Characterization of novel exopolysaccharide from Lacticaseibacillus rhamnosus YT: Structural features, biosynthetic gene expression, physical properties and bioactivities

In this work, a novel slime exopolysaccharide produced by Lacticaseibacillus rhamnosus YT was investigated. The yield of crude EPS was approximately 144 ± 4 mg/L after 15 h of incubation in chemically defined medium. After cellulose DEAE-52 and gel permeation chromatography, two purified fractions named EPS-1-1 and EPS-2-1 were obtained, and their structures were characterized by Fourier transform infrared (FTIR) spectroscopy, high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy. The results indicated that EPS-1-1 was primarily composed of arabinose, fructose and glucose in a molar ratio of 5.2:1.0:17.7. Whereas, EPS-2-1 mainly consisted of xylose, fructose and glucose in a molar ratio of 3.2:1.0:5.4. Additionally, gene clusters involved in EPS biosynthesis was identified which was helpful to understand its production level and composition. Afterwards, EPS-2-1 was found thermal stable with a degradation temperature of 263.75 °C and displayed coarse surface and lamellar structure. Moreover, Congo red test implied that EPS-2-1 possessed prominent biological activity. Finally, EPS-2-1 was demonstrated to have the concentration-dependent antioxidant activity, cholesterol adsorption capacity and α-amylase inhibitory activity. These findings suggested that EPS from L . rhamnosus could be used as a potential natural source in food industry with functional properties. • L. rhamnosus YT was isolated from the feces of healthy and long-lived elderly Chinese people. • A novel slime exopolysaccharide (EPS-YT) produced by L. rhamnosus YT was obtained. • The production, structures and eps -clusters of the EPS-YT were closely associated. • EPS-YT displayed attractive physical properties and bioactivities. • EPS-YT may be potential natural source in food industry as healthy additive.