Whey protein isolate film with oxygen scavenging function by incorporation of ascorbic acid.

摘要

AA can be incorporated and function as an oxygen scavenger in WPI films/coatings providing an active barrier to oxygen permeation and eliminates oxygen initially present in the package headspace. AA-WPI films are transparent and have acceptable mechanical properties. Addition of AA decreased film tensile strength, increased % elongation, and decreased elastic modulus, indicating a plasticizer effect of AA on WPI film properties. However, adding AA reduced oxygen permeability, which may indicate a change in film morphology and/or some oxygen scavenging at oxygen permeability test conditions.AA-WPI films were effectively stabilized against premature oxidation by lowering casting solution pH to below the AA pKa1 (4.04 at 25°C). AA-WPI films have good storage stability under ambient conditions (30 +/- 5% RH, 23 +/- 3°C), suggesting feasibility that AA-WPI film can maintain oxygen-scavenging capability for a reasonably long time before being used to protect foods from oxidation. Stability of AA-WPI films and their color change were found to be mainly affected by the pH of casting solution and the storage temperature. Oxidative degradation was the major pathway of AA-WPI films. Stability of AA-WPI films followed Arrhenius behavior.The oxygen scavenging function of AA-WPI film can be activated by contact with food models with the appropriate aw, pH and metal catalyst. The rate of AA-WPI film oxidation follows first-order kinetics. The a w was found to be a rate-limiting factor controlling diffusion of triggering agents (H+ and metal ions) from the food models, hence the oxygen-scavenging rate of AA. At high aw levels, increasing pH and presence of catalyst accelerated the oxidation rate.The ability of WPI film to retard oxidative deterioration of foods was enhanced by incorporating an oxygen-scavenging property provided by AA. In dry foods, activation of oxygen scavenging function of AA was limited due to restricted mobility, despite the availability of triggering agents such as metal catalysts or H+ in the foods. In intermediate and high moisture food, the oxygen scavenging function of the AA-WPI film was more fully activated by the higher aw, pH or metal catalyst content.