Exopolysaccharides of Pseudomonas protegens ML15: Optimization of Production, Characterization, and Potential Application as an Edible Coating for Fruits

Microbial exopolysaccharides (EPS) are increasingly recognized for their diverse applications, including their potential as edible coatings. This study aimed to optimize the production of EPS synthesized by Pseudomonas protegens ML15, characterize its properties, evaluate its biological activities, and assess its suitability as an edible coating. EPS production was optimized through response surface methodology (RSM). Key parameters, including incubation time, temperature, and pH, were systematically evaluated to identify the optimal conditions for maximizing EPS yield. This optimization led to a significant enhancement in EPS yield, with a 73.6% increase, compared to non-optimized conditions. Characterization of the EPS revealed substantial antioxidant and antifungal properties. Compositional analysis using GC–MS, NMR, and FTIR confirmed the presence of characteristic polysaccharide peaks and identified glucose, mannose, galactose, and xylose as the primary monosaccharides in the EPS. Additionally, structural analysis via SEM demonstrated the well-preserved morphological integrity of the EPS. In situ experiments indicated that tomatoes coated with EPS exhibited significant reductions in post-harvest gray mold rot caused by Botrytis cinerea, alongside improvements in quality parameters such as reduced weight loss, increased levels of ascorbic acid, citric acid, and phenolics, and enhanced antioxidant activity. Notably, the EPS coatings effectively preserved tomato quality under infection conditions, suggesting their potential as a valuable tool for protecting fruits from phytopathogenic fungi, extending shelf life, and maintaining post-harvest quality.