Soy protein concentrates
contain at least 70% protein on a dry weight basis and
are made by extracting the proteins in aqueous alcohol or
with a dilute acid solution in the pH range of 4.0 to 4.8. Soy
protein isolates contain a minimum of 90% protein on a dry
weight basis and are produced by extracting the soy flour
with a dilute alkali (pH 9) followed by centrifugation
(Mounts and others 1987). The extract is adjusted to pH 4.5
with a food grade acid such as sulfuric, hydrochloric, phosphoric,
or acetic to enable precipitation of proteins. The
acid-precipitated protein curd is then centrifuged, washed,
neutralized, and spray-dried to produce the soy protein isolate
(Circle and Smith 1978)