WPI and cellulose nanofibres bio-nanocomposites: effect of thyme essential oil on the morphological, mechanical, barrier and optical properties

Abstract

The uncertainty of consumers about the toxicological effects of synthetic antioxidants incorporated into the packaging has led to a demand for natural substituents that exhibit antioxidant activity without adding risk to the consumers. In this context, the effects of adding different concentrations of thyme essential oil (TEO) (20, 30, and 40% w/w) to whey protein isolate (WPI) and cellulose nanofibre (CNF) bio-nanocomposites developed by casting were studied. Scanning electron microscopy showed a reduction in the dispersion of CNF's in all films with the addition of TEO. The addition of TEO also decreased the water vapor permeability, increased the glass transition temperature, and crystallinity index. For the mechanical properties, the addition of TEO produced less rigid and elastic films with decreased in tensile strength, elongation at break, puncture strength, puncture deformation, and elastic modulus. In addition, the mechanical properties showed the formation of non-interactive systems and the FTIR spectra showed maintenance of the phenolic compounds of the TEO after the synthesis of the films. The optical properties showed that films were less yellow (b*) with a tendency to green (a*), less saturated (c*), and less transparent when compared with the control (0% TEO). The addition of TEO to bio-nanocomposites of WPI and CNFs, in the concentration range tested, enabled the formation of materials with properties that encourage the studies for various applications.