Rheological Analysis of the Aggregation Behavior of a Soymilk Colloidal System

Abstract

The applicability of Einstein's and Krieger-Dougherty's theories of viscosity was examined using soymilk. Under dilute conditions, the relative viscosity of the emulsion with suspended oil bodies was proportional to the volume fraction of oil bodies, and the slope increased to greater than 2.5. Under concentrated conditions, the oil body suspension showed a Krieger-Dougherty-like dependency on volume fraction. The oil bodies in soymilk behaved as suspended substances and it was possible for us to predict the relative viscosity from the volume fraction of oil bodies. We also focused on the coagulation of soymilk by magnesium chloride and examined the validity of the novel viscous model, combining the extended Einstein equation and the Krieger-Dougherty equation, on the effect of crosslinkers. At 10℃ and 25℃, the equation could be applied to various soymilk samples. In addition, the viscosity during coagulation could be predicted when the parameter h c of the dispersion system was utilized.Keywords: soymilk, einstein, Krieger-Dougherty, rheology, oil body, suspension IntroductionSoymilk production has increased because of the heightened consumer interest in the functionality of this protein-laden beverage.There has been a significant amount of research published about soybean proteins (Mori et al., 1986;Thanh and Shibasaki, 1977;Yuan et al., 2009) and soybean protein isolates as new food materials (Campbell et al., 2009;Fukushima, 2001). However, very little information about the physicochemical properties of soymilk is available (Nik et al., 2008;Nsofor and Osuji, 1997;Ringgenberg et al., 2012). Understanding the physicochemical properties of soymilk, including viscosity, is required in the development of soymilk products. Viscosity equations were developed in order to predict viscosity in colloidal food systems. Viscosity is a physical property that can be effectively utilized in characterizing the effect of quality control of a manufacturing process or mechanical and thermal processing. Soymilk is a colloidal system produced as an extract from swelled and ground soybeans; therefore, almost all of the components (protein, lipid, and saccharides) of the soybean seeds are present in the soymilk (Shurtleff and Aoyagi, 2000). It was reported that about 70% of the lipids in soybeans were extracted to the soymilk (Poysa and Woodrow, 2002). Dispersed substances consist of oil bodies and protein particles and the dispersion medium is the liquid containing the dissolved proteins, sugars, and minerals such as potassium. Oil bodies consist of a triacylglycerol (TAG) matrix core surrounded by a layer of phospholipids and intrinsic oleosin (Li et al., 2001;Tzen and Huang, 1992). The average particle diameter of an oil body in soymilk is approx. 250 nm (Iwanaga et al., 2007). Oil bodies containing soymilk lipids were stabilized by the presence of oleosin and phospholipids on their surface (Chen and Ono, 2010).Einstein developed a theory for the viscosity of a dilute suspension of small hard spheres in a continuous fluid (Eins...

Coagulation and rheological behaviors of soy milk colloidal dispersions

“…Furthermore, the higher the solid content, the smaller K c becomes, indicating that the packing state for massive aggregates formed in high cross-linking agent concentrations becomes looser the higher the solid content. 27) Applying this viscosity model to soy milk samples of various concentrations revealed a negative correlation between the h c and K c parameters obtained (Fig. 8) and the looser packing state in soy milk where bulky clusters formed was also experimentally proven.…”

“…1). 27) These results suggest that oil bodies behave as rigid spheres when they exist in a diluted state and a layer is formed at the interface between the surfaces of oil body and the dispersion medium that contributes hydrodynamically. In addition, it was found that in a suspension in which oil bodies are added to a continuous phase of defatted soymilk the viscosity of suspension tended to diverse at a lower oil body volume fraction condition compared with a system in which oil bodies are suspended in a buffer solution.…”

“…This suggests that oil bodies in soy milk behave like suspended matter and that relative viscosities can be predicted from the oil body volume fraction. 27) The coagulation process of soy milk using a crosslinking agent was selected as a system in which there is a marked change in dispersion state. This system was studied using a viscosity theory that takes into account cross-linking.…”

Influence of Acidity Regulators on the Stability of a Soymilk Colloidal Dispersion System

“…In contrast, as the size of the aggregate decreased, bulky aggregates became more bulky. Additionally, because the data were plotted on the same curve regardless of the type of acidity regulators, even if the internal structure of the isolated aggregate differed depending on the difference in crosslinking mechanism, the macroscopic aggregation behaviors were thought to be similar.Even when coagulating with a crosslinking agent such as magnesium chloride, a negative correlation between h c and K c is obtained in previous work[20]. In crosslinking aggregation, the interaction between colloidal particles is electrostatic interaction.…”

Effect of Oleosins on the Stability of Oil Bodies in Soymilk

“…Additionally, regarding the stability of colloidal particles at different pH values, it was suggested that the lipid content of the soybeans affected the stability of the soymilk (Oizumi et al, 2016). Furthermore, in the colloidal soymilk dispersion system, an interaction between lipids and proteins was identified; the effect of increased concentrations of magnesium chloride on the lipids was also examined (Toda et al, 2008;Idogawa and Fujii, 2015;Fujii, 2017). Based on these findings, it was suggested that the presence of proteins and lipids in soymilk has an important effect on colloidal stability.…”