Comparison of ethanol and trichloracetic acid fractionation for measurement of proteolysis in emmental cheese

Crude fractionation of cheese by various precipitants and subsequent determination of soluble nitrogen (N) represents a well-established method for quantification of proteolysis in cheese. Attempts have been made to replace precipitation with 12% trichloracetic acid (TCA) by fractionation with differing concentrations of ethanol (EtOH). In order to compare these procedures, aqueous extracts of Emmental cheeses were fractionated with EtOH at concentrations ranging from 30 to 70%. N recovery increased significantly with increasing cheese age and, for each cheese, decreased with increasing EtOH concentration. For young cheese, precipitation with 30-40% EtOH gave comparable results to fractionation with 12% TCA. For mature cheese, however, 70% EtOH was necessary to achieve N values corresponding to precipitation with 12% TCA. Analytical ultrafiltration of aqueous cheese extracts and N recovery in fractions thereof prepared by TCA and EtOH, as well as SDS-PAGE and RP-HPLC of the EtOH-soluble and EtOH-insoluble fractions, showed that variations in cut-off levels can be attributed to qualitative differences in extract composition.