Pre-harvest chelated or nano-chelated zinc treatment impact on enzymatic browning in apple

Flesh browning is an important postharvest problem that can affect consumer attitudes about apples. In this study, the effect of preharvest zinc (Zn) sprays on flesh color changes and associated browning metabolism at harvest and after storage was investigated. Trees of apple (Malus domestica cultivars 'Delbard Estival' and 'Kohanz') were sprayed with water (control), 0.13% of Oligo Zn-EDTA, or 0.13% of nano-chelated Zn. The browning index (BI), total color changes (∆E), total phenol (TP) contents, and activities of polyphenol oxidase (PPO) and peroxidase (POD) of the fruit were measured at spray time, 3 and 4 weeks after spray time (H1 and H2) and also after 3 weeks of storage (H1+3W and H2+3W) at 4°C (95% RH). Treatments increased TP contents and POD activity but decreased ∆E, BI, and PPO activity of both cultivars relative to the control. These findings suggest that the preharvest spray with Zn can affect EB and fruit flesh color changes in apples.