Pre-harvest zinc spray impact on enzymatic browning and fruit flesh color changes in two apple cultivars

Enzymatic browning (EB) in apple occurred during processing or fresh consumption as fresh cut. EB in response to pre-harvest Zn spray at two apple cultivars was investigated. Trees of apple (Malus domestica cultivar 'Delbard Estival' and 'Kohanz') were sprayed with water (control), 0.13% of Chelated Zn (C-Zn) or 0.13% of Nano-Chelated Zn (NC-Zn) three or four weeks before harvest. Assessments were carried at spray time, three or four weeks (H1 and H2) after spray and also after 3 weeks of storage (H1 + 3 W and H2 + 3 W) at 4 °C with 95% (RH). The browning index (BI) and total color changes (ΔE) decreased from spray time until harvest time. BI and ΔE in treated fruit were lower than control at all time points except in H1. Starch index was delayed in fruit treated with C-Zn or NC-Zn. The highest firmness of 'Delbard Estival' and 'Kohanz' cultivars was observed in NC-Zn than other treatments at all sampling times. Titratable acidity, soluble solids content and total phenol showed no distinct changes during time. The ascorbic acid, total antioxidant activity and superoxide dismutase in C-Zn or NC-Zn treatments were higher than control in both cultivars except superoxide dismutase activity at H1 for NC-Zn. The polyphenol oxidase activity in both cultivars treated with C-Zn or NC-Zn was lower than control at all sampling time except at H1 in 'Kohanz' cultivar. These findings suggest that the pre-harvest spray with Zn and especially NC-Zn can improve flesh color changes and quality parameters in apples.