ANTHOCYANIN DECOLORISATION AND ITS ROLE IN LYCHEE PERICARP BROWNING

Mature red lychee fruit were stored at 3 different temperature and rel ative humidity regimes. Total anthocyanin concentration, pigment distr ibution, pH of the pericarp homogenate, Hunter a values (redness index ), and visual colour were measured as a function of pericarp weight lo ss. Pericarp colour rapidly deteriorated during both ambient and high temperature storage, resulting in a uniform browning of the pericarp s urface. The degree of tissue browning was proportional to the rate of pericarp desiccation. Although anthocyanin degradation occurred concur rently with tissue browning, visual colour and Hunter a values were no t consistent with total anthocyanin concentration. Instead, a more sig nificant correlation was seen between Hunter a values and the pH of th e pericaip homogenate. Pericarp colour could be altered by external pH . Acidification of whole fruit increased pericarp redness, whereas alk aline treatment caused discoloration. Both colour responses occurred i ndependently of anthocyanin synthesis and degradation and were complet ely reversible. These results question the current theory that brownin g is due to anthocyanin degradation. No evidence of browning was obser ved in the anthocyanin-containing mesocarp, and acidification of alrea dy brown tissue significantly increased pericarp redness independently of anthocyanin synthesis. We believe that anthocyanin pigments were p rogressively decolorised during ambient storage, possibly due to chang es in pericarp pH. Once colourless, independent tissue browning became visual and was enhanced.