Postharvest Browning of Litchi Fruit by Water Loss and its Prevention by Controlled Atmosphere Storage at High Relative Humidity

Postharvest browning of litchi fruit caused by water loss was investigated in relation to anthocyanin content, polyphenol oxidase (PPO) activity, pH value, and membrane permeability. Total anthocyanin concentration decreased with pericarp desiccation. Fruit stored at 90% relative humidity (RH) had the lowest loss of total anthocyanins over the storage period, while total anthocyanin content of fruit stored at 60 and 70% RHs significantly declined. Polyphenol oxidase activity with 4-methylcatechol as a substrate tended to increase with reduced storage RH, but no activity towards anthocyanins was detected. Furthermore, in the presence of 4-methylcatechol, the oxidation of anthocyanins by PPO was observed. The pH value was initially low, and then increased with pericarp desiccation, which was associated with increased PPO activity. Conversely, the integrity of membrane systems, which increased with reduced storage RH and increased storage time, showed that membrane structure became more vulnerable. These results indicate that oxidation of both phenolic and anthocyanins by PPO seems to affect the response of litchi fruit to water loss in terms of browning, and suggest that substrate-enzyme contact should be emphasized as this could promote enzymatic reaction leading to browning. Storage at 1°C under controlled atmosphere (3-5% O2and 3-5% CO2) at 90% RH gave good browning control and fruit quality maintenance.