Emulsifying and Interfacial Properties of Vicilins: Role of Conformational Flexibility at Quaternary and/or Tertiary Levels

Abstract

Although the functionality of plant proteins (and soy proteins in particular) has been widely investigated in the last decades, the importance of conformational characteristics to their functionalities is still far away from being understood. The aim of the present work was to unravel the role of conformational flexibility at the quaternary and/or tertiary levels in the emulsifying and interfacial properties of phaseolin, an ideal vicilin (or 7S globulin) from red kidney bean. The conformational flexibility at quaternary and tertiary levels of phaseolin was modulated by urea with increasing concentrations from 0 to 8 M, as characterized by using dynamic light scattering (DLS), intrinsic fluorescence and derivative UV spectroscopy, and differential scanning calorimetry (DSC). The emulsifying and interfacial properties, including emulsifying ability, flocculated state of oil droplets (in fresh emulsions), emulsion stability against creaming, and adsorption dynamics at the oil-water interface, were characterized at a specific protein concentration of 0.5% (w/v). The results indicated that increasing the urea concentration resulted in a progressive dissociation of trimeric phaseolin molecules into monomeric subunits, and even a structural unfolding of dissociated subunits; the urea-induced conformational changes at quaternary and/or tertiary levels were reversible, and the molecules at high urea concentrations shared similar structural features to the "molten globule state". On the other hand, increasing the urea concentration progressively improved the emulsifying ability of the protein, and flocculated extent of oil droplets in the fresh emulsions, but led to a progressive decrease in interfacial protein concentration. The improvement of the emulsifying ability was not related to diffusion (during initial adsorption) and penetration at the interface, but highly dependent on ease of structural rearrangement of the adsorbed proteins. These observations clearly confirmed that the flexibility of phaseolin at quaternary and/or tertiary levels plays a vital role in its emulsifying ability, mainly through the way of affecting the ease of structural rearrangement of adsorbed proteins at the interface. The findings could provide an in-depth understanding of the importance of conformational flexibility for the emulsifying properties of oligomeric storage globulins, and thus are of great help to guide the modifications of the proteins for better emulsifying properties.

Foaming, emulsifying properties and surface hydrophobicity of soy proteins isolate as affected by peracetic acid oxidation

“…The above results indicated that although peracetic acid oxidation could significantly change the emulsifying properties of SPI, the SPI structural changes caused by different peracetic acid concentrations only showed differences in the emulsifying stability of oxidized SPI, but not in the emulsifying capacity of oxidized SPI. This is consistent with the works of Tang et al [29,30] They found that the conformational flexibility plays a crucial role in different aspects of emulsifying properties; however, the progressive improvement of the emulsifying ability is not related to the initial adsorption rate and amount of adsorbed proteins, but highly dependent on the ease of structural rearrangement of adsorbed proteins at the interface. Because the emulsifying capacity of SPI was measured at the initial stage of emulsification and the emulsifying stability of SPI was determined after 30 min of emulsification, the changes of protein structure caused by different peracetic acid concentration only showed differences in emulsifying stability, but not in emulsifying ability.…”

Nanocomplexation of soy protein isolate with curcumin: Influence of ultrasonic treatment

“…3 B and C. The size of particles in the non-treated SPI solution ranged from 4 to 100 nm, with D z calculated to be around 52 nm (Figs. 2 and 3 A), which is well consistent with the observations of our previous work (Liu & Tang, 2013), confirming the prominence of 7S-or 11S-form proteins in the SPI (Liang & Tang, 2013;Utsumi, Matsumura, & Mori, 1997). After the ultrasonic treatment, the particle size distribution of SPI was slightly shifted towards lower sizes, while the D z slightly but insignificantly declined (Figs.…”

Physicochemical and functional characteristics of plant protein‐based meat analogs

“…Several researchers explained that the dissociation and partial unfolding of globular proteins led to the exposure of hydrophobic amino acids residues resulted in increased surface activity and adsorption of higher EA proteins at the oil and water interface (Ghribi et al, ; Nir, Feldman, Aserin, & Garti, ). The flexibility of proteins at quaternary and/or tertiary levels might also affect the ease of structural rearrangement of adsorbed proteins at the interface (Liang & Tang, ). The effect of pH on EA and ES (Figure ) have shown a similar trend as the protein solubility (Figure ), which was in agreement with the study of Chau et al ().…”