A comparative study of proteolysis in cheddar cheese and yeast-inoculated cheddar cheese during ripening

English: Proteolysis is regarded as the most important event in the ripening of Cheddar cheese to contribute to the development of flavour. The characteristic proteolysis of each type of cheese is brought about by the enzymes used in the manufacturing process, e.g. rennet, as well as enzymes from the specific microbial cultures used in each cheese type. The effect of an inoculated yeast, Oebaryomyces hansenii, and its enzymes on proteolysis in Cheddar cheese was investigated. Proteolysis and development of peptides of the yeast-inoculated Cheddar cheese was followed throughout the ripening process and compared to the proteolysis in a standard Cheddar cheese. In a sensorical comparative study, no difference was found by a consumer panel between the two types of cheese, nor was any of the two significantly preferred. An expert panel however, judged the yeast-inoculated Cheddar cheese to be bitter. The proteins and peptides from the cheeses were extracted and fractionated by virtue of differences in solubility and molecular size. Yeast-inoculated Cheddar cheese contained less water-soluble nitrogen indicating a difference in proteolysis between the two types of cheese. Urea-polyacrylamide gel electrophoresis of the waterinsoluble fraction indicated that in the yeast-inoculated cheese rennet hydrolysis of o.si-casein was increased with faster formation of one primary peptide, o.s1-1as well as (o.s1-CN(f102-.)), with little further hydrolysis. The ~-casein was hydrolyzed slowly but with several additional peptides occurring. Reversed-phase high performance liquid chromatography of the watersoluble fraction indicated that a different peptide profile was formed, with at least five unique peptides at high amounts.