Transparent and Edible Films from Ultrasound-Treated Egg Yolk Granules

Whole egg yolk can be easily separated into two fractions, plasma and granules, the former of which is rich in lipids and the latter has a high protein content. Searching for new applications for each fraction could increase the value of the whole egg. In this work, the egg yolk granule fraction is being proposed and used to create transparent, edible films. For that purpose, a solution of egg yolk granules was pre-treated using high intensity ultrasound. A Box-Behnken design was established to determine the effect of temperature, ultrasound intensity and the pre-treatment time on the clarity of the granules solution and the transparency of the films obtained. Furthermore, the films were analysed to test the effect of the ultrasound pre-treatment on their mechanical properties, solubility, colour, thermal stability and structure. The optimal conditions for obtaining highly transparent films from egg yolk granules solution were found to be the following: 45 A degrees C, for 40 min and applying ultrasounds at 60% amplitude. With this pre-treatment, the puncture strength value of the films improved from 9 N/mm, in the case of the untreated granules solution, to 31.6 N/mm. The puncture deformation showed a similar trend. All the films made with egg yolk granules showed a low water solubility. The colour of the films was not affected by the ultrasound pre-treatment.