In vitro gastrointestinal digestion and colonic fermentation evaluation of dialdehyde starch--epicatechin gallate conjugate

Epicatechin gallate (ECG) has various bioactivities (e.g., antioxidant, antibacterial and anti-inflammatory activities). However, the poor structural stability of ECG makes it unable to stably pass through the human digestive system and reach the colon, which greatly limits its biological activity in vivo. In this study, ECG was conjugated onto dialdehyde starch by an acid-mediated coupling method to synthesize a dialdehyde starch--ECG conjugate (DAS-ECG) with improved digestion stability. Then, the digestive and fermentative properties of DAS-ECG were further elevated through simulated saliva-gastro-intestinal digestion and in vitro colonic fermentation systems. The results suggested that simulated saliva-gastro-intestinal digestion had little effect on the molecular weight distribution of DAS-ECG. The total phenol content of DAS-ECG was only decreased by 7.78%. In addition, the structure of DAS-ECG was not remarkably altered. Meanwhile, DAS-ECG maintained strong antioxidant activity during saliva-gastro-intestinal digestion. During in vitro colonic fermentation, DAS-ECG was gradually degraded and utilized by gut microbiota, showing a remarkably decreased molecular weight and changed structure. In addition, the total phenol content and antioxidant activity of DAS-ECG were obviously reduced. Meanwhile, DAS-ECG had a certain regulatory effect on gut microbiota, especially increasing the relative abundance of beneficial bacteria (e.g., Bifidobacterium, Faecalibacterium, Prevotella, Blautia, Agaricus, Butyricimonas, Barnesiella and Enterococcus) and decreasing the relative abundance of harmful bacteria (e.g., Lachnoclostridium, Megamonas and Streptococcus). Furthermore, DAS-ECG could significantly improve the levels of short-chain fatty acids. Our results were of great significance to reveal the in vivo digestion process of DAS-ECG and to broaden the applications of DAS-ECG in functional foods.