The physicochemical characteristics, amino acid composition, and functional properties of Nigella sativa (NS) seedcake protein extracts were evaluated to establish their potential in nutraceuticals and functional foods. The highest yield (20.2%) of protein isolate (NSPI) from NS seedcake was achieved at an alkali concentration of 0.16 M, a buffer to sample ratio of 1/25 (w/v), extraction time, 15 min, and extraction temperature, 25°C. Amino acid analysis showed that the isolated protein is a good source of amino acids with a significant essential to total amino acid (E/TN) ratio. Further, the protein isolate exhibited maximum solubility at pH 11. The results of the physicochemical analysis clearly indicated that the protein isolate had good water and oil holding capacity, emulsification property, foaming capacity, and foaming stability. The secondary structure of NSPI contained α-helix, β-sheet, and β-turns. In addition, NSPI showed excellent antioxidant, anti-diabetic, and protein digestibility activities. From the experimental data, it could be concluded that NSPI could be an excellent source of proteins for the development of foods with promising functional properties. PRACTICAL APPLICATIONS: Nigella sativa seeds are frequently used as a natural food additive and have been a part of naturopathy for centuries due to their anti-inflammatory, antibacterial, anticancer, antidiabetic, immunomodulatory, and cardioprotective properties. Nigella sativa seedcakes obtained as by-products of the oil extraction process are rich in protein content and can be used as a sustainable source of dietary proteins to cater to a wide range of consumers. Being plant-based, they inherently possess several medicinal properties. Analyzing the physicochemical and functional properties of protein isolated from seedcakes allows us to optimize the protein extraction process while providing a better perspective on its potential in the nutraceuticals and food industries. It can be used as an energy supplement in animal feed as a source of protein to replace soybeans and barley. The antioxidant proteins when added to meat-based products have been known to protect the meat from oxidative stress as well as pathogenic organisms, thus, improving its shelf-life. Nigella sativa protein isolates have several applications in the pharmaceutical industry as well.
Keywords: Nigella sativa protein isolate (NSPI); antioxidant; functional properties; nutraceutical; optimization; structural characterization.
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