Resistant Starch Contents and the in Vitro Starch Digestibility of Thai Starchy Foods

Abstract

Samples from 29 starchy foods and 11 cultivars of banana were analyzed for their contents of resistant starch (RS), digestible starch and total starch, as well as the in vitro starch digestibility. The RS analysis was based on á-amylase and amyloglucosidase hydrolysis followed by colorimetric assay of the glucose released. The results showed that the main RS sources were found in the legume group (10.3 ± 1.2% to 22.9 ± 0.0%), glass noodle products (9.1 ± 0.8% to 11.3 ± 1.5%) and bananas (52.2 ± 4.1% to 61.4 ± 2.3%). For the rice group, the effect of processing methods on the retrograded RS formation was investigated. Khanomjean produced with fermentation had a higher RS content (8.5 ± 1.1%) than that of the cooked white rice of the high-amylose cultivar. With the rice snacks, the process for puffing kaotung and kaokreupvor by frying and roasting produced a higher RS content (2.6 ± 0.0% and 2.9 ± 0.3%, respectively) than in the raw samples. Among the rice noodles, vermicelli contained a higher RS content than the others. Moreover, a gelatinization effect on the RS contents was clearly evident, with the gelatinized cassava starch (2.2 ± 0.0%) having a lower RS content than the commercial starch (44.6 ± 0.3%), whereas the commercial RS content was high (58.5%). Finally, the test on in vitro starch digestibility showed that the legume samples, particularly with red beans, had the lowest rate of starch digestibility compared to the other samples.