Effects of NaCl concentration on salting-in and dilution during salting-out on soy protein Fractionation

Glycinin and beta-conglycinin are the main storage proteins in soybeans that can be fractionated by using alkali extraction, SO2, salting-in with NaCl, salting-out by dilution and pH adjustment to produce a glycinin-rich fraction, a beta-conglycinin-rich fraction, and an intermediate fraction, which is a mixture of the two proteins. Two different strategies were employed to optimize the procedure to achieve high efficiency in recovering the beta-conglycinin-rich fraction was obtained at 500 mM NaCl, but at the expense of the purity. The optimum NaCl concentration was 250 mM, at which good yield (18.5%) and purity (84.5%) were achieved. At higher NaCl concentrations, the protein yields of the intermediate fractions were significantly lower, and the protein loss in the whey fraction increased. The second strategy was to improve the salting-out step for the beta-conglycinin-rich fraction. At 0- and 0.5-fold dilution, the purities and yields of the beta-conglycinin-rich fractions were significantly lower than at 1.0- and 2.0-fold dilution. There were no differences in protein yields or purities when using 1.0 or 2.0-fold dilution. According to these results, the recommended NaCl concentration for the salting-in step is 250 mM and the dilution factor for salting-out is 1.0.