Characteristics and emulsifying properties of two protein fractions derived from the emulsion formed during aqueous extraction of Camellia oil

Emulsification is a key issue which makes oil hard to be separated during aqueous extraction from Camellia Oleifera Abel. seeds. Therefore, de-emulsification is required to recover and enhance oil yield. To investigate the major protein components resulting in a stable emulsion, the emulsifiable proteins of Camellia oleifera Abel. seeds (CSEP) were obtained from the emulsions formed during aqueous extraction of Camellia oil, and two major protein fractions (CSEP-A and CSEP-B) were isolated and purified from CSEP. CSEP-A consisted of a small amount of polysaccharides and seven major subunits/proteins with a molecular weight ranging from 13 to 35 kDa. CSEP-B was a protein mixture with a molecular weight range of 13-15 kDa. At neutral pH condition, CSEP-A had higher intrinsic fluorescence intensity and surface hydrophobicity compared to CSEP-B. There were more beta-sheet, but lesser a-helix in protein secondary structure of CSEP-A. Both CSEP-A and CSEP-B were rich in Glu, Arg and Asp. However, hydrophobic amino acids contents in CSEP-A (33.47 +/- 2.35%) was significantly higher (p < 0.05) than that in CSEP-B (18.70 +/- 0.03%). CSEP-A had a significantly higher (p < 0.05) emulsifying activity index (EAI), significantly lower (p < 0.05) creaming index (CI) and similar emulsion stability index (ESI) compared to CSEP-B, and the emulsion droplets formed with CSEP-A showed better stability. Oleosins were found to be major emulsifiable proteins in CSEP-A, which may contribute to the excellent emulsifying properties of CSEP-A.