The effect of protein particle size reduction on the physical properties of CO2-precipitated casein films

Casein precipitated with high pressure-CO2 (CO(2)CAS) has unique properties compared to commercial acid-precipitated casein. CO(2)CAS is less water-soluble and films made from it are less susceptible to high humidity environments; however, the films are opaque and hazy. The appearance of CO(2)CAS films is important especially if applied as a food coating. To improve the appearance properties, the particle size of CO(2)CAS film was plasticized with glycerol was reduced. The effect of protein particle size reduction on tensile properties, water vapor permeability (WVP), and gloss was studied using ASTM methodology. As particle size of the CO(2)CAS was reduced from 126 mu m to 111 mu m, tensile strength and modulus of the films increased, while WVP decreased. With the same particle reduction, gloss increased from 55.3 gloss units on average to 73 gloss unites, but films were still hazy. With a particle size less than 86 mu m, CO(2)CAS films were glossy and transparent, however, tensile strength decreased and WVP increased. Depending on desired application, the properties of CO(2)CAS films can be optimized by changing particle size.