Preparation and characterization of antioxidant soy protein isolate films incorporating licorice residue extract

Antioxidant films were prepared by incorporating licorice residue extract (LRE) into soy protein isolate (SPI) films, and the effects of different concentrations of LRE (0, 10, 30, 50, and 70 g kg(-1) based on the weight of SPI) on the microstructure, physical properties, and antioxidant activities of SPI films were investigated. Fourier transform infrared spectroscopy indicated that the interaction between the SPI and LRE was via hydrogen bonds. The microstructure of SPI films with LRE was rough as observed by scanning electron microscopy. Moreover, the incorporation of LRE significantly decreased the monolayer moisture content, swelling degree, the water vapor and oxygen permeability of the SPI based films. The tensile strength of films was increased from 7.69 to 10.83 MPa with increasing content of LRE from 0 to 50 g kg(-1). The films with LRE had excellent UV barrier properties, the surface color became deeper brown with increasing LRE content. In addition, the films with LRE released significantly more total phenolic content and antioxidant into alcoholic and fatty food simulants compared with control films, and possessed stronger 2,2-`diphenyl-1-picrylhydrazyl (DPPH) and 2,2 '-azinobis(3-ethylbenzothiazoline-`6sulfonate) (ABTS) scavenging activities. SPI film incorporating LRE is an ideal active food packaging material for fatty food preservation. (C) 2017 Elsevier Ltd. All rights reserved.