Abstract

Litchi (Litchi chinensis Sonn.) is an important subtropical fruit crop with high market value. However, rapid pericarp browning and decay of litchi fruits caused by infection of microorganisms during storage can result in up to 50% of postharvest loss prior to consumption. New methods are urgently needed for effectively overcoming these problems. In this study, we tested the efficacy of chlorine dioxide for the control of postharvest diseases of litchi fruit. Inactivation kinetics of litchi anthracnose by ClO₂ solution concentrations ranging from 5, 10, 20, 40, 60, 80 and 120 mg/l was also studied. The fruits of the cultivar ‘Huaizhi’ were first treated with 80 and 120 mg/l ClO₂ and then stored at 20°C for 7 days. The effect of the ClO₂treatments on the postharvest physiology was investigated. The results showed that 5 mg/l ClO₂ solution could significantly inhibit litchi anthracnose spore germination. In addition, treatments with 80 and 120 mg/l of ClO₂ significantly reduced postharvest decay and peel browning of the fruit, inhibited polyphenol oxidase (PPO) and peroxidase (POD) activity, retained total soluble solids (TSS)and titratable acidity (TA) content, and increased phenylalnine ammonialyase (PAL) activity and malondialdehyde (MDA) content. However, ClO₂ solution did notsignificantly influence CO₂ and C₂H₄ production of the fruits, compared with those in the untreated control. Overall, 120 mg/l ClO₂ solution treatment was effective in inhibiting postharvest diseases and improving the quality of litchi fruits.

Key words: Litchi, chlorine dioxide, Colletotrichum spp, polyphenol oxidase, peroxidase.

Abbreviation

ClO₂, Chlorine dioxide; PPO, polyphenol oxidase; POD,peroxidase; PAL, phenylalnine ammonialyase; MDA,  malondialdehyde; SO₂,sulphur dioxide; TA, titratable acidity; BI, browning index; DI, disease incidence.