excess 0.0333 N iodine are added; the copper precipitate dissolves, and the unreacted iodine is back-titrated with 0.0333 N sodium […]

GIFSQ — Global Institute for Food Safety & Quality Principle Reducing sugars reduce the copper in an alkaline copper reagent (Luff solution) to cuprous oxide on boiling. After cooling, the unreduced copper is determined iodimetrically: potassium iodide and dilute sulphuric acid liberate iodine, which is titrated with 0.1 N sodium thiosulphate using starch as indicator. […]

GIFSQ — Global Institute for Food Safety & Quality Principle Solutions of sucrose rotate the plane of polarized light. The angle of rotation varies with the concentration of the optically active substance, the length of the light path through the solution, the wavelength of the light, and the temperature. Sucrose in sugar is therefore determined […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is digested with H₂SO₄, HNO₃ and HClO₄ (perchloric acid). The digest is treated with a reducing solution; mercury vapours are flushed into the gas flow-through cell of an atomic absorption spectrophotometer; light from a mercury hollow cathode lamp is passed through the cell, […]

GIFSQ — Global Institute for Food Safety & Quality Principle Food samples are digested with HNO₃, H₂SO₄ and HClO₄ (perchloric acid). Lead in the digest is coprecipitated with strontium sulphate (SrSO₄); the precipitate is separated from the digest and converted to carbonate by agitation with ammonium carbonate solution; the carbonates are dissolved in 1 N […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sample is digested with HNO₃, H₂SO₄ and H₂O₂. All metals are extracted from the digest with dithizone in chloroform at pH 9.0; cadmium is removed from the extract by acidifying the dithizone extract with dilute HCl, and is determined with an atomic absorption spectrophotometer […]

GIFSQ — Global Institute for Food Safety & Quality Principle Atomic absorption spectroscopy and flame photometry are used for the detection and determination of metals in foods. When a test solution is aspirated into a flame, the metal atoms remain largely in the ground state; they can be made to absorb radiation of the correct […]

GIFSQ — Global Institute for Food Safety & Quality Principle After preliminary extraction of the digest with diethylammonium diethyldithiocarbamate solution, the arsenic in the extract is converted to the arsenomolybdate complex, which is reduced with hydrazine sulphate to a molybdenum-blue compound measured at 840 nm. The method suits 1.5 to 15 μg of arsenic in […]

GIFSQ — Global Institute for Food Safety & Quality Principle After destruction of the organic matter by wet oxidation and distillation as the trichloride, the arsenic is reduced by nascent hydrogen to arsine (arsene), which produces a stain on mercuric chloride paper; the extent of the stain is taken as the measure of arsenic by […]

GIFSQ — Global Institute for Food Safety & Quality Principle Arsenic in the wet digest of the sample is reduced to arsine (arsene) by nascent hydrogen, which produces a stain on a strip of mercuric bromide paper; the length of the stain is proportional to the arsenic concentration and is estimated by comparison with the […]

GIFSQ — Global Institute for Food Safety & Quality Principle When ammoniacal cyanide solution of dithizone is added to a solution containing lead, a red lead-dithizone complex soluble in chloroform or carbon tetrachloride is formed; the red colour is measured at 510 nm. Dithizone is not specific for lead — it forms coloured compounds with […]

GIFSQ — Global Institute for Food Safety & Quality Principle Lead, copper, cadmium, bismuth, antimony, mercury and silver are eliminated from the digest as sulphides; cobalt is removed as the alpha-nitroso-beta-naphthol complex and nickel as the dimethylglyoxime complex with chloroform. Zinc is then extracted as zinc dithizonate, which is measured colorimetrically at 540 nm. Apparatus […]

GIFSQ — Global Institute for Food Safety & Quality Principle Tin in an aliquot of the digest is reduced to the stannous form by nascent hydrogen (from aluminium foil in acid) in an atmosphere of CO₂ to exclude oxygen; the stannous tin formed is titrated with potassium iodate in the presence of potassium iodide, using […]

GIFSQ — Global Institute for Food Safety & Quality Principle Copper is determined colorimetrically as copper diethyldithiocarbamate at pH 8.5 in the presence of ethylenediaminetetraacetic acid (EDTA) as chelating agent. Copper reacts with sodium diethyldithiocarbamate in alkaline solution producing a yellow to brown colour depending on the amount of metal present; the colour is soluble […]

