Heat-Induced Changes Occurring in Oil/Water Emulsions Stabilized by Soy Glycinin and β-Conglycinin

Abstract

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.

Covalent modification of soy protein isolate by (−)‐epigallocatechin‐3‐gallate: effects on structural and emulsifying properties

“…In general, the droplet size tends to decrease with the increase in protein concentration, and increases with extended storage time. Similar trends have been widely observed for O/W emulsions made with protein stabilizers, such as sodium caseinate, soybean protein, and wheat gluten . The initial droplet sizes of modified SPI are slightly smaller than those of unmodified SPI ( P > 0.05) at low concentrations (10 and 20 mg mL −1 ).…”

“…Similar trends have been widely observed for O/W emulsions made with protein stabilizers, such as sodium caseinate, soybean protein, and wheat gluten. [33][34][35] The initial droplet sizes of modified SPI are slightly smaller than those of unmodified SPI (P > 0.05) at low concentrations (10 and 20 mg mL −1 ). As the concentration rose to 30 mg mL −1 , the initial droplet size of the emulsion stabilized by modified SPI was significantly smaller than that of unmodified SPI (P < 0.05).…”

Adsorption of Soy Protein Isolate in Oil‐in‐Water Emulsions: Difference Between Native and Spray Dried Isolate

“…1). These finding are in agreement with previous studies [10,16,27]. The thermal transition of the PP-SPI was quite different from that of the N-SPI solution (Fig.…”

Stabilization of acidic soy protein-based dispersions and emulsions by soy soluble polysaccharides

“…bconglycinin is a w180 kDa trimer consisting of three subunits (a, a 0 , and b of 62, 65, and 47 kDa, respectively) (Thanh & Shibasaki, 1976;Utsumi & Kinsella, 1985). Both glycinin and b-conglycinin have emulsifying ability and are capable of stabilizing emulsions by lowering the interfacial tension between water and oil and by forming 30e40 nm thick adsorbed layers (Keerati-u-rai & Corredig, 2010) at the oilewater interface (Aoki, Taneyama, & Inami, 1980;Mitidieri & Wagner, 2002;Molina, Papadopoulou, & Ledward, 2000;Palazolo, Mitidieri, & Wagner, 2003). They are most effective at pH values away from their isoelectric points (IEP) (pH w 4.6) where their solubility is highest (Aoki et al, 1980).…”