Abstract: The objective of this research was to reveal the effect of high pressure homogenization on the change in protein secondary structure and physicochemical and functional properties of soybean protein isolate (SPI)-lecithin system through characterizing conformational changes by circular dichroism spectroscopy and through measuring emulsifying capacity, emulsion stability, surface hydrophobicity and droplet size distribution. The results showed that high pressure homogenization improved emulsion activity index and emulsion stability index of the complex system significantly. The surface hydrophobicity of SPI significantly increased at higher pressure of homogenization, implicating considerable exposure of surface hydrophobic groups and increased interaction between soybean protein and phospholipid. After the homogenization treatment, the average droplet diameter of the composite system decreased from 33.21 to 3.61 μm, and the droplet size distribution was uniform with a slight shift towards smaller droplet sizes. Circular dichroism spectral results showed that high pressure homogenization resulted in conformational changes of the composite system, implying the occurrence of interaction between protein and lecithin. However, with further increasing homogenization pressure, only a little reduction in α-helix content was observed compared with untreated samples.

Key words: high pressure homogenization, soybean protein, lecithin, structural properties, functional properties