Harvest maturity stage affects watercore dissipation and postharvest quality deterioration of watercore 'Fuji' apples

Watercore 'Fuji' apples, with their special watercore shape and unique flavor and texture, are a very popular specialty fruit in the Asian markets. However, watercore disappearance and quality deterioration of apples during postharvest storage are serious problems. In this study, we compared the differences among three harvest maturity stages of apples in watercore dissipation and fruit quality deterioration. In this study, the physiochemical attributes (visual quality, watercore incidence, and firmness), flavor substances (TSS content, TA content, and TSS/TA), aroma volatiles, and cellular structure were analyzed in 'Fuji' apple fruits of low maturity (LM) at early harvest stage, medium maturity (MM) at mid harvest stage, and high maturity (HM) at late harvest stage, during a cold storage at 0 ± 1 °C for 120 d. The results showed that harvest maturity stage had a significant effect on postharvest storage quality parameters of watercore 'Fuji' apples. Specifically, L*, b*, firmness, and TA values of the flesh decreased significantly from the LM to the HM levels. However, the watercore incidence of apples significantly increased from LM to HM levels. Moreover, the parameters including L*, b*, firmenss, TA, and watercore incidence of apples with different harvest maturity stages gradually decreased as the storage time increased. In contrast, the TSS, TSS/TA, and a* values showed an increasing trend from LM to HM apples. In particular, the TSS tended to increase first and decrease after 60 d of storage. Moreover, the microstructure and cellular structure gradually deformed as the structural porosity and cell size decreased from LM to HM apples. Furthermore, the microstructure of the watercore and non-watercore sites is significantly different. Meanwhile, the content of soluble sugars and aroma volatiles increased with the advancing maturity. Non-watercore sites of apples with the same level of maturity contained higher levels of sucrose, fructose, maltose, and sorbitol than watercore sites. Furthermore, the MM apples maintained better sensory qualities during the shelf life after cold storage. Overall, the MM apples showed higher quality and were more acceptable to consumers, which suggested watercore 'Fuji' apples from mid harvest stage showed the optimal harvest-ready maturity for post-harvest long-term cold storage.