Improving the quality of grapes by coating chitosan–zinc oxide nanoparticles

Abstract

The current work aimed to improve the grape nutritional quality, by coating applications through the combined treatment of chitosan–zinc oxide nanoparticles and essential oil. Four coating syntheses have been prepared. The control was prepared with the addition of distilled water, 1% glycerol, and 0.5% acetic acid, the second treatment chitosan (CS) was prepared by mixing 1 g chitosan powder with 0.5% acetic acid solution, 1% glycerol, and stirred for 12 hours at a temperature of 40 °C, the third treatment CS-ZNO was prepared with 1% zinc oxide nanoparticles and CS mother solution, while the fourth treatment (CS-ZNO-EO) synthesis was prepared to blend CS-ZNO with 1% essential bergamot oil (BO). Several physical, chemical and biological parameters evaluation was carried out on grapes every (0, 4, 7, 14, and 16 days). The study findings revealed that the berry abscission index was positively affected by CS-NZO and CS-NZO-EO treatments, which presented lower values of 2.58% and 1.77% respectively. The inhibitory effects were increased during the whole shelf life to reach 3.62–5.47 Log CFU/Berry at the end of the storage period, nevertheless of the orders of the various treatments. The maximum decrease in microbial contamination (3.62 Log CFU/Berry) was observed in the CS-NZO-EO treated samples on the 16th day. Though, the lowest soluble solid content (SSC) value was established by the control that was the worst to reach 12.11% towards the end of the storage period. In the same trend, CS-NZO and CS treatments recorded similar values of 13.5% and 12.78%, respectively. The lowest value for titratable acidity (TA) was detected for the control samples on the 16th day of storage 0.32 g/100 g citric acid. The highest TA value was established for CS-NZO-EO and CS treatments that reported 0.46 g/100 g and 0.45 g/100 g citric acid, respectively. The value of catalase enzyme activity (CAT) reached the bottom 21.55 U/g after 16 days for control samples. CS-NZO increased again between 14 and16 days to achieve the highest value of 39.74 U/g; while the CAT activity of grape samples coated with single CS or CS-NZO-EO detected increases on the 16th day to reach 38.47 and 32.74 U/g, respectively. Further studies on combined treatment therapy are needed to optimize the applications of the protective coating of foods in the food industry.