Effect of Alkali Treatments on the Physicochemical Properties of Egg White Gels
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Abstract:
Difference of gel properties and the mechanisms between alkali-induced egg white gel and lime-preserved egg white were investigated by studying the variations of texture profile analysis (TPA), solubility, sulphydryl content, disulfide bond content, surface hydrophobicity, protein fractions, microstructure and protein secondary structure of egg white gels obtained from different alkali treatments. The results showed that protein molecules of egg white obtained from both alkali treatments formed highly cross-linked gel network structures, and closer and more orderly protein aggregates with denser network were observed in alkali-induced egg white gel. The hardness (186.73±3.29 g), cohesiveness (0.98±0.02), chewiness (176.21±6.13), solubility (55.68±1.20%), exposed sulphydryl content (60.34±1.01 μmol/g) and disulfide bond content (29.42±0.57 μmol/g) of alkali-induced egg white gel were higher than that of lime-preserved egg white, while total sulphydryl content (64.60±2.28 μmol/g) and surface hydrophobicity (419.80±17.22) were lower. Protein secondary structure of alkali-induced egg white gel was mainly in β-sheet (31.24%), which showed the strong total hydrogen bonding interaction in the molecules. And the content of α+β conformation (33.65%) was lower in protein secondary structure for the lime-preserved egg white, but contents of β1 (21.21%), T-turn (25.36%) and γ-random (19.78%) coil were higher. Therefore, egg white proteins denatured obviously by the two alkali treatments.
