Evaluation of the stability of tyrosol esters during in vitro gastrointestinal digestion

Lipophenols such as tea polyphenol palmitate derivatives (palmitoyl esters of tea polyphenols) have been classified as non-toxic food additives due to their better protective effects on lipidic food matrices from oxidation, but their digestion and absorption have remained unexplored. In this study, the digestive stability of tyrosol acyl esters (TYr-Es) with fatty acids of different chain lengths and different degrees of unsaturation such as C12:0, C14:0, C16:0, C18:0, C18:1, C18:2, and C22:6 was evaluated using an in vitro simulated gastrointestinal tract model containing various digestive enzymes (pancreatin, pancreatic lipase and phospholipase A2). HPLC-UV measurements demonstrated that only pancreatin and pancreatic lipase, but not phospholipase A2, could hydrolyze TYr-Es to free TYr. The degree of TYr-E hydrolysis negatively correlated with the chain length but positively correlated with the degree of unsaturation of their lipid moiety. In addition, the fact that TYr in fatty acid ester forms could be absorbed by the intestinal lumen, at least partially in the form of free TYr, may explain a sustained release behavior of TYr-Es to TYr during the time-course following the digestion process.