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.