THE CONTROL OF LYCHEE (LITCHI CHINENSIS SONN.) POSTHARVEST SKIN BROWNING USING SULPHUR DIOXIDE AND LOW PH
Lychee, like most arillate fruits, deteriorate rapidly once harvested. The first visual symptom of deterioration is skin browning. When stored under ambient conditions, the original bright red colour may be lost within 48 h. It has been suggested that lychee skin browning is primarily the result of polyphenol oxidase activity degrading the anthocyanins and producing brown coloured by-products. In some countries, sulphur dioxide fumigation has been recently introduced to control skin browning. Sulphur dioxide is an effective inhibitor of polyphenol oxidase and is widely used to control enzymic browning Application of sulphur dioxide however causes a rapid bleaching of the lychee skin. Colour will progressively return, but only to a dull orange colour. Application of 1 N HCl after sulphur dioxide treatment was shown to restore fruit to initial skin colour. Acid treatment is suggested to reverse the bleaching process by affecting the pigment structure.
Underhill, S.J.R., Bagshaw, J., Prasad, A., Zauberman, G., Ronen, R. and Fuchs, Y. (1992). THE CONTROL OF LYCHEE (LITCHI CHINENSIS SONN.) POSTHARVEST SKIN BROWNING USING SULPHUR DIOXIDE AND LOW PH. Acta Hortic. 321, 732-741