No abstract

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