A fourier transform infrared spectroscopy study of the effect of temperature on soy lecithin-stabilized emulsions

The effect of temperature on soy lecithin-stabilized emulsions was studied using Fourier transform infrared spectroscopy (FTIR). Oil-in-water (o/w) 4% (wt/vol) soy lecithin emulsions were prepared in 6% (vol/vol) medium-chain triglycerides and 94% (vol/vol) water using a two-stage homogenizer set at a pressure of 3000 psig. Three types of emulsions were used in this study: emulsions containing Lecigran and Lecimulthin as emulsifiers and a control emulsion, with no emulsifier added. After preparation, the emulsions were cooled to 4°C, held at this temperature, and spectra were collected after 1 h. The emulsions and reference water were raised to room temperature (22°C) and held at that temperature for 1 h and the spectra collected. The temperature was raised 15°C over the temperature range of 22 to 82°C, and spectral data were collected similarly. The four regions used for this determination in the subtracted spectra of the emulsion were those contributing to -OH vibration, -CH₂ stretching, H-O-H bending vibrations, and P=O, C-O-C, and P-O-C vibrations. The control emulsion was greatly affected at temperatures other than room temperature. This was due to the lack of lecithin as an emulsifier, resulting in a destabilization of the emulsion with temperature increases. The vibrational peaks for the emulsion containing Lecimulthin were found to be lower than those for the emulsion made with Lecigran due to greater water bonding. The control had the highest peaks at the -OH regions because of reduced interaction at the oil-water interface. Both of the emulsions with phospholipids remained stable throughout the temperature range. FTIR is a potentially powerful tool that could be used in the rapid determination of emulsion stability in food systems by measuring emulsifier-water interactions.