Graduate Thesis Or Dissertation

 

A method for the determination of the free fatty acids of Cheddar cheese Public Deposited

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  • The free fatty acids of Cheddar cheese are important components in the over-all flavor and aroma of the cheese. Although the more volatile fatty acids probably contribute most, there is reason to believe that the higher fatty acids may contribute, to some extent, in imparting typical flavor characteristics. Before the advent of gas-liquid chromatography the quantitative separation of the entire spectrum of fatty acids was difficult to achieve. Earlier workers were forced to resort to methods of distillation and later to methods of partition chromatography in attempting to determine the free fatty acids in cheese and other biological materials. In general, the earlier investigators were only successful in separating some of the more volatile free fatty acids. The purpose of this investigation was to appraise the recent developments in the field of column and gas-liquid chromatography and to utilize these methods for the analysis of the complete series of free fatty acids in Cheddar cheese. The more volatile fatty acids were determined by two methods of column chromatography. The celite column of Wiseman and Irvin (107) was adapted to the determination of formic, acetic, and propionic acids. Butyric acid was determined by a modification of the silicic acid column developed by Keeney (59, p. 212-225). In determining butyric acid it was necessary to collect the eluate from the column as ten milliliter fractions and to titrate these separately. The total moles of acids with carbon chains longer than butyric also were determined by titration of the fractions preceding butyric acid from the column. The determination as individual acids of the free fatty acids with carbon chains longer than butyric acid required both the measurement of the total molar concentration by means of the silicic acid column and the determination of the molar ratio between individual acids by gas-liquid chromatography. The modified method of Hornstein (46) was used to isolate the free fatty acids from a portion of fat obtained by centrifuging whole acidified cheese. The free fatty acids were converted to methyl esters directly from the ion exchange resin used for isolation and then extracted with ethyl chloride. The ethyl chloride extract was concentrated in a special reflux system and the methyl esters analyzed by gas-liquid chromatography. The use of two internal standards resulted in improved precision and accuracy in the analysis of free fatty acids. Eight samples of Cheddar cheese were analyzed. Formic and propionic acids were not found in any of the cheeses; the average concentration in mg/kg of other major free fatty acids was as follows: 2:0, 949. 6; 4:0, 131.0; 6:0, 43. 6; 8:0, 46.4; 10:0, 59.5; 12:0, 89.2; 14:0, 242.5; 16:0, 543.3; 18:0, 189.8; 18:1, 504.6; 18:2, 79.3; 18:3, 45.2.
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