GIFSQ — Global Institute for Food Safety & Quality Principle Sodium in solution is atomized into an oxyhydrogen or oxyacetylene flame. The flame excites the sodium atoms, causing them to emit radiation at specific wavelengths; the amount of radiation emitted is measured on a spectrophotometer and is proportional to the sodium concentration in the solution […]

GIFSQ — Global Institute for Food Safety & Quality Principle In acid solution potassium is precipitated as the yellow double salt sodium potassium cobaltinitrite. The precipitate is dissolved in hot dilute acid and titrated with standard potassium permanganate; since the end point is indeterminate, a standard quantity of sodium oxalate is added at the end […]

GIFSQ — Global Institute for Food Safety & Quality Principle Potassium in solution is atomized into an oxyhydrogen or oxyacetylene flame. The flame excites the potassium atoms, causing them to emit radiation at specific wavelengths; the amount of radiation emitted is measured on a spectrophotometer and is proportional to the potassium concentration in the solution […]

GIFSQ — Global Institute for Food Safety & Quality Principle Iron in the food is converted to the ferric form with oxidizing agents such as potassium persulphate or hydrogen peroxide, and treated with potassium thiocyanate to form the red ferric thiocyanate complex, which is measured colorimetrically at 480 nm. Apparatus required Stoppered measuring cylinders Colorimeter […]

GIFSQ — Global Institute for Food Safety & Quality Principle Phosphorus reacts with molybdic acid to form a phosphomolybdate complex, which is reduced with 1-amino-2-naphthol-4-sulphonic acid to molybdenum blue; the blue colour is measured colorimetrically at 650 nm. Apparatus required Volumetric flasks, 50 ml Colorimeter or spectrophotometer (650 nm) Reagents a. Molybdate solution: dissolve 25 […]

GIFSQ — Global Institute for Food Safety & Quality Principle In an alkaline solution from which calcium and iron have been removed, magnesium is precipitated as magnesium ammonium phosphate. The precipitate is dissolved in acid and the phosphorus it contains is determined colorimetrically as molybdenum blue; magnesium is then calculated from the phosphorus (1 ml […]

GIFSQ — Global Institute for Food Safety & Quality Principle Calcium is precipitated as calcium oxalate from the ash solution. The precipitate is filtered, dissolved in hot dilute sulphuric acid and titrated with standard potassium permanganate; the volume of permanganate consumed is proportional to the calcium present (1 ml of 0.01 N KMnO₄ = 0.2 […]

GIFSQ — Global Institute for Food Safety & Quality Principle Fruits, vegetables and their products contain organic matter that must be destroyed before minerals can be estimated. Destruction is carried out by dry ashing or by wet digestion. The choice depends on the nature of the organic material, the inorganic constituents present, the metal to […]

GIFSQ — Global Institute for Food Safety & Quality Principle Folic acid is extracted from food samples using a mild alkaline buffer, oxidised with permanganate, and the resulting amine is diazotized. The diazotized compound is coupled with N-(1-naphthyl)ethylenediamine, and the colour developed is determined at 550 nm after extraction into iso-butyl alcohol. Apparatus required Volumetric […]

GIFSQ — Global Institute for Food Safety & Quality Principle Riboflavin fluoresces in light of wavelength 440 to 500 nm, and the intensity of fluorescence is proportional to the concentration of riboflavin within a certain range. The vitamin is extracted from the material with hot dilute acids, interference by other substances is eliminated by treatment […]

GIFSQ — Global Institute for Food Safety & Quality Principle Thiamine is extracted from the food material with hot dilute acid, and the extract is treated with phosphatase to release thiamine from the bound form. The extract is passed through a base-exchange silicate column to remove interfering substances. Thiamine is eluted from the column and […]

GIFSQ — Global Institute for Food Safety & Quality Principle 2,4-Dinitrophenylhydrazine forms an osazone with dehydroascorbic acid and diketogulonic acid, which dissolves in concentrated H₂SO₄ forming an intense red solution measurable colorimetrically at 520 nm. Ascorbic acid is estimated after oxidation with bromine to dehydroascorbic acid, followed by osazone formation. Three prepared solutions separate the […]

GIFSQ — Global Institute for Food Safety & Quality Principle The method follows the direct colorimetric method, except that the excess of dye is taken up in xylene and the colour is measured in the xylene layer. It is particularly suitable for fresh materials and stored products containing considerable interfering substances, and enables the determination […]

