WATER-VAPOR PERMEABILITY OF CASEINATE-BASED EDIBLE FILMS AS AFFECTED BY PH, CALCIUM CROSS-LINKING AND LIPID-CONTENT

Edible films were cast from solutions of sodium or calcium caseinate a nd from emulsions of these proteins with acetylated monoglyceride, bee swax, and stearic acid. The water vapor permeabilities of the films we re evaluated at 25-degrees-C using the ASTM E96-80 method, modified to calculate the % relative humidity at the film underside. Adjustment t o pH 4.6 (isoelectric point), calcium ion crosslinking and combined ef fects of calcium ascorbate buffer (pH 4.6) reduced water vapor permeab ility of sodium caseinate films by 36%, 42%, and 43%, respectively. Ca lcium caseinate-beeswax emulsion films had water vapor permeabilities up to 90% lower than pure sodium caseinate films. Water vapor permeabi lity varied by a factor of two depending on emulsion film orientation, indicating nonisotropic structure.