Heat-denatured and alcalase-hydrolyzed protein films/coatings containing marjoram essential oil and thyme extract

Abstract In this study, heat-denatured and alcalase-hydrolyzed whey and soy protein films/coatings containing marjoram essential oil (MEO) and thyme extract (TE) were investigated comparatively in terms of physicochemical and functional properties. Heat-denaturated high protein solutions produced self-standing, smooth, transparent and viscoelastic films in the presence of glycerol. Enzymatic hydrolysis provided transparency, elasticity and extensibility to the films of low protein solutions. The addition of MEO and TE triggered hardness and brittleness especially in hydrolyzed high protein films and remarkably changed film color, thickness and viscosity possibly affecting surface adherence of films. Heat denatured films exhibited higher water vapor permeability (WVP) than alcalase-hydrolyzed ones. The lowest hardness was obtained in hydrolyzed low protein films with considerable adhesiveness. Hydrolyzed protein solutions coated to cheese provided better protection against moisture loss and MEO added films caused elevated hardening of cheese. MEO and TE incorporated in film matrices were seemed to suppress mycelial growth and sporulation of Aspergillus niger. This study presented valuable new findings on functional protein films produced by enzymatic hydrolysis as an alternative to heat treatment.