FOOD PRESERVATION METHODS
Ensuring that harvested commodities are alive with sustained chemical and respiration processes and the need to maintain moisture content and quality of produce during storage and to reduce diseases are very important steps in post-harvest storage.
Extension of shelf life of foods can be carried out using refrigeration and freezing, canning, drying and dehydration, film packaging, smoking, chemicals or food additives, forced-air cooling, modified/controlled atmospheric storage, irradiation and high-pressure food processing. Some examples of selected storage methods for various foods.
However, it must be noted that in order to extend shelf life and maintain quality of fresh fruits and vegetables, temperature management must be considered as an important factor. Developed a mathematical model based on heat transfer, water vapour, temperature and other parameters for horticultural storage facilities and the results obtained correlated with those obtained for a potato storage facility.
Exposure of microorganisms to low temperatures reduces their rates of growth and reproduction. This principle is used in refrigeration and freezing. The microbes are not killed. In refrigerators held at 5°C, foods remain unspoilt. In a freezer at -5°C the crystals formed tear and shred microorganisms. This may kill many microbes but some are able to survive, like Salmonella spp. and streptococci. For these types of microorganisms rapid thawing and cooking are necessary. Deep freezing at -60°C forms smaller crystals and which reduces the biochemical activity of microbes.
Blanching 'of fruits and vegetables by scalding with hot water or steam prior to deep freezing inactivates plant enzymes that may produce a change in color, etc. Brief scalding prior to freezing also reduces the number of microorganisms on the food surface by up to 99% and enhances the color of green vegetables.
Refrigeration is the cooling of space and/or material below the general environmental temperature. It is applied to food material for the purpose of preservation. Refrigeration is used to extend the useful life of fresh and processed food that is required to be stored or transported from one place to another. Before the advent of modern refrigeration systems, perishable foods were kept in a cool environment such as cellars or buckets immersed in water. Sometimes ice from ice-making machines was used in cities to preserve foods. The advent of mechanical refrigeration systems significantly simplified the application of refrigeration to food preservation. The first patent for mechanical refrigeration was issued in 1834 in Great Britain to the American inventor Jacob Perkins. Although this requires access to a regular electricity supply it was one of the easiest methods for preserving food.
Frozen foods have the advantage of resembling the fresh product more closely than the same food preserved by other techniques. Frozen foods also undergo some changes as freezing causes water in food to expand and tend to disrupt the cell structure by forming crystals. In quick freezing the ice crystals are smaller, producing less cell damage than if a product is frozen slowly. The quality of the product, however, may depend more on the rapidity with which the food is prepared and stored in the freezer than on the rate at which it is frozen. Some solid foods that are frozen slowly, such as fish, may, upon thawing, show a loss of liquid called drip, while liquid foods that are frozen slowly, such as egg yolk, may become coagulated.