IMPROVEMENT OF THE OFF-FLAVOR OF SOY PROTEIN ISOLATE BY REMOVING OIL-BODY ASSOCIATED PROTEINS AND POLAR LIPIDS

The precipitate formed by ultracentrifuging a defatted soybean extract at 200,000 x g for 50 min at pH 7.5 was composed of particles of 100- 200 nn in diameter and enriched with 34-kDa, 24-kDa and 18-kDa protein s. An SDS-PAGE analysis showed these proteins to migrate to a position identical to that of oh-body-associated proteins (OBAPs; Herman, Plan ta, 172, 336-345, 1987).(1)), They were recovered in the precipitate o f soy protein with 30-40% saturated ammonium sulfate in the presence o f 10 mM 2-ME. The lipid composition of the precipitate by a TLC analys is showed that most of the polar lipids in the soybean extract had bee n condensed in the fraction, suggesting the association between OBAP a nd the polar lipids. Removal of OBAP and the polar lipids from the soy bean extract by conventional centrifugation (10,000 x g for 10 min) in the presence of 30 mM Na2SO4 and 30 mM CaCl2 at pH 2.8 was achieved w ith concomitant improvement of the volatile off-flavor. A soy protein isolate (SPI) prepared from such a soybean extract contained far fewer volatile off-flavor compounds than normal SPI did.