The free fatty acids of milk fat are believed to be involved in
imparting flavor properties to milk and other dairy products. In the
past the free fatty acids have largely been related to quality deterioration
and hence the methods for measurement have been devised to
determine the changes in the free fatty acid content and to relate
these data with quality. No method has been reported to determine
the quantities of individual free fatty acids. The purpose of this investigation
was to evaluate procedures and adapt methods for isolation
and measurement of the free fatty acids of milk fat and then to
evaluate adapted methods by quantitative measurement of the individual
acids in fresh cream fat samples and in butter made therefrom.
The ion exchange method of Hornstein et al. (50) was modified
to isolate and esterify the free fatty acids from milk fat. The
free fatty acids were adsorbed on Amberlite IRA-400 resin, the resin was made fat free and the bound acids were simultaneously esterified
and eluted with anhydrous methanol-HCl. The methyl esters were
extracted from the reaction mixture with ethyl chloride (b.p. 12.3°C.).
The ethyl chloride was evaporated and the esters weighed. The
methyl esters were then separated by gas-liquid chromatography
using the thermal conductivity detector. The recovery of each saturated
even numbered fatty acid from 4:0 to 18:0 was checked. The
percent recoveries obtained were: 4:0, 71.4; 6:0, 86.5; 8:0, 66.6;
10:0, 75.1; 12:0, 94.3; 14:0, 100.2; 16:0, 99.5 and 18:0, 92.5.
The ion exchange resin was checked for its fat hydrolysing
capacity, for retention of fatty acids when used in successive analyses
and for leachings of brown polymers during each analysis. The
resin did not show detectable hydrolysis of triglycerides nor did it
retain or exchange fatty acids from previous use. It was necessary
to pretreat the resin with stearic acid and anhydrous methanol-HCl
to avoid interference of a leached polymer with quantitative results.
An average of 5.0 mg of residue leached from the resin during every
analysis, but this did not interfere with the quantitative determination
of free fatty acids.
Twenty samples of milk fat; ten from pasteurized sweet
cream, nine from cultured butter and one from sweet cream butter
were analyzed for free fatty acids. The results obtained were compared
with the esterified fatty acid content of milk fat. The percent composition of free fatty acids was similar to that of the esterified
fatty acids in milk fat. Also the manufacturing process of butter had
little or no effect upon the free fatty acid composition of the fat. The
values obtained for volatile fatty acids, especially 4:0, were not consistent.
One reason for this probably was that evaporation of the
ethyl chloride from the solution of the methyl esters was carried out
at room temperature and the evaporation rate was not controlled. It
is believed that the results would be more consistent if the evaporation
of ethyl chloride were carried out under controlled and standardized
conditions and if internal standards are employed for quantitative
references rather than weighing the ester mixture.
Samples of autoxidized milk fat, sweet cream fat and rancid
cream fat were analyzed for further evaluation of the method. / Graduation date: 1963
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28197 |
| Date | 08 March 1963 |
| Creators | Khatri, Lakho Lilaram |
| Contributors | Day, Edgar Allan |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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