Comparison of gas chromatographic methods for analysis of butyric acid in milk fat and fats containing milk fat |
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Authors: | J Molkentin and D Precht |
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Affiliation: | (1) Bundesanstalt für Milchforschung, Institut für Chemie und Physik, Postfach 6069, D-24121 Kiel, Germany, DE |
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Abstract: | The analysis of butyric acid (C4) is of importance for the determination of the proportion of milk fat in mixed fats. Three
gas chromatographic methods were compared with regard to their precision for the measurement of C4, i.e. analysis of butyric
acid methyl ester after trans-esterification of fat by sodium methylate (method A) or trimethyl sulphonium hydroxide (method
B), as well as analysis of free butyric acid (method C), using an internal standard with each method. The examination of 30
milk fats which varied greatly in terms of their C4 content, using methods A, B and C, resulted in mean values of C4 of 3.42
g/100 g fat, 3.71 g/100 g fat and 3.06 g/100 g fat, respectively. The value determined using method B seemed too high, and this may have been due to the presence of co-eluting artefacts, whereas the value determined using method
C was clearly too low, and can probably be attributed to losses during sample preparation. The standard deviation (SD) of
0.015 obtained from repeated analyses using method A was quite good. Results obtained using methods B and C had SDs of 0.029
and 0.074, respectively. Different levels of free fatty acids did not affect the results obtained using method A. When method
A was checked by analysis of the reference fat, CRM 164, the C4 level determined was found to deviate from the certified C4
content of 3.49 (± 0.06) g/100 g fat by only 0.05 g C4/fat 100 g. Thus method A proved the most suitable for the determination
of the proportion of milk fat in mixed fats by analysis of butyric acid.
Received: 1 October 1997 |
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Keywords: | Milk fat Mixed fat Milk fat content Butyric acid Gas chromatography |
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