Effects of ultraviolet radiation on properties of films from whey protein concentrate treated before or after film formation

Abstract

Properties (water vapour permeability, solubility in water, colour, mechanical properties and microstructure) of whey protein concentrate films treated with ultraviolet radiation were evaluated.Ultraviolet treatments at different doses (0.12, 4.0 and 12.0 J cm−2) were applied to film-forming solution or to preformed films. These films were compared to untreated films and heat treated films (from solutions subjected to heat treatment). Besides, some structural changes induced to proteins (free sulfhydryl groups, degree of aggregation and denaturation and secondary structure) by radiation have also been investigated.Ultraviolet treatment only affected significantly most mechanical properties and solubility when was applied to film-forming solution and at the highest dose. These films showed significantly higher tensile strength, puncture strength and puncture deformation and lower solubility than untreated films. Films treated with the highest dose of ultraviolet radiation in solution showed tensile strength similar to heat-treated films. Ultraviolet radiation caused that the films were more yellow, greener and darker than untreated films, although the effect of the treatment on colour was higher when was applied to the film-forming solution. Ultraviolet radiation of solutions at high doses increased the concentration of free sulfhydryl groups and induced aggregates formation comparing to untreated films but the changes were lower than those observed in heat-treated films; the denaturation was higher in α-lactalbumin than in β-lactoglobulin. No changes in the secondary structure of proteins were detected. Differences in microstructure were found among films. According to the results, ultraviolet radiation modifies the properties of the films and in different way that heat treatment.