Inhibitory Mechanism of Lactic Acid Bacteria Cell-Free Supernatant Against Stored Grain Molds

Grain is highly vulnerable to contamination by fungi during storage, leading to reduced product quality and substantial economic losses. Lactic acid bacteria (LAB) have the potential to be used as antifungal agents; however, strains aimed at inhibiting stored grain molds remain limited, and the inhibitory mechanisms require further investigation. To solve this problem, 71 LAB strains were isolated from various samples. Among these, 17 strains exhibiting inhibitory activity against A. flavus, A. niger and P. citrinum were selected using a dual-layer plate assay. Based on morphological characterization and 16S rRNA gene sequence analysis, these strains were classified as Weissella cibaria, Pediococcus pentosaceus, and Lactiplantibacillus paraplantarum. Further investigations involving pH adjustment, catalase, and proteinase K treatments confirmed that organic acids were the primary antifungal substances in LAB cell-free supernatant (CFS). HPLC quantification identified acetic acid, malic acid, lactic acid, phenyllactic acid and citric acid contained in the CFS. Antifungal assays verified that acetic acid and lactic acid exhibited the strongest inhibitory effects against P. citrinum and A. flavus, whereas phenyllactic acid and acetic acid demonstrated the most potent suppression against A. niger. These findings established a theoretical basis for the application of LAB CFS in grain storage.