DETERMINATION OF CASEINOMACROPEPTIDE WITH CAPILLARY ZONE ELECTROPHORESIS AND ITS APPLICATION TO THE DETECTION AND ESTIMATION OF RENNET WHEYSOLIDS IN MILK AND BUTTERMILK POWDER

The presence of rennet whey solids in milk powder and buttermilk powde r could be detected by analyzing the caseinomacropeptide (6.7 kDa) con tent by capillary zone electrophoresis. A hydrophilically coated capil lary 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 sin gle peak. This afforded a detection limit of 0.4% of rennet whey solid s in combination with large volume injections and on-column isotachoph oretic concentration of the sample. The detector response (UV at 214 n m) was linear in the range of 1-20% rennet whey solids and the recover y of caseinomacropeptide was 98%. Pseudo-caseinomacropeptide, lacking the N-terminal Met-residue, could be separated from caseinomacropeptid e, thus preventing false positive results for some types of acid butte rmilk powder.