SOP: Determination of Total Ash — Spices
GIFSQ — Global Institute for Food Safety & Quality
The ash of a foodstuff is the inorganic residue remaining after complete burning away of the food, usually at a temperature not exceeding red heat. Ash can often serve as a measure for adulteration of a food. The higher the ash content of the sample, the higher the inorganic adulterant. Conversely, a low level of ash might indicate the food/spice with low inorganic material.
1. Principle
When spices are ignited at high temperature, in a furnace (550 ± 25°C), organic matter is burnt out and mineral and other inorganic matter remain in the ash.
2. Application
This method is applicable to measure the total inorganic material in spices and also in other food products.
3. Apparatus
- Silica crucible
- Drying oven
- Electric balance
- Muffle furnace
- Desiccator containing an efficient desiccant such as anhydrous calcium sulfate or silica gel
4. Procedure
Place dry silica crucible in desiccator about half an hour (to avoid moisture)
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Take weight of moisture free crucible
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Take appropriate wt. of sample in the weighed crucible (2 gram in spices commodities). Pour about 2 mL of ethanol on the material and ignite it. When the ethanol is burnt off, heat the dish carefully over a small flame to char the material
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Place the crucible in the entrance of the open muffle, then ignite in a muffle furnace at 550 ± 25°C for 3–4 hours
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Cool and wet the ash with a few drops of water. Evaporate carefully to dryness
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Heat at 550 ± 25°C for an additional 30 min until the ash is white gray
(If carbon persists, leach ash with hot water, filter through quantitative paper, wash paper thoroughly, transfer paper and content to ashing dish, dry, ignite at 550 ± 25°C until ash is white. Cool dish, add filtrate, evaporate to dryness on steam bath, and heat in furnace 30 min.)
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Cool the crucible in the desiccator and weigh
5. Calculation
% Ash = [Wt. of ash ÷ Wt. of sample taken] × 100
6. Notes
- In case of Nutmeg, Mace, Ginger and Cloves, the ignition should be carried out at 600 ± 25°C.
- Ground mustard or mustard flour: Ignite as above and heat 30 min at 550 ± 25°C. Leach the ash with hot water, filter and wash filter paper thoroughly. Transfer the filter paper and contents to the dish, dry and heat in muffle furnace 30 min. Remove dish, let it cool, add 5–10 drops nitric acid, evaporate to dryness, and heat in furnace 30 min. Repeat nitric acid and heating treatment until residue is white. Add filtrate, evaporate to dryness, and heat in furnace 30 minutes; cool and weigh as above.
References
AOAC 21st edn. 2019, Official Method 941.12, Ash of Spices; IS Specification No. IS 1797–1985, Methods of Test for Spices and Condiments.