Fractionation and enzymatic hydrolysis of soluble protein present in waste liquors from soy processing.

A waste effluent from a soymeal concentrates plant was centrifuged and ultrafiltered by successive processing in membranes of 10, 30, and 50 kDa, with further concentration of the resulting stream using a 5 kDa membrane. The separated fractions (5-10, 10-30, 30-50, and >50 kDa) were subjected to chemical, nutritional, and functional characterization. Resuspension of the retentates in salt-containing systems improved the protein solubility, the emulsifying capacity, and the gelation capacity, whereas the emulsion stability and the foam capacity and stability decreased with respect to the values obtained using distilled water, and the oil absorption capacity was not affected. The digestibility of the fraction >50 kDa was comparable to that of casein. The fractions of higher molecular mass (30-50 and >50 kDa) were subjected to enzymatic hydrolysis with a commercial protease, to give products with improved emulsifying activity and stability, particularly for hydrolysates with a degree of hydrolysis between 20 and 30%.