Evaluation of purple onion peel by-product extract alongside commercial purple fruit–vegetable flours as functional ingredients in bread

This study investigated purple onion peel extract (POPE), a by-product-derived single-source phenolic ingredient, alongside commercial purple fruit–vegetable fortified flours as reference formulations in bread production. Dough and bread samples containing 1% and 3% POPE, commercial purple flour 1 (CPF1) and purple flour 2 (CPF2) were evaluated for total phenolic content, DPPH antioxidant activity, color, texture, and sensory quality. In bread, total phenolic content increased from 0.37 mg GAE/g in the control to 0.75 mg GAE/g with 3% POPE and 1.73 mg GAE/g with CPF2. Baking generally increased phenolic content and antioxidant activity compared with dough, suggesting improved extractability of antioxidant compounds after thermal processing. CPF2 showed the highest TPC and DPPH values but produced firmer bread and stronger color changes. 1% POPE improved bioactive properties while maintaining bread quality closer to the control. The results indicate that POPE can be used as a sustainable functional ingredient for bread enrichment.