Electrophoretic ripening index for the evaluation of proteolysis and the deduction of the age of Parmesan cheese |
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Authors: | Helmut K Mayer |
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Affiliation: | (1) Department of Dairy Research and Bacteriology, University of Agriculture, Gregor Mendel-Strasse 33, A-1180 Vienna, Austria |
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Abstract: | We have established an electrophoretic method to evaluate proteolysis in Parmesan cheese by means of an objective ripening index. The separation of caseins by alkaline polyacrylamide gel electrophoresis (PAGE) (12% T, 2.6% C, pH 8.9, 5 M urea) is followed by the densitometric analysis of the - and -casein fractions. The relationship between the resulting coefficients ( -Cn/ -Cn) and the age of reference samples of Original Italian Grana Padano (6–22 months) was linear up to 15 months, allowing an evaluation of the extent of proteolysis and therefore a deduction of the age of the Parmesan samples analysed. Based on this calibration we propose to use a threshold level of 1.3 ( -Cn/ -Cn) to verify the required age, i.e. 12 months, of Parmesan cheese, retailed as a loaf or prepacked slices. Commercially grated Parmesan samples may contain 20% cheese rind, which has a very low degree of casein breakdown. So a threshold level of 0.8 ( -Cn/ -Cn) is proposed for all grated Parmesan products. The preparation of reference solutions with defined coefficients ( -Cn/ -Cn), corresponding to the proteolysis indices of reference samples of different aged Grana Padano is described. The coefficients ( -Cn/ -Cn) as well as the -casein content of two additional series of reference samples and of 49 commercial Parmesan samples taken from retail outlets in Austria and Italy are presented. |
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Keywords: | Parmesan cheese Proteolysis Ripening index Electrophoresis Ripening age |
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