Effect of intermittent warming on alleviation of peel browning of 'Nanguo' pears by regulation energy and lipid metabolisms after cold storage

Refrigeration slows postharvest ripening of 'Nanguo' pears (Pyrus ussuriensis Maxim.), but the peel of the pears is prone to browning when the fruit are returned to room temperature. Intermittent warming (IW), in which the fruit were exposing to 20 ± 1 °C for 1 day every 20 d during storage at 0 ± 0.5 °C, retarded the occurrence of peel browning (PB) of the pears in this study. IW-treated pears showed higher firmness and ethylene production in peel of fruit during the early stage of shelf life. An increase in ATP concentration and energy charge (EC) was detected in IW-treated fruit. The concentration of malondialdehyde (MDA) and the electrolyte leakage were lower in IW-treated fruit. Higher enzyme activity and increased gene expression of transcripts for ATP synthase (ATPase), NADH dehydrogenase (NDA) and vacuolar proton-inorganic pyrophosphatase (VPP), which were associated with oxidative phosphorylation, were found in IW-treated fruit during the shelf life. Lower enzyme activity and down-regulated gene expression levels of phospholipase D (PLD) involved in glycerophospholipid metabolism were found in fruit under IW treatment. These results indicate that the PB of 'Nanguo' pears can be effectively alleviated by IW treatment and the possible mechanisms are discussed.