28-6 |
Proteolytic changes in Cheddar cheese from seven states in the United States |
T. CONSIDINE1, N. A. Khilla, and N. Y. Farkye. (1) Dairy Products Technology Center, California Polytechnic State University, 1 Grand Avenue, San Luis Obispo, CA 93407 Cheddar cheese is one of the most important cheese varieties in the U.S. The maturation process involves microbial and chemical reactions whereby complex milk proteins are broken down to small peptides and free amino acids that influence changes in body, texture and flavor developments in cheese. Peptides profiles also have been used as indices of maturation as a possible means of understanding differences in starter strains and differentiating cheeses made from milk of a different source. Thirteen cheeses were received at Cal Poly from 7 states (NY, VT, ID, CA, MI, WI, WA) in the U.S. The cheeses were already ripened for 7-10 months in locations specific to each manufacturer. On receipt at Cal Poly, the cheeses were ripened for a further 6 months at 8ºC under controlled conditions. Samples were assessed for proteolysis after day 0, month 1, 3, and 6 (equivalent to actual cheese age of 7-10, 8-11, 10-13 and 13-16 mo. respectively). The composition of the cheeses was within the normal range for Cheddar. Water soluble nitrogen (WSN) as a percent of total nitrogen and free amino acids were used as indices of ripening in the cheese. The concentrations of %WSN and free amino acid varied with cheese from different regions. Mean %WSN and free amino acids ranged from 18-35% and 5-6.6 mg Leu/g cheese, respectively for the 13-16 mo. old cheeses. Urea-polyacrylamide gel electrophoretograms (Urea-PAGE) of cheese showed similar proteolytic products of the caseins. This was expected since the levels of proteolysis detectable by PAGE are mediated mainly by chymosin and plasmin. Comparison of peptide profiles in water soluble fraction showed qualitative differences in the cheese from the various regions. Future work entails determination of the individual amino acids to determine the concentration of amino acids from region to region and study the degradation products formed as a result of amino acid catabolism which act as major precursors of specific flavor compounds.
Session 28, Dairy Foods: Developments in microbiology and chemistry of cheese
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