Isolation of caseinomacropeptide from rennet whey by a multi-stage ultrafiltration process. I: Studies in the apparent molecular weight of caseinomacropeptide as a function of pH

Studies in the apparent molecular weight (MW) of CMP in rennet whey were carried out in dependency on pH-value (3.5 and 7.0). For this reconstituted whey (6.5% w/w) was carefully defatted and then ultrafiltered according to the two-stage ultrafiltration (UF) process of KAWASAKI et al. (1993). A modified spectrophotometric method was used for quantifying CMP during the UF process. Size-exclusion chromatography (SE-FPLC) using the Superose 12 column was applied for estimations of MW of pure CMP isolated from whey. Results obtained by SE-FPLC revealed no monomer forms of CMP, neither at pH 3.5 nor at 7.0. In aqueous solution CMP existed as dimer and/or trimer with MW between 20.3 and 17.5 kDa (pH 3.0, 7.0). The formation of aggregated CMP near the neutral point was followed by the spectrophotometric method. These aggregates were concentration-depended and dissociated on dilution. Results of apparent MW were applicable to explain basic aspects of the UF process. From this it was derived that the methodical approach applied here is reliable.