Solubility and Moisture Sorption Isotherms of Whey-Protein-Based Edible Films as Influenced by Lipid and Plasticizer Incorporation

Plasticized whey-protein and whey-protein emulsion films were produced using sorbitol and glycerol as plasticizers and butterfat and candelilla wax as lipids. Protein, plasticizer, and lipid ratios were optimized to obtain acceptable free-standing flexible films. Water solubility (20 degrees C, 24 h) and moisture sorption isotherms (0.18-0.90 a(w), 25 degrees C) of the films were determined. The experimental moisture sorption isotherm values were fitted using the Guggenheim-Anderson-DeBoer (GAB) model. Solubility and equilibrium moisture contents (EMC) of the films were influenced by plasticizer and lipid incorporation. EMCs of all films increased rapidly at a(w) > or = 0.65. Incorporation of lipids reduced solubilities and EMCs of sorbitol- and glycerol-plasticized films. The effects of plasticizer and lipid type on GAB constants were also determined.