Effect of a small amount of sodium carbonate on konjac glucomannan-induced changes in wheat starch gel

Abstract Wheat starch gels were produced with konjac glucomannan (KGM) and low concentrations of Na 2 CO 3 (0.1–0.2 wt% of starch) using a rapid viscosity analyzer (RVA). The gelling properties of wheat starch in varying ratios of KGM and Na 2 CO 3 were characterized by differential scanning calorimetry (DSC), rheometry and confocal laser scanning microscopy (CLSM). A small amount of Na 2 CO 3 resulted in gels with increased elasticity whereas structural ordering during retrogradation was insignificantly affected. Comparison of CLSM images of composite gels revealed that Na 2 CO 3 at 0.2 wt% of starch allowed the formation of fiber-like extensions around scattered swollen granules by KGM and amylose interaction, making swollen granules disperse within the micro phase, which was not typical in CLSM images of gels in the absence of Na 2 CO 3 . Dynamic storage modulus and dynamic power law exponent were substantially higher than those observed for the same concentration of KGM in the presence of Na 2 CO 3 , supporting the hypothesis that Na 2 CO 3 could promote strong interchain associations between KGM and starch components.