Mechanism of Enzyme-Assisted Aqueous Extraction of Soybean Oil

Aqueous extraction processing (AEP) of soy is a promising green alternative to hexane extraction processing. To improve AEP oil yields, experiments were conducted to probe the mechanism of oil release and the effects of mechanical and enzymatic treatments. Microscopy of extruded soy flakes before and after both simple aqueous and protease-assisted aqueous extraction indicated that unextracted oil is sequestered in an insoluble matrix of denatured protein and that protease addition reduces the integrity of this matrix. With the mechanical treatment of milling the soy flakes to a flour, unextracted oil is contained as intact oil bodies in undisrupted cells, or as coalesced oil droplets too large to pass out of the disrupted cellular matrix.

These results suggested that emulsification was needed to reduce the size of oil droplets to enable release from the residual barriers and increase yield. Protease and SDS were both successful in increasing extraction yields, and we propose that this was because they disrupted a viscoelastic protein film at the droplet interface, facilitating droplet disruption. An extraction model based on oil droplet coalescence and the formation of a viscoelastic film was able to fit kinetic extraction data well.