FEED8-Accelerated Biotransformation of Hydroxycinnamic Acids and Anthocyanins into Hydroxyphenyl-Type Pyranoanthocyanins and Characterization of Their Stability and Antioxidant Capacity.

Hydroxyphenyl-type pyranoanthocyanins are anthocyanin-derived pigments with a vivid and stable color and biological activity, making them natural food colorants with potential applications. In this study, hydroxyphenyl-type pyranoanthocyanins, cyanidin-3-glucoside-4-vinylcatechol (C3G_VC) and cyanidin-3-glucoside-4-vinylphenol (C3G_VP), were efficiently prepared by the biotransformation of caffeic acid and p-coumaric acid with cyanidin-3-glucoside (C3G) using FEED8 (FEED8) fermentation at 37 °C in a model system (pH = 3.5). After 24 h of fermentation, C3G_VC and C3G_VP were further isolated and purified by medium-pressure liquid chromatography, and their structures were confirmed by LC/MS and NMR spectroscopy. Moreover, these stability evaluation results showed that C3G_VC and C3G_VP possessed greater pH stability and stronger resistance to bisulfite-induced bleaching than the precursor C3G. In terms of thermostability, the retention rates of C3G_VC and C3G_VP were about 20% higher than that of C3G (only 8.7%) at 90 °C. Simultaneously, further findings indicated that C3G_VC had a longer half-life than C3G_VP at the same heating temperature. Additionally, the stronger antioxidant capabilities of C3G_VC and C3G_VP in vitro were evaluated, including radical-scavenging activities and the ferric-ion-reducing power. The study illustrated that FEED8 fermentation efficiently biosynthesized hydroxyphenyl-type pyranoanthocyanins, which provided a new type of pigment ingredients for the development of functional foods.