Total Protein Isolate from Milk by Ultrafiltration: Factors Affecting Product Composition

Skim milk (prepared from reconstituted NDM) was ultrafiltered by a combination of concentration and diafiltration to produce purified total protein isolates with the desired protein: lactose ratio. The rejection of protein and lactose followed expected trends. However, rejection of ash increased to 100% toward the end of the process due to insolubility of salts or their binding to proteins. At the natural pH of skim milk, the minimum ash content was 7 to 8% of the retentate solids, resulting in a limiting protein content of 90%.