Graduate Thesis Or Dissertation
 

Studies of the major free fatty acids in milk

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  • The purpose of this investigation was to modify the procedure of Bills, Khatri and Day for use in the development of a suitable method for determining the quantitative distribution of the free fatty acids (FFA) in normal, heated, and rancid milk and milk fractions The method consists of extracting the FFA from lyophilized milk, separating the FFA from neutral fat, converting the FFA to methyl esters, and analyzing the methyl esters by gas-liquid chromatography (GLC). The salts of FFA present in lyophilized milk or milk fractions were released by lowering the pH of the sample with H₂SO₄, and subsequently extracted with ethyl ether. The extracted FFA were simultaneously isolated from the extract and methylated by using the one-step procedure of Bills, Khatri and Day. A specially designed concentration flask was employed with a reflux system to concentrate the methyl esters. The esters were then separated by GLC. Quantitative calculations were made from the GLC peak areas using internal standards. The major esterified fatty acids of milk are n-saturated, evennumbered 4:0-18:0 and unsaturated 18:1 and 18:2 acids. The distribution of major FFA in whole milks was found to be essentially the same as that of the esterified fatty acids of milk fat. Heat treatments of milk, whether pasturization or extended holding at 100°C, effect a progressive reduction in total FFA. Decreases in long chain fatty acids are also characteristic of extended heating. Milks determined to be rancid by acid degree value and organoleptic analysis showed high levels of FFA, 1.5-3.6% of the fat content of the sample. The increases in 6:0-12:0 resulting from lipase hydrolysis approximate the amounts shown by Al-Shabibi and co-authors to produce rancid flavor when added to good quality milk. Milk triglycerides, fat globule membrane, skim milk, and buttermilk show characteristic FFA patterns which appear to be related to the solubility properties of the individual acids. Seventy-one percent of the total FFA in a given portion of 40% cream was found in the triglyceride fraction, 26% in the crudie fat globule membrane preparation and 3% in the skim milk fraction. The total concentrations of FFA were found to be: 1% of the fat in whole milk or 0.04% of the fluid milk weight; 0.16% of the total weight of 40% cream; 0.28% of centrifuged triglycerides; 1.7% of the fat globule membrane; and 0.008% of the fluid weight of skim milk.
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