The effect of pH on heat denaturation and gel forming properties of soy proteins

This study is focussed on the influence of pH on the gel forming properties of soy protein isolate and purified glycinin in relation to denaturation a nd aggregation. At pH 7.6 more fine-stranded gels were formed characterised by low G' values, and a smooth, slightly turbid appearance, whereas at pH 3.8 coarse gels were obtained with a high stiffness and a granulated, white appearance. Low G' values, as found at pH 7.6, correlate with a high solub ility of glycinin and soy protein isolate (ca. 50%) after heating at low pr otein concentration. At pH 3.8 all protein precipitated upon heating, which correlates with relatively high G' values. The role of beta-conglycinin du ring gelation of SPI seems to be minor at pH 7.6, which is indicated by the fact that, in contrast to pH 3.8, notable gel formation did not start upon heat denaturation of beta-conglycinin. Furthermore, the mechanism of gel f ormation seems to be affected by pH, because at pH 7.6, in contrast to pH 3 .8, the disulphide bridge between the acidic and the basic polypeptide of g lycinin is broken upon heating. (C) 2000 Elsevier Science B.V. All rights r eserved.