Food technology is a vast field. The salient features of food processing which has some relevance to bioprocess engineering and technology are given here.
In general, the food processing is carried out to achieve the following objectives:
a. For the purpose of storage and transport.
b. To protect from contamination
c. To increase the shelf-life
d. To make it attractive for the consumers.
For appropriate processing of food, many criteria need to be taken into account. These include the ability of the microorganisms and pests to invade and grow on foods, and the chemical instability and biological activity of foods.
Among the many food processing techniques, food preservation is the most important one. Selected food preservation processes are briefly described.
Exposure of foods to sunlight and drying is a natural, and an earliest method of food preservation. Drying involves the removal of water. Consequently, the moisture content of the food falls, and the invading microorganisms cannot grow. Hot air is most frequently used to remove moisture.
In actual practice, foods are dried by using different types of equipment:
a. Shallow-bed dryers (drying is carried out in perforated conveyor beds).
b. Deep-bed dryers (drying occurs in bins).
c. Spray dryers (to dry liquid foods and food slurries).
d. Freeze dryers (to dry soup ingredients, beverage extracts).
The technique of chilling is commonly used to preserve foods without freezing. The process of chilling is carried out around 0°C with humidity between 85-95%. The shelf-life of fresh foods like meat, fish and dairy products can be extended by chilling (usually less than a month). It is reported that the if chilling is done under low oxygen conditions, the shelf-life of foods increases. Chilling is frequently used for long distance shipping of meat, apples, vegetables etc.
Foods can be preserved in a frozen state (-30° to -10°C). At a very low temperatures, the water activity and reactant mobility are low, hence the chemical reactions are reduced. Foods can be frozen by using a stream of refrigerated air, or by passing inert refrigerant or cryogenic gas. Rapid freezing is advocated to minimize the adverse effects on the texture of foods.
By applying heat (comparable to sterilization), majority of the microorganisms and spores present in the foods can be killed. Thermal processing is carried out in sealed containers devoid of oxygen, and thus aerobic organisms cannot grow. Further, higher temperature also leads to inactivation of enzymes, and consequently microbial growth will be retarded.