Effect of simulated gastrointestinal digestion in vitro on the antioxidant activity, molecular weight and microstructure of polysaccharides from a tropical sea cucumber (Holothuria leucospilota)

The physicochemical properties of Holothuria leucospilota polysaccharides (HLP) were measured, and the changes of molecular weight (Mw), antioxidant activity and microstructure in vitro were studied. The Mw of HLP was approximately 52.80 kDa, and the monosaccharide composition was primarily fucose, rhamnose and glucuronic acid. HLP showed good antioxidant activity at high concentration (>= 2 mg/mL), and the DPPH (1,1-Diphenyl-2-picryl-hydrazil) free radical scavenging rate reached approximately 84%. It was observed that saliva did not have an effect on the Mw and antioxidant capability of HLP. Gastric and intestinal digestion significantly reduced the Mw of HLP (from 52.80 kDa to 14.67 kDa and 12.01 kDa) and maintained high antioxidant activity. In addition, the structure and surface morphology were markedly altered. After simulated gastric digestion, the HLP changed from a smooth, irregular, and angular structure to a layered honeycomb with a large volume. This result demonstrated that the decrease of Mw after gastric digestion was caused by the destruction of aggregates. Due to the decomposition of glycosidic bonds after digestion in intestine, HLP showed loose, small and blocky structures. Thus, HLP had antioxidant activity, and this activity was improved after gastric and intestinal digestion.