pH-Induced modifications in the thermal stability of soybean protein isolates
1996
Petruccelli, S. | Anon, M.C.
pH-induced modifications in the thermal stability of soybean protein isolates were studied by differential scanning calorimetry. The thermal stability of the 11S globulin was higher than that of the 7S globulin and was very sensitive to pH changes. The glycinin denaturation temperature decreased by 10 degrees C when the pH was increased from 6 to 11, while the 7S globulin denaturation temperature did not change. At pH 11, soybean isolate gave only one endotherm representing both globulins. 11S globulin underwent conformational changes as the pH increased, which were reflected by lower cooperativity in the denaturation process. 11S globulin also had a higher activation energy for the denaturation process than did 7S globulin. The activation energy of 11S globulin was higher than that of 7S globulin (in the pH 6-10 range) and shows a maximum kinetic stability at pH 8. The 7S and 11S globulin half-lives at different treatment temperatures were calculated to pHs between 6 and 11, and thermal treatments causing different degrees of denaturation were carried out to produce a maximum increase of the surface hydrophobicity (Ho). For thermally untreated isolates, the increase in pH led to an increase in exposed hydrophobicity. The combination of pH 10-11 and thermal treatments at temperatures of about 66 degrees C led to higher exposure of hydrophobic groups, conditions for which would be most suitable for obtaining isolates with a higher emulsifying capacity. Denaturing thermal treatments at this pH value induced aggregation along with thus a fall in Ho.
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