Processing-Induced Changes in Phenolic Composition and Dough Properties of Grape Pomace-Enriched Wheat Buns

The study aimed to elucidate compositional changes in free phenolic compounds (fPHEs) during bakery processing of wheat flour supplemented with grape pomace (GP) and to assess dough rheology, bun shape and physical characteristics. Three GP variants were used—two from white cultivars (Rhine Riesling; Rhine Riesling + Muscat of Moravia) and one from a red blend (Saint Laurent and André)—at substitution levels of 5, 10, 20, and 30%. Thirty-four fPHEs were quantified by high-resolution UHPLC-MS-Orbitrap; dough rheology was assessed by Mixolab; and potential fPHE–wheat macromolecule interactions were examined via FTIR spectroscopy. Wheat flour contained only six fPHEs at low concentrations. Both white GP samples had similar profiles of 32 fPHEs, dominated by miquelianin (526–683 µg/g) and hyperoside + isoquercetin (390–476 µg/g). Red GP was highly enriched in anthocyanins (>30,000 µg/g) and generally exceeded white GP in most fPHEs. Even 5% GP substantially increased fPHE concentrations throughout processing. Several compounds (e.g., gallic acid, miquelianin) exceeded theoretical values, suggesting release from bound forms during fermentation and heating, whereas anthocyanins lost at least 30% during baking. Rheological analysis showed shorter dough development and reduced stability with increasing GP. White GP enhanced starch gelatinization (C3), gel stability (C4), and retrogradation, whereas 20% red GP markedly impaired gelatinization. GP additions ≥10% deteriorated bun shape and physical properties. FTIR confirmed spectral shifts likely due to fPHE–protein/starch interactions. In summary, incorporation of just 5% GP enhanced the nutritional profile of wheat buns.