20-1 |
Overview of endogenous fruit and vegetable enzymes |
D. M. BARRETT, Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., 114 Food Science & Technology Bldg., Davis, CA 95616-8598 Naturally occurring, or endogenous enzymes present in plant tissues are proteins with catalytic properties due to their power of specific activation. Enzymes are active participants in the growth of fruits and vegetables, and they continue to function after fruits and vegetables are harvested and stored. While many enzymes are critical to the maintenance of metabolism, others have deleterious effects on color, flavor, odor, texture and nutritional value. Inactivation of specific endogenous enzymes is often a necessary step in extension of the shelf life of processed fruit and vegetable products. Factors that affect enzyme activity include: temperature, pH, substrate concentration, enzyme concentration, presence of activators or inhibitors, and compartmentalization of enzyme and substrate(s). In this presentation we will provide an overview of the most important endogenous quality-related enzymes in fruits and vegetables. Pectin methylesterase (PME), polygalacturonase and amylase affect textural integrity; polyphenol oxidase catalyzes browning; lipoxygenase, lipase and peroxidase influence flavor and odor; and ascorbic acid oxidase activity results in a loss of nutritional value. Various fruits and vegetables, and their processed products, will be compared in terms of initial enzyme activities and residual levels following processing. Thermal and non-thermal methods for either activation or inactivation of these enzymes will be reviewed, and the consequences of residual activity on quality will be discussed.
Session 20, Enzymes in fruit and vegetable processing
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