Preservation by radiation and Preservation by drying or dehydration

Preservation by Radiation:

Food can be preserved by using radiation where thre is process of exposing food to ionizing and non-ionizing radiation for the purpose of food safety and its preservation.It could be used to replace chemical food preservatives as well as thermal treatment. It is considered as cold pasteurization of food . Non-ionizing and ionizing radiation like UV light, X-rays, Gamma ray, cathode ray, etc. are used. Non-ionizing radiation like UV rays with wavelength 260nm is absorbed by purine and pyrimidine bases especially by thymine for abnormal structure. Germicidal lamp which emits radiation in food industries. Depending upon the intensity, of time of exposure and nature of food. The lamp are available in various size and power.

Ionizing radiation like X-ray, Gamma ray, cathode ray, etc. ionize the water and similar molecules generate free radicales. These free radicales have mutagenic effect or may have toxic effect to microorganisms. Among the potent chemicals which have toxic effect on microorganisms is Hydroxyl radicle (OH).

Food (H₂O₂/ H₂O ) → Reducing agent + Oxidizing agents

(Reducing) ↓

Enters into cells and alter biological structure like DNA

These radiations are used for following purposes for food preservations:

• These radiations are used for teatment of water used for beverages.
• It is used for prevention of growth of yeast on prickles,vinegar, sauerkraut, etc.
• It is also used for treatment of knives for slicing bread.

Mode of action in preservation by Radiation:

1. Direct effect (Non-ionizing radiation) : A swiftly (fast) moving electromagnetic radiation strike to complex biological structure and alter or destroy biological functions (like mutation to microorganisms. )
2. Indirect effect (Ionizing radiation): Radiolysis of water produce highly reactive ions such as hydrogen ion (H⁺), hydroxyl radical (OH^-)and in presence of oxygen, free radicle is converted into toxic form and finally shows toxicity to microorganisms.

Advantages and disadvantages of use of radiations in food :

• Advantages :

1. The irradiated rays like Gamma rays are highly used in dairy products, X-ray used to inactivate the food borne pathogen form surface of food, etc.
2. It used to preserve the shelf life of food items and prevent its spoilage form harmful microorganisms, enhance its safety level and also prevent trade-barrier.
3. It helps to maintain the proper nutritional value of food with its original texture, flavor and its consistency.
4. There is no any radioactive effect on food products because there is no any reaction between food source and radioactive source.

• Disadvantages:

1. It is most expensive and sophisticated method of food preservations.
2. There harmful effect on human health through this methods if rays are used hapazardly in an irrevational manner.

Drying / Dehydration :

It is one of oldest method of food preservations and have long shelf-life as after drying there will be low moisture content and microbial activity. The application of heat under controlled condition to remove majority of the water normally in food by evaporation or sublimation. Drying of food is one of the preservative method that reduces the amount of available moisture i.e. lower the water activity (a_w) in food. Drying may be accomplished by a number of methods from exposure to sunrays to the modern artificial method.

Drying process:

Fig: Flow chart of process of Drying

Drying is a method of food preservation that is simple, safe, easy to learn. Drying also created new food product such as fruit leathers, banana chips, pumpkin seeds, etc. Drying remove moisture from the food so bacteria, yeast, mold cannot grow. It also slows down the action of food enzyme and helps in the preservation.

• Method of Drying:

There are many methods of drying process used for preservation of food. These method preserves the food by bactericidal activity, sterilizing mechanism, through heat treatment and through inhibiting water activity. Some of the major methods of dehydration / drying are as follow:

1. Solar drying.
2. Drying by mechanical dryers.
3. Freeze drying.
4. Drying smoking.
5. Drying by addition of salt and sugar.

Solar drying:

It is the easiest method of drying in presence of sunlight and by atmosphere. In this method food is spread out on tray and exposed to hot sun.

Drying by mechanical dryers:

It is an artificial drying that involves the passes of hot air (heated air) with controlled relative humidity over the food to be dried.

Freeze drying:

It is the sublimation of water from a frozen feed by mass of vacuum pump together with heat applied. It is used for drying food like meat, sea foods, vegetables, fruits, etc.

Drying smoking:

Drying of food by means of smoking also serves as a good preservative factors for food. In addition to drying, smoking also contains some antimicrobial agent and act as preservative factors.

Drying by addition of salt and sugar:

High concentration of salt and sugar create high osmotic pressure, which is responsible for drying food.

#Advantages of drying :

1. It increases the shelf-life of food by decrease in its moisture content, water activity and inhibit microbial deterioration.
2. It helps to add flavor and texture to food maintainging its nutritional value.
3. Dried food items can be stored in container, and easy in export also.

Reference:

1. Jay, MJ. Modern Food Microbiology. 3rd. Delhi: CBS Publications and Distributors, 1987.
2. Frazier, Wc and Westhoff DC. Food Microbiology. 3rd. New-Delhi: Tata MCGraw-Hill Publishing Company Limited, 1986.