Antifungal, antioxidant activity, and preservation effect of caffeic acid quaternary ammonium salt-modified chitosan

This study modified chitosan (CS) using caffeic acid (CA) and 1-(4-carboxyphenyl)-N, N, N-trimethylammonium chloride (TMAC) to enhance its antifungal and antioxidant activities. The modified products were determined using FTIR and ¹HNMR. The modified product's in vitro antifungal activity against five plant pathogens was investigated using the mycelial growth rate method. Chitosan co-grafted with both CA and TMAC (TMACSCA) exhibited the best inhibitory effect against Phytophthora capsici (EC₅₀ = 37.826 μg/mL). Through analysis of the microscopic morphology of the mycelium, we found that this modified product damages the ultrastructure of fungal hyphae, which inhibits their growth. In vivo and antioxidant testing indicates that TMACSCA exhibits excellent therapeutic and protective properties, as well as outstanding antioxidant activity. TMACSCA extends the shelf life of fresh peppers by 21 days and mangoes by 18 days. This study provides theoretical guidance for the further developing modified chitosan for antimicrobial and preservation applications.