Antibacterial and antifungal activity of zinc oxide nanoparticles produced by Phaeodactylum tricornutum culture supernatants and their potential application to extend the shelf life of sweet cherry (Prunus avium L.)

Abstract

In the current work, zinc oxide nanoparticles (ZnONPs) synthesized by the cell-free supernatant of Phaeodactylum tricornutum cultures were first examined for their physicochemical and antimicrobial proprieties. They were then applied as spray coating on the surface of fresh sweet cherries to evaluate their efficacy on quality maintenance of the fruit over 10 days of storage at 25 °C. Synthesized nanoparticles showed a large-scale inhibitory effect against Escherichia coli (ATCC 25922), Staphylococcus aureus MRSA (ATCC 43300) and Candida albicans (ATCC 14053) with minimum inhibitory concentrations (MIC) ranged between 0.078 and 0.156 mg/mL. Furthermore, ZnONPs at 100–1000 mg/L effectively inhibited mycelia growth of Mucor heimalis, a causative agent of Mucor rot in sweet cherries. The results also indicated that ZnONPs significantly delayed the changes of visual and biochemical attributes of the fruit. Compared to untreated control, coated cherries with ZnONP at a concentration of 500 mg/L showed very small change in moisture and total sugar content. Therefore, all coated fruits exhibited less decay rates. In addition, spray coating with ZnONPs had a positive effect on maintaining suitable amounts of ascorbic acid (29.74 mg/100 g FW), polyphenols (579.2 μg/g FW) and flavonoids in the fruits (1991.87 μg/g FW). Data from this study showed 5.11% and 11.63%, increase in flavonoid content and antioxidant activity in the fruits coated with 500 mg/L ZnONPs, respectively, at the end of storage. These data together suggest that green ZnONPs-based coating is one of the safest and effective ways to preserve commercial fruits for prolonged storage.