Abstract:The effect of amylose content on pasting and rheological properties of corn starches(waxy,normal and high-amylose corn starch)/guar gum mixtures were studied. The mechanism of interaction between amylose and guar gum was also analyzed. Rapid visco-analysis(RVA) data showed that guar gum addition increased the peak,breakdown,final,and setback viscosities of starches. This effect was more pronounced for normal corn starch than waxy corn starch. The pasting temperature of the waxy corn starch /guar gum mixtures was higher than the control,while quite an opposite result was obtained,for the normal corn starch,where the addition of guar gum lowered the pasting temperature. Flow tests showed that all pastes exhibited time-dependent shear-thinning (thixotropic) with yield stress behavior in which the hysteresis loop areas were significantly decreased by guar gum addition,whereas the other rheological parameters varied differently among the samples. The results could be attributed to interactions between the hydrocolloids molecules and amylose molecules. Dynamic shear data revealed that weak gel-like behavior in all paste samples,and dynamic modulus of each system responded to guar gum in a different way,depending on the amylose content of corn starch. The amylose content is higher,the effect of interactions between amylose and gum is more significant. This effect led to all mixed gels softer.
