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ARS Home » Research » Publications at this Location » Publication #124529
Title: INHIBITION OF LOQUAT ENZYMATIC BROWNING BY SULFHYDRYL COMPOUNDS

Author
item DING, CHANG-KUI - ZAAS, ZHEJIANG, CHINA
item CHACHIN, KAZUO - OPU, OSAKA, JAPAN
item UEDA, YOSHINORI - OPU, OSAKA, JAPAN
item Wang, Chien

Submitted to: Journal of Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Loquat fruit contains high concentration of polyphenols and high activity of polyphenol oxidase. The fruit tissue is easy to turn brown after cutting because of oxidation of the phenolic compounds. Therefore, browning is a problem for fresh-cut loquat and for processing into juice, etc. It is important to find ways to prevent or reduce tissue browning. In the present study, the effectiveness of a series of sulfhydryl compounds in inhibiting polyphenol oxidase activity was investigated. The results showed that L-cysteine appeared to be an effective browning inhibitor. The required concentration of L-cysteine for browning inhibition varied with loquat cultivars depending on the endogenous phenolic concentration inherent in each cultivar. These data are useful for other researchers and for industry interested in reducing browning of loquat for fresh-cut or processing.

Technical Abstract: The effectiveness of a series of sulfhydryl compounds in inhibiting polyphenoloxidase (PPO) activity in a model system (chlorogenic acid solution) and in loquat juices was evaluated. Application of different concentrations of sulfhydryl compounds to chlorogenic acid solution and fresh loquat juice showed that L-cysteine appeared to be an effective browning inhibitor. The required concentration of L-cysteine for 90 percent browning inhibition depended on loquat cultivars, and ranged from 0.6 mM for "Nagasaki" to 2.0 mM for "Yukawa" or "Toi". The difference may be due to the concentration of endogenous phenolic compounds inherent in each cultivar. The results from oxidized product analysis by loquat PPO implied that the mechanism of browning inhibition by thiols was caused by the formation of a thiol-conjugated reaction product.