The interactions between wheat starch and Mesona chinensis polysaccharide: A study using solid-state NMR.

The interaction between wheat starch and Mesona chinensis polysaccharide (MCP) was found to change the molecular mobility of the water and carbohydrate populations in starch-MCP gels, when measured using proton and carbon nuclear magnetic resonance relaxation methods. The starch and MCP mobilities appeared similar at a micron scale. However, at a distance of less than 5 nm could they be detected as having separate mobility states, indicating close interaction between the starch and MCP. The carbon-6 of the starch glucan monomer was observed to have the largest mobility change in the presence of MCP. Two mobility populations of carbon-6 were observed, possibly corresponding to the carbon-6 in the linear chains of both amylose and amylopectin, and another to the carbon-6 involved in the branching of amylopectin. The change in the mobility of one of the carbon-6 populations indicates an increase in molecular freedom of movement in the presence of MCP.

The effect of gel structure on the in vitro digestibility of wheat starch-Mesona chinensis polysaccharide gels.

The digestibility of wheat starch gels in the presence of Mesona chinensis polysaccharide (MCP) was studied. MCP was found to be the most effective polysaccharide in reducing wheat starch digestion in comparison to starch gels of similar hardness containing xanthan, guar, locust bean gum (LBG) and agar. A 33% reduction in the digestibility of intact starch gels containing 5% w/w MCP (after 120 minutes of digestion) was observed and this was attributed to the strengthening of the gels in the presence of high concentration of the polysaccharide. In contrast, despite a reduction in the firmness of the gel when 2% w/w MCP was present, there was a 7% reduction in starch digestibility and hence, firmness was deduced to be not solely responsible for the digestibility of the gels. When these gels were macerated, starch digestibility was reduced regardless of the MCP concentration. Starch digestion in the macerated samples seemed to cease after 10 minutes with about 30% more starch remaining when 5% w/w MCP was present, suggesting that the amount of starch available for digestion was reduced in the presence of MCP. The reduced availability of starch for digestion was hypothesised to be due to starch-MCP interactions, which formed amylose-MCP complexes that are likely to be resistant to enzymatic digestion. Overall, this work shows the potential for MCP to be utilized as an ingredient to reduce the glycaemic index.