Isoelectric precipitation of soybean protein using carbon dioxide as a volatile acid

A novel process is presented for the isoelectric precipitation of soy prote in, using carbon dioxide as a volatile acid. By contacting a soy meal extra ct with pressurized carbon dioxide, the solution pH was decreased to the is oelectric region of the soy proteins. Complete precipitation of the precipi table soy proteins could be achieved for protein concentrations up to 40 g/ l at pressures less than 50 bar. Isoelectric precipitation with a volatile acid enabled accurate control of the solution pH by pressure and eliminated the local pH overshoot, usual in conventional precipitation techniques. Th e advantage of the improved precipitation control was reflected by the morp hology of the precipitate particles. Protein aggregates formed by CO2 were perfectly spherical whereas protein precipitated by sulfuric acid had an ir regular morphology. The influence of process variables to control particle size is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.