Influence of Guar Gum on the In Vitro Starch Digestibility—Rheological and Microstructural Characteristics

The present study investigates the effect of guar gum on the digestibility of a waxy maize starch in vitro under simulated gastric and intestinal conditions. A detailed rheology and confocal scanning laser microscopy of the digesta were performed in order to study the possible mechanisms of interactions involved during in vitro hydrolysis of starch. No starch hydrolysis was observed under simulated gastric conditions, whereas more than 90% hydrolysis was observed at the end of digestion under simulated intestinal conditions. In the presence of guar gum, the starch hydrolysis was reduced by nearly 25% during the first 10 min and by 15% at the end of in vitro intestinal digestion. The rheological behavior of the digesta was significantly affected in the presence of the gum. The viscosity of digesta decreased during intestinal digestion; however, the extent of decrease was quite low in the presence of guar gum. The consistency index increased and flow behavior index of digesta decreased in the presence of gum after 1 min of intestinal digestion. All the samples (digested or undigested) displayed a pseudoplastic behavior as their apparent viscosity (η a) decreased with an increase in shear rate. A negative correlation between the starch hydrolysis (%) and storage modulus for the starch sample without gum and a positive correlation for the starch sample with gum were found. Large granule remnants observed through confocal micrographs have shown that the solubilization of starch granule remnants during in vitro digestion is significantly reduced in the presence of gum.