Thermal and mechanical properties of mandelic acid-incorporated soy protein films

Different contents of mandelic acid (2.5-10 %) were mixed with glycerol-plasticized soy protein isolate (SPI) to prepare mandelic acid incorporated soy protein isolate films. The effects of the mandelic acid content on the morphology and properties of the glycerol-plasticized SPI films were investigated by scanning electron microscopy, dynamic mechanical thermal analysis, differential scanning calorimetry, thermogravimetric analysis, water resistivity and tensile testing. The tensile strength of the mandelic acid incorporated SPI films decreased while elongation at break increased. The results indicated that, at 10 mass% of mandelic acid, strong interactions occurred both between the mandelic acid and the SPI matrix, leading to appearance of endotherms at 148.8 A degrees C. Mandelic acid-incorporated soy protein films were also tested for their antibacterial properties.