Influence of CaCl2 on the water vapor permeability and the surface morphology of mesquite gum based edible films

Oil-in-water (O/W) emulsions with a dispersed phase mass fraction (φm) of 0.175 were prepared by dispersing a blend of candelilla wax/mineral oil (2:1 ratio) in 10 g of mesquite gum per 100 g of water containing either CaCl2 (0.0, 0.1, 0.2, 0.3, 0.4 or 0.5 g) alone or combined with 1.5 g of glycerol. The mean volumetric droplet size (d3,0), the rate of droplet coalescence (C) and the viscosity-shear rate behavior of the emulsions were affected by the addition of CaCl2 alone or combined with glycerol. The Carreau–Yasuda model fitted best the viscosity-shear rate data of all the emulsions. The surface morphology of the edible films, analyzed by Atomic Force Microscopy (AFM), exhibited a strong dependence on the CaCl2 concentration. Maximum roughness occurred with a CaCl2 concentration of 0.3 g per 100 g. Films with glycerol showed significantly higher roughness than those with only CaCl2. Water vapor permeability (WVP) was significantly lowered as the concentration of CaCl2 increased from 0.1 to 0.3 g per 100 g in the coatings, but increased again at CaCl2 concentrations of 0.4–0.5 g per 100 g. Coatings containing glycerol displayed significant higher WVP.