EFFECT OF LOW AND HIGH OXYGEN‐CONTROLLED ATMOSPHERES ON ENZYMATIC BROWNING OF LITCHI FRUIT

Experiments were conducted to test the effect of low and high O2 concentration on enzymatic browning of harvested litchi fruits. Litchi fruits were kept in air (control), 5 or 60% O2 for up to 6 days at 28C and 90–95% relative humidity. Changes in pericarp browning and disease development were evaluated. Contents of anthocyanins and total phenols, activities of phenolic metabolism-associated enzymes, polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL) and anthocyanase, membrane permeability, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power were also measured. Exposure of 5 or 60% O2 delayed significantly pericarp browning and reduced rot development. The inhibition of pericarp browning was associated with high contents of anthocyanins and total phenols and reduced activities of PPO, POD and anthocyanase, as well as low membrane permeability. Moreover, the enhanced beneficial effects were obtained when 5% O2 was used compared with 60% O2. However, application of controlled atmosphere at low and high oxygen levels activated PAL activity, which was related to accumulation of anthocyanins. In addition, there were higher levels of DPPH radical scavenging activity and reducing power in litchi fruits kept in low and high oxygen atmospheres, compared with the fruit kept in air. Thus, it appeared that 5% O2 was more potential to inhibit pericarp browning and extend shelf life of harvested litchi fruit. PRACTICAL APPLICATIONS Pericarp browning is the major cause of deterioration in postharvest litchi. Conventional controlled atmosphere with low O2 and high CO2 is effective in maintaining quality and extending shelf life of fruits and vegetables, including inhibition of tissue browning. Using nonconventional gas mixtures such as superatmospheric O2 also attract the interest of postharvest scientists. In this study, 5 and 60% O2-controlled atmosphere delayed significantly pericarp browning and reduced rot development. It could potentially be useful as a postharvest technology of litchi fruit for reducing or replacing the use of chemicals such as SO2 and fungicides, but it requires further investigation.