Delivering Phenolic Acids in Soy Protein Gels: Noncovalent Interactions Control Gastrointestinal Bioaccessibility

This study aimed to explore how the delivery of added phenolic acids was affected by the soy protein gel matrix using the INFOGEST static in vitro digestion protocol. Gels were prepared by two consecutive heating steps and by adding glucono-delta-lactone (GDL) as an acidifier or magnesium sulphate (MgSO4) as a salt coagulant. The addition of phenolic acids in GDL gels doubled their elastic modulus (G') (p<0.05), without showing the same effect on MgSO4 gels. Nevertheless, the bioaccessibility of phenolic acids was not significantly different between the gel matrices (p>0.05). The release of all phenolics was almost complete (>80%) at the oral phase (pH 7) and significantly lower at gastric phase (pH 3), then at intestinal phase, the release was either increased or significantly reduced depending on the phenolic acid structure. The results of this study suggest that the bioaccessibility of the added phenolic acids is controlled by their interactions with the soy protein gels rather than the protein digestion kinetics of the gels.