Chemical and physical deterioration of frozen foods

Abstract

The basic principles of food freezing, including the properties of water and ice, the concepts of supercooling and glass transition, phase and state diagrams, ice formation mechanisms (nucleation and crystal growth), the presence of intra- and extracellular ice in food tissues and the mathematical modeling of freezing rate are discussed. Freezing, an efficient method for food preservation, inhibits the growth of micro-organisms, retards biochemical and enzymatic reactions and decreases water activity. The formation of ice involves different physicochemical modifications during freezing, frozen storage and thawing, and these affect food quality; case studies are described. The most important physical changes induced by freezing are: modifications of cell volume, water dislocation during freezing, mechanical damage, freeze-cracking, moisture migration during storage, freezer burn, recrystallization of ice and exudate production. Storage temperature has a marked effect on the quality of frozen foods and some recommendations on how to increase shelf life are presented. The concept of cryostabilization (storing frozen food below the glass transition temperature of the maximally freeze-concentrated matrix) and its influence on physical deterioration processes are discussed.