FREEZING PRESERVATION retains the quality of agricultural products over long storage periods. As a method of long-term preservation for fruits and vegetables, freezing is generally regarded as superior to canning and dehydration, with respect to retention in sensory attributes and nutritive properties. The safety and nutrition quality of frozen products are emphasized when high quality raw materials are used, good manufacturing practices are employed in the preservation process, and the products are kept in accordance with specified temperatures.
The proportion of fresh food preserved by freezing is highly related to the degree of economic development in a society. As countries become wealthier, their demand for high-valued commodities increases, primarily due to the effect of income on the consumption of high-valued commodities in developing countries. The commodities preserved by freezing are usually the most perishable ones, which also have the highest price. Therefore, the demand for these commodities is less in developing areas. Besides, the need for adequate technology for freezing process is the major drawback of developing countries in competing with industrialized countries. The frozen food industry requires accompanying developments and facilities for transporting, storing, and marketing their products from the processing plant to the consumer. Thus, a large amount of capital investment is needed for these types of facilities. For developing countries, especially in rural or semi-rural areas, the frozen food industry has therefore not been developed significantly compared to other countries.
In the Pre-process of freezing the most important step is blanching. Blanching is the exposure of the vegetables to boiling water or steam for a brief period of time to inactivate enzymes. Practically every vegetable (except herbs and green peppers) needs to be blanched and promptly cooled prior to freezing, since heating slows or stops the enzyme action, which causes vegetables to grow and mature. After maturation, however, enzymes can cause loss in quality, flavour, colour, texture, and nutrients. If vegetables are not heated sufficiently, the enzymes will continue to be active during frozen storage and may cause the vegetables to toughen or develop off-flavours and colours. It destroys some bacteria and helps remove any surface dirt.
In Pakistan most of the industries use Hot Water Blanching (HWB). In this type of blanching the vegetables are simply submerged in the hot water for a specific period of time and temperature. But in Pakistan most of the vegetable freezing industries do not even have a blancher and if some have they do not have any mechanism to control the time and temperature. As the blanching process is meant to de-activate the enzymes which cause spoilage but if the process is not adequate enough then how one can ensure product quality. The research have shown that if the blanching process has not been carried out properly then one cannot control spoilage and microbial growth even if the product was stored under -18oC.
The enzymes used as indicators of effectiveness of the blanching treatment are peroxidase, catalase, and more recently lipoxygenase. Unfortunately the most elite industries of Pakistan engaged in the business of freezing vegetables have not developed a facility to check either the blanching was adequate or not. Then how one can ensure the claim of quality frozen goods?
Microorganisms differ significantly in their sensitivity to freezing, thus the main concern about the microbiological aspects of freezing is the growth of organisms during thawing rather than during freezing. In general, the freezing process does not significantly destroy the microorganisms that may be present in fruits and vegetables even after blanching. A sufficient number of survivors are still present that can multiply and cause spoilage of the product during thawing. If the blanching was not adequate then the spoilage due to microorganism will be more during storage and thawing. Fluctuation in storage temperature is one of the main reasons for microbial deterioration of frozen products during storage. Thus, a careful inspection of frozen products is essential to ensure proper freezing storage with constant temperatures.
The transportation of the frozen foods is also very important step. During transportation it is essential to control the temperature of the product, as required. The temperature fluctuation causes thawing and then re-freezing, this process of thawing and re-freezing cause the formation of bigger ice crystal. These bigger ice crystals enhance the spoilage and microbial growth. Unfortunately most of the transportation companies carry mix loads of entirely opposite temperature requirements. So this means that even if all process of production and storage were carried out best even then product would be deteriorated before reaching to the customer.
If we wish to improve our industry of frozen food products we need to take some actions as early as possible. Although most of us know that the taste, flavour and aroma which vegetables of sub-continents have are not found all over the world; then why we are having lesser share in global market than Europe and USA? This all is because of our poor processing techniques, non-availability of proper testing and lab equipment, improper and unstable freezing process, and unreliable transportation systems.
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