A Rapid Spectrophotometric Method for Measuring Cheese Ripening

Abstract

Summary A rapid method for estimating the degree of proteolysis in ripening cheese was studied by measuring absorption of ultraviolet light by a clear, sodium citrate-hydrochloric acid extract of cheese at pH 4.4±0.05; these measurements were closely correlated with the per cent of soluble nitrogen in the cheese extract. Measurements of the optical density of the cheese from 40 lots of varying ages revealed peaks of all absorption spectra between 274 and 275 mµ. The coeffieient of correlation between optical density of the cheese extract and percentage of soluble nitrogen measured in the cheese extract by Kjeldahl was 0.958. Concentrations of soluble tyrosine and soluble tryptophane were measured spectrophotometrically at optical densities of 270 and 290 mµ. Equations were developed by Vierordt's method of analysis of two component systems for this pair of wave lengths. Relationships between these compounds and percentage of soluble nitrogen in the cheese were linear and highly significant; the coefficient of correlation between soluble tyrosine and percentage of soluble nitrogen was 0.964; whereas, that between soluble tryptophane and percentage of soluble nitrogen was 0.886. Flavor intensity estimated in the 40 lots of cheese by professional judges showed a linear relationship to soluble tyrosine.