Food Preservation, Adulteration and Food Safety Notes

Food begins to spoil the moment it is harvested or slaughtered, and almost every technique of food preservation is an attempt to stop the three agents of that spoilage: micro-organisms, the food's own enzymes, and oxygen. Food safety law adds a second layer by fixing what may be added to food and what may not, and by punishing adulteration. The subject is a steady favourite in General Science and General Awareness papers, and it returns to the news whenever the food regulator issues fresh standards, such as the draft rules on pesticide residue limits in tea and on added sugars in infant foods. The lasting facts below are what examiners actually ask.

Why food spoils

Bacteria, yeasts and moulds need moisture, warmth, a near-neutral pH and oxygen to multiply. Remove any one of these and growth slows or stops. Enzymes inside the food continue to act even after harvest, which is why a cut apple browns and why peas lose sweetness. Fats turn rancid by oxidation. Preservation therefore works by one of four strategies: killing the micro-organisms, removing their water, making the surroundings hostile to them, or slowing every chemical reaction by cooling. Using two or three mild methods together instead of one harsh one is called hurdle technology, and it is how most packaged food is kept safe today.

Methods of preservation

Low temperature does not kill microbes; it only slows them. Refrigeration at about 0 to 5 degrees Celsius slows respiration and microbial growth, which is why fruit kept in a cold chamber has a longer storage life. Freezing at about minus eighteen degrees Celsius halts growth altogether. Heat destroys microbes: pasteurisation of milk uses either the low-temperature long-time method at about 63 degrees Celsius for thirty minutes or the high-temperature short-time method at about 72 degrees Celsius for fifteen seconds, followed by rapid chilling. Ultra-high temperature treatment uses roughly 135 to 150 degrees Celsius for a few seconds and gives milk that keeps unopened for months. Canning, invented by Nicolas Appert, seals food in an airtight container and then heats it; Louis Pasteur later explained why such heating works.

Drying and dehydration remove the water microbes need. Freeze-drying, or lyophilisation, freezes the food and then removes the ice directly as vapour under vacuum by sublimation, which preserves flavour and is used for instant coffee and vaccines. Osmotic methods bind the remaining water: heavy salting cures fish and meat, high sugar concentration preserves jam and squash, and acid in vinegar or in oil pickles lowers the pH below what spoilage organisms tolerate. Fermentation lets harmless lactic acid bacteria acidify the food themselves, as in curd, idli batter and pickles.

Chemical preservatives are divided by Indian food standards into two classes. Class I preservatives are natural and may be used without restriction: common salt, sugar, dextrose, spices, vinegar, honey and edible vegetable oils. Class II preservatives are chemical and are permitted only in listed foods and listed quantities: benzoic acid and sodium benzoate, sulphur dioxide and sulphites, sorbic acid and sorbates, nitrites and nitrates for cured meat, and propionates against mould in bread. Antioxidants such as ascorbic acid and tocopherols are added against rancidity rather than against microbes. Irradiation exposes food to gamma rays from a cobalt-60 source to kill insects, delay sprouting in onions and potatoes and destroy pathogens; it does not make the food radioactive, and irradiated food carries the international Radura symbol. Vacuum packing and modified atmosphere packaging replace oxygen with carbon dioxide or nitrogen.

Common adulterants and simple tests

Calcium carbide, once used to ripen mangoes artificially, is banned in India because it releases acetylene and carries traces of arsenic and phosphorus; controlled ripening with ethylene gas is the permitted alternative. Formalin in fish, oxytocin injected into milch animals and industrial dyes in sweets are other prohibited practices.

Food safety law in India

The Food Safety and Standards Act, 2006 replaced a group of older laws, chief among them the Prevention of Food Adulteration Act, 1954, and created a single regulator, the Food Safety and Standards Authority of India, which works under the Ministry of Health and Family Welfare and has its headquarters at New Delhi. Every food business must hold an FSSAI licence or registration, and the number printed on the pack lets a buyer trace the manufacturer. Internationally, food standards are set by the Codex Alimentarius Commission, created jointly by the Food and Agriculture Organization and the World Health Organization. World Food Safety Day is observed on 7 June and National Consumer Day in India on 24 December. Fortified food carries the plus-F logo, agricultural produce graded under the Agricultural Produce (Grading and Marking) Act carries the AGMARK seal, and processed goods under compulsory certification carry the ISI mark of the Bureau of Indian Standards.