Determination of caseinomacropeptide with capillary zone electrophoresis and its application to the detection and estimation of rennet whey solids in milk and buttermilk powder

The presence of rennet whey solids in milk powder and buttermilk powder could be detected by analyzing the caseinomacropeptide (6.7 kDa) content by capillary zone electrophoresis. A hydrophilically coated capillary was used in combination with 6 M urea in a citrate buffer at low pH. Under these conditions, genetic A and B variants migrated as a single peak. This afforded a detection limit of 0.4% of rennet whey solids in combination with large volume injections and on-column isotachophoretic concentration of the sample. The detector response (UV at 214 nm) was linear in the range of 1–20% rennet whey solids and the recovery of caseinomacropeptide was 98%. Pseudo-casei-nomacropeptide, lacking the N-terminal Met-residue, could be separated from caseinomacropeptide, thus preventing false positive results for some types of acid buttermilk powder.