Internal quality of coated eggs with soy protein isolate and montmorillonite: Effects of storage conditions

The development of the bio-nanocomposite coating materials for eggshells has received more attention because of the decline in interior egg quality. This work evaluated the effects of weight loss, Haugh unit, yolk index, air space and albumen pH, eggshell strength, number of microorganisms on eggshells, contact angle and water vapor permeability of uncoated eggs and eggs coated with soy protein isolate/montmorillonite emulsions (5/0, 5/0.20, 5/0.50, 5/0.80; w/w) during 6 weeks at 25°C. A scanning electron microscope was used to visualize morphologies of soy protein isolate and the soy protein isolate/montmorillonite composite coatings, and the scanning probe microscope was determined. Compared with uncoated and soy protein isolate-coated eggs, the interior egg quality was improved by the increase of Haugh unit, yolk index, air space or eggshell strength, and decrease in weight loss, albumen pH, or the number of microorganisms on eggshells. The higher contact angle indicated the hydrophobicity of coatings. The values of water vapor permeability with 0.2% montmorillonite, 0.5% montmorillonite, and 0.8% montmorillonite were reduced by 21.14, 57.78, and 69.13%, respectively, as compared to those of soy protein isolate coatings. The images by a scanning electron microscope indicated that coatings could cover the cracks of eggshells to preserve the interior egg quality. The experimental values of the scanning probe microscope showed that montmorillonite would not penetrate through the eggshell pores, and it was safe to coat with montmorillonite. This study highlights the use of soy protein isolate/montmorillonite coating to maintain the internal quality and enhance the shelf life of eggs stored at 25°C.