The necessity of blanching (scalding) vegetables to be preserved by freezing has been recognized since the report by Joslyn and Cruess (12) in 1929. The deterioration in flavor and color and the off-odors which develop in raw or under-blanched vegetables during freezing storage have been ascribed to the action of enzymes. I n many instances, the enzyme sytem or systems responsible for the deteriorative changes have not been identified. Nevertheless, it has become common practice t o use certain enzyme tests as indices of adequacy of heating in vegetables to be preserved by freezing. Some question still remains as to which enzyme best serves this purpose.Diehl and Berry (6) in 1933 stated that catalase activity served as an index of adequacy of blanching for peas and indicated that Alderman peas blanched for a time sufficient to destroy catalase activity retained satisfactory quality when stored at -5°F. (-20.6"C.). Later, Arighi, Joslyn, and Marsh (1) observed that catalase appeared to be quantitatively inactivated at a much more rapid rate than the enzymes concerned in the production of off-flavors in peas. In view of these findings, Joslyn (11) suggested that "the use of catalase activity as an index of adequacy of scald, particularly when the less reliable qualitative methods are used, is not a generally reliable method."Mergentime (20) and Balls (2) suggested that peroxidase activity might serve as an index of adequacy of heating. In a review paper, Joslyn (11) refers to earlier worE in which it was found that peroxidase activity more closely paralleled the formation of off-flavors in frozen vegetables than did catalase activity. However, he cautions that the correlation varied markedly with nature of the substrate used for detecting peroxidase activity.The first study quantitatively relating degree of peroxidase inactivation to quality retention in frozen vegetables was that of Masure and Campbell (18,28). I n this study, rapid methods were devised for the quantitative and semiquantitative estimation of peroxidase in various vegetable tissues. The latter method was developed for quality control in processing plants. These tests are based on an observed relationship between time required for appearance of color produced by the residual peroxidase in a filtered extract of vegetable in a guaiacol and hydrogenperoxide substrate, on the one hand, and retention of quality in the frozen product 011 the other.Specifications for the semiquantitative test were based on correlation 480

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