Whey Protein Film with Oxygen Scavenging Function by Incorporation of Ascorbic Acid

Residual O2 in a package headspace can be removed by an O2-absorbing sachet, which can be harmful if swallowed by the consumer, or by a chemically-active plastic packaging film, which is difficult to recycle. An edible, O2-absorbing film would avoid these disadvantages. The objective of our research was to assess the O2-scavenging potential of an edible whey protein isolate (WPI) film incorporating ascorbic acid (AA). AA at 0.05, 0.1, or 0.2 M was added to 5% (w/w) heat-denatured WPI film-forming solutions with WPI : glycerol (Gly) ratio of 1 : 1.00, 1 : 0.80, or 1 : 0.67. The pH of solutions was then adjusted to 3.5 (below pKa1 of AA), to stabilize AA against oxidation, before film casting. The mechanical properties, O2 permeabilities, and thermal transitions of films were measured. Activation of the O2-scavenging function of the AA-incorporated films was accomplished by adjustment of the films to pH = 7. O2-scavenging ability of AA-incorporated WPI films was determined by measuring residual O2 in the headspace of a high-barrier container. Incorporation of AA into WPI film decreased film tensile strength and further reduced O2 permeability at each WPI : Gly ratio. AA-containing films adjusted to pH = 7 demonstrated O2 absorption proportional to AA content, consistent with theoretical O2-scavenging capacity. Thermal transition measurements indicated that AA was involved in WPI structural modification and decreased the degradation temperature of WPI-based film. The demonstrated O2-scavenging function, improved O2 barrier and acceptable mechanical properties of AA-incorporated films indicate potential commercial usefulness.