Effect of non-starch polysaccharides on the in vitro digestibility and rheological properties of rice starch gel

► Prepared rice starch gels mixed with konjac glucomannan, xanthan gum, and agar. ► Effects of NSP on the starch digestibility and rheological properties were investigated. ► Clarified that added NSP suppressed starch hydrolysis in the starch gel. ► The impact of NSP on the rheological properties of starch gels depended on the type of NSP. ► The suppressive effect of NSP on starch digestibility was not only due to the gel rigidity. The starch digestibility and rheological properties of gels were evaluated in the presence of three non-starch polysaccharides (agar, xanthan gum and konjac glucomannan) with rice starch. Each polysaccharide was added to 30% (w/w) rice starch suspension at defined concentrations and starch gels were prepared. The extent of starch gel digestibility was determined by an in vitro method and rheological properties by a dynamic oscillatory test and a compression test. The added polysaccharides suppressed starch hydrolysis in the gels compared with the control, and a concentration dependency of this suppressive effect was observed. Adding agar and xanthan gum increased the storage shear modulus (G′) of starch gels, while adding konjac glucomannan decreased G′ values. The results indicate that the suppressive effect of non-starch polysaccharides on starch digestibility appears to be not only due to the rigidity of the gel, but also the interaction between starch and non-starch polysaccharides.