Effects of In Vitro Static Digestion and Fermentation on Phenolic Profiles and Antioxidant Activity of Pitaya (Selenicereus undatus) Flower Tea.

Pitaya flower tea is a traditional hot-water infusion rich in polyphenols, but the digestive transformation, antioxidant activity, and intestinal transport potential of its water-extractable phenolics remain unclear. In this study, pitaya flower tea infusion was prepared by hot-water brewing to simulate ordinary consumption and then subjected to in vitro static oral, gastric, small-intestinal digestion, and simplified colonic enzymatic fermentation. Changes in total phenolic content, antioxidant activity, phenolic composition, and Caco-2 transport potential were evaluated using colorimetric assays, oxygen radical absorbance capacity assay, high-performance liquid chromatography, and widely targeted ultra-performance liquid chromatography-tandem mass spectrometry metabolomics. Total phenolic content increased from 8.55 ± 0.31 to 18.20 ± 0.20 mg gallic acid equivalents/g dry weight during digestion, accompanied by the highest antioxidant activity in the small-intestinal digesta. High-performance liquid chromatography analysis showed stage-dependent remodeling of flavonol glycosides and aglycones, with a marked increase in isorhamnetin-3-O-glucoside and aglycone forms after the colonic phase, suggesting enzymatic release and transformation of matrix-associated phenolics. Metabolomics detected 296 phenolic metabolites and revealed clear compositional differences among small-intestinal digesta, colonic digesta, and their transported fractions. Relative Caco-2 transport efficiency was strongly structure-dependent: phenolic acids showed the highest transport efficiency, flavonol glycosides were moderately transported, and anthocyanins showed poor transport. These findings indicate that digestion and simplified colonic transformation enhance bioaccessibility and selectively affect the potential intestinal transport of pitaya flower tea polyphenols. However, the results should be interpreted as in vitro bioaccessibility and Caco-2 transport potential rather than true in vivo bioavailability.