Inhibitory effect of bioactive compounds from quinoa of different colors on the in vitro digestibility of starch

This study aimed to compare the bioactive compounds presented in quinoa of various colors, and investigated their inhibitory effect on α-glucosidase activity and the in vitro digestibility of starch. The primary bioactive compounds identified in quinoa included betaine and polyphenols (kaempferol, quercetin, rutin, etc.), with their contents increased as the color of quinoa darkened. The half maximal inhibitory concentration (IC₅₀) values of quercetin, kaempferol, and rutin in inhibiting α-glucosidase activity were 0.29, 0.34, and 1.21 mg/mL, respectively, compared to the extracts from white quinoa (1.25 mg/mL), red quinoa (0.59 mg/mL), and black quinoa (0.41 mg/mL). All extracts exhibited a dose-dependent inhibitory effect on α-glucosidase, characterized by a reversible mixed noncompetitive and anti-competitive inhibition mode. The hydrolysis rate of starch in white, red, and black quinoa flours was 33.6 %, 31.7 %, 30.2 %, respectively, and these rates increased upon the removal of bioactive compounds. After in vitro digestion, the release rates of free betaine and polyphenol from quinoa flours reached 36.9 % ~ 39.9 % and 26.5 % ~ 37.4 %, respectively. This research contributes to the advancement of whole-grain and functional foods incorporating quinoa.