Md. Arafat Rahman: Food preservation is the process of preserving food from the attack and damage of various pathogens for the future. The main purpose of effective food preservation is to preserve the basic quality of the food as much as possible and to maintain nutritional value. Traditional methods and techniques are still used in Bangladesh for food preservation and to prevent putrefaction. These include the use of salt, smoke, sugar, vinegar, etc., and preservation of dried food ingredients. Modern food preservation has now created opportunities to preserve many types of food items by applying wider methods.

The main methods of food preservation include sun drying, use of heat, storage of food in extreme cold, use of various chemicals and application of radioactive radiation. The method of preserving food by drying in the sun is very ancient and it is widely used in preserving fish, fruits, grains, vegetables, meat etc. in Bangladesh. The preservation of dried fish and meat is thought to have been in use since 2000 BC.

About a hundred years ago, dried vegetables were also sold. Dried fish is regularly stored in Chittagong, Cox`s Bazar, St. Martin`s Island, Sonadia and many other coastal areas of Bangladesh. Every year a large quantity of fish is dried for local consumption and export. The tradition of drying mangoes and plums in fruits still exists. Frozen food preservation methods are usually confined to cities. Although this is one of the most convenient ways to preserve food, it doesn’t destroy microorganisms or prevent their growth completely.

Vegetables, meat, milk, fish, eggs, butter and other perishable items are usually stored in the fridge for daily use at home. Although the digestion process is largely stopped in the cold, the action of enzymes in the uncooked food continues somewhat. At present, there are about many private and government cold storages for potato storage across the country. There are about 80 cold storages in Munshiganj district alone. They play an important role in preserving different varieties of potatoes.

Although the method of preserving canned food through high heat consumption is expensive, the effects of microorganisms and enzymes are not present here. Food containers are tightly sealed to protect against bacterial contamination. Some organizations in the country are now preserving and marketing fish, meat, vegetables, fruits, soft drinks etc. in this manner. One of the most common methods of preventing the growth of microorganisms is the use of acetic acid, which is one of the ingredients in vinegar. With the help of vinegar, mustard oil and some spices, different types of pickles are made in this country at family and institutional level.

Various chemicals have been used in food preservation for many centuries. Commonly used products include sodium chloride, sodium and potassium nitrate, sodium salicylate, benzoic acid, ascorbic acid, vinegar, alcohol, etc. Concentrated sugar solutions are widely used in Bangladesh for making jellies and jams. The use of salt in food preservation has been practiced since ancient times. In Bangladesh, in addition sun, heat and smoke are also used. Edible salt is mainly used in this country for preservation of hilsa fish.

By ensuring radiation protection safe levels and food safety measures through the application of radioactive radiation release methods is a scientific process, which prevents the invasion and growth of insects and microorganisms and thus increases the usability time of stored food. The Food and Agriculture Organization of the United Nations estimates that about one-fifth of the world`s food grains are affected by pests, microorganisms, and other insects. In many developing countries where high temperatures and high humidity prevail, the amount of damage is close to 50%.

The nutritional value of some foods can be improved by using radiation processes. For instance, the high protein content of soybean flour, which is added to bread, is greatly increased when used with irradiated wheat flour. The Institute of Food and Radiation Biology of the Bangladesh Atomic Energy Commission conducts research on increasing the life span of different types of pulses, potatoes, onions, fish, dried fish, poultry and vegetables. The Government of Bangladesh has already declared 13 foods that have been irradiated suitable for human consumption and issued unconditional permits, including potatoes, onions, wheat flour, spices, chicken, fish and fish products (cold and frozen), frozen shrimp, rice and rice products, various pulses, papaya and mango.

The main food grains of Bangladesh paddy, wheat and maize are often kept in warehouses for some time. The level of loss of stored food grains after harvest is about 10-25 percent in Bangladesh. Insect and fungal attacks in warehouses are partly responsible for this. Post-harvest losses are in fact dependent on proper threshing, cleaning, drying and warehousing. Drying is the removal of excess water by leaving the right amount of water in the dried grain. In Bangladesh, food grains are traditionally sun-dried. Sun-drying of agricultural products is the most followed method in this country. In this conventional method, wet grains are spread on flat land, usually on level ground in direct sun for a certain period of time.

The use of high temperature dryers used in developed countries is not economically viable in Bangladesh. Since there is a lot of solar radiation in all parts of the country, the method of sun drying is widespread here. The introduction of solar-dryers appears to be promising, environmentally sound and pollution-free. Mechanical dryers / solar powered dehumidifiers for limited quantity of seeds and application of batch-type drying and warehousing methods for large quantities of seeds may be potential for Bangladesh.

The primary goal of warehousing is to prevent deterioration of crops. The work is not done directly but indirectly through humidity control, uninterrupted ventilation and prevention of bacterial infections, insects and rodents. In Bangladesh, farmers store food grains to meet their food needs and to use as seeds. The grains stored in this way can be 10-100% of the total production. The average warehousing amount is about 70% of the grain produced.

In rural areas warehousing is 80% of the total crop production and it is done in traditional warehousing system. Traditional warehousing techniques are rooted in cultural norms and have been passed down through the generations. Storage capacity of granaries is determined according to the type of food and the quantity of grains. In Bangladesh, about 8 different types of warehousing methods are used at the farm level. The most common are granaries or medium and large sized tubular or rectangular pots made of cane or bamboo, fences or medium capacity pots made of bamboo and doles or small capacity bamboo funnel pots.

Md. Arafat Rahman, Columnist & Asst. Officer, Career & Professional Development Services Department, Southeast University, E-mail: arafatrahman373@gmail.com