Effect of Dry Heat Treatment With Xanthan Gum on Physicochemical Properties of Different Amylose Rice Starches

Abstract

High amylose (HA), medium amylose (MA), low amylose (LA) (amylose content = 37.85, 27.55, and 9.98%, respectively) rice starches are modified by dry heat treatment (130 °C) with xanthan gum (X). The physicochemical properties of dry heated xanthan‐rice starch samples (modified sample: HAX‐130, MAX‐130, and LAX‐130) are investigated and compared with native rice starches (HA, MA, and LA) and two controls including dry heated rice starch samples (control I: HA‐130, MA‐130, and LA‐130); xanthan‐rice starch mixed samples (control II: HAX, MAX, and LAX). Granule swelling of dry heated xanthan‐rice starch samples is restricted, and upon complete gelatinization, their granules’ edge still maintained visible when observed by means of hot‐stage microscopy. Furthermore, morphological analysis of modified samples exhibited that xanthan gum, visualized by methylene blue staining, is anchored to swollen granules and not dispersed upon cooking, which suggested that some interactions between xanthan gum and starch molecules induced by dry heat treatment. A relatively lower breakdown viscosity and higher final viscosity are obtained for dry heated xanthan‐rice starch samples, which implied that granule rigidity of native rice starches is improved by dry heat treatment with xanthan gum. Rheological analysis also demonstrated that storage modulus of modified samples, in particular low amylose rice starch (G′ = 70.7 and 528.3 Pa, at 95 °C for LA and LAX‐130, respectively), are significantly improved. This also could be another evidence for proving the modification of native rice starches happened upon dry heat treatment with xanthan gum.