Novel pickering high internal phase emulsion gels stabilized solely by soy β-conglycinin

Abstract

There is fast increasing interest in the development of food-grade high internal phase emulsions (HIPEs). In the work, we reported that native soy β-conglycinin (β-CG; a major 7S globulin in soybeans) could perform as an outstanding Pickering-type stabilizer for oil-in-water HIPEs. The protein concentration in the continuous phase (c) for the formation of homogenous and gel-like HIPEs could be as low as 0.2 wt%; and increasing the c from 0.2 to 1.0 wt% led to a progressive decrease in droplet size, but a progressive increase in stiffness of the HIPEs. The fabricated HIPEs at low c values (e.g., 0.2–0.5 wt%) were a kind of HIPE gels in essence with a gel network that could not be disrupted by 6 M urea, while the HIPE at c = 1.0 wt% was a highly concentrated emulsion that could be diluted by water. All the HIPEs at c values of 0.2–1.0 wt% were extremely stable against heating (at 100 °C for 15 min), or an elongated storage up to 60 days, but they were very prone to a freeze-thawing treatment. The freeze-thawed HIPEs could be repeatedly recovered back to a similar state to the untreated ones, when subject to another emulsification, indicating an extraordinary temperature-responsiveness. The β-CG molecules suffered a structural dissociation at the quaternary conformational level into separate subunits when adsorbed at the oil-water interface. The dissociated subunits from adsorbed β-CG showed a similar tertiary and secondary conformation to that of native β-CG, confirming the Pickering-nature of these subunits. All the HIPEs exhibited a surface coverage of around 60% in regard to the subunits of β-CG. The findings would be of importance not only for extending the knowledge about the Pickering stabilization of HIPEs by native oligomeric globulins, but also for the development of novel, eco-friendly and sustainable HIPEs for food, cosmetic and medicine formulations.