Influence of guar gum on the in vitro digestibility of tapioca starch

In this study, the influence of guar gum (GG) content on tapioca starch (TS) digestibility and the mechanism underlying this effect were examined. A difference in starch digestibility was observed between GG and TS mixed at ratios of 1: 90 or 1: 80 and those mixed at ratios of 1: 701: 20. The final starch hydrolysis rate at mixing ratios of 1: 90 and 1: 80 improved by 4.79% and 4.10%, respectively. However, starch hydrolysis was negatively correlated with the mixing ratio when the mixing ratio was increased further. Mixing at 1: 20 resulted in the lowest amount of rapidly digestible starch. Nuclear magnetic resonance and Fourier transform infrared spectrometry indicated that water mobility and hydrogen-bonding interaction strength are important factors for digestibility. Scanning electron microscopy revealed that, at a GG: TS ratio of 1: 80, the mixtures had a porous and loose-fracture morphology, whereas the microstructure was denser at 1: 40 and 1: 20. Fluorescence microscopy revealed that the presence of GG around starch served as a protective barrier and retarded hydrolysis at GG: TS ratios of 1: 40 and 1: 20. These results confirm that the hydrogen-bonding interaction strength is responsible for differences in starch digestibility among the different combinations of GG and TS.