Owing to the rapidly growing interest in the preservation of fruits and vegetables by freezing storage, investigations have been conducted in the Fruit Products Laboratory, University of California, during the past three years on several important problems encountered in the industry. This report presents the results of preliminary studies upon one of these problems, that of factors affecting the changes during freezing and subsequent thawing. Description of commercial methods and directions

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... preparing, packing, and freezing fruits and vegetables are given in Circular 320. A number of physical, chemical, and bacteriological changes occur during the freezing and subsequent thawing of fruits and vegetables. It is necessary to know the nature of these changes in order to determine what fruits and vegetables can be preserved satisfactorily by freezing and how they should be prepared, packed, frozen, and stored. The changes that occur serve as criteria of the degree of success attained in preserving these products. They also determine the suitability of the product for use by preservers, jelly and jam manufacturers, ice cream manufacturers, and by the housewife. The physical changes that occur during freezing storage depend chiefly upon ice formation and osmotic action ; they involve changes in volume, drained weight, and texture. These physical changes occur principally during freezing and during thawing, but generally not during freezing storage, especially if a constant storage temperature is maintained. The results of studies on rates of temperature change in various products under different conditions are included with physical changes. The chemical changes that occur during preparation, freezing, and thawing involve changes in composition such as hydrolysis of pectin and sucrose by the hydrolytic enzymes present ; changes in color and flavor due to oxidation, largely arising through the activity of oxidizing enzymes ; and changes in flavor due to anaerobic respiration and other i