Physical and antioxidant properties of flexible soy protein isolate films by incorporating chestnut (Castanea mollissima) bur extracts

• Soy protein films with chestnut bur extracts are good barriers to UV light.
• Chestnut bur extracts increased the hydrophilic properties of soy protein films.
• Chestnut bur extracts improved the tensile strength of soy protein films.
• The chestnut bur extracts improved antioxidant activities of soy protein films.

The physical and antioxidant properties of soy protein isolate (SPI) films were investigated incorporated with chestnut bur extract (CBE) at different levels, 20 g/kg, 50 g/kg, 80 g/kg, and 100 g/kg (based on SPI content). Increased protection against UV light and oxygen barriers were observed in the SPI films containing CBE. The antioxidant properties of SPI films were improved with the addition of CBE as determined by 2, 2-diphenylpicrylhydrazyl radical scavenging activities. The tensile strength of SPI/CBE film reached the maximum value of 2.1 ± 0.1 MPa when 80 g/kg CBE was added. Fourier transform infrared spectra indicated that the addition of CBE influenced the SPI film mechanical properties by changing the distribution of secondary protein structures in the films. The cross-section of the SPI/CBE films viewed using scanning electron microscopy became more compact as the CBE level increased. These results suggest that SPI/CBE film is an ideal choice for food packaging and preservation.