Before the green revolution, the Ultimate Aim of the country was Food Security but now when our country is secure in terms of availability of food, the Concern has Shifted towards increasing the Shelf life of Commodities so that the consumers can enjoy it for a longer period of time. The shelf life is the period of time in which a food may be kept under certain conditions of storage Maintaining its Optimum Quality and Safety. So let’s see Methods to Improve Shelf Life.
Significance of Shelf Life to Consumers
The ultimate Aim of Shelf Life is to Help Consumers make safe and informed use of products. Consumers should be aware of the time limit up to which the consumption of the food is considered safe. Consumers need to follow the Storage Instructions such as temperature and use of the product after opening.
How the Shelf Life of Food Products is Determined?
The Processors Test the Product’s Shelf Life when introducing a new product in the market. This is done by testing prepared products for a range of spoilage organisms over a predetermined time period until the levels exceed the allowable levels.
Numerous methods are being practiced in food processing industries to increase the shelf life of food products. Some of these are:-
Fermentation: It is the traditional method of food preservation in which there is Controlled Action of Microorganisms which alter the quality of food products, preserve them by the Production of Acids and Alkali and produce subtle flavours and aromas which increase the quality and value of raw materials. Parameters such as Temperature, pH, Oxygen Consumption and Carbon Dioxide Formation are measured and controlled to optimize the fermentation process.
Processing By Application of Heat
1. Drying: It is a unit operation in which Moisture Content to the Food Product is Reduced to a certain extent to prevent the growth of spoilage organisms and some undesirable enzymatic activity by the application of heat under controlled conditions. The main purpose is to extend the shelf life by reducing water activity. For these purposes, different types of dryers are used like Freeze dryers, Vacuum dryers, Heat pump dryer, Spray dryer, Drum dryer etc.
2. Pasteurization: It is a mild heat treatment given to the food commodities Below 100 °C to reduce the microbial load. Minimal changes are caused by sensory characteristics and nutritive value. Particular Temperature and Time combination is selected depending upon the type of commodity and microbial load. The most common of these combinations are HTLT (High-temperature long time) which is operated at 72 °C for 15 seconds and another one is LTLT (Low-temperature long time) which is operated at 63 °C for at-least Half an Hour.
3. Blanching: It is a mild heat treatment (Pre Heat Treatment) done with Hot or Boiling Water which generally aims to cause enzyme inactivation. It is mainly used for vegetables. Generally, fruits are not blanched. Blanching is also known as Scalding, Parboiling or Precooking. The factors which influence blanching time are:
- Type of vegetable or fruit.
- Size of pieces of food
- Blanching temperature
- Method of heating
4. Heat Sterilization: It is a unit operation in which Food Products are Heated at Sufficiently High Temperature and for a longer period of time to destroy microbial and enzyme activity. This is the reason that the shelf life of sterilized food products has a Shelf Life of almost 6 Months.
There are two types of Heat Sterilization:
a) Dry Heat Sterilization: It is the earliest form of sterilization in which Hot Air that is Free from Water Vapor or has very little amount of it is used.
b) Moist Heat Sterilization: It describes sterilization techniques that utilize Hot Air laden with Water Vapor. The moisture plays an important role in sterilization.
5. Dielectric, Infrared and Ohmic Heating: Food products are heated by direct method or by the indirect method. The indirect method, heat is generated within the product (Example-Dielectric and Ohmic Heating) while in indirect method, heat is generated externally and is applied to the food product mostly by means of radiation (Example-Infrared Heating). But these Three Methods are entirely different by the means of providing heat. In Dielectric Heating, molecular friction is generated in the water molecules present in the commodity due to which heat is generated. In Ohmic Heating, heat is generated perhaps due to the electrical resistance of food. In Infrared Heating, heat is generated outside and is conducted to the food commodity by radiation as mentioned earlier.
Processing By Removal of Heat
1. Chilling: It is a unit operation in which the Temperature of Food is Reduced to between -1 to 8 °C. The purpose is to reduce the rate of biochemical and microbial changes. It is often used in combination with other unit operations such as fermentation and pasteurization. Advantages of chilling are:-
- There is very little change in flavour, color, texture or shape.
- Nutritional qualities are retained.
- Fresh foods can be kept for a longer period of time.
2. Freezing: It is a unit operation in which the Temperature of the Food Product is Reduced Below its Freezing Point and a proportion of water undergoes a change in state to form ice crystals. The water which is now frozen to ice becomes unavailable for various microorganisms and chemical reactions. It is generally found that Frozen Foods are Better Nutritionally and Organoleptically and the food products preserved by freezing have a comparatively longer shelf life than other methods. A freezer is generally kept between the ranges of -18 to -25 °C.
Post Processing Operations
Waxing: In waxing, the surface of fruit or vegetable is coated with a certain wax to Reduce the Moisture Loss. Waxing also enhances the appearance of fruit or vegetable. Different types of waxes are used. Commonly used are:-
- Bee Wax (Yellow and White)
- Carnauba Wax (Brazil Wax and Palm Wax)
- Shellac Wax
- Paraffin Wax
Food processing technology principles and practice, 2nd edition by P J Fellows
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