Microbial desugarization of native and treated egg white
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Native egg white, lysozyme-reduced egg white, and the addition of iron, aluminum, and zinc chloride as substrates were used to study bacterial desugarization. Six bacteria were selected; Klebsiella pneumoniae, Klebsiella oxytoca, Lactobacillus plantarum, Lactobacillus casei, Leuconostoc mesenteroides, and Streptococcus diacetylactis. Removal of 93% of the lysozyme permitted K. oxytoca and K. pneumoniae to grow more rapidly. Gram positive bacteria also grew better in lysozyme-reduced egg white than in native egg white. The addition of iron chloride to native egg white overcame its antimicrobial properties to L. casei. Desugarization was completed within 36 hr. Agarose isoelectric focusing, an electrophoretic technique with high resolution, was used to investigate the effect of bacterial desugarization on egg white proteins. Using Pharmalyte in the pH range of 4.0-6.5 proved appropriate for the separation of egg white proteins. Bacterial desugarization reduced the level of 3 proteins (pl = 5.09, 5.57, and 5.72) in egg white. Three forms of ovotransferrin and iron-ovotransferrin complexes were found when 0.36 mM iron chloride was added to egg white at pH 7.0. Zinc ions were loosely bound to ovotransferrin as indicated by the intensity of 3 zinc-ovotransferrin protein bands. Three metallic ions (ZnCI2 , FeCI3, and AICI3) were used at various pH and concentration levels to desugar egg white with K. oxytoca and L. casei. The growth of K. oxytoca in egg white containing iron chloride was primarily dependent on pH. Both the availability of free iron and the ability of L. casei to compete with ovotransferrin for iron appeared to be affected by pH. The concentration of iron needed to saturate ovotransferrin at pH 6.0 was 0.36 mM whereas saturation was achieved with about 1.44 mM of iron at pH 7.0. Thus, it was concluded that at the lower pH, the equilibrium was shifted toward the bound state. Combination of aluminum chloride and high pH had a positive affect on the growth of K. oxytoca . Zinc was toxic to K. oxytoca and L. casei at high concentration and at low pH.
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