Stability of polyphenols in chokeberry (Aronia melanocarpa) subjected to in vitro gastric and pancreatic digestion

Berries and red fruits are dietary sources of polyphenols with reported health benefits. As part of the diet, polyphenols are ingested as complex mixtures immersed in a food matrix which is digested in the gut. Epithelial cells lining the gut are regularly exposed to these digested mixtures. To understand the effects of dietary polyphenols on human gut health it is essential to determine their stability and fate in the lumen. In this work, we investigated the effects of an in vitro gastric and pancreatic digestion on the stability and composition of the major polyphenols in chokeberry juice. Digestion was carried out with a mixture of pepsin-HCl for 2 h, followed by a 2 h incubation with pancreatin and bile salts at 37 °C with shaking, in the absence of light and under N₂. After digestion, the chokeberry samples were acidified, filtered and HPLC-DAD/HPLC–MS–MS analysed to determine the content of total soluble recovered phenolics. Gastric digestion had no substantial effect on any of the major phenolic compounds in chokeberry, namely anthocyanins, flavan-3-ols, flavonols and caffeic acid derivatives. However, these compounds were significantly altered during the pancreatic digestion and this effect was more marked for anthocyanins (approximately 43% was lost during the 2 h treatment with pancreatin). Flavonols and flavan-3-ols decreased by 26% and 19%, respectively. Neochlorogenic acid decreased by 28% whereas chlorogenic acid was increased by 24%. In vitro digestion of standard phenolic compounds, representing each of the groups of phenolics in chokeberry, confirmed some of the observed changes. Interactions with the digestive enzymes were not responsible for the observed losses which were mostly due to the chemical conditions during pancreatic digestion. Our results, in accordance with previously published results, show that dietary polyphenols are highly sensitive to the mild alkaline conditions in the small intestine and that a good proportion of these compounds can be transformed into other unknown and/or undetected structural forms with different chemical properties and, consequently, different bioaccessibility, bioavailability and biological activity.