SOP: Determination of Extraneous Material in Alimentary Paste Products

GIFSQ — Global Institute for Food Safety & Quality

1. Principle

Extraneous material in alimentary paste is divided into light filth and heavy filth. Light filth elements (insects, insect fragments, mites, hairs, feather barbules) are isolated by acid digestion of the product, sieving, and separation in a mineral-oil interface in a percolator. Heavy filth particles (sand, soil, metal, glass, insect and rodent excreta pellets) are isolated from the drainings by settling, decanting, and, where needed, flotation with chloroform. Both are examined under a stereoscopic microscope at 30× magnification (70× only to confirm questionable particles), identified with the aid of the method’s insect tables, and recorded by type, number and size range. Heavy filth is also determined gravimetrically by weighing before and after ashing.

2. Apparatus required

• Balance
• Two 2.0 L beakers with lids (watch glasses)
• Autoclave: either (a) slow-exhaust type (set slow exhaust to lower the pressure from 1.15 to 0 kg per sq. cm in 15–20 min.) or (b) non-slow-exhaust type (let cool to 0 kg per sq. cm before opening or venting)
• U.S. standard No. 230 sieve
• Shallow pan, 20 cm in diameter
• Smooth magnetic stirring bar, Teflon coated (1 × 5 cm)
• Stirrer hot plate
• 2 L percolator, premarked at 250 and 1700 mL levels
• Wash bottles
• Rubber policeman
• Suction filtration apparatus with Buchner or Hirsch funnel (5–7 cm perforated plate)
• Ruled filter paper (larger than the funnel plate, 7–9 cm)
• Petri dishes to suit the size of filter paper used
• Stereoscopic microscope (10–30×)
• Ashless filter paper (larger than the funnel plate, 7–9 cm)
• Drying oven (40–60°C)
• Crucible
• Desiccator
• Muffle oven

3. Reagents

• Concentrated HCl
• Antifoam solution: BDH Antifoam B
• Detergent: 1% sodium lauryl sulphate
• To prepare: dissolve 1 g of sodium lauryl sulphate in distilled water and make up to 100 mL.
• Mineral oil: paraffin oil, white, light, 125/135 Saybolt Universal Viscosity (38°C), specific gravity 0.840–0.860 (24°C)
• Alcohol: either 95% ethanol or 99% isopropanol
• Glycerol-alcohol (95%) mixture (1:1)
• To prepare: mix equal volumes of glycerol and 95% ethanol (for example, 50 mL of each).
• Chloroform (CHCl₃)

4. Sample collection and preparation

• Scrutinize the entire lot for live infestation. If live infestation is found, do not sample until after fumigation or other effective treatment.
• Obtain three sample units selected at random from the lot, each of at least 225 g, using appropriate sampling equipment and containers. Three sample units constitute a sample.
• Keep each sample unit separate and label them 1, 2, 3. Record lot size, weight of individual containers, country of origin, exporter, importer or domestic manufacturer, and product and lot identification; this information accompanies the sample.
• Thoroughly mix a sample unit and weigh out 225 g of alimentary paste; this 225 g constitutes an analytical unit.
• Repeat the previous step for the remaining two sample units.

5. Procedure

Isolation — light filth

Transfer an analytical unit to a 2 L beaker. For spaghetti, break it into lengths that will not lie flat on the bottom of the beaker — if large amounts of spaghetti lie on the bottom they may not digest completely

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Add 1 L of HCl (30 mL concentrated HCl + 970 mL water) and 0.3 mL of antifoam solution; cover with a lid; set the beaker in a larger container in case of breakage

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Autoclave for 30 min. at 121°C

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Wet-sieve on a No. 230 sieve with hot tap water (50–70°C) to remove all original liquid and a major portion of fine material

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If any fat material remains, defat: place the sieve in a shallow pan, cover the residue to a depth of about 2 cm with hot (50–70°C) detergent, leave for 5 min., drain, and wet-sieve with hot tap water until all suds have washed through (take care not to let suds foam over the sides of the sieve). Repeat the defatting at least once or until all visible fat is removed

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Transfer the sieve retainings to the original beaker with hot water (50–70°C) and dilute to about 1 L; add 30 mL concentrated HCl, a magnetic stirring bar and 50 mL of mineral oil

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Stir magnetically at the maximum speed that does not produce visible or audible splashing, for 6 min.

