EFFECTS OF BLANCHING ON GRAPES (VITIS VINIFERA) AND CHANGES DURING STORAGE IN SYRUP

Abstract

This paper studies the effects of conventional and microwave blanching on grapes that are being processed for storage in syrup. An analysis was made of the blanching effects on macro- and micronutrients, as well as on color and mechanical properties. To test the effectiveness of these blanching treatments, enzymatic residual activity was measured for polyphenol oxidase, peroxidase and pectinmethylesterase. Both blanching treatments reduced enzyme activity in the grapes, especially polyphenol oxidase (99%). Blanching treatments also caused significant decrease in tartaric acid (TA) also as in color and mechanical changes, more marked in conventional-treated samples. As for the effect of storage, microwave treatment supposed a greater stability of TA and total phenols than conventional one, also as a greater antioxidant activity of grapes. From this point of view, microwave treatment of samples immersed in water can be proposed as a good alternative to conventional heating in boiling water for grapes blanching. © 2011 Wiley Periodicals, Inc.