Microwave‐assisted degradation of chitosan with hydrogen peroxide treatment using Box‐Behnken design for enhanced antibacterial activity

Summary Low molecular mass ( MM ) chitosan with high degree of deacetylation ( DDA ) has excellent bioactivity including antioxidant, antibacterial and encapsulation properties. In this work, to reduce the MM of chitosan, microwave‐assisted heating treatment ( MAHT ) conditions were investigated using three factors at three levels Box‐Behnken design ( BBD ). Microwave heating ( MH ) time, H 2 O 2 concentration and solid‐to‐liquid ratio significantly affected the DDA and MM of chitosan. The antibacterial activities of chitosan before and after degradation were investigated based on minimum inhibitory concentration ( MIC ) and minimum bactericidal concentration ( MBC ). The results showed that a second‐order polynomial equation fitted the observed values using multiple regression analysis and had a high coefficient of determination ( R 2  = 0.9591 and 0.9161 for the DDA and MM of chitosan, respectively). An optimisation study was performed using Derringer's desirability function methodology, and the optimal conditions were 80‐s MH time, 1.5% H 2 O 2 concentration and 1:40 solid‐to‐liquid ratio. The MIC and MBC of chitosan before and after degradation against Escherichia coli and Salmonella typhimurium were 0.031 and 0.063 mg mL −1 , and 0.25 and 0.125 mg mL −1 , respectively. The optimised DDA and MM of chitosan were 90.58 ± 2.04% and 124.25 ± 14.36 kD a, respectively, which significantly reduces the use of oxidant reagent.