Precipitation behaviour of caseinomacropeptides and their simultaneous determination with whey proteins by RP-HPLC

A reversed-phase high-performance liquid chromatographic (RP-HPLC) method on polyvinylbenzene/divinylbenzene copolymer resin was applied for the quantitative determination of glycosylated and non-glycosylated caseinomacropeptides (CMP), in presence of the major whey proteins (α-lactalbumin and β-lactoglobulin). The peak profile of the CMP-fractions was calibrated using the response factor determined by amino acid analysis. By omitting any critical precipitation step (e.g. trichloroacetic acid, TCA) usually applied to remove whey proteins, the method allows the simultaneous determination of the major whey proteins and CMP—the complete native spectrum—in a single run. As a prerequisite for forthcoming kinetic studies of CMP release, the precipitation sensitivity of individual whey proteins or CMP fractions against TCA or perchloric acid (PCA) was studied systematically. All CMP fractions were partially precipitated even at low TCA concentrations, whereas PCA treatment resulted in negligible decrease of CMP solubility.