Effects of Extraction Methods on Physicochemical, Functional and Nutritional Properties of Protein Extracted from Mustard (Brassica juncea) Seed Meal Residue.

Agro-industrial by-product valorization promotes the circular bioeconomy, food security, and sustainability by recycling waste products into reusable resources. This study evaluated various protein extraction methods for processed mustard seed (Brassica juncea) meal, including conventional alkaline (CON), enzyme-pretreated alkaline (ENZ), ultrasound-assisted alkaline (US), and enzyme-pretreated and ultrasound-assisted alkaline (ENZ+US) extraction methods. The protein content extracted from the various treatments ranged from 70.67% to 82.31% (molecular weights: 10-75 kDa), with morphology shifting from rough to smooth surfaces in enzymatic treatments. Viscozyme L hydrolysis of cell-wall polysaccharides in ENZ and ENZ+US treatments facilitated co-extraction of non-protein bioactives as shown by enhanced antioxidant capacities through hydrogen/electron donation mechanisms, including superior Folin-Ciocalteu reducing capacity (7.20-7.95 mg GAE/g), radical scavenging (DPPH•: 8.75-9.33; ABTS•+: 42.97-56.86 mg TE/g), and ferric-reducing antioxidant power (FRAP: 13.59-14.49 mg TE/g). Conversely, the US treatment may generate reactive species that reduce antioxidant capacity while increasing visual lightness (L*) and preserving in vitro digestibility (66.19%) at a level comparable to that of CON (67.63%). Meanwhile, the CON treatment exhibited the highest protein solubility across all pH levels, driving a higher emulsifying activity index (42.15 m2/g). In summary, this research demonstrates that B. juncea seed waste can be transformed into high-value functional ingredients by tailoring the extraction method to targeted product properties. However, low extraction yields present a significant bottleneck, and therefore industrial and economic feasibility will depend on future yield optimization in order to drive sustainable plant-based protein development.