Principles of preservation of fruits and vegetables

Preservation: Preservation means just protecting the foods against spoilage, but scientifically it may be defined as a science that deals with the process of prevention of decay or spoilage of the food are called preservation. In other words, preservation is just controlling the physical, chemical or microbial changes in the food.

1. Physical Changes: Colour, flavour, texture and taste etc.

2. Chemical Changes: Carbohydrates, fats, proteins, vitamins and minerals.

3. Microbial changes: Mould, yeasts and bacteria.

Why do we preserve food?

 To increase the shelf life of the food for increasing the supply.

 To make the fruits and vegetables available throughout the year.

 To add variety to the diet.

 To save time by reducing preparation, time and energy by fire.

 To stabilise the prices of the food in the market.

 To improve the health of the population.

Principles of preservation-

There are three main principles:

1. Prevention or delay of the microbial decomposition of the food.

2. Prevention or delay of the self-decomposition of the food.

3. Prevention or damage by insects, animals, or mechanical causes.

1. Prevention or delay of the microbial decomposition of the food.

A. Asepsis: It means preventing the entry of microorganisms by maintaining of general cleanliness while picking, grading, packing and transporting fruits and vegetables, increasing their keeping quality and the product prepared from them will be superior quality.

B. Filtration: Fruit juice, beer, soft drinks, wines etc. enter through a bacteria proof filter is made of asbestos pad or unglazed porcelain-type of materials. These filters contain the microorganisms and allow the water or juice to percolate through with or without pressure.

C. Anaerobic conditions:

It can be maintained by:

Replacing the O2 by CO2 ---------- Carbonation

Evacuating the sealed container (fruit juice)

Use of oils from the top of the food (pickles)

D. Exposing at high temperature:

Fruits can be exposed to high temperatures such as;

Canning: Food is exposed to a high temperature (>100 degree C) which reduces spoilage and inactivates the enzyme present in the food. The process of sealing food stuffs hermetically (airtight, protecting from outside agencies) in containers and sealing them by heat for longer storage is called canning.

Irradiation: In the case of irradiation, the food is exposed to radiation to kill the surviving microorganisms by ionising and non-ionising radiation like α, β and γ rays. Here, food is exposed to electromagnetic or ionizing radiation or various frequencies ranging from low-frequency electromagnetic rays to high-frequency i.e. gamma rays which destroy the microorganisms present in the food.

2. Prevention/ delay of the self-decomposition:

a. By destruction or inactivating the enzyme – Blanching.

b. Prevention / delay the non-enzymatic chemical reactions – Antioxidant

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 which has to soften the tissues to facilitate packaging.

 To preserve the original colour and flavour.

 To destroy certain enzymes which are undesirable.

 Elimination of the air.

 Mostly done for vegetables.

 Remove microorganisms

 Remove astringent taste and toxins.

B. Antioxidant: Anti-oxidants are substances which are used to protect the food against deterioration caused by exposure to the air.

 BHA- Butylactic Hydroxy Anisole & BHT- Butylactic Hydroxy Toluene (vegetable oils)

 Gellales: Animal fat, Vegetable oil

 Tocopherols: Animal fat

 Ascorbic acid: Fruit juices, Citrus oil, Wine, Beer etc.

 Lactic acid: Processed fruits and vegetables, canned fruits.

 Phosphoric acid: Vegetable oil, Animal fat and Cola drinks.

3. Prevention or damage by insects, animals, or mechanical causes:

This principle of preservation deals with the prevention of damage caused by various external agencies other than micro-organisms and enzymes i.e. animals, man, insects, rodents etc. These agencies generally cause physical damage to the food material, rats may eat peels of oranges in storage, animals may also eat the food if kept within their reach etc. But in none of these cases, these damages are deleterious to human health. If you consume a half-eaten apple or orange you are generally never going to die or experience any health risks, but if the food is spoilt by microorganisms, and you consume the spoilt food your health shall definitely be at risk. The damage of food by animals, man, insects, rodents etc. may, later on, give way to the initiation of microbial and self-decomposition. Proper packing of the food is predominantly the effective solution for the prevention of damage caused by the agencies considered under this principle of preservation. Overall from the food processors' point of view, the three principles are to be considered in decreasing order of importance and emphasis. The highest emphasis is given on the control of microbial decomposition followed by self-decomposition, ultimately followed by damage caused by animals, insects, rodents etc.