Application of an in vitro digestion model to study the metabolic profile changes of an herbal extract combination by UHPLC–HRMS

STW 5 is a fixed herbal combination containing extracts from nine medicinal plants: bitter candytuft, greater celandine, garden angelica roots, lemon balm leaves, peppermint leaves, caraway fruits, licorice roots, chamomile flowers, and milk thistle fruit. STW 5 is a clinically proven treatment for functional dyspepsia and irritable bowel syndrome. Using a static in vitro method, we simulated oral, gastric, and small intestinal digestion and analyzed the metabolic profile changes by UHPLC–HRMS to determine the impact of oro-gastro-intestinal digestion on STW 5 constituents. STW 5 was incubated according to the InfoGest consensus method. Samples of each digestive phase were analyzed by UHPLC–HRMS in ESI positive and negative modes. After data processing, background subtraction, and normalization, the peak areas of detectable compounds were compared to untreated reference samples and recovery ratios were calculated to monitor the metabolic profile of STW 5 during simulated digestion. Although the levels of some constituents were reduced, we did not observe complete degradation of any of the constituents of STW 5 upon in vitro digestion. We did not detect any new metabolites beyond increased levels of caffeic acid and liquiritigenin due to degradation of progenitor compounds. Changes observed in intestinal bioaccessibility ratios were mainly a result of isomerization, hydrolysis, protein binding, and low water solubility. The majority of STW 5 constituents are stable towards simulated in vitro digestion and can reach the colon to interact with gut microbiota if they remain unabsorbed in the upper intestinal tract.