MECHANICAL-PROPERTIES, WATER-VAPOR PERMEABILITY, AND MOISTURE CONTENTS OF BETA-LACTOGLOBULIN AND WHEY-PROTEIN FILMS USING MULTIVARIATE-ANALYSIS

Mechanical and barrier properties of beta-lactoglobulin (beta-Lg) and whey protein isolate (WPI) films were studied using sorbitol(S) as a p lasticizer. The films were cast from heated aqueous solutions and drie d in a climate chamber at 23 degrees C and 50% relative humidity for 1 6 h. The multivariate analysis used has proved to be a valuable tool f or evaluating and quantifying the influences of the variables in the s pecified experimental domain. Two identical factorial designs were app lied to evaluate the influence of the concentration of beta-Lg and WPI , the concentration of S, and the pH. The two materials, beta-Lg and W PI, show similar results, which can be attributed to the dominating pr otein beta-lactoglobulin. At pH 9, Young's modulus and stress at break are not affected when the concentration of beta-Lg, WPI, or S varies. At pH 7 and 8, Young's modulus and stress at break increase when the concentration of beta-Lg and WPI increases, and they decrease when the concentration of S increases. Strain at break increases when pH incre ases from 7 to 9, a more pronounced effect being observed for the WPI films. Water vapor permeability (WVP) decreases and increases for pH 7 and 9, respectively, as the concentration of beta-Lg and WPI increase s. This contrast in behavior at different pH values is probably due to a structural difference that occurs above pH 8. Moisture content and WVP increase when S increases. Here a clear distinction can be observe d between the two film materials: the beta-Lg films show higher values for both moisture content and WVP measurements.