Use of the Cd-ninhydrin reagent to assess proteolysis in cheese during ripening

Summary A new method for monitoring the terminal stages of proteolysis in cheese, i.e. the formation of free amino acids, using the Cd-ninhydrin reagent is reported. The assay was very specific for free amino acids and may be performed on citrate-soluble, water-soluble or phosphotungstic acid-soluble fractions of cheese, but not on trichloroacetic acid-soluble extracts; water-soluble extracts were chosen for routine analysis. Application of the assay to several experimental cheeses showed almost linear increases in free amino acids during ripening for up to 12 months with a slightly faster rate of formation during the later stages of ripening.