Evaluation of the antifungal activity of cell-free supernatant of Lactobacillus species against the fig (Ficus carica. L) postharvest fungal pathogens through in-vitro and in-silico analysis

Fig fruits are highly susceptible to postharvest decay, which is often, caused by postharvest pathogens. To reduce the postharvest decay in fig fruits, the use of a specific antifungal agent is necessary. Hence, the in-vitro method was employed to investigate the antifungal activity of postbiotic or cell-free supernatant (CFS) acquired from Lactobacillus plantarum and Lactobacillus delbrueckii subsp lactis. It was observed that an 8 % and 10 % CFS of L. plantarum and L. delbrueckii, respectively, displayed a 100 % growth inhibition of L. theobromae, whereas a 10% of L. plantarum and L. delbrueckii CFS, completely, suppressed the growth of A. niger. The antifungal activity of CFS resulted from volatile compounds (VOCs) and organic acids, synthesised by the Lactobacillus bacteria. The existence of VOCs and organic acids, such as lactic, formic, citric, malic, and acetic acids in CFS of L. plantarum, and L. delbrueckii, was determined using GCMS and HPLC techniques. Besides, the VOCs and organic acids were docked with chitin synthase to predict the major compounds, which are responsible for the antifungal action. In-silico studies revealed that citric acid, malic acid, 1,2 Benzenedicarboxylic acid, 3-Benzylhexahydropyrrolo[1,2-a]pyrazine-1,4‑dione, and 3-Isobutylhexahydeopyrrolo[1,2-a]pyrazine-1,4‑dione, manifested better antifungal efficacy. This demonstrates the fact that the CFS of L. plantarum and L. delbrueckii effectively inhibits the fig postharvest pathogens. Therefore, the CFS of Lactobacillus could be a promising agent to protect the fig fruits from post-harvest pathogens.