Effects of Heat Moisture Treatments on the Digestibility and Physicochemical Properties of Various Rice Flours

Heat moisture treatment (HMT) is a processing method used to improve the physicochemical properties of starch. Here, to inform technology with respect to increasing resistant starch (RS) in rice, three rice flours with different starch structures—namely, Koshihikari, Koshinokaori, and Goami2 (GA2)—were treated at 120 °C and 14%–26% humidity and compared with cornstarch. HMT increased the RS content of all specimens, with GA2 showing a marked RS increase up to 11.0%. HMT also increased the gelatinization temperature (Tgel) of all samples, as shown by differential scanning calorimetry, and RS content tended to increase with increasing Tgel values. As shown by the increase in relative crystallinity by X-ray diffraction and change in the iodine absorption spectrum, HMT easily changed the starch structure in GA2, leading to increased RS. These results support GA2 as a suitable rice cultivar for bio-functional rice products such as low glycemic index foods.