MONITORING CHEDDAR CHEESE RIPENING BY CHEMICAL INDEXES OF PROTEOLYSIS.1. DETERMINATION OF FREE GLUTAMIC-ACID, SOLUBLE NITROGEN, AND LIBERATED AMINO-GROUPS

Free L-glutamic acid (Glu), soluble nitrogen (N), and liberated amino groups (amino-N) were evaluated as indicators of proteolysis and matur ation in a study of Cheddar cheese ripening. The analytical methods in volved standardized extraction and fractionation procedures, enzymatic determination of Glu, the measurement of N by Kjeldahl and amino-N by a rapid spectrophotometric assay with o-phthaldialdehyde. Cheddar che eses from two different production plants were stored at both 4-degree s-C and 10-degrees-C for nine months. All cheeses were periodically an alyzed for Glu in an aqueous extract and for N and amino-N in citrate extracts soluble at pH 4.6 and in 12% trichloroacetic acid. All indice s correlated well with each other and with the age of the cheese at a highly significant level. It was demonstrated that these parameters ar e well suited to determine the extent of proteolysis as an indication of the degree of maturity of ripening cheese, thus providing an object ive measurement for age classification and raw material control. The c onvenient assays for Glu and o-phthaldialdehyde-reactive amino-N were proved suitable for routine applications, enabling a fast and sensitiv e check on the degree of proteolysis in cheese without sophisticated e quipment.