Effects of in Vitro Fermentation of Citrus medica var. sarcodactylis Polysaccharides on Hypoglycemic Activity, Gut Microbiota and Structural Alterations

This study focused on the purified polysaccharide (FCP-2-1) which isolated from Citrus medica var. sarcodactylis (Buddha's hand) to investigate its in vitro simulated digestion characteristics, as well as the effects of in vitro fermentation on its hypoglycemic activity, modulation of gut microbiota, and production of short-chain fatty acids (SCFAs). The structure of its fermentation degradation products was also analyzed. The results indicated that the molecular weight of FCP-2-1 did not exhibit significant changes after in vitro simulated digestion. Degradation products of FCP-2-1 fermented for 8 hours by gut microbiota (DFPG-8) displayed strong inhibitory effects on α-amylase and α-glucosidase activities, with inhibition rates of 51.73% and 55.67%, representing increases of 11.37% and 17.57% respectively compared to the pre-fermentation stage. Additionally, following 8 hours of in vitro fermentation, FCP-2-1 was able to reduce the Firmicutes/Bacteroidetes (F/B) ratio, while increasing the relative abundance of beneficial bacteria such as Eubacterium eligens_group, Faecalibacterium and Bifidobacterium. Furthermore, there was a significant increase in the concentrations of acetic acid, propionic acid, and butyric acid. Structural analysis revealed that, compared to the unfermented FCP-2-1 (DFPG-0), DFPG-8 exhibited a reduced average molecular diameter and its surface morphology became rougher, likely due to microbial degradation. The molecular weight was reduced from 1.503×10⁴ Da to 1891 Da. The composition monosaccharides were altered from arabinose, galactose, and galacturonic acid (0.342:0.280:0.276) to arabinose, galactose, galacturonic acid, and rhamnose (0.117:0.208:0.326:0.123). FT-IR spectroscopy revealed both α- and β- configurations in the polysaccharide, and a notable attenuation of the absorption peak at 1735 cm⁻¹. These findings suggest that FCP-2-1 is resistant to digestion in the gastrointestinal tract, but is fermented by gut microbiota, resulting in structural modifications and enhanced hypoglycemic potential.