Optimized extraction and comprehensive characterization of sunflower meal protein for functional application in plant-based meat analogs

Sunflower meal is a byproduct obtained after oil extraction and contains a significant amount (30–50%) of protein. Response Surface Methodology (RSM) with Box-Behnken design was employed for the optimized ultrasonic-assisted extraction (UAE) of sunflower seed meal protein isolate (SSM-PI). Protein yield was significantly (p < 0.05) affected by pH, extraction time, and sample to solvent proportion however, protein recovery rate was significantly (p < 0.05) influenced by only pH and extraction time. Under optimal conditions, the protein yield, content, and recovery rate were 15.1%, 81.5%, and 43.0%, respectively. The protein was characterized by Fourier-transformed infrared spectroscopy (FTIR), SDS-PAGE, thermal analysis, and circular dichroism (CD) spectroscopy. SDS-PAGE analysis of SSM-PI showed two distinct protein groups: sunflower albumins (< 20 kDa) and helianthinins (> 20 kDa). Densitometric analysis further revealed that helianthinins (67.0% of total protein) were almost twice the amount of albumins (28.0% of total protein). The secondary structure elements of SPC-PI were 18.5% α-helical, 13.5% β-sheet, 14.7% β-turn, and 53.3% coil content. SSM-PI was used to formulate meat analogs (patties) with 5.0% and 10.0% protein. Proximate analysis showed that patties containing 10.0% SSM-PI had higher protein (39.6%) and ash (2.7%) contents than chicken meat patties. Sensory evaluation indicated that the vegetable control sample had significantly higher overall acceptability (6.86) in comparison to T1 (6.18) and T2 (5.76) meat analogs. SSM-PI enriched meat analogs had low scores for appearance and color due to the green hue of the protein. Sunflower meal is an underutilized low-cost source of functional proteins that can be used as a functional food ingredient in the formulation of meat analogs.