Flash desolventizing defatted soybean meals washed with aqueous alcohols to yield a high-protein product
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A vapor-type desolventizer was developed previously at this laboratory to recover hexane and concentrated alcohols from soybean mares. The work reported in this paper extends the application of this unit to the recovery of dilute alcohols. Soybean protein meals washed with aqueous alcohols are debittered to yield a better flavored product with a significant increase in protein content. The protein of defatted meal was increased from about 50 to 70 or 75% by washing with methanol, ethanol, or isopropyl alcohol in a concentration range of 50–70%. System modifications and critical variables were investigated so as to minimize residual alcohol and to yield a free-flowing homogeneous product. Residual alcohol in the desolventized flakes was 0.25–1.0%. Facility of removal followed the order—methanol, isopropyl alcohol, and ethanol. Two-stage flash desolventization as well as the use of the more dilute alcohols resulted in lower residual alcohol content of the desolventized product. After a minimum value for residual alcohol in the flakes is reached, further removal is difficult. However, water continues to be removed so that the alcohol water ratio becomes higher with an increased vaporization force as with increased temperature. It is postulated that the alcohol is held by adsorption or hydrogen bonding. The desolventized products analyzed: protein 72–77%; Nitrogen Solubility Index 4–16; water absorption values 328–410%. The products were light-colored, granular, and free flowing. The soybean flakes extracted with methanol exhibited the best flavor.
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