Optimization of Antifungal Activity and Determination of Antifungal Mechanism in Lacto-Fermented Palm Kernel Cake Against Colletotrichum gloeosporioides

Anthracnose disease caused by Colletotrichum gloeosporioides reduces the postharvest quality of fruits and vegetables which creates large economic losses. Natural preservation methods of fruits have been popular due to the preference of modern consumers to consume chemical-free fruits. Therefore, there is a requirement for industrial-level natural preservation techniques for fruits and vegetables. The current study aimed to optimize the antifungal activity of previously produced fungal growth inhibitor (PKCL1) by Lactobacillus plantarum cultivated in palm kernel cake (PKC) against Colletotrichum gloeosporioides and to determine the antifungal mechanism. Box Behnken design under response surface methodology was applied to optimize the fermentation conditions. The antifungal mechanism of optimized PKCL1 was determined by the leakage of intercellular components, ergosterol synthesis, and the morphological changes of treated fungi. The substrate ratio, fermentation time, and temperature influenced the production of antifungal compounds while altering the antifungal activity. The combinations of optimum fermentation conditions comprised of substrate ratio of 24.75%, fermentation time of 96 hours, and fermentation temperature of 37°C to obtain 88.1% C. gloeosporioides inhibition. Significant differences were observed in the protein concentration, DNA, sugars, and ergosterol synthesis between the treated and non-treated fungi. Thus, PKCL1 was affected in the cell membrane structure and biosynthesis pathways of C. gloeosporioides. Besides, PKCL1 changed the cell morphology and destroyed the cell wall structure. Box Behnken design is an appropriate model to optimize the fermentation conditions to maximize the antifungal activity of PKCL1. It was concluded that optimized PKCL1 has a strong capability to destroy C. gloeosporioides.