No abstract

No abstract

Although soy proteins are often employed as functional ingredients in oil-water emulsions, very little is known about the aggregation state of the proteins in solution and whether any changes occur to soy protein dispersions during homogenization. The effect of dynamic high pressure homogenization on the aggregation state of the proteins was investigated using microdifferential scanning calorimetry and high performance size exclusion chromatography coupled with multiangle laser light scattering. Soy protein isolates as well as glycinin and beta-conglycinin fractions were prepared from defatted soy flakes and redispersed in 50 mM sodium phosphate buffer at pH 7.4. The dispersions were then subjected to homogenization at two different pressures, 26 and 65 MPa. The results demonstrated that dynamic high pressure homogenization causes changes in the supramolecular structure of the soy proteins. Both beta-conglycinin and glycinin samples had an increased temperature of denaturation after homogenization. The chromatographic elution profile showed a reduction in the aggregate concentration with homogenization pressure for beta-conglycinin and an increase in the size of the soluble aggregates for glycinin and soy protein isolate.

Glycinin and β-conglycinin are the two major proteins in soy protein isolate, and their emulsifying behavior was the subject of this study. These proteins form a thin layer of 30-40 nm when adsorbed at the interface. Microcalorimetric experiments showed that the thermal transitions of these proteins in the emulsion were very similar to those of the proteins in solution. The results also suggested that molecular rearrangements occurred during adsorption of β-conglycinin, as an endothermic transition peak appeared at high temperature when this protein was present at the interface. In general, β-conglycinin exhibited greater emulsifying activity than glycinin, confirming previous reports. Heating at 95 °C for 15 min caused a decrease in solubility of glycinin, and interactions between the oil droplets, with an increase in the apparent viscosity, shear thinning behavior, and droplet particle size distribution of the emulsions. While, similar behavior was noted in b-conglycinin after heating at both 75 and 95 °C. Furthermore, the order of processing affected the subunits' composition at the interface. Heating the solution before emulsification caused a higher protein load at the interface and with all of the subunits present. On the other hand, when heating was carried out after homogenization, the basic glycinin polypeptide and the β subunit of β-conglycinin were absent from the interface, suggesting that heat-induced complexes between these subunits formed and remained soluble in the unadsorbed phase.

No abstract