Effect of Lactiplantibacillus plantarum fermentation on the physicochemical, antioxidant activity and immunomodulatory ability of polysaccharides from Lvjian okra

Okra polysaccharides exhibits a range of biological activities. To date, its processing using microbial fermentation has not been explored. This study investigated the fermentation of okra juice with various lactic acid bacteria , followed by the extraction and characterization of crude polysaccharides (termed OPS-F), in contrast to their non-fermented counterpart (OPS). Changes in physicochemical properties, antioxidant activity and immunomodulatory ability were noted. The results demonstrated that OPS-F had a 7.42–12.53 % increase in total polysaccharides content compared to OPS. However, high-performance size-exclusion chromatography indicated a reduction in the molecular weight of OPS-F (7.9–9.5 × 10 5  Da) relative to OPS (1.66 × 10 6  Da). Compared to OPS, OPS-F had reduced levels of mannose , glucose, glucuronic acid and arabinose , but increased rhamnose , galacturonic acid and galactose , exhibiting enhanced solubility and lower apparent viscosity. Fourier transform infrared spectroscopy and nuclear magnetic resonance analysis showed minimal changes in polysaccharide structure post-fermentation. Moreover, despite a decrease in antioxidant activity post-fermentation, OPS-F exhibited superior immunomodulatory potential. In conclusion, fermenting okra juice with lactic acid bacteria alters the physicochemical properties of crude polysaccharides and enhances their immunomodulatory activity, offering a promising approach for developing new functional food resources.