Effects of sorbitol, glycerol and lactic acid on different properties of thin layers made from casein

Effects of addition of each plasticizers (sorbitol, glycerol or lactic acid) having concentration of 0-40% on mechanical properties and water vapor permeability (WVP) and oxygen permeability (OP) of casein composite films have been studied. The best formulation for each composite film having optimum amounts for mechanical properties, WVP and OP have been determined. The amounts of WVP, OP and mechanical properties for the composite films with optimum formulation at three different relatives humidity (RH =32, 52, 75 %) have been also compared. The value of WVP has been measured using a vial coated by a film. The value of OP for a film was determined from measurement of peroxide value for a definite amount of oil that is placed in a vial and coated by the film. Mechanical properties were measured using a tensile machine. The results showed that addition of 20% each plasticizer to casein was the best concentration to achieve optimum mechanical properties (elongation, tensile strength and elastic modulus). Further increase in concentration of plasticizer led to a decrease in tensile strength and elastic modulus and negligible increase in elongation and significant increase in WVP. Thin films containing sorbitol at RH 32% and thin films containing glycerol at RH 75% had WVP greater than that of two other RH. Thin films containing sorbitol at three RH had OP smaller than that of the films containing lactic acid and glycerol.