Red Grape Pomace Flour: Exploring its Physicochemical composition, Antioxidant Characteristics and Technological Performance in Breadmaking

Red grape pomace (RGP), a winery by-product mainly composed of grape skins and seeds, has traditionally been considered a waste material with limited applications. Nowadays, it is recognized as a valuable source of antioxidant polyphenols with potential health-promoting effects. Therefore, its transformation into flour and physicochemical characterization represent a first step toward its valorization as a food ingredient with potential health-properties. The study evaluated the physicochemical composition and antioxidant properties of RGP flour obtained at different drying temperatures, and its impact on breadmaking performance. RGP was dried at 40 or 60 °C, ground, and sieved to obtain RGP-F40 and RGP-F60 flours. Both flours were characterized for physicochemical composition and antioxidant properties, including total polyphenols (TP), anthocyanins, and in vitro antioxidant capacity (AC; FRAP, ABTS, and DPPH assays). The technological performance of RGP flour was evaluated by replacing wheat flour at levels from 0 (control) to 30%. Gluten quality, rheological properties, and breadmaking performance were assessed and compared with control. Both flours showed similar protein contents (10.75%) and energy values (362 kcal/100g). However, RGP-F60 exhibited higher fibre (21.74%), lignin (9.45%), fat (7.27%), ash (10.5%), and moisture contents (7.6%), and lower carbohydrate levels (64%). RGP-F60 also showed greater AC determined by FRAP (214 µmol/g) and ABTS (454 µmol/g), whereas TP (35 mg/g), anthocyanins (3.9 mg/g), and DPPH (4.5 µmol/g) values were not affected by drying temperature. Substitution of wheat flour with RGP-F60 progressively reduced dough quality and breadmaking performance. Dough cohesiveness was lost at substitution levels ≥20%. Acceptable loaf volume and flavour, although with a slightly denser crumb structure, were obtained at 5% substitution, while higher levels impaired dough development and baking performance. Overall, drying RGP at 60 °C enhanced its fibre content and AC without affecting TP and anthocyanin contents. This flour could be successfully incorporated at 5% into bread formulations, providing an opportunity to develop value-added food products while contributing to the valorization of winery by-products.