Abstract
In this study, an integrated characterisation through polyphenol and caffeine content and antioxidant activity was combined with chemometric analysis to assess the effects of simulated in vitro gastrointestinal digestion on the bioaccessibility of these bioactive compounds from nine different tea infusions. Tea infusions were characterised based on total flavonoids, total polyphenols and antioxidant activity, together with the determination of individual polyphenol content. Fourteen phenolic compounds, including phenolic acids, stilbenes and flavonoids, were selected based on their reported bioactivity and high accessibility, attributed to their low molecular weight. Both polyphenols and caffeine were initially monitored in raw tea infusions and through the different 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 decaffeination 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 caffeic 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.
Highlights
Polyphenols are secondary metabolites of plants currently used in pharmaceutical and food industries, with a variety of extensive biological activities [1,2,3]
Tea infusions were characterised in terms of pH, Total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities (TAA and DPPH)
The current study has clearly demonstrated how tea type and processing significantly influences the pattern, gastrointestinal stability and bioaccessibility of some tea phenolic compounds and caffeine, and, on their relationship to health benefits
Summary
Polyphenols are secondary metabolites of plants currently used in pharmaceutical and food industries, with a variety of extensive biological activities [1,2,3]. Epidemiological studies on the role of polyphenols in nutrition and nutraceuticals are largely based on research on digestion and intestinal absorption, supported by the fact that the most widespread polyphenols in food and beverages are not necessarily the most bioaccessible nor the most bioactive [1]. Tea, obtained by processing of the dried leaves of Camellia sinensis plant, is one of the most popular and frequently consumed beverages worldwide, reaching 6.3 million tons [4]. Several tea styles are accessible to the consumer, further differentiated by the type and extent of processing of the leaves: non-fermented (white, yellow and green), partly fermented (oolong), fermented (black tea) and post-fermented (pu-erh) [5], together with their decaffeinated varieties. Emerging experimental and epidemiological studies have revealed that tea consumption exhibits multiple health benefits, attributed to the action of various bioactive phytochemical compounds, polyphenols and purine alkaloids such as caffeine [2, 3].
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