Harnessing apple pomace as a bioactive bread ingredient: Influence of exogenous soluble polysaccharides on water dynamics and structure-dependent polyphenol stability

Apple pomace is composed predominantly of cell walls enriched with polyphenols. Its incorporation as a fortifying hydrocolloid in bread-making poses two principal challenges: its elevated water-binding capacity, which interferes with the hydration dynamics of gluten and starch, thereby impairing dough structure and bread quality; and the susceptibility of pomace-derived polyphenols to degradation under the thermal and oxidative stresses encountered during bread-making, potentially diminishing their bioactivity. This study investigates the chemical stability of pomace polyphenols (at subclass and compound levels via UPLC-ESI-QTOF-MS/MS) during bread-making and evaluates the efficacy of co-formulated soluble polysaccharides in modulating water availability and protecting polyphenols against degradation. Wheat breads were prepared with 5% pomace (W:POM), with and without the co-addition of psyllium (W:POM:PSY) or pectin (W:POM:P). W:POM showed lower volume, double the hardness and reduced proportion of free water compared to wheat bread (W). Adding psyllium or pectin to W:POM improved dough/crumb hydration, balanced water dynamics and resulted in similar volume and texture to W. Incorporating 5% apple pomace into dough doubled the total polyphenol content, with bread-making primarily affecting dihydrochalcones and monomeric flavanols, while HBAs, HCAs, and oligomeric flavanols showed minimal changes. Significant variability in the degradation patterns of individual flavonols suggested that discrete polyphenol structures, rather than core subclass structures, influence their stability during baking. Psyllium and pectin generally prevented the loss of dihydrochalcones and flavanols, with pectin enhancing HBAs, HCAs, and oligomeric flavanol recovery. Hierarchical clustering indicated that polyphenol stability is influenced by both their chemical makeup and the molecular structure of the polysaccharides.