Structural elucidation and α-amylase/α-glucosidase inhibition properties of xyloglucan and RG-I types polysaccharides from tamarind (Tamarindus indica L.) pulp.

A neutral (TFP-WA) and an acidic polysaccharide (TFP-0.2 A) were purified from tamarind (Tamarindus indica) pulp. The fine structures of the isolated polysaccharides were elucidated by integrated sequential partial acid hydrolysis, enzymatic hydrolysis, and multiple analytical techniques. As a result, the TFP-WA is composed of repeating →4)-α-Xylp-(1 → 4)-β-Glcp-(1 → residues in the backbone, and branched at O-6 of Glcp residues with linear arabinoxylan and galactan motifs. Whereas, TFP-0.2 A possesses a rhamnogalacturonan-I (RG-I) backbone composed of repeating →2)-α-Rhap-(1 → 4)-α-GalpA-(1 → units with O-4 of Rhap substituted by galactan, arabinan, glucan, xylan structural motifs. Both TFP fractions acted as mixed-type inhibitors against α-amylase and α-glucosidase in vitro. Moreover, the acidic fraction TFP-0.2 A showed an enhanced hydrophobic interactions and microenvironmental perturbations. The oral glucose tolerance test (OGTT) demonstrated that TFP-0.2 A significantly suppressed glucose elevation at 30 min and decreased the area under the curve (AUC). The FITC-labeled polysaccharides revealed minimal systemic absorption, with both TFP polysaccharides predominantly accumulating in the large and small intestine at 24 h post-administration. These findings support their potential development as natural hypoglycemic agents targeting postprandial glycemic control through localized intestinal enzyme inhibition.