Purple-fleshed sweet potato acylated anthocyanins: Equilibrium network and photophysical properties

•PFSP anthocyanins have a high colour stability over a broad pH range.•Fluorescence intensity of PFSP is more pronounced at higher pH values.•PFSP anthocyanin quinoidal bases may be responsible for the fluorescence properties.•Native PFSP anthocyanins may be visualized in gastrointestinal cells for biological studies. Two anthocyanins from purple-fleshed sweet potato were isolated and characterized by LC–MS and NMR analysis. They were identified as peonidin-3-(6′-hydroxybenzoyl)-sophoroside-5-glucoside and peonidin-3-(6′-hydroxybenzoyl-6″-caffeoyl)-sophoroside-5-glucoside. The acid–base dynamics of these acylated anthocyanins was evaluated by means of pH jump techniques. Equilibrium and kinetic constants were determined and, in general, these anthocyanins demonstrated a higher capacity in retaining the red and blue colors at acidic and basic pH values, suggesting a higher resistance to pH variations compared to the parent anthocyanin, peonidin-3-O-glucoside. The presence of acyl groups and additional glucoside moieties seems to determine this particular characteristic. The fluorescence properties of these anthocyanins were evaluated. Overall, the species present at higher pH values (7–9) showed higher fluorescence intensity for both anthocyanins, with an optimum λex/λem pair at λex 610 nm/λem 640 nm. The fluorescence characteristics of these anthocyanins were used to evaluate their location in gastric and intestinal cells by fluorescence microscopy.