GIFSQ — Global Institute for Food Safety & Quality Principle Ascorbic acid decolorizes 2,6-dichlorophenol-indophenol solution. The extent of decolorization — in sample extracts and in standard ascorbic acid solutions — is measured colorimetrically. Since interfering substances reduce the dye slowly, a rapid determination measures mainly the ascorbic acid. Apparatus required Colorimeter or spectrophotometer (reading at […]

GIFSQ — Global Institute for Food Safety & Quality Principle Ascorbic acid reduces the dye 2,6-dichlorophenol-indophenol — blue in alkaline solution, red in acid solution — to a colourless form. The reaction is quantitative and, in the pH range 1 to 3.5, practically specific for ascorbic acid. The amount of dye reduced is determined by […]

GIFSQ — Global Institute for Food Safety & Quality Principle Individual anthocyanins must be separated before each one can be quantified. With fresh or frozen fruits the crude pigment may be separated without purification; with sweetened products, preliminary purification (basic lead acetate precipitation or Amberlite CG-50 ion-exchange chromatography) is essential to remove or reduce the […]

GIFSQ — Global Institute for Food Safety & Quality Principle A simple direct total-anthocyanin determination cannot be made when chlorophyll or its degradation products, or brown degradation products of anthocyanins, interfere. The pH differential method developed by Fuleki and Francis measures absorbance in samples diluted with pH 1.0 and pH 4.5 buffers: at pH 1.0 […]

GIFSQ — Global Institute for Food Safety & Quality Principle Anthocyanins are extracted with ethanolic HCl (95% ethanol–1.5 N HCl, 85 : 15) and the colour is measured at the wavelength of maximum absorption. The total anthocyanin content is calculated using the molecular extinction (ε max) values given in the source’s Table 4-1, or by […]

GIFSQ — Global Institute for Food Safety & Quality Principle Anthocyanin pigments are extracted from fruit with acidified methanol or n-butanol, purified by ion-exchange (Amberlite CG-50, Dowex 50WX4) or lead-acetate precipitation, and separated into individual pigments by paper chromatography, silicic-acid or polyamide column chromatography. The separated pigments are crystallized; their absorption spectra are taken and […]

GIFSQ — Global Institute for Food Safety & Quality Principle Chlorophyll is extracted with acetone and its colour is measured at 660 nm against a calibration curve. The colorimeter is calibrated with a series of dilutions of a plant extract whose absolute chlorophyll concentration is determined spectrophotometrically at 660 nm and 642.5 nm (see SOP: […]

GIFSQ — Global Institute for Food Safety & Quality Principle The method measures the optical density of an ether extract of chlorophyll at 660 nm and 642.5 nm, then applies the specific absorption coefficients of Comar and Zscheile to obtain the total chlorophyll and the separate chlorophyll a and b concentrations. For total chlorophyll alone, […]

GIFSQ — Global Institute for Food Safety & Quality Principle Pure lycopene is prepared from bright-red tomato paste by saponification with methanolic potassium hydroxide, filtration through filter aid, extraction of the lycopene crystals from the cake with warm acetone, recrystallization from chloroform–methyl alcohol, and drying under vacuum. The pure crystals serve as the reference standard […]

GIFSQ — Global Institute for Food Safety & Quality Principle The red colour of tomato is due to the pigment lycopene (C₄₀H₅₆). Its two absorption maxima lie at 473 nm and 503 nm; the molecular extinction coefficients for all-trans lycopene are 18.6 × 10⁴ at 473 nm and 17.2 × 10⁴ at 503 nm. A […]

GIFSQ — Global Institute for Food Safety & Quality Principle The total carotenoid content — carotenes, xanthophylls and xanthophyll esters together — is estimated from the petroleum ether extract of the sample without chromatographic separation, by measuring the colour at 452 nm against a β-carotene standard curve. Apparatus required Volumetric flasks, 100-ml Spectrophotometer or colorimeter […]

GIFSQ — Global Institute for Food Safety & Quality Principle Carotenoid pigments are separated by chromatography. The method separates the biologically active carotenoid pigments from the total carotenoid pigments in an extract on an adsorbent column that retains the different pigments with different strengths. β-Carotene moves off the column before all other pigments and its […]

