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Interaction of hydrocolloids (xanthan gum, locust bean gum, guar gum, and high-methoxyl pectin) with macrocomponents of dough (water, starch, and protein) was evaluated by different techniques. (1)H spin-spin NMR relaxation assays were applied to study the mobility of the gluten-hydrocolloid-water matrix, and the amount of freezable water was determined by differential scanning calorimetry (DSC). Starch gelatinization parameters (T, enthalpy) were also analyzed by DSC. The influence of additives on the protein matrix was studied by Fourier transform (FT) Raman assays; analysis of the extracted gliadins and glutenins was performed by electrophoresis (SDS-PAGE). A significantly higher molecular mobility was found in matrices containing xanthan gum, whereas pectin led to the lowest molecular mobility. Freezable water showed a trend of increasing in the presence of hydrocolloids, particularly under conditions of water restriction. Starch gelatinization final temperature was decreased when hydrocolloids were added in the presence of enough water. In general, FT-Raman and SDS-PAGE indicated that hydrocolloid addition promoted a more disordered and labile network, particularly in the case of pectin addition. On the other hand, results obtained for dough with guar gum would indicate a good compatibility between this hydrocolloid and the gluten network.

Hydration properties of acidic soy protein gels, prepared with different salt solutions, were studied. The type of bonds that stabilize gel structure and the nature of protein species that make up and stabilize such structure were also investigated. The microstructure of gels was evaluated by scanning electron microscopy (SEM) and water-holding capacity (WHC) assays. The stability and nature of protein fractions of gel matrices were analyzed by solubility measurements and sodium dodecyl sulfate−polyacrylamide gel electrophoresis. The WHC of gels prepared with NaCl and CaCl2 decreased with increasing salt concentration. This fact suggested, as was corroborated by gel SEM, that at high ionic strength a more open matrix was formed. The structure of acidic gels, stabilized by noncovalent bonds, changed with NaCl addition. Both 7S and 11S globulin subunits participated via hydrophobic interactions to the stability of pH 2.75 gels. At pH 3.50 the gel matrix was stabilized by hydrophobic interactions among β-conglycinin subunits, whereas the AB-11S subunit and the AB-11S polymers, linked by disulfide bonds, would be soluble in the matrix interior due to the glycinin fraction that remains native after thermal treatment. Keywords: Soy protein gelation; gelation in acidic conditions; heat-induced gelation; salt effect; gel protein structure

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

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