FOOD SCIENCE ›› 2013, Vol. 34 ›› Issue (5): 55-59.doi: 10.7506/spkx1002-6630-201305012

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Changes in Total Polyphenol Content and Antioxidant Activity of Thompson Seedless Grapes during Hot-Air Drying

ZHANG Li-juan,SHI Jun-ling*   

  1. College of Food Science and Engineering, Northwest A&F University, Yangling 712100, China
  • Received:2011-12-22 Revised:2013-01-11 Online:2013-03-15 Published:2013-04-16
  • Contact: ZHANG Li-juan E-mail:zhanglijuan_1514@126.com

Abstract:

Browning is an unavoidable problem during hot-air drying of Thompson seedless grape. In order to evaluate
the influence of browning on nutritive and functional properties of raisin, we investigated the changes in color, total phenol
content, and antioxidant properties such as DPPH, ABTS+· scavenging capacity and reducing power during hot-air drying
(30 ℃) of Thompson seedless grapes. The browning of Thompson seedless grapes started on the 8th day of drying and then
became serious with increasing drying time; as a result, an increase in a* value and a decrease in L* value, b* value and
c* value were observed. Total polyphenol content showed an overall decrease despite the sudden increase on the 8th day
followed by a dramatic decrease. This increase on the 8th day corresponded to the time of appearance of browning and a*
peak. During the entire drying process, total polyphenol content was extremely significantly positively correlated with DPPH,
ABTS+· scavenging capacity and reducing power. This finding indicates that total polyphenols are mainly responsible for
the antioxidant activity of Thompson seedless grapes, and the observed decrease in total polyphenol content and antioxidant
activity is related to aggregated browning.

Key words: thompson seedless, hot-air drying, polyphenol, antioxidant activity, color

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