Effect of glycerol and sorbitol on the mechanical and barrier properties of films based on pea protein isolate produced by high‐moisture extrusion processing

Abstract

AbstractDisposable food packaging accounts for a large proportion of the plastic waste in the environment. Bio‐based and biodegradable alternatives could help to reduce plastic pollution but must perform similarly to current synthetic materials. Here, we investigated the effect of two plasticizers (glycerol and sorbitol) on the mechanical and barrier properties of films composed of extruded pea protein isolate. We evaluated physical properties such as tensile strength, elongation at break, moisture content, surface energy, residence time distribution, and gas barrier properties as a function of plasticizer concentration. The flexibility and workability of the films generally increased with higher concentrations of the plasticizer. The residence time distribution (RTD) showed that sorbitol mixtures remained in the extruder longer than glycerol mixtures, exacerbating the loss of quality. Glycerol films generally retained more moisture than sorbitol films and the tensile strength declined with increasing glycerol content, but the elongation at break increased. The polar fraction of the surface energy increased with higher concentrations of sorbitol, indicating that sorbitol is more polar than the pea protein isolate. In terms of barrier properties, both the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) were higher for films plasticized with sorbitol. Specifically, the OTR for sorbitol‐plasticized films at 50% (vol/vol) was 519 cm3*100 μm/(m2*d*bar) compared to 300 cm3*100 μm/(m2*d*bar) for the glycerol‐plasticized films, and the WVTR for sorbitol‐plasticized films at 50% (vol/vol) was 2633 g*100 μm/(m2*d) compared to 895 g*100 μm/(m2*d) for the glycerol‐plasticized films. For both plasticizers, the WVTR increased with increasing plasticizer concentration. In contrast, the OTR declined with increasing glycerol concentrations, whereas no trend was observed for sorbitol. Our study shows that pea protein isolate is suitable for the manufacture of bio‐based films and confirms that plasticizers influence the resulting mechanical and barrier properties. Further research is necessary to optimize the properties of the films.