Characterization of antifungal cyclic dipeptides of Lacticaseibacillus paracasei ZX1231 and active packaging film prepared with its cell-free supernatant and bacterial nanocellulose

Fungal infection and/or spoilage are major concerns of crop and food security worldwide, prompting the developments and application of various antimicrobial agents. In this study, nine strains of lactic acid bacteria (LAB) with antifungal activities were isolated from the traditional Chinese fermented wort of Meigui rice vinegar, where fungi coexist. The cell-free supernatant (CFS) of Lacticaseibacillus paracasei ZX1231 exhibited significant inhibitory activities against Aspergillus niger, Penicillium citrinum, Penicillium polonicum, Zygosaccharomyces rouxii, Talaromyces rubrifaciens, and Candida albicans. Among the four cyclic dipeptides (CDPs) uncovered from the CFS, cyclo(Phe-Leu) and cyclo(Anthranily-Pro) were found in the family Lactobacillaceae for the first time, which inhibited the C. albicans filamentation by targeting upon RAS1-cAMP-PKA pathway. CFS antifungal activities were optimally combined with a bacterial nanocellulose (BNC) matrix to prepare the active quality packaging CFS-BNC films. The challenge tests confirmed that CFS-BNC films significantly inhibited the fungi growth and thus prolonged the shelf life of bread, beef, cheese and soy sauce. L. paracasei ZX1231, its CFS, and the CFS-BNC film may have extensive applications in food preservation and food packaging.