Degradation of anthocyanin from litchi fruit pericarp by H2O2 and hydroxyl radical

Abstract

Litchi (Litchi chinensis Sonn.) is one of the most desirable subtropical fruits with high commercial values, which is significantly affected by its skin colour due to the embedded anthocyanin pigments. This work was conducted with a view to explaining the unexpected observation that litchi polyphenol oxidase (PPO) did not oxidise directly anthocyanins. Litchi fruit were stored for 4 days at 25 °C and 80–90% relative humidity. Browning index and H2O2 and OH contents of pericarp tissues of litchi fruit during storage were determined. The browning index of litchi fruit rapidly increased while H2O2 and OH contents decreased and then increased markedly, as storage time progressed. The obvious pericarp browning was associated with the rapid increases in H2O2 and OH contents of litchi fruit after 4 days of storage. Furthermore, litchi anthocyanins were purified by column chromatography and then H2O2 and hydroxyl radical were used to examine their degradation roles in the purified anthocyanin. It was found that the purified litchi anthocyanin was degraded markedly in the presence of H2O2 or hydroxyl radical. Increasing concentration of H2O2 or hydroxyl radical enhanced the anthocyanin degradation, of which the latter exhibited a greater effect on the anthocyanin degradation although no peak of litchi anthocyanin appeared after the treatment with 0.1% H2O2 for 10 min. This study can account for the pericarp browning of postharvest litchi fruit during storage based on the oxidative degradation of anthocyanin caused by PPO.