The present studies were carried out in a n effort to determine the relationship, if any, between the inactivation of certain enzymes and the retention of ascorbic acid and of other quality factors in frozen vegetables. It was desired to ascertain which of the enzymes are causative factors in the losses of ascorbic acid and in the deterioration of quality in frozen foods. Furthermore, it seemed desirable to determine what degree of enzyme inactivation is required i n order to reduce or prevent these changes.The literature contains extensive data relating to the effects of blanching and of frozen storage on the retention of ascorbic acid in vegetables ( 1 4 ) . I n recent years there also have been published the results of a number of studies relative to the inactivation of enzymes, particularly catalase and peroxidase, and the retention of quality in frozen vegetables (5). There have been very few reports, however, in which the effect of blanching on both the ascorbic acid content and on enzyme activity have been studied simultaneously.In the present studies, the ascorbic acid content a i d the activities of catalase, ascorbic acid oxidase, peroxidase, and polypheiiol oxidase in broccoli, green beans, Lima beans, peas, spinach, and in summer squash were determined. These determinations were made on samples of the vegetables before and after three degrees of blanching and before and after various periods of frozen storage a t 0°F. (-172°C.). These six vegetables represented various types of plant tissues as leaves, flowers, immature seeds, etc.
E X P E R I M E N T A L METHODSProcessing of the vegetables. Fresh vegetables of good quality were first washed and where necessary cut into appropriate size. The heads of broccoli (DeCieeo variety) were sub-divided, all large leaves being removed, and the stalks were cut into pieces. 4% inches or less in length. Stalks which were more than 1/2 inch thick were also cut lengthwise. The green beans (Bountiful variety) were first washed, the ends snipped off, and the beans broken into pieces 1 to 2 inches in length. The spinach (Bloomsdale variety) was sorted, washed twice in cold water, and allowed to drain for an hour before being blanched. Small Zucchini squash, 6 to 8 inches long and 1% to 3 inches in diameter, were used. They were first washed and then cut into slices about y~ inch in thick ness. Freexonian peas and Henderson's bush Lima beans were used.The hand picked vegetables were blanched f o r % to 4 minutes, in water at 200°F. (93.3"C.) using a ratio of 1 pound of vegetable t o 1 gallon of blanching water. After "Authorized f o r publication on April 5, 1951, as paper No. 1665 in the JournaI Present address :
