Preparation of cross-linked canola protein films by wet casting and compression method

Canola protein isolate (CPI) films were prepared by wet casting followed by heat compression. It was found that high tensile strength could be obtained under low compression pressure of 1.5 MPa, attributed to the pre-denaturation of protein during wet casting. High temperature (150 °C) could lead to degradation of the CPI matrix, while low temperature (≤ 90 °C) resulted in incomplete melting of the CPI matrix. To obtain CPI films with maximal tensile strength, the optimal curing conditions were 110 °C for 8 min or 130 °C for 5 min. Chemical modification of CPI using bisepoxide as a chain extender markedly increased the tensile strength of the modified CPI (MCP) film. FTIR and DSC results indicated cross-linking occurred. TGA results confirmed the degradation of the CPI matrix cured at 150 °C; furthermore, the thermostability of the modified CPI films was increased, attributed to the introduction of cross-linked structure in the CPI matrix. Therefore, the optimal curing temperature range to obtain maximum quality of CPI films was broadened by the chemical modification to 110 to 150 °C to meet the requirement as a packaging film for food and non-food products.