Synthesis in situ of heteropolysaccharide by Levilactobacillus brevis AM7 during fermentation of oat and hemp and its effect on the techno-functional properties of oat yogurt type model

Plant raw materials, such as oat bran concentrate (OBC), oat flour (OF), and hemp protein concentrate (HP), are significant sources of dietary fibers and proteins with high nutritional quality. Exopolysaccharides (EPS) synthesized by lactic acid bacteria (LAB) during fermentation are natural texturing agents that can replace hydrocolloid additives (e.g., carrageenan, guar gum, and pectin). This study aimed to evaluate EPS synthesis in OBC, OF, and HP during fermentation with Levilactobacillus brevis AM7 supplemented with glucose. Monosaccharide analysis identified that EPS from L. brevis AM7 was a heteropolysaccharide (HePS) consisting of rhamnose, mannose, glucose, and glucose-amine. Rheological analysis revealed that HePS production led to increased viscosity and viscoelastic moduli (G′ and G″) of the fermented materials compared to control. Fermented OBC exhibited the most stable structure among the three materials. Fermented OBC also showed the lowest acidity level, whereas fermented HP exhibited intensive acidification. This was likely due to the more abundant flour endogenous sugars (sucrose, raffinose, and stachyose) in HP and their fast utilization during fermentation. A yogurt alternative product was prepared from fermented OBC milk, showing a high LAB cell density, a pH of 4.2, and a significantly higher viscosity than the chemically acidified control. The in situ synthesized HePS counteracted the viscosity loss and inhibited syneresis of the yogurt alternative product during four days of storage at 4 °C. Overall, the use of L. brevis AM7 producing HePS enabled improved techno-functional properties of plant raw materials and showed potential for application in yogurt alternatives.