Bio-enzymatic grafting phenolic acid to chitosan derivative is an efficient and environmentally friendly molecular synthesis technology. In the present study, N-carboxymethyl chitosan (CMCS) was grafted with gallic acid (GA) using recombinant bacterial laccase from Streptomyces coelicolor as a catalyst. GA and CMCS were successfully grafted as determined by measuring amino acid content, Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-Vis) spectroscopy. Then, the effect of GA-g-CMCS coating on the freshness of strawberries at 20 ± 2 °C was explored. The physiological and biochemical quality indicators of strawberries during storage were monitored. The 1.5% GA-g-CMCS coating helped to protect the antioxidant properties and nutrients of strawberries and extend the shelf life. Specifically, it reduced the weight loss of strawberries during preservation (originally 12.7%) to 8.4%, maintained titratable acidity content (TA) residuals above 60% and reduced decay rate from 36.7% to 8.9%. As a bioactive compound, GA-g-CMCS has the potential to become an emerging food packing method. These results provide a theoretical basis and reference method for the subsequent synthesis and application of CMCS derivatives.

In this study, a novel protein glutaminase derived from Chryseobacterium lactis CGMCC 33780 (CLPG) was successfully purified via a one-step cell surface display approach, yielding its mature form. Subsequently, the enzymatic properties of CLPG were characterized. It exhibited optimal activity at a pH of 5 and a reaction temperature of 50 °C, and retained over 70% of its activity after a 12 h incubation at 50 °C. The study further investigated the impact of CLPG-mediated deamidation on the structural and functional attributes of krill protein isolate (KPI). A comprehensive analysis was conducted on the deamidation extent, conformational alterations, and microstructural morphology of KPI, employing techniques such as FTIR, CD, DSC, and SEM. After deamidation treatment with CLPG, the foaming and emulsifying properties of KPI were moderately shifted. When the CLPG dosage was 1.0 U/g with a corresponding deamidation degree of 15.18%, the emulsifying property of KPI reached the maximum value of 23%. These property enhancements were possibly primarily attributed to the increased electrostatic repulsion and hydrophobicity induced during the deamidation process. This work not only pioneers a novel method for the expression and purification of protein glutaminase but also applies it to the modification of krill protein, offering fresh insights for the development and application of protein glutaminases.