Chitosan nanoparticles (CSNPs) have attracted wide interest; however, there has been no substantial information about a direct comparison of the antimicrobial activity of CSNPs on bacteria and fungi. Thus, in this study, simple, economically feasible CSNPs were synthesized and assessed for their antimicrobial activity. This investigation indicated that the coordination inducing effect of CSNPs could dissociate the tryptophan (Trp) and tyrosine (Tyr) residue groups on the peptide chain of the bovine serum albumin (BSA) molecule, thereby increasing the absorption intensity. The growth of E. coli and S. aureus could be completely inhibited when the concentration of CSNPs in the solution was higher than 0.6 mg/mL. The CSNPs showed more potent antibacterial activity against Gram-negative bacteria (E. coli) than against Gram-positive bacteria (S. aureus). In addition, the CSNPs were effective at initiating cellular leakage of fungal mycelia and damping off fungal pathogens, and their antifungal effects were stronger on P. steckii than on A. oryzae. Furthermore, the antimicrobial activity of the CSNPs was found to be more effective against bacteria than against fungi. This study thus ascertained the antimicrobial activity of synthesized CSNPs against different microorganisms, as well as their different degrees of inhibition.

Blueberries are a rich source of health-promoting compounds such as vitamins and anthocyanins and show a high antioxidant capacity. Thus, considerable commercial and scientific interest exists in prolonging its postharvest life to meet the year-round demand for this fruit. In this investigation, the effect of a chitosan-based edible coating, as well as a chitosan-based edible coating containing nanosized titanium dioxide particles (CTS-TiO₂), on the postharvest quality of blueberry fruit quality was evaluated during storage at 0 °C. The blueberries were treated with a chitosan coating (CTS) and a CTS-TiO₂ composite, respectively. The most suitable chitosan and nano-TiO₂ fraction concentrations to be incorporated in the coating formulation were prepared based on the wettability of the corresponding coating solutions. Changes in firmness, total soluble solids (TSS), titratable acidity (TA), ascorbic acid (VC), malondialdehyde (MDA), polyphenol oxidase (PPO), and peroxidase (POD) activities, anthocyanins, flavonoids, total phenolic content, and microbiological analysis were measured and compared. This combined treatment prevented product corruption. Compared with CTS, the CTS-TiO₂ composite coating application effectively slowed down the decrease in firmness, TSS, VC, and TA in the blueberries. Additionally, changes in the total polyphenol, anthocyanin, and flavonoid contents and the antioxidant capacity of CTS-TiO₂ composite coating blueberry fruits were delayed. Therefore, these results indicated that the chitosan/nano-TiO₂ composite coating could maintain the nutrient composition of blueberries while playing a significant role in preserving the quality of fruit at 0 °C.

The use of chitosan and chitosan composite coatings for the preservation of fruits and vegetables during storage is attracting increasing attention. In this study, a chitosan-based edible coating, as well as a second chitosan-based edible coating containing salicylic acid (CTS + SA), a third containing nanosized titanium dioxide particles (CTS + TiO₂), and a fourth containing a combination of these two (CTS + SA + TiO₂) were evaluated in terms of their effects on the postharvest quality of blackcurrant fruit during storage at 4 °C. The results showed that compared with the other three treatment groups, the blackcurrants treated with CTS + SA + TiO₂ underwent the smallest changes in weight loss, total soluble solids, titratable acidity, vitamin C, and total anthocyanin content, and retained the highest total flavonoid content. This combined treatment significantly inhibited polyphenol oxidase activity during storage, and the CTS + SA + TiO₂ samples also displayed the lowest malondialdehyde content. These results, thus, indicate that the CTS + SA + TiO₂ composite coating could maintain the nutrient composition of blackcurrants, thereby playing a significant role in preserving the quality of this fruit at 4 °C.