1. Freezing

Many food products can have their shelf-life extended by storing them at 4°C or below. Fresh fruits and vegetables, eggs, dairy products, and meats are all commonly refrigerated foods. However, some items, such as tropical fruits (bananas, for example), are destroyed by low temperatures. Freezing is an excellent way to preserve the nutritional value of foods. It’s done at a temperature of –18°C to –4°C. The majority of juices are kept by freezing.

  1. Chemicals used

Sulphur dioxide is a bleaching and antioxidant agent. Sulphite, bi-sulphite, and metabisulphite are some of the salts that are employed. The permissible level in fruit juices, including RTS and nectar, is 100 parts per million; however, it is 350 parts per million in squash, crush, and cordial. Sulphur dioxide keeps beverages’ original colour for a longer time than benzoic acid.

Benzoic acid, in the form of sodium benzoate, is allowed up to 100 parts per million in RT5 and nectar, and 600 parts per million in squash, crush, and cordial.

  1. Dehydration

Dehydration is the process of removing moisture from food materials in order to preserve them. The temperature of dehydration starts at 43°C and gradually rises to 60–66°C (for vegetables) and 66–71°C (for meat) (for fruits).

  1. For vegetables, the moisture content in dried products should not exceed 6–8 percent, and for fruits, 10–20 percent.

  2. Sweating is a process that is used to equalise the moisture content of preserved materials by storing them in bins or boxes.

  3. Sulphuring is a method of preventing discoloration by fuming food materials (especially potato slices) with sulphur dioxide.

  4. Freeze-drying is accomplished by using high vacuum conditions that allow for precise temperature and pressure.

Other types of preservation may Include irradiation, jellying, jugging, processing of pulsed electric fields, modified atmosphere, ground burial, biopreservation, and high pressure.

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