Physicochemical and digestion properties of amylosucrase-treated starch mixed with galactomannan

Abstract

Starch can have lowered digestibility when galactomannan (guar gum or locust bean gum) is added. The objective of this study is to elucidate the digestive patterns and physicochemical characteristics of amylosucrase-treated starch mixing with galactomannan. In this study, the digestibility of starch decreased to a greater extent with added galactomannan after amylosucrase treatment. It could be attributed to the increased contact between starch and galactomannan due to elongated branch chains of amylopectin after amylosucrase treatment. Guar gum was more effective on lowering digestibility of starches, because guar gum can interact more easily with starch compared to locust bean gum, which could be connected to the results of glucose release and rheology test. In the steady shear rheological analysis, guar gum exhibited more shear thinning behavior. Presumably, guar gum was in more extended form because of more galactose branches which can prevent the formation of intramolecular hydrogen bonding, compared with locust bean gum. Fewer galactose branches of locust bean gum led to the formation of a coil and the consequent decrease in interaction with starch. Dynamic shear rheological analysis revealed that AS-treated starches could form more stable gels than AS control starches. The stability of AS-treated starch was higher with guar gum than with locust bean gum. According to the glucose release measurement, guar gum had a greater ability to suppress glucose release and to adsorb more glucose than locust bean gum. Besides, the results of differential scanning calorimetry showed that the onset temperature of starch gelatinization was higher, and its endothermic enthalpy was reduced after mixing starch with galactomannan. It indicates that galactomannan reduced free water required for starch gelatinization. In short, this study presented an appropriate methodology for lowering starch digestibility by mixing starch and galactomannan.