Effects of extraction techniques on the structural and physicochemical characteristics of Silybum marianum seed meal protein

The extraction method usually affects the structure and physicochemical properties of the protein. In this paper, Silybum marianum protein was isolated by reverse micelle extraction, and alkaline extraction and acid precipitation. The structure of the proteins was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and SDS-PAGE, and the effects of the extraction method on the physicochemical properties and antioxidant activity of proteins were also analyzed. The results showed that proteins isolated by reverse micelle extraction (SPRME) were dominated by globular and fibrillar proteins with smooth surfaces and intact edges. Compared to the proteins isolated by alkaline extraction and acid precipitation (SPAE), SPRME contained a greater concentration of proteins in the 10–25 kD range. The β-fold contents of SPRME and SPAE were 26.73% ± 0.18% and 37.78% ± 0.74%, and the β-turn contents were 18.90% ± 0.67% and 14.02% ± 0.72%, respectively. The solubility, oil holding property, foaming capacity, emulsification, and emulsification stability of SPRME were higher than those of SPAE. SPRME has a superior antioxidant capacity than SPAE. These results indicate that milk thistle protein extracted by the reverse micelle method has a complete structure and better functional properties.