Physicochemical and functional properties of two kinds of Schisandra proteins and their antioxidant activity in H2O2-treated HepG2 cells

Schisandra chinensis protein (SCP) and Schisandra sphenantherae protein (SSP) were extracted by alkali extraction and isoelectric precipitation, and the amino acid compositions, structures, and physicochemical properties of the two proteins were analyzed to evaluate their functional properties. The effects of SCP and SSP on proliferation, protection, and anti-apoptosis of H₂O₂-treated HepG2 cells after oxidative stress were investigated. The results showed that SCP had a higher content of essential amino acids (16.27 ± 0.76) than SSP. Scanning electron microscopy and Fourier-transform infrared spectroscopy analyses, as well as substituent distribution in electrophoresis, revealed the structural differences between the two proteins; in particular, the disulfide bond content is higher in SCP, which was also found to be more stable in terms of heat tolerance (114.7 °C), solubility (47.18 %), emulsification (158.57 m²/g), emulsion stability (89.53 %), foaming (226 %), and foaming stability (90.32 %). In an in vitro experiment, SSP was more effective in protecting HepG2 cells from H₂O₂-treated oxidative damage, effectively inhibiting the levels of reactive oxygen species and malondialdehyde, maintaining the stability of cell membranes, promoting antioxidant mechanisms, and decreasing apoptosis by regulating the expression of genes and proteins related to the mitochondrial apoptotic pathway. These results suggest that both SCP and SSP are suitable as novel food additives, and that the excellent functional properties and thermal stability of SCP make it a potential nutritional resource in the food industry. In addition, SSP has potential as a protein resource with antioxidant activity.