Whey protein film properties as affected by ultraviolet treatment under alkaline conditions

The effects of UV radiation treatment on film-forming solutions adjusted to two alkaline pH values (9 or 11) on the properties (water vapour permeability, solubility, mechanical properties, colour and microstructure) of whey protein concentrate films, and on some structural characteristics of proteins (free sulphydryl groups, degree of aggregation, denaturation and secondary structure) were evaluated. UV radiation increased protein aggregation at both pH values. Ultraviolet treatment of pH 9 solutions increased free sulphydryl groups and produced films with higher solubility, tensile strength, elastic modulus, and puncture properties and lower elongation at break; UV radiation at pH 11 decreased free sulphydryl groups and films showed higher solubility and elastic modulus and lower puncture deformation and elongation at break than untreated films. The treatment also affected film colour differently depending on the pH. In conclusion, ultraviolet treatment modifies the properties of the films in different ways depending on the pH of the solutions.