Preserved effect of nano-Fe3+/TiO2 modified PVA-based composite preservation coating for eggs

Abstract: Eggs are highly nutritional food, and contain a variety of amino acids, proteins, minerals, lecithin, sterols, and other essential nutrients that can be fully absorbed by human body. However, the quality of unsterilized and unwashed eggs will deteriorate rapidly during storage, including such conditions as water evaporation, weight loss, and yolk coefficient decrease. In such cases, cleaned and sterilized eggs can effectively suppress harmful pathogens and extend the shelf life of egg products. But cleansing and sterilization could possibly destroy the outer shell membrane of eggs, which causes the eggs to be vulnerable to microbial contamination, as the outer shell membrane has been destroyed. The outer shell membrane can prevent microbial invasion of eggs, so the destruction of the outer shell membrane makes water evaporate through the pores of the shell membrane, and finally causes the spoilage of fresh eggs. Therefore, one of the most effective ways of keeping eggs fresh is to coat eggs with an antimicrobial film. In this paper, polyvinyl alcohol/shellac/ nano-Fe3+/TiO2 composite film prepared by the author is used to preserve eggs by fully covering them. The composite film materials include nano-Fe3+/TiO2 which is fabricated by blending nano-Fe3+ with nano-TiO2 in a solution and then calcining them at 400℃ for 3 hours, PVA (polyvinyl alcohol), and shellac. For antimicrobial film preparation, the first step is preparing the coating film solution by slowly dissolving 5 g/mL PVA in distilled water while stirring and then heating the coating film solutions up to 85°C. The second step is incorporating nano-Fe3+/TiO2, which is dissolved in anhydrous ethanol, into the coating film solution and then shocking composite film solutions with ultrasonic at 65 W/L for 15 min in an ultrasonic bath. The third step is incorporating succinylated monoglycerides and shellac, which are dissolved in anhydrous ethanol into PVA/nano-Fe3+/TiO2 composite film solutions, while stirring and then cooling the solution to 60°C. After preparing the composite film solutions, fresh eggs were used as experimental material and were cleaned and disinfected, and then were coated with composite film. Sensory quality, weight loss, Haugh units (HU), egg yolk coefficient, chromatic aberration, pH, and total number of colonies of different groups were measured, and quality changes of different treatment groups were compared during their storage period. The result shows that quality indicators of fresh eggs in different groups significantly changed (P<0.05). The total number of colonies of fresh eggs during the storage period had a significant upward trend. The shelf life of fresh and cleaned eggs was 20-30 d depend on the change of quality indicators. The shelf life of fresh eggs coated by PVA single film was up to 50-60 d, and the shelf life of fresh eggs coated by PVA/shellac/nano-Fe3+/TiO2 composite film was up to 70-80 d. In addition, the preservation properties of fresh eggs coated by PVA/shellac/nano-Fe3+/TiO2 composite film were significantly better than fresh eggs coated by PVA single film, and PVA/shellac/nano-Fe3+/TiO2 composite film significantly reduced the rate of change of weight loss, Haugh unit, and yolk coefficient of fresh eggs during storage period (P<0.05) compared to other groups. Therefore, PVA/shellac/nano-Fe3+/TiO2 composite film achieved the purpose of extending the shelf life of eggs and it can be applied to package fresh eggs. This paper provides reference for the application of nano-modified composite film materials in the preservation of fresh eggs.