Isolation and determination of the free fatty acids of milk fats Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3197xq23c

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  • 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.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-03-08T22:36:21Z (GMT) No. of bitstreams: 1 KHATRILAKHO1963.pdf: 4183386 bytes, checksum: 99e24336640f4445f93380af29ffcf0c (MD5)
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