This article throws light upon the top twelve methods used for food material preservation. The methods are: 1. Asepsis 2. Pasteurization 3. Sterilization 4. Refrigeration 5. Freezing 6. Chemicals 7. Dehydration 8. Carbonation 9. Sugars 10. Salts 11. Acids 12. Antibiotics.
Method # 1. Asepsis:
Asepsis is the prevention of microbes by maintaining general cleanness during picking, grading, packing and transportation of food materials.
Method # 2. Pasteurization:
Pasteurization is carried out as heat treatment food material at 72°C for 15 seconds, or 63°C for 30 minutes, or 90°C for 0.5 second immediately followed by rapid cooling to 7-4°C. The high-temperature-short-time (HTST) treatments cause less damage to the nutrient composition and sensory characteristics of foods and therefore are preferred over the low temperature- long-time (LTLT) treatments.
Method # 3. Sterilization:
Sterilization is the complete exclusion of microbes. Fruits and acidic vegetables like tomato can be sterilized at 100°C for 30 minutes; whereas, non-acidic vegetables require treatment of 116°C temperature for 30 minutes.
Method # 4. Refrigeration:
The shelf life of many food materials may be increased by storage at 4°C or below. Commonly refrigerated foods include fresh fruits and vegetables, eggs, dairy products, and meats. However, some foods, such as tropical fruits (e.g., bananas), are damaged if exposed to low temperatures.
Method # 5. Freezing:
Freezing provides an excellent means of preserving the nutritional quality of foods. It is done at -18°C to -4°C. Juices are mostly preserved by freezing.
Method # 6. Chemicals:
According to FPO (1955), two chemicals viz. Sulphur dioxide and Benzoic acid, are allowed in India to be used as preservatives.
(a) Sulphur dioxide acts as an antioxidant and bleaching agent. It is used in the form of its salts like sulphite, bi-sulphite and metabisulphite. Permissible amount in fruit juices including RTS and nectar is 100 ppm whereas in squash, crush and cordial it is 350ppm. Sulphur dioxide retains the original colour of beverages for longer period than benzoic acid.
(b) Benzoic acid is used in the form of sodium benzoate and permitted up to 100 ppm in RT5 and nectar, 600ppm in squash, crush, and cordial.
Method # 7. Dehydration:
Dehydration is removal of moisture from the food materials for preservation. The initial temperature of dehydration is usually at 43°C, which is gradually increased up to 60-66°C (for vegetables) and 66-71°C (for fruits).
I. Moisture content in dried products should not be more than 6-8% for vegetables and 10-20% for fruits.
II. Sweating is the process, which is done to equalize the moisture content by keeping preserved material into bins or boxes.
III. Sulphuring is process of fuming food materials (particularly potato slices) through sulphur dioxide to prevent discolouration.
IV. Freeze-Drying is done by employing high vacuum conditions, permitting specific temperature and pressure.
Method # 8. Carbonation:
Carbonation is the process of dissolving sufficient carbon dioxide in water or beverages to inhibit the microbial activity. Complete inactivation of microbial activity (moulds including yeast) can be achieved by mixing 14.6 g CO2 per liter for juice or beverage.
Method # 9. Sugars:
Sugars preserve food by the process of osmosis. Approximately 66% or more sugar is necessary for preservation of fruits. Fruit syrup. Jam, Jelly, Marmalade, Preserve, Candy, Crystallized fruit and glazed fruit are preserved using sugars.
Method # 10. Salts:
Salts about 15-25% concentration are sufficient to preserve most of the food products.
Method # 11. Acids:
Acids like vinegar, acetic acid, citric acid and lactic acid are used for preservation of food materials including fruits by inhibiting the growth of microbes responsible for food spoilage. Food material containing 1-5% acetic acid solution can be kept fresh for longer period.
Method # 12. Antibiotics:
Antibiotics are also used as preservatives for food materials. Nisin is used for canning of mushrooms, tomatoes, and milk products. Pimaricin (used primarily against Pythium spp.) is used for treating fruits for fruit juices.