Thermally induced protein gelation: Gelation and rheological characterization of highly concentrated ovalbumin and soybean protein gels

Abstract

SynopsisIn order to optimize the use of proteins as functional ingredients in foods, one needs more insight into the effects of environmental conditions (pH, ionic strength, and temperature) on the functional properties of protein. This paper summarizes the results of an extensive study on heat-induced gelation of ovalbumin (egg-white protein) and soybean protein in the concentration range from 10 to 35 g/100 g. It was the aim of the study to relate the rheological properties of thermally induced protein gels to the microstructure of the gel and the physicochemical properties of the constituent protein.The gelling behavior of the protein was quantified with rheological techniques, and the physical properties of the gels were determined, at small and large deformations. From the swelling/dissolving behavior of the gels in various media, the nature of the crosslinks was determined qualitatively. The microstructure of the gels was determined with electron microscopy. Nmr-spectroscopy was applied in order to elucidate changes in conformation during heating. It was found that the formation of a continuous covalently crosslinked network is not a prerequisite for thermally-induced protein gelation. The properties of a gel strongly depend on the pH at which the gel is formed. When heatset at high pH(pH-lo), a homogeneous, strong, and almost transparent gel is formed, consisting of flexible crosslinked protein gels. Heat-setting at low pH (pH 5) leads to the formation of a heterogeneous and weak gel, which easily exudes water. This gel consists of crosslinked aggregated protein. The ionic strength of the solvent in which the protein is dissolved and heat-set has a much lower effect on gel properties.

Contribution of Disulfide Bonding to Viscoelastic Properties and Microstructures of 11S Globulin Gels from Soybeans: Magnesium Chloride-Induced Gels

“…These viscoelastic data indicate that 11S formed stiffer and more solid gels than SPI. These results are consistent with previous reports that of all the soybean proteins, 11S has the greatest ability to form heat-induced gels (Saio et al, 1973;van Kleef, 1986;Nakamura et al, 1986;Renkema et al, 2001).…”

“…These viscoelastic data indicate that 11S formed stiffer and more solid gels than SPI. These results are consistent with previous reports that of all the soybean proteins, 11S has the greatest ability to form heat-induced gels (Saio et al, 1973;van Kleef, 1986;Nakamura et al, 1986;Renkema et al, 2001).Effect of 2-mercaptoethanol (2-ME) on viscoelastic properties of 11S and SPI gels The reducing agent 2-ME prevents disulfide bond formation between protein molecules during the formation of heat-induced gels (Utsumi and Kinsella, 1985ab). Therefore, to examine the contribution of disulfide bonds to gel structure, the effects of 2-ME on emission was measured at 580 − 690 nm.…”

“…Soybean protein isolate (SPI) is prepared from water-extracted soybean proteins by acidic precipitation and consists mainly of 7S and 11S. Rheological properties of heat-induced 7S, 11S, and SPI gels have been extensively studied (Saio et al, 1973;Hermansson, 1986;van Kleef, 1986;Nakamura et al, 1986;Yamauchi et al, 1991; Nagano et al, 1994ab;Renkema et al, 2001;Lakemond et al, 2003;Renkema, 2004). Most studies have reported that of all the soybean proteins, 11S has the greatest ability to form heatinduced gels.…”

Gelation properties of salt-extracted pea protein isolate induced by heat treatment: Effect of heating and cooling rate

“…Globular proteins from various sources play important roles in many foods, both because of their nutritional value and their contribution to food texture (van Kleef, 1986). These textural contributions come from the network structures created by protein crosslinking.…”

Protein–Protein Interactions in High Moisture‐Extruded Meat Analogs and Heat‐Induced Soy Protein Gels

“…Protein gels consist of a threedimensional network in which water is entrapped. The main interactions found in soy protein gels are also disulfide linkages, hydrophobic and electrostatic interactions [15][16][17][18][19][20]. Therefore, some early studies on the mechanism of protein-protein interaction during extrusion tended to consider the structure of extrudates (products formed after extrusion) as being similar to a protein gel [7].…”