Role of anthocyanin degradation in litchi pericarp browning.
Zhang ZhaoQi, Pang XueQun, Ji ZuoLiang, and Jiang YueMing
Food Chemistry, Volume 75, Number 2, November 2001 , pp. 217-221
2001
บทคัดย่อ
Pericarp browning is the main problem of postharvest litchi fruit, resulting in an accelerated shelf life and reduced commercial value of the fruit. Anthocyanin decolorization has been known to play a role in litchi pericarp browning. However, in some instances, there was not an obvious change in the content of anthocyanins when the litchi (cv. Huaizhi) fruit exhibited browning. This work was conducted with a view to explain this unexpected observation. Litchi pericarp browning index increased, while the content of anthocyanins decreased with storage time when 0.1 M HCl was used as the extract solution instead of acidic methanol. The visible spectrum of the anthocyanin extract, at a range of 400-600 nm and pH values of 1.0, 3.0 and 5.0, were recorded, with an absorbance peak of about 510 nm. The colour of the extract depended on the pH values and the half-degradation constants for anthocyanins at pHs 1.0, 3.0 and 5.0 were, respectively, 29, 15.3 and 10.5 days, as calculated from the kinetics of the degradation. Compared with the anthocyanin extract, anthocyanidin is more vulnerable, with faster half-degradation rates. Furthermore, the product from the anthocyanidin degradation had a similar structure to catechol (a good substrate for polyphenol oxidase [catechol oxidase]), which, in turn, could accelerate enzymatic browning reaction by polyphenol oxidase. In addition, an anthocyanase, catalysing anthocyanin hydrolysis and producing anthocyanidin, was extracted from litchi fruit pericarp. High activity of the enzyme was observed in the pericarp. Thus, it is suggested that anthocyanase might contribute to the browning of litchi pericarp involved in the anthocyanase-anthocyanin-PPO reaction