At-harvest fruit maturity affects sucrose metabolism during cold storage and is related to chilling injury in peach

We investigated the effects of at-harvest maturity of 'YuLu' peach fruit on soluble sugar metabolism and their relationship with chilling injury susceptibility. Peaches were sorted into four maturity groups at harvest by I-AD (index of the absorbance difference between 670 and 720 nm) then stored at 5 degrees C for 28 days. Fruit quality parameters, flesh browning index, malondialdehyde (MDA) content, soluble sugar content, gene expression, and enzyme activities associated with sucrose metabolism were measured. The more mature fruit groups had significantly (p < 0.05) lower firmness, higher soluble solid content, a* values of background color, sorbitol and sucrose content at harvest. During the cold storage, the higher flesh browning index in the mature groups (M3 and M4) maybe due to the double stress of senescence and chilling injury because there was concomitant sharp increase in MDA content. However, the most immature at-harvest group (M1) had the significantly (p < 0.05) higher MDA content after 14 days of cold storage, and a flesh browning index significantly (p < 0.05) higher than the M2 group (the next more mature group), late in the storage period. Moreover, the M1 group had lower sucrose content at postharvest and higher activities and transcript levels of sucrose degrading enzymes and lower levels of sucrose synthesis enzymes, which was responsible for the lower sucrose levels than M2 group during storage. It was concluded that the more immature peach fruit with lower sucrose content, have a higher chilling susceptibility than more mature fruit.