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.

Automated summary

This study examined the effects of partial acid hydrolysis and heat-moisture treatment on the physicochemical properties and resistant starch content of rice flour. Acid-hydrolyzed rice flour with high amylose content was selected for further heat-moisture treatment. The combined treatment had different properties compared to native and control samples, including increased amylose content, decreased pasting characteristics, increased gelatinization temperature, broader temperature range, decreased enthalpy of gelatinization, and significantly increased resistant starch content. AH-HM rice flour could be a promising ingredient in various health food products.