Valorization of Nigella sativa Seed Meal and Whey as Functional Ingredients to Enhance Nutritional, Rheological and Sensory Properties of Rice-Based Gluten-Free Bread

This study investigated the valorization of agro-industrial by-products, namely Nigella sativa seed meal (BCSM) and whey, as functional ingredients to improve the quality of rice-based gluten-free bread. A Response Surface Methodology (RSM) approach was applied to optimize formulation parameters and evaluate their effects on physicochemical, rheological, nutritional, and sensory properties. The optimized formulations showed distinct performance profiles depending on the rice matrix and ingredient balance. The optimized brown rice bread (OBRB), characterized by the highest BCSM incorporation (10 g), showed the most relevant functional and nutritional improvements, including increased dietary fiber, enhanced antioxidant activity, and reduced hardness and chewiness compared with the corresponding control. In contrast, the optimized red rice bread (ORRB), characterized by low BCSM content and higher whey incorporation, mainly contributed to improved specific volume and crumb structure. Rheological analysis revealed distinct structural behaviors, with BCSM contributing to a more rigid and structured matrix, while whey promoted a softer and more compliant dough system. Sensory evaluation confirmed that the incorporation of these by-products did not negatively affect acceptability, with overall acceptability scores ranging between 5 and 6. Overall, these results indicate that OBRB was the most promising formulation for functional enrichment, whereas ORRB was mainly associated with structural optimization. This study demonstrates that BCSM and whey can be strategically used as formulation-dependent ingredients for developing nutritionally enhanced and structurally improved gluten-free bread, contributing to the sustainable valorization of food industry by-products.