19-3 |
Control of wound-induced browning in fresh-cut frutis and vegetables by suppression of wound signal with heat shock, and other stresses |
M. E. SALTVEIT, Dept. of Vegetable Crops, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616-5200 Signals are produced by stressed tissue and migrate from the site of injury into adjacent cells and induce the wound response characteristic of the type of stress and tissue (e.g., increased PAL activity, increased ethylene production, increased respiration, depolarization of membranes, etc.). Bruising, crushing, and wounding induce the synthesis of enzymes in the phenylpropanoid pathway and promote the synthesis and accumulation of phenolic compounds that cause browning. Phenylalanine ammonia-lyase (PAL) is the first enzyme in the phenylpropanoid pathway and reducing PAL activity reduces wound-induced tissue browning. Currently, browning is controlled by using low temperatures, dips in aqueous solutions of food grade chemicals, and/or packaging under modified atmospheres (i.e., atmospheres low in oxygen and high in carbon dioxide). There appears to be a hierarchical order to the plant’s response to different abiotic stresses. Living organisms respond to temperatures ca. 10 °C above the growing temperature with the production of a unique set of proteins called heat-shock proteins (HSPs). HSP synthresis is often accompanied by a marked reduction in the synthesis of other proteins that were being synthesized before the heat-shock. When lettuce is wounded and heat-shocked, the heat-shock diverts protein synthesis away from the wound-induced production of enzymes of phenylpropanoid metabolism and toward the production of HSPs and prevents the increase in wound-induced PAL activity and browning. This diversion of wound-induced protein synthesis by heat shock might be used to prevent browning in other crops that normally have low phenolic content; e.g., celery and lettuce. The persistence of the ability of a heat shock to preferentially induce the synthesis of heat shock proteins (hsps) in place of wound-induced enzymes of phenylpropanoid metabolism offers a new way to control browning in lightly processed fruits and vegetables.
Session 19, Emerging technologies for enhancement of fruit and vegetable quality and safety
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