Grape pomace flour as a sustainable ingredient in cookie formulation for fiber, free, and bound phenols improvement

This study aimed to evaluate the substitution of wheat flour (WF) for grape (Vitis vinifera L.) pomace (GP) on cookie formulation. The techno-functional properties of GP flour (GPF) were characterized, and cookie formulations containing 15% (C15) and 20% (C20) GPF were developed. To evaluate the antioxidant and functional potential, free (FPF, soluble phenols) and bound phenolic fraction (BPF, insoluble phenols) were extracted. The total phenolic content (TPC) and antioxidant potential (ABTS and DPPH assays) were measured. The GPF shows differences in oil and water retention, non-foaming properties, and non-significant differences in swelling capacity compared to WF. C15 and C20 show L* values from 27.9 to 36.2, b* values from 2.22 to 2.64, and a* values from 8.84 to 10.49. GPF addition elevates ash and fiber content by 3.5–4.2 and 14–31.6 times. GPF cookie (C15) exhibited a significantly higher TPC compared to WF. Although the FPF fraction in the cookies was higher compared to BPF, the contribution of BPF to antioxidant activity was high (DPPH = 29.9%, ABTS = 16.3%) compared to FPF (DPPH = 26.3%, ABTS = 20.3%). Given that FPF is traditionally the only antioxidant fraction measured, the antioxidant potential of incorporating grape by-products is being underestimated; this is the first report of this in a cookie.