Protein Purification, Alcohol Washing of Soybean Protein

Abstract

Soybean protein isolated by acidification of an aqueous extract of hexane-defatted soybean meal contains 2 to 4% of a phospholipide-like material. These lipides cannot be removed by isoelectric precipitation, washing with water, dialysis, or ammonium sulfate precipitation. However, they are extractable with aqueous alcohols. The concentration of alcohol used to wash the protein has a pronounced effect on the amount of material removed and on the nitrogen content of the extracted protein. Optimum concentrations of alcohol are: methyl, 95 to 97% (v./v.); ethyl, 84 to 88% (v./v.); and isopropyl, 78 to 88% (v./v.). The effects of extraction time, temperature, pH, and solvent to protein ratio were also studied. The washed protein has improved color and flavor and produces extremely stable, low density foams and whips similar to egg white and commercially available soy products. Food utilization of soybeans in the United States is still expanding, and the potential is much greater than its present use.Extensive reviews (Z, 25, 30) on the use of soybean protein products in foods have been published. They indicate that color and flavor of soybean protein are important considerations.

Properties of soy protein isolate prepared from aqueous alcohol washed soy flakes

“…During the past decades, many researches have been carried out to improve the flavor, color and functionalities of the isolated protein. Among these, alcohol leaching has demonstrated high potential in improving the quality of soy protein product (Beckel & Smith, 1944;Baker, Mustakas, & Warner, 1979;Eldridge, Wolf, Nash, & Smith, 1963;Grant et al, 1986).…”

Soybean protein flavor components: A review

“…Demonstration that measurable amounts of lipid material remain in protein isolated from hexane-extracted soybean flakes suggests that oxidation of lipid components may be a factor in the flavor of soybean protein products (7). Removal of much of the flavor and lipid material by extraction of dehulled, defatted soybean flakes with alcohols supports this suggestion (8).…”

“…Earlier we mentioned some studies involving extraction with alcoholic solvents. Alcoholic treatment does partly inactivate enzymes in soybeans and does remove substantial amounts of hpids and flavor (5,7,8,20). Alcohol suffers from some of the same disadvantages as cooking and steaming.…”

β‐Cyclodextrin‐Mediated Removal of Soy Phospholipids from the Air–Water Interface

“…It has been shown that oleosin-PL complexes remain intact during SP extraction from soybean and are isolated along with purified SP [7]. Previously, removal of PLs from SP has been attempted using solvents like aqueous alcohols (78-97%, v/v) [8]; hexane/alcohol azeotropes [9,10]; methylene chloride, and aqueous acetone [11]. While these treatments proved very effective in reducing PL levels and concomitantly improving SP flavor, exposure to solvent resulted in severe protein denaturation and subsequent loss of solubility [9,10,12].…”