Soybean Protein Dispersions at Acid pH. Thermal and Rheological Properties

Abstract

The influence of pH, protein concentration, and ionic strength, on rheological properties of thermally treated acidic soy protein dispersions, was studied. Structural changes due to pH effect and thermal treatment were analized. DSC-thermograms at pH 3.5 showed a shoulder at 74.1160.168C that could be attributed to both b-conglycinin and the hexameric form of glycinin; and a peak at 81.8860.298C corresponding to 11S dodecameric form. At pH 2.75 one endotherm corresponded to denaturation of b-conglycinin. The acidic dispersions presented pseudoplastic behavior with h app values higher than those at pH 8.0. At pH 3.50 the h app was higher than at pH 2.75. The maximum viscoelasticiy was obtained with addition of 0.1 and 0.25M NaCl in the dispersions of pH 3.50 and 2.75, respectively. The increase in viscoelasticity was enhanced by the formation of 11S native fraction dimers.To prepare the acid isolates (pH 2.50, 2.75, 3.00, 3.25, and 3.50) and that at pH 8.0, the isoelectric precipitate was dispersed in distilled water and adjusted to the desired pH with either 2N HCl or 2N NaOH. Dispersions thus obtained were lyophilized.To determine the extent of influence of the pH treatment on protein denaturation, alkaline isolates previously modified by treatment at different pHs were also prepared. Different acid dispersions(pH 2.50-3.0) were prepared from the isoelectric precipitate, by adjusting the pH with 2N HCl; these dispersions were then kept at the corresponding pH for 1h at 20ЊC, and then adjusted to pH 8.0 with 2N NaOH prior to lyophilization. Preparation of 7S and 11S-enriched fractions

Foaming Properties of Soy Protein Isolate Hydrolysates

“…Similar results on the partial hydrolysis of β-conglycinin were previously reported [16], [20]. A partial reversal of the effect of acid treatment resulted from neutralization prior to thermal treatment of HpHs, leading to a DDeg of c.a.…”

Improvement of the Physicochemical Properties of Soybean Proteins by Enzymatic Hydrolysis

“…The thermal stability of glycinin and β-conglycinin at various pH values has been investigated by DSC analysis (Koshiyama, 1972;Puppo & Añón, 1999). The endothermic peak temperature (Tp) of glycinin was lower than that of β-conglycinin in the acidic pH range.…”

Effect of Acid Treatment on Interfacial and Foam Properties of Soy Proteins

“…2) showed two endothermic peaks: one with a lower Td n value, corresponding to the 7S globulin; and another peak corresponding to the 11S globulin, which had already been shown to be a contaminant in the SDS-PAGE analysis [21][22][23][24]. In the thermogram of the 7St sample, the endothermic peak that was attributed to the 11S globulin disappeared, whereas the other endotherm showed lower Td t and ΔHd t values than its native counterpart (the 7Sn sample).…”

“…The SPIn thermogram showed two endothermic peaks characteristic of the thermal denaturation of soybean 7S and 11S globulins [21][22][23][24]. Table 1.…”