Preparation and characterization of soy protein isolate films modified with sorghum wax

The effect of increasing the concentration of sorghum wax paste on the characteristics of soy protein isolate (SPI) films was investigated. Water vapor permeability (WVP), tensile strength (TS), elongation at break (E), and total soluble matter (TSM) of cast SPI films were determined. Sorghum wax paste extracted with ethanol was added to film-forming solutions of SPI at 5, 10, 15, or 20% w/w of protein. As the concentration of wax paste increased, mean WVP, E, and TSM values of SPI-sorghum-wax-paste composite films decreased and were lower than those of control SPI films. Mean TS values were lower than the control upon addition of 5 and 10% wax paste; however, TS values increased at 15 and 20% wax concentrations. Although no differences in components of sorghum wax were observed between paste extracted with ethanol and wax extracted with hexane, paste extracted with ethanol was miscible with the film-forming solution. SPI-sorghum wax paste films had better water barrier and physical properties compared to control films.