Regulation of plum fruit cracking process during cold storage period by treatment of preharvest chitosan

Cracking fruit is a serious quality change phenomenon in the storage and transportation of postharvest plum fruit. To reduce the cracking rate of plum fruit during cold storage, the 'Guofeng No.7′ plum was sprayed with chitosan with 1.5% concentration 30d from preharvest. The postharvest plum fruit was stored at (0 ± 0.5) °C and (85–90) % relative humidity. The results showed that chitosan treatment could reduce the reactive oxygen species (ROS) level of plum fruit, effectively delaying the fruit cracking. Compared with the control, chitosan treated fruits inhibited the increase of free radical content such as O₂⁻· and H₂O₂ and delayed the increase of membrane permeability and the accumulation of MDA (from 71.9 mmol/g to 53.5 mmol/g). It also regulates lipoxygenase (LOX), peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) (enzymatic activity from 34.15 g/min to 42.21 g/min) and ascorbate peroxidase (APX) activity and gene expression during fruit cracking to maintain membrane integrity and intracellular compartmentalization, thereby increasing the crack tolerance of plum fruit during cold storage. These results indicate that preharvest chitosan treatment can inhibit the metabolism of active oxygen species, increase the activity of ROS scavenging enzymes and gene expression, and delay the postharvest cracking of plum fruit.