Relationship between the method of obtention and the structural and functional properties of soy protein isolates. 2. Surface properties.
Petruccelli S. | Anon M.C.
The surface properties of soy protein isolates that had been exposed to different neutralization conditions (pH 7 or 9), thermal treatments (98 degrees C, 5 and 30 mini 80 and 92 degrees C, 6 and 12 min), reduction conditions (0.05% Na2SO3; 0.05% Na2SO3-6 M urea or 2% Na2SO3), and enrichment on 7S or 11S fractions were studied. These treatments affected the 7S and 11S contents, degree of denaturation and aggregation, surface hydrophobicity, content of free sulfhydryl groups, etc. The behavior of isolates was evaluated by means of parameters that provide information about the different stages in the emulsion formation and stabilization processes. It was found that isolates having the best emulsifying properties were those exposed to a short thermal treatment, and the isolates chemically reduced in the presence of Na2SO3 and urea have a high surface hydrophobicity and solubility. Better emulsifying properties were found in isolates at pH 9 than at pH 7, as well as in those enriched in 7S. Electrophoretic analysis of the remaining components in the aqueous phase showed a lower migration to the emulsion interface of A-11S polypeptide than the rest of protein species (alpha, alpha, and beta-7S, and B-11S polypeptide). Nondialyzed isolates were better foaming agents than dialyzed isolates. Modifications of either 7S or 11S content had no effect on the foaming properties.
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