Interactive effects of free and cell wall-bound polyphenols on starch pasting, retrogradation, gelation and digestibility

This study examined how polyphenol-cell wall interactions affect the pasting, storage behavior and digestibility of wheat starch. A controlled model system was developed using wheat starch, a bacterial cellulose analogue of the apple cell wall (aACW), and an apple pomace polyphenol extract. Blends-starch+polyphenols (S-PP), starch+aACW (S-aACW), starch+aACW+polyphenols (S-aACW-PP), and starch+polyphenol-pre-loaded aACW [S-(aACW:PP)]-were subjected to simulated hydrothermal processing followed by storage and in vitro digestion using an standardized digestion model including pooled human saliva in the oral phase. Polyphenols in both starch and S-aACW lowered pH and significantly reduced granular swelling and breakdown upon heating. These reductions were mitigated when polyphenols were pre-loaded within aACW, while their aACW-entrapment had no effect on breakdown, setback (short-term retrogradation), or water mobility. During storage, polyphenol or aACW inclusion increased the enthalpy of retrograded amylopectin, an effect intensified by combining free polyphenols and aACW (S-aACW-PP) but not when polyphenols were pre-loaded within aACW [S-(aACW:PP)]. During gelation, polyphenol pre-loading into aACW introduced additional dissipative interactions to the gels that increased their structural resilience under increasing strain (i.e., stiffness) while reducing their strength to be fractured at macroscopic scale. aACW alone moderately slowed early intestinal starch digestion, likely via steric hindrance and enzyme adsorption, whereas polyphenols reduced digestibility by inhibiting α-amylase and stabilizing ordered starch structures. Notably, this effect at the end of the intestinal phase persisted only with free polyphenols, not with those pre-bound to aACW. Results highlighted the role of cell wall-polyphenol interactions in modulating starch functionality, advancing current understanding beyond pairwise interactions.