Preharvest promotion or inhibition of colouration: Which is the more conducive to improving litchi postharvest quality?

Litchi (Litchi chinensis Sonn. cv. 'Feizixiao') has a high market value. However, its value declines during postharvest storage because its quality deteriorates, and its pericarp turns brown. Therefore, safe and effective ways of improving litchi quality and inhibiting postharvest browning are required. In this study, 5-aminolaevulinic acid (5-ALA) and thidiazuron (TDZ) were applied to litchi fruit before harvest to determine their relative effects on litchi colour and postharvest storage characteristics. The results showed that preharvest 5-ALA application significantly increased postharvest fruit weight, anthocyanins, total phenol, vitamin C and antioxidant activity relative to those in the untreated fruits. Compared with the control, TDZ significantly increased fruit weight but inhibited anthocyanin accumulation and did not significantly alter antioxidant activity. Both preharvest treatments significantly reduced the browning index, the relative leakage rate and polyphenol oxidase activity after 6 d of storage. A membership function analysis indicated that preharvest 5-ALA application was the most beneficial for postharvest storage whereas TDZ treatment was relatively less effective. Preharvest colour promotion was preferable for improving litchi quality and inhibiting postharvest browning.