Effect of carbon source on the synthesis and antioxidant properties of exopolysaccharides of lactic acid bacteria

The present study analyses the impacts of varying carbon sources (glucose, maltose, lactose, sucrose, raffinose) on the development, exopolysaccharide synthesis, and antioxidant activity of silage-derived lactic acid bacteria, encompassing Limosilactobacillus fermentum AG8, Lactiplantibacillus plantarum AG1, AG9, AG10, and Lacticaseibacillus rhamnosus AG16, with Lactobacillus bulgaricus serving as a control. The lactic acid bacteria were cultivated in MRS broth and growth was measured via optical density. The exopolysaccharide yield was quantified using the phenol–sulfuric acid method, and the antioxidant activity was assessed via DPPH radical-scavenging assays. The results showed that disaccharides (maltose and sucrose) promoted optimal growth, with AG9 and AG10 exhibiting the highest biomass. exopolysaccharide production peaked in sucrose media, particularly for L. bulgaricus and L. rhamnosus AG16. The highest antioxidant activity per total exopolysaccharide was found in sucrose-derived exopolysaccharide, but recalculating the results per mg revealed superior activity in exopolysaccharide cultured in maltose and raffinose. AG16 exopolysaccharide exhibited the greatest specific radical-scavenging activity (10.58 %/mg) in the presence of maltose. These findings emphasise the importance of selecting the correct carbon source for maximising lactic acid bacteria functionality. Sucrose enhances exopolysaccharide yield, while maltose and raffinose improve antioxidant efficiency. This study highlights the potential of silage-derived lactic acid bacteria for producing bioactive exopolysaccharide for use in the food and health industries.