Effect of Lactobacillus plantarum NCU116 Fermentation on Asparagus officinalis Polysaccharide: Characterization, Antioxidative, and Immunoregulatory Activities

Lactic acid fermentation represents a novel method to produce bioactive functional ingredients, including polysaccharides. In this work, a selected lactic acid bacteria strain NCU116 was used to ferment Asparagus officinalis (asparagus) pulps. Two polysaccharides were subsequently separated from both unprocessed and fermented asparagus pulps, namely, asparagus polysaccharide (AOP) and fermented-AOP (F-AOP). The physicochemical and bioactive properties of AOP and F-AOP were characterized and investigated. High-performance anion-exchange chromatography showed that fermentation increased the proportions of rhamnose, galacturonic acid, and glucuronic acid in polysaccharides by 46.70, 114.09, and 12.75‰, respectively. High-performance size-exclusion chromatography revealed that fermentation decreased the average molecular weight from 181.3 kDa (AOP) to 152.8 kDa (F-AOP). Moreover, the fermentation reduced the particle size and changed the rheology property. In vitro, F-AOP displayed superior free radical scavenging properties compared to AOP, using 2,2-diphenyl-1-picryhydrazyl, hydroxyl, and superoxide anion radical scavenging assays. In vivo, F-AOP administration dose-dependently promoted a gradual shift from Th17-dominant acute inflammatory response (IL-17 and RORγt) to Th1-dominant defensive immune response (IFN-γ and T-bet). These results indicated that the Lactobacillus plantarum NCU116 fermentation was practical and useful to obtain promising bioactive polysaccharides.