Interaction of soybean protein isolate and phosphatidylcholine in nanoemulsions: A fluorescence analysis

Abstract

Two types of nanoemulsions were prepared using ultrasound (US) treatment and high pressure homogenization (HPH) with optimized conditions. The effect of US and HPH on the structure and the interaction between soybean protein isolate (SPI) and phosphatidylcholine (PC) were studied using fluorescence spectrum. Results showed that these two preparation methods were capable of producing stable nanoemulsions. The nanoemulsions prepared using HPH had smaller average particle size, higher surface charge, lower turbidity and greater emulsifying yield than US, but the specific energy required for the HPH (4.0 kJ/g) was nearly 1.5 times higher than that of US (2.7 kJ/g). Fluorescence data showed that the fluorescence quenching of SPI with PC was the result of the formation of SPI-PC complex. According to the Stern–Volmer equation, the association constant (KA) of the SPI-PC interaction using HPH was higher than US at three different temperatures. The positive enthalpy and entropy changes suggested that hydrophobic interactions were the dominant binding force in stabilizing the complex. The distance r for binding between HPH treated PC and SPI was lower suggesting that the binding was stronger. These comparative results showed that the HPH-nanoemulsions were more stable than US-nanoemulsions, which was proposed to be due to HPH promoting the exposure of more hydrophobic residues on the surface of SPI, which would permit more PC to interact with SPI. But US is a relatively more energy-efficient method as compared to HPH and may better meet industrial needs.