|Abstract or Summary
- 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;