Biochemical and physiological changes involved in browning of litchi fruit caused by water loss

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Abstract
Summary The browning of litchi fruit pericarp caused by water loss was investigated in relation to total phenolic concentration, phenylalanine ammonia-lyase (PAL) activity, reduced glutathione content, polyphenol oxidase (PPO) and peroxidase (POD) activities, and peroxide content. Development of pericarp browning increased with reduced storage relative humidity (r.h.; from 90% to 60% r.h.) and increased storage time (from 1–3 d), and there was a strong time 2 r.h. interaction. Water loss from the pericarp increased PAL activity of pericarp of fruit stored at 60% or 70% r.h. with a maximum after 2 d storage, while activity of this enzyme stored at 80%, 90% or 95% r.h. remained at lower levels. Total phenolic compounds of litchi pericarp was initially high, and tended to decrease. Reduced glutathione content as an indicator of antioxidant capacities was lower for low storage r.h. values than for high ones, whereas a higher content of peroxides for lower storage r.h. was observed. PPO and POD activities of litchi pericarp tended to increase with reduced storage r.h. Accordingly, the results suggest that water loss-induced browning of litchi pericarp may be due to both a reduction in antioxidant capacities and an increase in oxidation of phenolics catalyzed by PPO and POD.

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