UBC Theses and Dissertations
A study of protein surface hydrophobicity and structure-function analysis of proteins in spray dried egg albumen Cheng, Eugene S. Y.
In examining functional properties of food proteins, the ultimate goal of all researchers is to understand basic information relating functional properties to particular conformational or structural features of the protein. It is generally accepted that the molecular property of hydrophobicity plays an important role in the function of food proteins. In the first part of the thesis, surface hydrophobicity (S₀) of 10 proteins, under varying conditions of pH (3.0, 7.0, and 9.0) and salt concentrations (0.01 and 1.0 M NaCl), measured using an uncharged fluorescent probe, PRODAN (6-propionyl-2- (dimethylamino)naphthalene) was compared with S₀ determined with an anionic probe, ANS (l-anilinonaphthalene-8- sulfonate). S₀ values measured by both PRODAN and ANS for each protein were statistically different (P < 0.05) as a function of pH and salt concentration. Overall, lowest S₀ values using PRODAN were found at pH 3.0, while S₀ values using ANS were generally higher at acidic than neutral or alkaline pH. These results demonstrate the need to consider charged probeprotein interactions when applying anionic fluorescent probes for surface hydrophobicity quantification. In the second part of the thesis, the structure-function relationships of spray dried egg albumen and its functional properties (e.g. gelation and foaming properties) were investigated. Protein structure was evaluated by measurement of surface hydrophobicity, net charge as zeta potential (ZP), sulfhydryl (SH) and disulfide (SS) groups, and by differential scanning calorimetry. Simple linear correlations were performed to better understand the structure-function relationship between structural parameters and functionality (gel strength and foam volume). In general, gel strength was positively correlated with S₀ determined by ANS, reactive S H groups, SS bonds and ZP (P < 0.001) and negatively correlated with total SH groups (P = 0.009). In general, foam volume was positively correlated with S₀ determined by PROD AN and ANS, reactive SH groups, and SS bonds (P < 0.05) and negatively correlated with total SH groups and ZP (P < 0.05). Significant correlations of structural properties to gel strength and foam volume were observed by multiple regression analysis using a full quadratic model (R² = 0.956 and R² = 0.918, respectively; P < 0.001; n = 53).
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