The effect of in vitro digestion on the chemical and antioxidant properties of Lycium barbarum polysaccharides

Although the antioxidant properties of Lycium barbarum polysaccharides (LBPs) are well known, little is known about how gastrointestinal digestion impacts their chemical and antioxidant properties. In this study, the molecular weight (Mw), total polysaccharide, protein and phenolic contents and the structural changes of LBPs were determined following digestion in vitro. During digestion, the decrease in the Mw of LBPs was observed. High Mw polysaccharides were found to be more stable compared to those with low Mw. There were 8 monosaccharides composed LBPs. The proportions of the monosaccharides increased except for the one of glucose after digestion. With the consuming of glucose, the percentages of glucuronic acid (GlcA) and galacturonic acid (GalA) significant multiplied from 1.18% to 1.94%, and 1.69%-4.25%, respectively. The total protein and phenolic contents were increased from 9.04% to 10.87% and 3.46%-3.89%, while the weight of total polysaccharides was decreased from 39.42% to 36.09%. Phenolics occur in their bound form, which conjugated to proteins or esterified to sugars. The changes of chemical features would take place in the gastric phase. The digestive product of LBPs (LBPs-IVD) exhibited a noticeably increase in antioxidant activities, as measured by oxygen radical absorbance capacity value, scavenging activity on ABTS+ free radical and reducing capacity. The increase in the bioactivity of LBPs-IVD is attributed to the high contents of phenolics and protein conjugated in LBPs and the high level of GalA and GlcA. Our results provide a new perspective for understanding the antioxidant properties of LBPs.