A combined analytical-chemometric approach for the in vitro determination of polyphenol bioaccessibility by simulated gastrointestinal digestion

In this study, an integrated characterisation through polyphenol and cafeine content and antioxidant activity was combined with chemometric analysis to assess the efects of simulated in vitro gastrointestinal digestion on the bioaccessibility of these bioactive compounds from nine diferent tea infusions. Tea infusions were characterised based on total favonoids, total polyphenols and antioxidant activity, together with the determination of individual polyphenol content. Fourteen phenolic compounds, including phenolic acids, stilbenes and favonoids, were selected based on their reported bioactivity and high accessibility, attributed to their low molecular weight. Both polyphenols and cafeine were initially monitored in raw tea infusions and through the diferent digestion stages (salivary, gastric and duodenal) by capillary high performance liquid chromatography coupled to diode array detection (cHPLC-DAD) and/or HPLC coupled to a triple quadrupole mass analyser (HPLC–MS/MS). Multivariate analysis of the studied bioactives, using principal component analysis and cluster analysis, revealed that the decafeination process seems to increase the stability and concentration of the compounds evaluated during digestion. The greatest transformations occurred mainly in the gastric and duodenal stages, where low bioactivity indices (IVBA) were shown for resveratrol and cafeic acid (IVBA=0%). In contrast, the polyphenols gallic acid, chlorogenic acid and quercetin gave rise to their availability in white, green and oolong infusion teas (IVBA>90%). Furthermore, highly fermented black and pu-erh varieties could be designated as less bioaccessible environments in the duodenum with respect to the tested compounds