Changes of heat-treated soymilks in bioactive compounds and their antioxidant activities under in vitro gastrointestinal digestion

Abstract

To investigate the influence of in vitro gastrointestinal digestion on contents of bioactive compounds and antioxidant activities of heat-treated soymilks, changes of total phenolics content (TPC), total flavonoids content (TFC), content and profile of isoflavones, oxygen radical absorbance capacity (ORAC), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and ferric-reducing antioxidant power (FRAP) were assayed after different heat treatments (at 95 °C for 20, 40, 60 min; 121 °C for 3, 6, 9 min and 143 °C for 20, 40, 60 s respectively) and gastrointestinal digestion. Results showed that digestion significantly influenced the contents of bioactive compounds and antioxidant activities of soymilks. Increases of DPPH radical scavenging activity, FRAP and ORAC of the heat-treated soymilks after gastric digestion were consistent with the increases of TPC (110.68–152.60 %) and TFC (4.48–31.10 %). In the dialysate fractions as the absorbable and utilized part, it was found that TPC, TFC, isoflavones and antioxidant activities (DPPH radical scavenging activity, FRAP and ORAC) were significantly decreased as compared with the gastric digestion fractions and duodenal fractions. Analysis showed that the bioaccessibility of TPC reached 107.17–125.14 %, TFC reached 34.63–67.19 % and total isoflavones reached 34.40–41.22 %, respectively, indicating the rich bioaccessible compounds in soymilk. Daidzein and its derivates were proven as the most bioaccessible isoflavones (about 36.99–44.14 %). Glucoside isoflavones showed the highest bioaccessibilities followed by malonylglucosides, acetylglucosides and aglycones. Overall, the soymilks treated at 95 °C and 60 min and 121 °C and 9 min had higher bioactive compounds contents, antioxidant activities and bioaccessibilities in the dialysate fractions.