ZnO Nanostructures in Active Antibacterial Food Packaging: Preparation Methods, Antimicrobial Mechanisms, Safety Issues, Future Prospects, and Challenges

The potential mitigation effect of ZnO nanoparticles on [Abelmoschus esculentus L. Moench] metabolism under salt stress conditions

Salt stress is known to be momentous abiotic stress which treats agricultural lands and crop production throughout the world and effects the system of food security. The current study aims to investigate the effect of foliar application of 10 mg/l of zinc oxide (ZnO) as a bulk or as a green synthesized nanoparticle (ZnO-NPs) which were hexagonal and spherical in shape and at size 16–35 nm to alleviate the impact of salinity concentrations (0, 10, 25, 50, 75 and 100% SW) on Okra (Abelmoschus esculentus L. Moench cv. Hasawi) species. The results demonstrated a gradual decrease in the photosynthetic pigments (i.e., chlorophyll a and b with total chlorophylls and carotenoids) with the growth of salinity conc. However, the sea water levels between 0 and 75% will led to increase in proline, total soluble sugar and activity of the antioxidant enzymes i.e., superoxide dismutase (SOD) and catalase (CAT) and then decrease at 100% SW. The addition of bulk ZnO or ZnO-NPs enhances the contents of the photosynthetic pigments, activity of both SOD and CAT and then lowers the accumulation of proline and total soluble sugar when equated with controls. Plants treated with ZnO-NPs showed the greatest results when compared with other treatments. The results of current study showed ZnO-NPs as an appropriate eco-friendly and low-cost application for plant growth under salinity which has an ability to moderate the salt stress effect of plants.

Antibacterial tragacanth gum-based nanocomposite films carrying ascorbic acid antioxidant for bioactive food packaging

Food packaging has a pivotal share to improve protection, safety and shelf-life time of foods and bioproducts. Herein, we prepared bioactive nanocomposite films that composed of tragacanth (TG), polyvinyl alcohol, ZnO nanoparticles (NPs) and ascorbic acid (AA) using glycerol as a plasticizer and citric acid as a cross-linker for food packaging. The SEM images showed a homogenous distribution of ZnO NPs with low aggregation in nanocomposite films. The water solubility of nanocomposite films reduced from 15.65 % to 10.81 with increasing of TG and ZnO NPs contents. The incorporation of AA and ZnO NPs into nanocomposite films improved antioxidant activity from 50 % to 66 % in 95 % ethanolic solution. Also, the nanocomposite films showed good antibacterial activity against Gram-negative and -positive bacteria. Soil degradation rate of nanocomposite films increased from 80 % to 91.46 as the wt% of TG increased. Therefore, prepared nanocomposite films could be employed as a promising candidate for food packaging applications.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphoslogies

Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.