Aqueous extraction processing technologies, having advanced in recent years, may be a viable alternative to hexane extraction to separate oil and protein from soybeans. Different extraction strategies incorporating various modes of comminution, extraction buffers, and enzymes allow production of a range of oil and protein products, but also create different processing challenges. Processes capable of achieving high free oil yields often result in a soluble protein fraction difficult to isolate and dilute oil emulsions difficult to break. Other processes can achieve high yields and purities of native soy protein, but with reduced free oil yield or require a high osmotic and ionic strength extraction buffer. This review article discusses these various advanced processes and their relative advantages and disadvantages. In addition, the current understanding of the underlying fundamental concepts of aqueous extraction is discussed in order to help direct future investigations to improve these technologies.

Oleosomes, with their unique structural proteins, the oleosins, are known to be useful in cosmetics and other emulsion applications. A procedure to fractionate intact oleosomes to produce soybean oil without the use of organic solvents was investigated. Process parameters, enzyme treatment, filtration, cell lysis, and centrifugation, were studied. Successive extractions of the residue, eliminating the filtration step, pressurization, or ultrasonication of soybean flour prior to enzyme treatment and enzyme treatment on the residue, were the key steps. A mixture of Multifect Pectinase FE, Cellulase A, and Multifect CX 13L in equal proportion gave 36.42-63.23% of the total soybean oil from oleosomes, respectively, for 45 and 180 s of blending time, compared to the conventional method with lower yields (34.24 and 28.65%, respectively, for 45 and 180 s of blending time). Three successive extractions of the residue increased the oil yield to a maximum of 84.65% of the total soybean oil recovered in intact oleosomes. The percentage of lipid in the supernatant fraction decreased to a minimum value of 0.33% with the use of the enzymes at a 3% dosage. The results are considered to be useful for developing large-scale and efficient extraction of oleosomes from soybean.

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An aqueous enzymatic procedure for oleosome fractionation from 25 g of soy flour was developed in our laboratory. This fractionation procedure was evaluated with 75 kg using pilot plant equipment to evaluate the effect of the scale-up on the recovery, proximate composition, soybean storage protein profiles, and subcellular microstructure of oleosome fractions. The process included enzymatic hydrolysis, grinding, and centrifugation, respectively. Pilot-scale grinding and centrifugation of the slurry were accomplished with a Stephan Ò Microcut mill grinder and a three phase decanter. A blender and swinging bucket rotor were used for the laboratory-scale fractionation. The oleosome fractions recovered in the pilot plant were similar in oil and protein content to those obtained in the laboratory. The pilot-scale process resulted in a significantly higher oil yield of 93.40% as total oleosomes compared to that of 76.83% achieved in the laboratory. Urea-SDS gel electrophoresis of proteins extracted from the oleosomes and supernatant from the pilot-scale fractionation had similar profiles to those obtained in the laboratory. Electron microscopy verified that the structure of isolated oleosomes was virtually identical with that of in situ oleosomes. This work confirms that large-scale fractionation of oleosomes from full fat soybean flour can be accomplished.

Oleosome extractions from soybean flour typically generate significant quantities of aqueous sucroseand sodium chloride-rich supernatant which could be recycled. To determine the feasibility of recycling the oleosome process aqueous supernatants, three extraction protocols were evaluated. The first extraction used the original extraction solution, 0.1 M fresh potassium acetate pH 4.6 containing 0.4 M sucrose and 0.5 M NaCl. The second protocol reused the aqueous supernatant obtained from the first extraction. The third protocol reused the aqueous supernatant obtained from the second protocol. Oleosome extraction yields were significantly higher in the first extraction with enzymes (Multifect Ò Pectinase FE, Multifect Ò GC, and Multifect Ò CX B, 1% each, v/w) compared to the yield when the supernatant was reused with no additional enzymes (81.41 ± 2.24 vs. 73.09 ± 3.39%, respectively). Oil yields from oleosome fractions were not statistically different when extractions were made with 0 or 3% enzymes in the third protocol. Protein was the predominant constituent in the supernatant in addition to mineral and carbohydrate. Soybean storage protein profile from recycled supernatants obtained without adding enzyme were similar to a traditional soy protein water extract but with a decrease of intensity of the b-conglycinin bands. Addition of 3% enzymes in both recycling protocols resulted in the disappearance of the a 0 and a subunits of the b-conglycinin due to a protease contaminant in Multifect Ò Pectinase FE. Results from this work revealed essential information for a promising possibility of the future industrial application of this technology.