To improve the antibacterial and antioxidant properties of chitosan (CS), CS grafted with gallic acid (GA) using recombinant bacterial laccase from Bacillus vallismortis fmb-103 (fmb-rL103) as a catalyst. The structures of grafted chitosans were identified using Fourier transform infrared spectroscopy (FT-IR) and UV visible spectrum (UV–Vis spectroscopy). After gallic acid grafting, the antibacterial properties of chitosans against Pseudomonas, Acinetobacter, Brochothrix thermosphacta, Escherichia coli, Staphylococcus aureus, Salmonella, and Listeria monocytogenes were significantly improved. Meanwhile, 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging results showed that the antioxidant properties of grafted CS increased as well. The preservative effects of the grafted chitosan on chilled meat were then investigated. For this purpose, the quality indexes of the chilled meat during the storage were monitored, including total bacterial count, total basic volatile nitrogen (TVB-N) content, pH value, color and thiobarbituric acid reactive substances (TBARS) and so on. The results showed that coating with the grafted chitosan retarded the growth of spoilage bacteria, and decreased TVB-N and TBARS values of meat. The shelf life of chilled meat coated by CS grafted with GA (GA-g-CS) also extended from 6 days to 18 days at 4°C. These results provided a theoretical basis for the future application of the GA-g-CS in the preservation of chilled meat. Highlights: (1) The temperature and pH-stable bacterial laccase was used to synthesize gallic acid grafted chitosan. (2) Antioxidant and antibacterial properties of chitosan were improved through grafting gallic acid. (3) Storage properties of chilled meat were improved by coating with gallic acid grafted chitosan.

Incorporating phenolic acids into polysaccharide films improves their physical properties, in turn improving their potential commercial applicability as a preservation material for different foods. This study aimed to develop films from curdlan and tea polyphenols, and determine the effect of their contents on the water vapor permeability (WVP) and mechanical properties (tensile strength and elongation at break) of the films. Different ratios of tea polyphenols were incorporated into the curdlan-based films to improve their properties. The results obtained showed that the tensile strength and elongation at break of films were likely to be significantly decreased by adding tea polyphenols, especially at a content of 0.6%, which resulted in a 50% decrease. Meanwhile, the WVP and moisture content of the films was also decreased. However, a low WVP can prevent moisture loss from food. Other film properties, such as antioxidant efficiency, were also investigated. The results showed that the antioxidant potential of the film can be improved by tea polyphenols. The composite films were also applied to the preservation of chilled meat, which resulted in the shelf life being extended by about 3–5 days. Some properties, such as water resistance and DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical scavenging capacity of the composite film, were improved.

Plipastatin, an antifungal lipopeptide, is synthesized by a non-ribosomal peptide synthetase (NRPS) in Bacillus subtilis. However, little information is available on the combinatorial biosynthesis strategies applied in plipastatin biosynthetic pathway. In this study, we applied module or individual domain deletion strategies to engineer the plipastatin biosynthetic pathway, and investigated the effect of deletions on the plipastatin assembly line, as well as revealed the synthetic patterns of novel lipopeptides. Module deletion inactivated the entire enzyme complex, whereas individual domain (A/T domain) deletion within module 7 truncated the assembly line, resulting in truncated linear hexapeptides (C16~17β-OHFA-Glu-Orn-Tyr-Thr-Glu-Ala/Val). Interestingly, within the module 6 catalytic unit, the effect of thiolation domain deletion differed from that of adenylation deletion. Absence of the T6-domain resulted in a nonproductive strain, whereas deletion of the A6-domain resulted in multiple assembly lines via module-skipping mechanism, generating three novel types of plipastatin derivatives, pentapeptides (C16~17β-OHFA-Glu-Orn-Tyr-Thr-Glu), hexapeptides (C16~17β-OHFA-Glu-Orn-Tyr-Thr-Glu-Ile), and octapeptides (C16~17β-OHFA-Glu-Orn-Tyr-Thr-Glu-Gln-Tyr-Ile). Notably, a unique module-skipping process occurred following deletion of the A6-domain, which has not been previously reported for engineered NRPS systems. This finding provides new insight into the lipopeptides engineering. It is of significant importance for combinatorial approaches and should be taken into consideration in engineering non-ribosomal peptide biosynthetic pathways for generating novel lipopeptides.