GIFSQ — Global Institute for Food Safety & Quality Principle Tannins are estimated by their oxidisability with potassium permanganate. An aliquot of the sample is titrated with standard permanganate in the presence of indigo carmine as the redox indicator, giving the total oxidisable (tannin-like) matter. A second aliquot is first treated with gelatin in acid […]

GIFSQ — Global Institute for Food Safety & Quality Principle The sugar moieties of some anthocyanins are acylated, most often with p-hydroxybenzoic, p-coumaric, caffeic or ferulic acid. An acylated anthocyanin betrays itself spectrally by an extra absorption peak in the ultraviolet characteristic of the acyl group, in addition to the usual ultraviolet peak. The acyl […]

GIFSQ — Global Institute for Food Safety & Quality Principle The identity of an anthocyanin is completed by its sugar component. Acid hydrolysis liberates the sugar, which is separated from pigment and salts on ion-exchange resins and identified by paper chromatography against authentic sugars. Since different sugars move very slowly on the paper, their mobilities […]

GIFSQ — Global Institute for Food Safety & Quality Principle Anthocyanins absorb strongly in the visible region while most other flavonoids absorb in the ultraviolet, so their spectra identify the pigment class. The pigment is dissolved in methanol containing 0.01% HCl, since anthocyanins are not stable to light or alkali, and the optical density is […]

GIFSQ — Global Institute for Food Safety & Quality Principle The colorimetric estimation of tannins is based on the measurement of the blue colour formed by the reduction of phosphotungstomolybdic acid (the Folin–Denis reagent) by tannin-like compounds in alkaline solution. A standard curve is prepared from tannic acid, and the tannin content of the sample […]

GIFSQ — Global Institute for Food Safety & Quality Principle Anthocyanins are the red, blue and purple glycosidic pigments of fruits and vegetables; they are stable as their salts and are extracted with acidic alcohol. The extract is concentrated and the pigments are separated by paper chromatography on Whatman No. 3 paper using the butanol–2 […]

GIFSQ — Global Institute for Food Safety & Quality Principle Leucoanthocyanins are colourless precursors that are converted by hot acid into the deeply coloured anthocyanidins. Three tests exploit this chemistry: direct heating with 2 N hydrochloric acid gives a red extract from which the coloured product partitions into iso-amyl alcohol; heating with a butanol–hydrochloric acid […]

GIFSQ — Global Institute for Food Safety & Quality Principle The phenolic fractions obtained by extraction are mixtures of many closely related compounds. Two-dimensional paper chromatography separates them on the basis of their partition between the stationary aqueous phase held by the paper and the moving solvent, and the separated spots are identified by their […]

GIFSQ — Global Institute for Food Safety & Quality Principle Polyphenols occur in plant foods as glycosides, catechins, leucoanthocyanins, flavones, flavonols and polymeric forms, with very different solubilities. The phenolic glycosides, catechins and leucoanthocyanins are generally soluble in water, while flavones and flavonols are only sparingly soluble. This procedure gives a general fractional-extraction scheme that […]

GIFSQ — Global Institute for Food Safety & Quality Principle Pectinases degrade pectin to galacturonic acid or low molecular weight polymers of it. Polygalacturonase (sometimes considered synonymous with pectinase) seldom occurs in higher plants, and then only in small amounts; it is produced by many bacteria and fungi and has been reported in snails. The […]

GIFSQ — Global Institute for Food Safety & Quality Principle Pectin methylesterase (pectase or pectinesterase) deesterifies pectin and makes it susceptible to precipitation by calcium or other polyvalent cations. In most plant tissues the enzyme is rarely in solution but is adsorbed on the insoluble cellular solids; it is therefore necessary to extract the plant […]

GIFSQ — Global Institute for Food Safety & Quality Principle The water-soluble pectic substances are sufficiently high-methoxyl pectins; in citrus juices these give the juice its body or consistency and serve as colloidal stabilizers for the insoluble suspended solids. The sodium hexametaphosphate-soluble pectic substances are the low-methoxyl pectinates of the polyvalent cations, magnesium and calcium; […]

GIFSQ — Global Institute for Food Safety & Quality Principle The water-soluble fraction includes pectin and those colloidal pectinic acids of sufficiently high methyl ester content which are located largely in the liquid phase of a food product; they contribute to consistency and serum viscosity, and act as colloid stabilizers that prevent settling or flocculation […]