Physicochemical and antioxidant properties of biopolymer/candelilla wax emulsion films containing hop extract – A comparative study

Abstract

Emulsion films based on different biopolymers: carboxymethyl cellulose (CMC), oxidized potato starch (OPS), soy protein isolate (SPI), gelatin (GEL) and containing different concentrations of ethanolic hop extract (EHE: 0, 0.1, 0.25, 0.50%) were obtained and evaluated in terms of microstructure, water affinity, optical, mechanical, and antioxidant properties. SEM analysis showed that EHE improved homogeneity of wax in the protein films. In contrast, EHE induced the increase in wax particle size in CMC films. With the exception of CMC films, the presence of EHE reduced the solubility of films (p < 0.05). Incorporation of EHE significantly increased the water vapor permeability (WVP) of the polysaccharide-based films while had no effect on the WVP of protein-based films. The increase in EHE addition level resulted in films with enhanced barrier properties against UV light. SPI films were characterized by the best UV-blocking properties. EHE decreased visible light transmission of the polysaccharide films, while an opposite trend was observed for SPI films. The derivatives of structural polymers (GEL and CMC) produced films with higher mechanical strength and stiffness compared with the plant storage polymers. EHE caused a significant reduction in toughness of GEL and CMC films but did not affect the mechanical strength of OPS and SPI films. As the content of EHE increased, the films showed an increase in ferric reducing antioxidant power, metal chelating power and antiradical activity. The films susceptible to solubilization (CMC and SPI) had higher release of EHE and, consequently, better antioxidant activity compared to water-swollen films (OPS and GEL).