Evaluation of nano ZnO edible coating effect on microbial, physicochemical and sensorial characteristics of black table grape during storage

Table grape is considered as the second horticultural product in Iran and therefore any, will have a most positive economic effect. The coating solutions based on nano ZnO, were prepared by dissolving and soliciting the nano ZnO powder in distilled water at different concentrations (e.g. 0, 0.25, 0.75 and 1.25 g/L, w/w). Treatments were performed by dipping the table grape cluster in the coating solution for 5 min, then drained, packaged and stored at 1 ± 1oC, 90% ± 5 RH. Microbial Load (yeasts and molds and total aerobic bacteria), physiochemical characteristics (ascorbic acid (AA), weight loss, firmness, titratable acidity, soluble solid content (SSC), anthocyanin content, total phenolic and antioxidant activity) and sensory attributes of the samples were evaluated after 0 and every 15 d interval up to 45 d of storage compared to uncoated fruits. Results showed that the nano ZnO coating significantly (p<0.01) reduced the weight loss and AA degradation and maintained firmness, anthocyanin and phenol contents and antioxidant activity in coated samples as compared to uncoated up to 45 d storage. The coating containing 0.75 g/L nano ZnO, meanwhile maintained the fruits quality characteristics compared to the others, showed the highest antibacterial activity (p<0.01) during 45 d of storage. However, the panelists assigned the heights scores in sensory properties to the coated fruits with 0.75 g/L nano ZnO.