Properties of beta-casein and edible beta-casein films

Physicochemical properties of β-casein interactions with water were characterized. Moisture sorption isotherms at +4°C and +22.5°C were obtained for β-casein after isolation and after 9 months of storage at –29°C and +22.5°C. Glass transition state diagrams (T_g vs. moisture) were determined for β-casein after storage. Results showed that the effects of storage temperature on moisture sorption isotherms were varied; however, at any a_w differences in moisture content between samples were small. The glass transition temperatures for β-casein were above room temperature, even at a_w = 0.76. Onset of stickiness occurred above a_w = 0.76.; Effects of storage conditions on the secondary structure of β-casein in powders, films, and solutions were determined. Fourier transform infrared spectroscopy absorbance spectra were obtained for β-casein samples after the protein had been stored for 16 months at –29°C or +22.5°C. Correlation coefficients of second derivative absorbance spectrum in the amide I region (1720–1600 cm-1) were used to compare secondary structures of β-casein. Secondary structure did not change as a function of storage temperature but was affected by the physical state of the protein (i.e. structure of β-casein in solution was different than that of β-casein films and powders).; A method was developed to produce viable edible β-casein films on a laboratory scale. Edible films were made using glycerol and β-casein that had been stored for 16 months at –29°C and +22.5°C. Water vapor permeability at +22.5°C was determined for two relative humidity gradients (53–11% and 53–75% RH). Stress-strain curves for mechanical property evaluation were obtained by the extension-film dynamic mechanical analysis method. Protein storage temperature did not significantly affect water vapor permeability or elongation properties; however, films made from β-casein stored at –29°C had higher ultimate tensile strength, modulus of elasticity, and yield strength than films made from +22.5°C stored β-casein.; Overall this research contributed to the understanding of the stability of physicochemical and structural properties of β-casein with respect to storage temperature and provided quantitative water vapor permeability and mechanical data for β-casein edible films.