Gum arabic-zinc oxide composite coating alleviated rind disorders and maintained quality attributes of mandarin (‘Kinnow’)

Mandarin fruits are prone to rind pitting disorder (RPD) during non-chilling temperatures (22°C), and this reduces their market value. Restricted use of synthetic fungicides applied with waxes in controlling rind disorders has led researchers to find alternative methods such as edible coatings enriched with nanoparticles. Application of gum arabic (GA) enriched with green synthesized ZnO nanoparticle (ZnO-NP) on ‘Kinnow’ mandarin in controlling RPD was investigated. ZnO-NP was synthesized using Bidens pilosa leaf extract and incorporated in GA (2%) at 0, 0.25, 0.5 and 1% to form composite coatings, GA+ZnO-NP 0%, GA+ZnO-NP 0.25%, GA+ZnO-NP 0.5% and GA+ZnO-NP 1%, respectively. Fruit were coated by dipping for 3 min in the coatings, with untreated fruit used as the control. Fruit were air-dried, packed in commercial cartons, and stored at 5±1°C and 90±5% relative humidity (RH) for 40 d. Sampling was done at 10-d intervals. To determine the incidence of RPD, the fruit were further stored at 20±5°C and 65±5% RH for 5 d. GA+ZnO-NP 1% alleviated RPD (13.2%), and the control fruit had a higher RPD incidence (45.2%). Coating the fruit with GA+ZnO-NP 0.5% delayed senescence of the fruit as evident by low weight loss (9.2%), electrolyte leakage (43.8%), and it had higher BrimA index (8.86), while the control had a higher weight loss (33.3%), electrolyte leakage (90.3%) and had lower BrimA index (5.96). Overall, given their varied positive effects on the storability of the ‘Kinnow’ mandarin fruit after 40 d storage, ZnO composite coatings between GA+ZnO-NP 0.5 and 1% could be recommended to control rind pitting disorders in ‘Kinnow’ mandarin.