Detoxified and antimicrobial-enhanced olive mill wastewater phenols capping ZnO nanoparticles incorporated with carboxymethyl cellulose for fresh strawberry preservation

The underutilized by-products of hydrophilicity olive mill wastewater phenols (OPs) have great antimicrobial potential. ZnO NPs is one of most wildly used nano material with anti-bacterial function as well. This study aimed to prepare the detoxified and antimicrobial-enhanced OPs capping ZnO nanoparticles (OPs-ZnO NPs) containing metal core of ZnO NPs and organic shell of OPs, respectively. The OPs-ZnO NPs was chemically coordinated/chelated driven by Lewis bases (NaOH) in aqueous solution. The results obtained by SEM and TEM showed that those irregular sphere OPs-ZnO NPs were ranged from 58 to 92 nm, with an OPs caption of 35.40% (w/w). Importantly, the in vitro results showed that the strategy of capping OPs in ZnO NPs decreased the toxicity of ZnO NPs (< 0.02 g/L). Moreover, OPs-ZnO NPs presented a higher stability in simulated gastrointestinal digestion (Zn2+ < 0.07 g/L after 12 h). The results also showed that the protective coating of OPs-ZnO NPs and OPs-ZnO NPs/CMC (carboxymethyl cellulose) enhanced the antimicrobial activity of Escherichia coli, Staphylococcus aureus and Aspergillus niger. Furthermore, the coating of OPs-ZnO NPs/CMC decreased the weight loss and the rotting ratio of fresh strawberry, and ultimately prolonged its shelf-life at least 4 days under 25 ºC. Therefore, this study provided a biosafety strategy for the preparation of detoxified and antimicrobial enhanced OPs-ZnO NPs and its CMC protective coating for fresh produce throughout storage.