Rheological properties and conformational states of β‐conglycinin gels at acidic pH

Abstract

SYNOPSISThe heat-induced gelation of P-conglycinin was investigated by dynamic viscoelastic measurements as a function of pH. At pH values below 5.5-6.0, the storage modulus G' rapidly increased with decreasing pH. The conformational states of both sols and gels of @-conglycinin were investigated by Fourier transform ir (FTIR) and by differential scanning calorimetry (DSC). The degree of protonation of the carboxyl groups of P-conglycinin, when examined by FTIR indicated that, as would be expected, the degree of protonation increased with decreasing pH below pH 6.0. DSC measurements suggest that 8-conglycinin tends toward thermal denaturation with decreasing pH (below pH 6.0). Second-derivative FTIR spectra for P-conglycinin gels show that a band at 1620 cm-' (associated with exposed &strands) develops with decreasing pH. The results suggest that P-conglycinin undergoes denaturation with increasing protonation of its carboxyl groups, resulting in an increase in the amount of exposed P-strands. The exposed P-strands then intermolecularly bond to form gel networks. This process is promoted with decreasing pH, and as a result, rigid gels form at acidic pH values.

Thermal behavior of emulsions manufactured with soy protein ingredients

“…The pH-dependent trends in HCTs in these emulsion results are consistent with those found by Hermansson (1977), Hermansson (1978), Iwabuchi, Watanabe, and Yamauchi (1991), Mohamed and Xu (2003) and Ryan et al (2008), where intact soy protein dispersions were found to be more heat stable at alkaline than at acidic pH. Nagano, Mori, and Nishinari (1994) also reported that lowering the pH caused the denaturation temperature of SPI, glycinin and b-conglycinin to shift to lower values which may, in part, also explain the results obtained. From Fig.…”

“…For example, the heat-induced aggregation behavior (40-100°C) of soy b-conglycinin in the presence of 2.5% (w/v) NaCl has been attributed to a reduction in the net surface charge density of the denatured protein promoting hydrophobic aggregation (Nagano et al, 1994). Furthermore, the observed decrease in HCT of milk protein on supplementation with Ca 2+ was attributed to the shielding of negative charges inducing a reduction in electrostatic repulsion between protein molecules leading to their subsequent aggregation (McCrae & Muir, 1995).…”

“…It appears that the degree of protonation of carboxyl groups provide a driving force for protein denaturation at low pH because of a change in the balance of electrostatic forces. When the pH is lowered, the distribution of charged sites is altered, resulting in mutual repulsion that, in turn, favours transition from a compact conformation to a denatured state (Nagano et al, 1994).…”

Physicochemical properties and microstructure of soy protein hydrogels co-induced by Maillard type cross-linking and salts

“…Their functional properties are used mainly to form three-dimensional networks such as hydrogels. A range of methods for gelling soy protein have been developed, from thermal gelation (Hermansson, 1985;Nagano, Akasaka, & Nishinari, 1994;Nagano, Hirotsuka, Mori, Kohyama, & Nishinari, 1992;Nagano, Mori, & Nishinari, 1994;Renkema, 2004;Renkema, Gruppen, & van Vliet, 2002;Renkema, Knabben, & van Vliet, 2001;Renkema, Lakemond, de Jongh, Gruppen, & van Vliet, 2000;Renkema & van Vliet, 2004;van Vliet, Martin, & Bos, 2002) to cold-set hydrogel formation (Maltais, Remondetto, Gonzalez, & Subirade, 2005;Maltais, Remondetto, & Subirade, 2008).…”

Study of conformation of vicilin from Dolichos lablab and Phaseolus calcaratus by Fourier-transform infrared spectroscopy and differential scanning calorimetry

“…Both FTIR and DSC have been used to study the structure and conformation of buckwheat globulin (Choi & Ma, 2005), soybean glycinin and b-conglycinin (Nagano, Akasaka, & Nishinari, 1995;Nagano, Mori, & Nishinari, 1994;Petruccelli & Añón, 1996), b-lactoglobulin (Boye, Ma, & Ismail, 1998;Boye, Ma, & Ismail, 2004), oat globulin (Harwalkar & Ma, 1987;Ma, Rout, & Mock, 2001) and bovine serum albumin (Boye, Alli, & Ismail, 1996).…”