Stability and mechanism of phenolic compounds from raspberry extract under in vitro gastrointestinal digestion

Raspberry extract (RE) is a raspberry product with high anthocyanins and low sugar. In the present study, to evaluate the metabolic behavior of phenolic compounds of RE under in vitro digestion (gastric (GF), gastric to intestinal (G-IF), and colonic fermentation (CF)), the changes of 30 phenolic compounds were investigated by High Performance Liquid Chromatography-Mass Spectrometry. The results showed that phenolic compounds were relatively stable in GF, but rapidly decreased in G-IF and CF. Five anthocyanins accounted for 61.1% of total polyphenol contents (TPCs). Among them, anthocyanins bound to glucose or with two hydroxyl groups on B-ring were metabolized more quickly. The catabolic activity of the human microbiota resulted in the production of a series of low molecular weight phenolics, such as hydroxybenzoic acids. Ellagic acid, accounting for 17.7% of TPCs, was rapidly metabolized to umlithin B and urolithin C in CF. Moreover, urolithin C showed the highest antioxidant activity in all ellagic acid metabolites by DPPH assay. Consequently, the metabolic behavior of phenolic compounds was mainly influenced by pH and intestinal microbiota, which provided the basis for further in vivo and in vitro study and efficient utilization of the extract.

Automated summary

Raspberry extract, rich in anthocyanins and low in sugar, undergoes metabolic changes in vitro digestion, with the stability of phenolic compounds mainly influenced by pH and intestinal microbiota. During the gastric to intestinal and colonic fermentation stages, the phenolic compounds rapidly decrease in concentration.