Effect of Melanin on the Stability of Casein Films Exposed to Artificially Accelerated UV Aging

Abstract

Petroleum-based polymer food packaging is causing increasing concern. Their biopolymer alternatives should have some added value to compete with them and push them out of the market. This article presents new information related to the effects of melanin on casein films and their protection against artificial UV aging. Casein films were modified with melanin as an active additive and then subjected to artificial aging using UV radiation to evaluate its effect on the preservation of the films’ properties. The films were tested for hydrological (moisture content and water solubility), mechanical, barrier against UV-Vis radiation, colorimetric, and antioxidant properties, and the content of free amino acids and sulfhydryl and disulfide groups were checked before and after aging. Melanin influenced the preservation of mechanical properties of the films (elongation at break increased by no more than 20% for melanin-modified samples compared to more than 50% increase for the control sample), better UV barrier properties, increased antioxidant properties (two-fold higher scavenging of DPPH radicals by films modified with the highest melanin content compared to unmodified films before aging, and four times higher scavenging of DPPH radicals after aging). In addition, the presence of melanin had protective properties for sulfhydryl bonds and proteins (the increase in free amino acids after aging for melanin-modified films was not statistically significant), and it also had the effect of increasing the abundance of bands corresponding to oligomers and polymers in electrophoretic separation. The results indicate that melanin has UV-protecting properties on casein films, and it can be assumed that the obtained casein films modified with melanin could potentially find application as food packaging or edible coatings.