Combined-acid hydrolysis and heat-moisture treatment of rice flour: physicochemical properties and resistant starch

This work investigated the effect of partial acid hydrolysis and heat-moisture treatment on the physicochemical properties and resistant starch content of rice flour. The acid-hydrolyzed (AH) rice flour of HCl (0.5 N or 1.0 N) with a hydrolysis time of 16 h provided high amylose contents of 25.62 and 30.53%, respectively; hence these AH conditions were selected for the further heat-moisture treatment (HMT). The combined acid-hydrolyzed and heat-moisture (AH-HM) treatments had different chemical, pasting, and thermal properties compared to the native and control (solely HMT) samples. The amylose content of all the AH-HM samples increased. The pasting characteristics of AH-HM flour clearly decreased compared to the native flour. Gelatinization temperature of AH-HM flour increased and the temperature range was broader. On the other hand, the enthalpy of gelatinization substantially decreased compared to the native flour. The AH-HM treatment synergistically enhanced the prefect crystalline structure of the rice starch granules, resulting in increase of resistant starch content by 6 times that of native flour. AH-HM rice flour may be an attractive alternative ingredient in various health food products.