Interactions between Salivary Proteins and Apple Polyphenols and the Fate of Complexes during Gastric Digestion.

Beneficial polyphenols in apples can reach the stomach as complexes formed with salivary proteins. The present study aimed at documenting the interactions between salivary proteins and cider apple polyphenols and the fate of complexes during gastric digestion. A polyphenolic extract was mixed with human saliva, and interactions were characterized by analyzing proteins and polyphenols in the insoluble and soluble fractions of the mixtures, before and after in vitro gastric digestion. Results confirmed that proline-rich proteins can efficiently precipitate polyphenols and suggested that two zinc-binding proteins can also form insoluble complexes with polyphenols. The classes of polyphenols involved in such complexes depended on the polyphenol-to-protein ratio. In vitro gastric digestion led to extensive proteolysis of salivary proteins, and we formulate the hypothesis that the resulting peptides can interact with and precipitate some procyanidins. Saliva may therefore partly modulate the bioaccessibility of at least procyanidins in the gastric compartment.

Bioaccessibility of phenolic compounds and antioxidant activity in raw and pickled capers.

Capers are excellent sources of phenolic compounds, which possess antioxidant activity and a variety of health benefits. Capers are often not eaten fresh due to their bitterness, instead, they are usually brined and eaten as pickles. For phenolics to display beneficial effects, they should be bioaccessible. This research aimed to investigate the bioaccessibility values of phenolics in raw and pickled capers. Before and after in vitro digestion, total phenolic content (TPC), total flavonoid content (TFC), ABTS, DPPH, and FRAP antioxidant activities and individual phenolics were determined in raw (RC) and pickled capers (PC). TPC, TFC, and antioxidant activity of capers were not affected by pickling. The bioaccessibility of TPC in RC and PC was 77.8% and 72.9%, respectively. In vitro digestion decreased ABTS, DPPH, and FRAP antioxidant activity values in RC and PC significantly (p < 0.05). Rutin (quercetin-3-O-rutinoside) and kaempferol-3-O-rutinoside were found to be the main phenolic compounds before and after in vitro digestion in all caper samples. After in vitro digestion, rutin content decreased, while kaempferol-3-O-rutinoside content in capers was stable. The results suggest that capers are really good sources of bioaccessible phenolics. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-023-05824-x.