Vakaleris-Price and Hull Methods for Determining Soluble Tyrosine and Tryptophan in Blue Cheese

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Abstract
To establish a suitable method for measuring the degree of proteolysis in blue cheese (as a measure of ripening), the Hull procedure and the Vakaleris-Price method were compared. In recovery experiments using 3 different spectrophotometers and known amounts of tyrosine and tryptophan, discrepancies between the 3 spectrophotometers in their absorbance readings at 290 nm were wide. To eliminate discrepancies that could have been caused by differing sensitivities of instruments, a wavelength of 285 nm instead of 290 nm was used. Seven loaves of domestic blue cheese were examined. High tyrosine contents were obtained in 5 of 7 blue cheese samples with the Vakaleris-Price method as compared with Hull procedure. Extracts from blue cheese contained interfering compounds that absorbed at the UV wavelength used with the Vakaleris-Price procedure.