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Promptly transfer the beaker contents to a percolator containing about 250 mL of water; rinse the beaker into the percolator with hot tap water, making certain to transfer all material including heavy filth; bring the volume in the percolator to 1700 mL with hot tap water

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Rinse the magnetic particles from the stirring bar into a beaker — first with water, then alcohol, finally with detergent — until all particles are washed off; filter the washings through ruled filter paper using the suction filtration apparatus; transfer the filter paper to a petri dish and moisten with glycerol-alcohol mixture

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After 3 min., drain the oil interface in the percolator to 250 mL into a 2 L beaker; retain the beaker contents for the heavy filth determination

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Refill the percolator by pouring hot tap water down the percolator sides to loosen adhering material, and refill to the 1700 mL mark

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After 2–3 min., drain the percolator to 250 mL, discard the drainings, and refill for 2 more cycles. The lower layer should be almost free of suspended material after refilling. If not, continue through further recycles (the source prints “$ 1 recycles” here)

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Finally, drain the oil-water interface to the 250 mL mark and drain the remaining contents into the original beaker. Promptly wash down the sides of the percolator with wash bottles, successively with about 50 mL portions (the source prints “$ 50 mL”) of hot tap water, alcohol and hot tap water; use detergent if necessary

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Using the suction filtration apparatus, filter the beaker contents through ruled filter paper with a minimum of 50 mL washes of hot water, alcohol and water or detergent; use a rubber policeman if necessary to clean the sides of the beaker

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Transfer the filter paper(s) to petri dish(es) and moisten with glycerol-alcohol mixture

Examination — light filth

Examine the paper(s) microscopically at 30× magnification for all types of extraneous material. Use a higher magnification (70×) only to confirm questionable particles.

Recording results — light filth

Classify insect fragments into the following three categories:

• Premilling insect fragments (the source prints “# 0.595 mm”) that cannot be identified or are identified as field insects (see Tables 1 and 2)
• Premilling insect fragments (the source prints “# 0.595 mm”) that are identified as stored food insects (see Tables 2 and 3)
• Postmilling insect fragments (> 0.595 mm) that cannot be identified or are identified as stored food insects (see Tables 2 and 3)

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Record the number and range in size (mm) of all light filth elements separately for each analytical unit.

Isolation — heavy filth

Stir the contents of the beaker containing the drainings from the light-filth oil-interface step (the 250 mL beaker retained earlier) with a rubber policeman for 30 sec., and let the suspension stand undisturbed for 30 min.

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Decant the suspended food material without disturbing the bottom contents

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Add 400–500 mL of water, stir 30 sec., and let stand 10 min.

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Repeat the water addition, stirring and standing until practically all plant tissue has been decanted

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If any heavy filth is present, add 100–200 mL of CHCl₃, stir 30 sec., let stand 10 min., and then decant the water layer (top layer) without disturbing or pouring off any of the CHCl₃-water interface

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Filter the beaker contents onto an oven-dried, preweighed ashless paper; transfer the filter paper to a petri dish

Examination — heavy filth

Examine the filter paper microscopically at 30× magnification for rodent pellets, insect excreta, insect larvae, insect eggs and other organic filth.

Recording results — heavy filth

Record the number and range in size of each type of heavy filth detected for each analytical unit separately

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Dry the filter paper in an oven and weigh; determine the weight of heavy filth by difference

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If there is an appreciable amount of residue, transfer the filter paper with its contents to a preweighed crucible and ash in a muffle oven at about 500°C for two hr.; cool the material in a desiccator and weigh; determine the ashed weight by difference and record

6. Insect identification tables

Table 1. Examples of field insects

Table 2. Examples of insects infesting whole undamaged grains in storage. These insects may also attack grains in the field in warm climates.

Table 3. Common insects infesting damaged and milled grain

7. Calculation

Weight of heavy filth = W₂ − W₁

Ashed weight = W₄ − W₃

Where,

• W₁ = weight of the oven-dried, preweighed ashless filter paper
• W₂ = weight of the dried filter paper with its heavy filth residue
• W₃ = weight of the preweighed crucible
• W₄ = weight of the crucible with the ashed material, cooled in a desiccator

8. Precautions

• Check the autoclave periodically for corrosive damage (caution: concentrated HCl is autoclaved).
• Do not sample a lot showing live infestation until after fumigation or other effective treatment.
• Keep the three sample units separate and labelled 1, 2, 3 throughout.
• Record the number and size range of filth elements separately for each analytical unit.
• Use 70× magnification only to confirm questionable particles; routine examination is at 30×.
• Interpretation of results for alimentary paste follows Table 1 of the “Guidelines for the General Cleanliness of Food — An Overview” (Compendium of Analytical Methods, Volume 1), for semolina-derived alimentary paste. If the acceptability of the lot is in question, contact the National Manager, Food Microbiology and Extraneous Matter Evaluation Section, Food Safety Division, CFIA.

9. References

Health Canada, Compendium of Analytical Methods, Volume 4 — HPB Method ExFHPB-01, March 2009: “Determination of Extraneous Material in Alimentary Paste Products” (replaces ExFHPB-1, dated January 2006).