Carbon dioxide induced soybean protein precipitation: Protein fractionation, particle aggregation, and continuous operation

A novel protein fractionation technique using a volatile electrolyte has be en developed. Carbon dioxide was used to isoelectrically precipitate 80% an d 95% pure glycinin and beta -conglycinin fractions from soybean isolate. T he protein fractions precipitated as primary particles 0.2-0.3 mum in diame ter, which under optimum conditions may be recovered as aggregates up to 50 0 mum in diameter. The dependency of protein fractionation efficiency on ag gregate settling rates has been demonstrated. The isoelectric points of the two main soybean fractions, glycinin and beta -conglycinin, were calculate d to be pH 5.2 and 4.95, respectively. Solution pH was accurately controlle d by pressure in the isoelectric pH range of the different soybean protein fractions, and a pH "overshoot" was eliminated. Volatile electrolyte techno logy was also applied to a continuous process in order to eliminate the par ticle recovery concerns associated with batch precipitation and to demonstr ate the potential for scale-up. Glycinin was effectively recovered on-line (94% glycinin recovery) with a purity approaching that of the batch process (95%).