Physical properties of whey protein coating solutions and films containing antioxidants

Antioxidants (ascorbyl palmitate and a-tocopherol) were incorporated into 10% (w/w) whey protein Isolate (WPI) coating solution containing 6.67% (w/w) glycerol (WPI:glycerol = 6 : 4). Before incorporation, the antioxidants were mixed using either powder blending (Process 1) or ethanol solvent-mixing (Process 2). After the antioxidant mixtures were incorporated into heat-denatured WPI solution, viscosity and turbidity of the WPI solutions were determined. The WPI solutions were dried on a flat surface to produce WPI films. The WPI films were examined to determine transparency and oxygen-barrier properties (permeability, diffusivity, and solubility). WPI solution containing antioxidants produced by Process 1 and Process 2 did not show any difference in viscosity and turbidity, but viscosity was greater for the WPI solution with rather than without antioxidants. WPI films produced by Process 2 were more transparent than the films produced by Process 1. Oxygen permeability of Process I film was lower than Process 2 film. However, both the diffusivity and solubility of oxygen were statistically the same in Process I and Process 2 films. Both control WPI films and antioxidant-containing WPI films had very low oxygen solubility, comparable to polyethylene terephthalate films. Permeability of antioxidant-Incorporated films was not enhanced compared to control WPI Mms.