Purification of polyphenol oxidase and the browning control of litchi fruit by glutathione and citric acid

• Published in: Journal of the science of food and agriculture 1999-05, Vol.79 (7), p.950-954
• Main Authors: Jiang, Yueming, Fu, Jiarui, Zauberman, Giora, Fuchs, Yoram
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; browning; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; glutathione; Litchi chinensis Sonn; polyphenol oxidase; purification
• ISSN: 0022-5142; 1097-0010
• DOI: 10.1002/(SICI)1097-0010(19990515)79:7<950::AID-JSFA289>3.0.CO;2-E

Polyphenol oxidase (PPO, EC 1.10.3.2) was purified to homogeneity from litchi peel yielding a single protein with a molecular weight of about 75.6 kD by Sephadex G‐100 gel filtration, and a 108‐fold purification of PPO achieved. The enzyme was determined to be composed of two similar subunits. Glutathione, L‐cysteine and citric acid suppressed PPO activity markedly, whereas ascorbic acid and n‐propyl gallate showed a little inhibition. Moreover, the effect was enhanced by the addition of citric acid. On the basis of the inhibition of PPO activity in vitro, the use of 10 mmol l −1 glutathione and 100 mmol−1 l citric acid was found to give good control of the browning of litchi fruit, and an 80–85% inhibition of PPO activity was observed. It is suggested that application of glutathione in combination with citric acid may slow down the browning of litchi fruit. © 1999 Society of Chemical Industry