Effects of the Lactobacillus fermentation on Dendrobium officinale polysaccharide: Structural, physicochemical properties and in vitro bioactivities

Structural modification of polysaccharides using microbial fermentation is of great interest due to its specificity and environmental friendliness. The aim of this research was to compare structure, physicochemical properties and in vitro bioactivities of the Dendrobium officinale polysaccharides before and after fermentation using Lactobacillus paracasei and Lactobacillus acidophilus. The main fractions of crude polysaccharides from unfermented Dendrobium officinale (DOP-1A) and fermented Dendrobium officinale (FDOP-1A) were obtained by column chromatography purification. Compare to DOP-1A, the molecular weight of FDOP-1A was significantly reduced (from 412.566 to 25.161 kDa), smaller particle size (from 21.05 to 19.35 μm) and lower apparent viscosity. Although the microscopic surface morphologies of DOP-1A and FDOP-1A were significantly different, neither formed a triple-helix structure. Additionally, FDOP-1A contained more t-Manp and less 4-Manp, and interestingly the (1 → 4)-β-D-Glcp glycosidic bond site between the repeat units →4)-2-O-acetyl-β-D-Manp-(1 → 4)-β-D-Glcp-(1→ and →4)-β-D-Manp-(1 → 4)-β-D-Glcp-(1→ was cleaved. Moreover, FDOP-1A exhibited excellent scavenging capacity for ABTS+, DPPH, hydroxyl radicals and inhibited Nitric Oxide production by RAW 264.7 macrophages, thereby demonstrating effective antioxidant and anti-inflammatory effects. In conclusion, Lactobacillus fermentation could improve physicochemical properties and enhance biological activities of Dendrobium officinale polysaccharide, which has potential prospects for development and application in dietary supplements.