Preparation and characterization of cross-linked canola protein isolate films

Cross-linked canola protein isolate (CPI) films were prepared using a bisepoxide as a chain extender by wet cast followed by heat compression. By DSC measurements, it was verified that the cross-linking reaction took place in the CPI matrix and was completed in 10min at 90°C. FTIR analysis confirmed that the chain extenders were covalently bonded with CPI chains. The reaction led to the formation of a cross-linked architecture which was revealed by an increase in molecular weight of the modified CPI films. The newly formed chain architecture increased the thermostability of CPI as evaluated by TGA; furthermore, the thermostability increased with the increase in cross-linking degree of the modified CPI films. DMA results of the unmodified CPI film showed that microcosmic phase separation occurred between two major proteins, cruciferin and napin in CPI; however, the extent of phase separation decreased with the increase of chain extenders and finally disappeared because of the increased compatibility between cruciferin and napin. Elastomeric mechanical behavior was observed with the introduction of cross-linked architecture in the modified CPI films. At low humidity of 55%, the cross-linked CPI films showed an increase in tensile strength and a decrease in elongation at break. At high humidity of 98%, the increase in hydrophobicity of cross-linked CPI matrix resisted the decreasing tensile strength seen in unmodified films.