Studies on the influence of temperature and soil moisture on peroxidase and hexose sugars in snap beans

With the expansion of the growing of vegetables for fresh market, and of the freezing and canning industry since 1920, the production of green beans has been increasing year after year. In 1960, the United States acreage of green beans for processing was 176,160 acres (51) and for fresh market, 139,830 acres (50). In the 1930’s as facilities for food freezing and retail distribution of frozen foods developed across the United States, frozen foods began to find their place in commerce. The frozen vegetable pack for 1960 was 1,955 million pounds, being the largest in the history of the industry. Green beans accounted for 86 million pounds valued at 14.2 million dollars (46).

The importance of blanching vegetables before freezing for the inactivation of enzymes causing deterioration in flavor and color has been recognized since the report by Joslyn and Cruess (25). Blanching in now a routine treatment in the processing of frozen pack vegetables.

Inactivation of peroxidase in vegetables is well established as an index of adequacy of blanch. Peroxidase has been found to be more heat resistant than other enzymes such a catalase, ascorbic acid oxidase and polyphenol oxidase. Underblanched beans and other vegetables with some degree of residual peroxidase activity undergo deterioration in quality through loss of ascorbic acid (38), color (13) and the development of off-odors. Overblanching results in the loss of ascorbic acid, poor color and sloughing.

In general, a temperature of 190° F. for a period of 2 to 2.5 minutes is used (7). This does not appear to be always adequate or optimum because in recent years defects in texture and flavor have developed in some lots of green beans during prolonged frozen storage (36). It became evident that beans vary in peroxidase content. Maturity, toughness and growing conditions have been considered as some of the factors affecting peroxidase content of green beans. Mundt and McCarty (36) found significant differences among varieties as to peroxidase activity. Climatic factors such as temperatures, rainfall and humidity seemed to influence the peroxidase content and blanching time.

The object of the present investigation is to study the influence of temperature and soil moisture on peroxidase and associated quality factors in green beans.