Role of anthocyanin degradation in litchi pericarp browning

Pericarp browning is the main problem of post-harvest litchi fruit, resulting in an accelerated shelf life and reduced commercial value of the fruit. Underhill and Critchley (1994). Anthocyanin decolorisation and its role in lychee pericarp browning. Australian Journal of Experimental Agriculture, 34, 115-122 found that there was not an obvious change in the content of anthocyanins when the fruit browned. This work was conducted with a view to explaining 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 spectum 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 a half-degradation of about 5.3 min at pH 5.0. Furthermore, the product from the anthocyanidin degradation had a similar structure to catechol (a good substrate for polyphenol oxidase), which, in turn, could accelerate enzymatic browning reaction by the enzyme polyphenol oxidase. In addition, an anthocyanase, catalyzing 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. Copyright © 2001 Elsevier Science Ltd.