Structural Properties of Heat-Induced Soy Protein Gels As Affected by Ionic Strength and pH

Abstract

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

Formation and properties of glycinin-rich and β-conglycinin-rich soy protein isolate gels induced by microbial transglutaminase

“…The thermal properties of MTGase-induced gels of soy proteins (including glycinin-rich and -conglycinin-rich SPIs) were evidently diVerent from that of heat-induced gels. In the heat-induced gelation of soy proteins, the protein denaturation induced by heat treatment is often a prerequisite for gel formation of soy proteins (van Kleef, 1986;Nakamura et al, 1986aNakamura et al, , 1986bPuppo and Añón, 1998;Renkema & Vliet, 2002a,b;Kinesella, 1985a, 1985b), since the exposed hydrophobic areas of denatured proteins can interact and aggregate to form gel-network upon cooling. In this case, the soy protein gels were completely thermoreversible at pH 3.8 or 5.2, and the gel strength declined after reheating-recooling cycle at pH 7.6 (Renkema et al, 2002b).…”

Aggregation of soy/milk mixes during acidification

“…If heating is performed on acidified systems (pH <3.5) acidic gels are stabilized mainly by non-covalent interactions. On the other hand, heating at neutral pH causes disulfide bridging, and the covalent interactions between the various soybean protein subunits (especially the acidic and basic subunits of 11S) strengthen the gel structure (Puppo & Anon, 1998;Puppo, Lupano, & Anon, 1999).…”

A Novel Fermented Food Product Prepared from Soybean Protein-Calcium-Gel with Monascus Fungus: Changes in Protein and Nitrogen Compounds during Fermentation

“…Due to its various physical functions, including gelation, viscosity, emulsification and foaming, (Kohyama et al, 1995, Nagano et al, 1996Puppo and Anon, 1998), soybean protein (SP) has generally been used in fabricated food products such as frozen tofu, ganmodoki, sausages, bacon, and many meatlike products (Adler-Nissen and Olsen, 1979;Smith and Circle, 1980: Parks andCarpenter, 1987). It has been also reported that soybean milk is coagulated by some proteinases (Fuke et al, 1985;Yasuda et al, 1999, Aoyama et al, 2000.…”