Abstract: The study investigated the effect of glycerol monolaurate (GML) addition on the properties of soy protein isolate (SPI) composite film, and discussed the formation mechanism of GML-SPI film by several analytical techniques including Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscope (SEM). The results showed that with the increase of GML addition, tensile strength and elongation at break increased at first and then decreased. Three other indicators including water vapor permeability, light transmittance and water solubility continuously decreased, while brightness and whiteness increased. FT-IR results showed that SPI and GML were bound mainly by hydrogen bonds, hydrophobic force or other secondary bonds. According to XRD and DSC results, the crystallinity and melting temperature of GML-SPI film were both increased due to the addition of GML. However, SEM pictures suggested that GML addition led to decreased internal voids in GML-SPI film. In addition, phase separation of GML and SPI in composite film could be observed when the amount of GML addition was larger than 0.8%. The study may provide a theoretical basis for the development and application of some new edible packaging materials such as soy protein isolate composite film.

Key words: soy protein isolate, film properties, Fourier transform-infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, scanning electron microscope