A soy protein product having a protein content of at least about 60 wt% (N x 6.25) d.b., preferably a soy protein isolate having a protein content of at least about 90 wt% (N x 6.25) d.b., is prepared from a soy protein source material by extraction of the soy protein source material with an aqueous calcium salt solution, preferably calcium chloride solution, to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution, separating the aqueous soy protein solution from residual soy protein source, concentrating the aqueous soy protein solution while maintaining the ionic strength substantially constant by using a selective membrane technique, optionally diafiltering the concentrated soy protein solution, and drying the concentrated and optionally diafiltered soy protein solution. Alternatively, the concentrated and optionally diafiltered soy protein solution may be diluted into water to cause the formation of a precipitate, separating the precipitate from the diluting water (supernatant), and drying the separated soy protein solution to form a soy protein product having a protein content of at least about 60 wt% (N x 6.25) d.b., preferably a soy protein isolate having a protein content of at least about 90 wt% (N x 6.25) d.b.. The supernatant may be processed to form soy protein products having a protein content of at least about 60 wt% (N x 6.25) d.b., preferably a soy protein isolate having a protein content of at least 90 wt% (N x 6.25) d.b. Alternatively, the precipitate from the dilution step and diluting water is acidified to resolubilize the precipitate and form a clear soy protein solution. The clear soy protein solution is concentrated while maintaining the ionic strength substantially constant by using a selective membrane technique followed by optional diafiltration and drying.Un produit de type protéine de soja présentant une teneur en protéine supérieure ou égale à environ 60 % en poids (N x 6,25) sur sec, de
