ABSTRACT
Blanching is an essential prior step in vegetable processing, which destroys the enzymes and microorganisms and helps in prevention of quality deterioration particularly during drying, freezing, frying, or storage. Besides, it also expels the air entrapped intercellularly inside the tissues. Blanching has also proved to aid reconstitution and textural improvement in the product. Hot water blanching is by far the most popular and commercially adopted process, as it is a simple technique whereby the mechanism of heat penetration is by conduction. In such systems the resistance to heat transfer at the surface is negligible compared to the internal resistance to heat transfer. It was shown that in such systems the rate of heat penetration is proportional to the square of the characteristic dimension of the object. The time required for blanching depends upon the time required for inactivation of enzymes and thus on the rate of heat transfer. The longer time required for the temperature rise at the slowest heating point, normally the geometric center of a relatively large object, could damage the quality of the kernels and result in considerable loss of nutrients such as carbohydrates, proteins, water-soluble minerals, vitamins, and sugars. On the contrary, shortening the blanching time could reduce the degree of enzyme inactivation and result in a shorter shelf life. Because of this, the practical blanching time of such product is quite often a compromise.
