Egg storage causes egg white to lose its viscous nature to form a thin liquid, commonly referred to as egg white thinning. To understand the mechanisms underlying egg white thinning, white-shell eggs were used in the present study to determine the proteome-level changes of egg white proteins occurred during storage. Egg white thinning was observed visually after 20 days of storage at ambient temperature (22 ± 2 °C) when the maximum number of proteome-level changes occurred. The proteins that showed significant changes in abundance during storage included ovalbumin, clusterin, ovoinhibitor, ovotransferrin, and prostaglandin D2 synthase. Among these, only the abundance of clusterin was observed to change continuously during the storage period. Hence, it is expected that the increase in the concentrations of clusterin and ovoinhibitor along with the change of ovalbumin content during storage might contribute to egg white thinning. Degradation of ovalbumin/clusterin during egg storage may be due to the combined effect of proteolysis and increase in pH; this may also be partly responsible for egg white thinning phenomenon.

Ovomucin, a key component in maintaining the viscous nature of egg white, is a glycoprotein contributing to 2-4% of the total egg albumin protein. Preparation of pure ovomucin remains a challenge due to the presence of coprecipitated proteins, mainly ovalbumin and lysozyme. The objectives of the study were to determine the effect of different salt concentrations on the extractability of ovomucin and to develop a simple method to purify ovomucin that could be adapted for further scale-up production. The protein compositions of ovomucin extracts were significantly affected by salt concentrations. The concentration of ovalbumin was increased, whereas that of lysozyme was decreased in the ovomucin extracts at increasing salt concentrations up to 500 mM; lysozyme was the major contaminant at low salt concentrations (<100 mM), whereas ovalbumin was the major contaminant at high concentrations (>or=200 mM). A 2-step method was developed for the first time to prepare ovomucin with a purity of greater than 90%. Egg white was first extracted in the presence of 100 mM NaCl at pH 6.0 to produce a precipitate containing moderate coprecipitated ovalbumin (14.6%) and lysozyme (15.9%); the contaminated proteins in the precipitate were further removed by using 500 mM NaCl. The yield of ovomucin was determined to be 400.2 mg/100 g of egg white. This 2-step method is simple, environmentally friendly, and easy for scale-up preparation.

Ovomucin, accounting for w3.5% of total egg white protein, is responsible for the thick gel characteristics of liquid egg white. Besides its excellent foaming and emulsion capacities, it possesses anti-viral, anti-bacterial, anti-tumor and other bioactivities. This paper reviews compositional, structural, physicochemical, functional and biological properties of ovomucin, as well as development of methods of extraction. As one of the least defined proteins in egg white, further study is required to characterize the structure and to explore its full potential in new applications as functional foods and nutraceuticals.

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