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Background Strawberry fruit is a rich source of antioxidants that are beneficial for human health. However, the rapid decline of strawberries dramatically reduces the shelf life and raises postharvest losses. To develop an efficient and ecological approach for maintaining the quality, strawberries (Fragaria x ananassa, cv. Festival) were treated with 0.5% chitosan coating (0.5% Ch), guava leaf-based chitosan nanoparticles coating (Gl-ChNps), and a combination treatment of 1.3 mW/cm2 laser light followed by Gl-ChNps coating (combined treatment), then stored for 12 days at 10 °C and 85–90% RH. The untreated fruit served as a control. Results Semi-spherical particles with an average size of 21.92 nm, a monodisperse nature, and high solution stability were formed. The findings revealed that the combined treatment completely suppressed fungal decay compared to 50% decay in control, and significantly reduced weight loss percentage to 4.68% compared to 27.35% in control. In accordance, the combined treatment had the maximum anthocyanin content and vitamin C, at 42 and 81.1 mg/100 g, respectively. The results showed that treated strawberries had less change in color, total soluble solids, titratable acidity, and pH during storage than untreated strawberries, which exhibited higher chemical changes. Conclusions The edible film of chitosan nanoparticles acted as a semi-permeable barrier that modified and restricted gas exchange, reduced water loss, and delayed fruit senescence. In addition, the combination of laser light with chitosan nanoparticles has been shown to control the pathogens and retain the freshness of strawberries. Graphical Abstract

Chitosan is polysaccharide polymer used for biomedical applications and food packaging. The aim of this investigation is to produce chitosan nanoparticles (ChNPs) using guava leaf (Psidium guajava L.) extract as green synthesis of nanoparticles using plant leaf extract is ecofriendly and cost-effective approach. The leaves of guava are nontoxic, full of bioactive compounds, and suitable alternative to avoid chemicals used in other methods. Variations in extract preparation method and ratio of chitosan to leaf extract were examined to investigate the effect of these factors on the particles size. The characterisation of chitosan nanoparticles was conducted using dynamic light scattering (DLS), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential analysis. The results showed semi-spherical nanoparticles were formed at pH=5 with an average particle size of 21.92 nm and narrow size distribution as, polydispersity index (PDI) value was 0.471. Zeta potential was −27.1 which gives reasonable stability to the nanoparticles in suspension. The effect of storage time of chitosan nanoparticles on the antibacterial activity against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis was also investigated.

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