In this study, lychee (Litchi chinensis Sonn.) pericarp powder was added to chitosan (CHS) matrix to develop active packaging films, and their structure, physicochemical, antibacterial, antioxidant, and functional properties were investigated. FT-IR results showed that intermolecular hydrogen bonds were formed between CHS and polyphenols in lychee pericarp powder (LPP), and the intermolecular interaction interfered with the assembly of CHS into semi-crystal structure, which reduced the crystallinity of CHS film. Incorporation of LPP significantly reduced water vapor permeability, water solubility, swelling degree, and elongation at break of CHS film (p < 0.05). However, UV-visible light barrier, tensile strength, and antibacterial and antioxidant properties of CHS films were increased by LPP incorporation. CHS-LPP film remarkably lowered the weight loss, firmness, titratable acidity, and total soluble solids of fresh-cut apple after five days storage. CHS-LPP film packaging effectively inhibited the browning of fresh-cut apple and the reduction of polyphenol content in apple juice caused by polyphenol oxidase (PPO)-mediated oxidation during storage. Therefore, CHS-LPP films have great potential as food packaging material to ensure the quality and extend the shelf life of food products.
Lactic acid bacteria are of interest to the food industry due to their antimicrobial properties. In this study, five strains of Lactobacillus plantarum were isolated from traditional fermented dairy food in Inner Mongolia; the strains displayed antifungal characteristics. Lactobacillus plantarum ALAC-4 was selected for further study due to its strong inhibitory effect on fungal development. The antifungal substances produced by L. plantarum ALAC-4 were characterised based on treatments with heat, pH and enzymes. The antifungal metabolites were analysed using gel-filtration chromatography and SDS-PAGE. The results showed that the antifungal substances were heat stable and active against most of the tested fungi, and maximal activity was observed at pH values from 4.0 to 4.5. The antifungal activity was decreased by protease treatments, which indicated the proteinaceous nature of the antifungal substances. Enhanced antifungal activity occurred after 28 h of incubation in de Man, Rogosa, Sharpe (MRS) broth with a 4% inoculum level at 34°C and initial pH of 7.0, which resulted in an increase from baseline data. The molecular mass of the antifungal substance determined by SDS-PAGE was approximately 40.32 kDa. This study demonstrated that L. plantarum ALAC-4 produces a peptide with a remarkable antifungal activity, which can be potentially used as a biopreservative in dairy products.
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