Enzyme-assisted aqueous extraction of oleosomes from soybeans (Glycine max).

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.

Oxidative stability of soybean oil in oleosomes as affected by pH and iron.

The oxidative stability of oil in soybean oleosomes, isolated using the Enzyme-Assisted Aqueous Extraction Process (EAEP), was evaluated. The effects of ferric chloride, at two concentration levels (100 and 500 µM), on lipid oxidation, was examined under pH 2 and 7. The peroxide value (PV) and thiobarbituric acid-reactive substance (TBARS) value of oil, in oleosome suspensions stored at 60 °C, were measured over a 12 day period. The presence of ferric chloride significantly (P<0.05) affected the oxidative stability of oil in the isolated oleosome, as measured by the PV and TBARS. Greater lipid oxidation occurred under an acidic pH. In the pH 7 samples, the positively charged transition metals were strongly attracted to the negatively charged droplets. However, the low ζ-potential and the high creaming rate at this pH, may have limited the oxidation. Freezing, freeze-drying or heating of oleosomes have an insignificant impact on the oxidative stability of oil in isolated soybean oleosomes. Manufacturers should be cautious when adding oleosomes as ingredients in food systems containing transition metal ions.

Process improvement for semipurified oleosomes on a pilot-plant scale.

Semipurified oleosomes were isolated on a pilot-plant scale using improved-process extraction conditions. The improved process consisted of continuous centrifugation in a three-phase decanter with recirculation of slurry until most of the oleosomes were recovered. Oleosome fractionation, oleosin identification, and isoflavone and saponin mass distributions and recoveries were investigated. The improved pilot-plant oleosome extraction process was achieved in 8 h. A total of 91%± 1% of soybean oil was recovered as intact oleosomes. The oil content of the aqueous supernatant and the residue fractions were low at 2% and 3%, respectively. The aqueous supernatant fraction contained 40% total soybean protein. About 76% of the proteins present in the oleosome fraction were soybean storage proteins. Washing the semipurified oleosomes with a 0.1 M Tris-HCl, pH 8.6 containing 0.4 M sucrose, and 0.5 M NaCl resulted in the recovery of the associated storage proteins. The recovery of these proteins in addition to the protein in aqueous supernatant accounted for 79% of the total soybean storage proteins fractionated by this process. Oleosins were detected at 17 and 18 kDa. Isoflavones and saponins partitioned into the oleosome, aqueous supernatant, and residue fractions at different ratios with the majority, about 82 and 63 mole%, respectively, in oleosome and aqueous supernatant fractions, making these fractions an attractive source for phytochemicals.