1. Physical changes: Colour, flavour, texture, taste, etc.
2. Chemical changes: Carbohydrates, fats, proteins, vitamins, and minerals.
3. Microbial changes: mold, yeast, and bacteria.

Why do we preserve food?

• To increase the supply of food by increasing the shelf life.
• Providing fruits and vegetables throughout the year.
• To diversify the diet.
• Preparing with fire saves consumers time and energy.
• To stabilize the prices of food in the market.
• To improve the health of the population.

Principles of preservation–There are three main principles:

1. Preventing or delaying the microbial decomposition of food.
2. Preventing or delaying the self-decomposition of food.
3. Prevention of damage caused by insects, animals, and mechanical.

1. Preventing or delaying the microbial decomposition of food:

• By keeping out the micro-organisms – Asepsis
• By removal of micro-organisms – Filtration
• By hindering the growth and activity of micro-organisms –Anaerobic condition
• By killing the micro-organisms- Exposing at high temperature.

A. Asepsis: It means preventing the entry of microorganisms, enhancing their quality, and thereby improving the quality of the finished product by maintaining general hygiene while picking, grading, packing, and transporting fruits and vegetables.

B. Filtration: Fruit juice, beer, soft drink, wine, etc. are filtered through bacteria-proof filters which are made of asbestos pad or unglazed porcelain type material.

These filters contain microorganisms and allow water or juice to seep through, with or without pressure.

C. Anaerobic Conditions: It can be maintained by:

• Replacing O₂ with CO₂ ———- Carbonation
• Evacuating (remove air) the sealed container (fruit juice)
• Use of oil on food (pickle)

D. Exposure to high temperature: Fruits can be exposed to high temperatures eg;

• Canning: Food is exposed to high temperatures (>100^OC) which reduce spoilage and inactivate enzymes present in the food. The process of sealing food items in containers by sealing them tightly (airtight, protecting from outside agencies) and sealing them with heat for long-term storage is called canning.
• Irradiation: In the case of radiation, food is exposed to radiation to kill living microorganisms by ionizing and non-ionizing radiation such as α, β, and rays. Here, the food is exposed to various frequencies ranging from electromagnetic or ionizing radiation or low-frequency electromagnetic rays to high frequency i.e. gamma rays which destroy the microorganisms present in the food.

2. Prevention/delay the self-decomposition:

• By destroying or deactivating enzymes –blanching
• Prevention/delay of non-enzymatic chemical reactions – Antioxidants

A. Blanching: Treatment of fruits and vegetables with boiling water or steam for short periods followed by cooling prior to canning is called” blanching”.

• It is a primary treatment in which tissues are softened to facilitate packaging.
• To retain the original color and taste.
• To destroy certain enzymes which are undesirable.
• For the elimination of air.
• Mostly used for vegetables.
• Removes micro-organisms
• Removes astringent taste and toxins.

B. Antioxidants: Anti-oxidants are substances that are used to prevent food from spoiling when exposed to air.

• BHA- Butylactic Hydroxy Anisole & BHT- Butylactic Hydroxy Toluene (Vegetable Oil)
• Gellales: animal fat, vegetable oil
• Tocopherols: Animal Fats
• Ascorbic acid: fruit juice, citrus oil, wine, beer, etc.
• Lactic Acid: Processed fruits and vegetables, canned fruits.
• Phosphoric acid: vegetable oils, animal fats, and cola drinks.

3. Prevention of damage caused by insects, animals, mechanical causes:

This principle of preservation deals with the prevention of damage caused by various external agencies other than micro-organisms and enzymes also i.e. animals, man, insects, rodents, etc. These agencies usually cause physical damage. For example for food items, rats can eat orange peel in storage, if the food items are kept within their reach, etc. But none of these damages are harmful to human health. You will usually never die or experience any health risks if you consume a half-eaten apple or orange, but if the food has been spoiled by microorganisms, and you consume the spoilt food your health shall definitely be at risk. Loss of food by animals, humans, insects, rodents, etc. can subsequently lead to the onset of microbial and self-decomposition. Proper packing of food is the main effective way to prevent the damage caused by the agencies falling under this principle of preservation.

Overall, all three principles should be considered in descending order of importance and conceptualization of the approach to food processors. The greatest emphasis is placed on the control of microbial decomposition, followed by self-decomposition, which eventually leads to damage caused by animals, insects, rodents, etc.