Cold-Pressed Black Cumin (Nigella sativa L.) Cake as a Functional Ingredient in Sustainable Food Systems

Black cumin (Nigella sativa L.) is an ancient culinary and medicinal plant whose cold-pressed oil industry now generates increasing quantities of nutrient-dense press cake (BC-cake). This by-product is rich in plant protein, dietary fiber, residual oil, and Nigella-specific phytochemicals such as thymoquinone, phenolics, and tocopherols, positioning it as a promising upcycled functional ingredient. This narrative review synthesizes recent evidence (2015-2025) on the composition, techno-functional behaviour, food applications, and sustainability implications of cold-pressed black cumin cake. Cold-pressing preserves native bioactives but leaves 15–25% residual oil and concentrated minerals and fiber in the cake, whose quality is influenced by seed origin, processing parameters, and post-press handling. BC-cake exhibits high water- and oil-holding capacity, relevant emulsifying potential, and texture-modifying effects through its proteins and fibers, while its phenolic fraction and thymoquinone confer notable antioxidant activity. Limited data suggest it can also contribute to gelation and viscoelastic structure in complex matrices. Applications in breads, pasta, gluten-free bakery products, cookies, and muffin formulations consistently enhance protein, fiber, mineral, and antioxidant contents, and in some cases lower predicted glycemic index. A kefir-like non-dairy beverage fermented on BC-cake further illustrates its suitability as a substrate in probiotic systems. However, strong aroma, bitterness, dark colour, and high water binding constrain inclusion levels and necessitate formulation adjustments. Safety-related knowledge gaps remain, including the anti-nutritional profile of BC-cake and its impact on acrylamide formation in baked products, although black cumin is generally recognized as safe and non-novel in many regulatory contexts. From a systems perspective, valorizing BC-cake exemplifies circular economy principles by converting an underutilized residue into value-added food ingredients with relatively low additional environmental burden. Future work should focus on standardizing functionality assessment, refining pre-treatments to improve sensory performance, and generating robust data on long-term safety and environmental impacts to support its broader adoption in sustainable food systems.