Complexation of high amylose rice starch and hydrocolloid through dry heat treatment: Physical property and in vitro starch digestibility

High amylose rice starch was modified by dry heat treatment for different heating times (0, 1, 2, and 4 h) after mixing with various hydrocolloid type (carboxymethyl cellulose (CMC), guar gum, and xanthan gum) to improve its processability and nutritional properties. The hydration/pasting properties, gel texture, and in vitro starch digestibility of dry heat treated hydrocolloid-starches were investigated and analyzed by principle component analysis (PCA). Dry heat treatment increased the pasting properties of rice starch, although a longer heating time led to lower pasting and hydration properties as well as gel strength. Highest peak viscosity and gel strength were observed for dry heat treated xanthan-starch, followed by CMC- and guar-starch. In the results of in vitro starch digestibility, dry heat treatment significantly decreased the rapidly digestible starch contents and predicted glycemic index (pGI) compared to native starch, while dry heat treated xanthan starch most effectively retarded starch digestibility. PCA indicated that hydrocolloid type affected the hydration properties, and that heating time was correlated with pasting properties and pGI. These results demonstrated that high amylose rice starch dry heat treated with xanthan for 2 h could be effective in changing the hydration, pasting and gel characteristics as well as in vitro starch digestibility.