Fatty acid analyses

Aldehydes, enals, dienals, ketones, and hydrocarbons, which are responsible for disagreeable odors, generally bok at lower temperatures than fatty acids. Analysis showkig a free fatty acid concentration of less than 0.05% is an kidication that deodorization is sufficientiy complete. Some of the dienals have very low odor thresholds and sensory evaluation of the finished ok is a judicious quaHty assurance step. 

A. Frostegard and E. Baath. The use of phospholipid fatty-acid analysis to e.stimatc bacterial and fungal biomass in soil, Biol. Eeiiil. Soll.s 22 59 (1996). 

Beverly, M. B. Basile, F. Voorhees, K. J. Fatty acid analysis of beer spoiling microorganisms using pyrolysis mass spectrometry. J. Am. Soc. Brewing Chemists 1997, 55,79-82. 

Prepare microsomes from borage seeds, lipid extraction, and fatty acid analysis according to Galle et al. (31). Protocol adapted from ref. (31). 

Greco, A. V., Mingrone, G., Gasbarrini, G. Clin. Chim. Acta 239, 1995, 13-22. Free fatty acid analysis in ascitic fluid improves diagnosis in malignant abdominal tumors. 

Ci8 unsaturated), and only relatively small amounts of saturated fatty acids. Animal fats have a much higher proportion of saturated fatty acid derivatives, but they still contain a substantial level of unsaturated fatty acids. The fatty acid analysis of butterfat, for example, shows it contains about 28% oleic acid. 

Table 3.3.3 Precision of the polyunsaturated fatty acid analysis assessed in control samples analysed over a 10-week-period. AVG Average, SD standard deviation, CV coefficient of variation ... 

Holman, R. T., Caster, W. O. and Wiese, H, F. 1964. The essential fatty acid requirement of infants and the assessment of their dietary intake of linoleate by serum fatty acid analysis. Am. J. Clin. Nutr. 14, 70-75. 

Divakaran, S. and Ostrowski, A.C. 1989. Fatty acid analysis of fish eggs without solvent extraction. Aquaculture 80 371-375. 

Sample preparation is probably the most important step in any analytical procedure. Poor preparation of lipid samples will only yield inferior or questionable results. Some commonly performed sample-preparation procedures for gas-liquid chromatographic (GC) analysis of fatty acids in food samples are introduced in this unit. Since the introduction of gas chromatography in the 1950s, significant progress has been made in fatty acid analysis of lipids however, fatty acid methyl esters (FAMEs) are still the most commonly used fatty acid derivative for routine analysis of food fatty acid composition. 

Settings in a GC system, the primary tool for fatty acid analysis, will affect the results of analysis greatly. A GC system has the following elementary parts carrier gas supply, injector, column, and detector. 

Rancidity measurements are taken by determining the concentration of either the intermediate compounds, or the more stable end products. Peroxide values (PV), thiobarbituric acid (TBA) test, fatty acid analysis, GC volatile analysis, active oxygen method (AOM), and sensory analysis are just some of the methods currently used for this purpose. Peroxide values and TBA tests are two very common rancidity tests however, the actual point of rancidity is discretionary. Determinations based on intermediate compounds (PV) are limited because the same value can represent two different points on the rancidity curve, thus making interpretations difficult. For example, a low PV can represent a sample just starting to become rancid, as well as a sample that has developed an extreme rancid characteristic. The TBA test has similar limitations, in that TBA values are typically quadratic with increasing oxidation. Due to the stability of some of the end-products, headspace GC is a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic and solid-phase microextraction (SPME) methods. Hexanal, which is the end-product formed from the oxidation of Q-6 unsaturated fatty acids (linoleate), is often found to be a major compound in the volatile profile of food products, and is often chosen as an indicator of oxidation in meals, especially during the early oxidative changes (Shahidi, 1994). 

Conductivity, in water activity measurement, 67-70 Confocal laser scanning microscopy to characterize lipid crystals, 575-579 description of, 575, 577 Conjugated dienes and trienes, determination of, 515-517 Conjugated linoleic acid (CLA), fatty acid analysis, 437-438, 445-446 Convection oven, gravimetric measurement of water, 7-8, 10-11... 

Transesterification, fatty acid analysis of lipids, 437, 439 Triacetin, lipase assays, 378 Triacylglycerol acylhydrolase, 371, 375, 378. See also Lipases Triacylglycerols, 432 Tributyrin, lipase assays, 378 Trichloroacetic acid (TCA) solubility index for protein hydrolysis, 152 in TBARS determination, 548-550 Trienes, conjugated, determination of, 515-517, 523-524, 526, 528 Trifluoroacetic acid (TFA), for determination of neutral sugars, 721-722, 724-725, 729-730... 

One hundred and fifty-one molecular species of TGs have been described previously in milk fat (125,130) the other 30 are described in Ruiz-Sala s (129) analysis for the first time. Due to the fact that this identification of TGs is based not only on the estimation of ECN, but also on a fatty acids analysis of HPLC fractions of the TG, some of the species described previously by other authors have not been found in this study. Bornaz et al. (125) show 26 molecular species that contained linolenic acid. However, their study shows only 9, and they contained other fatty acids in higher amounts. The rest of them are not shown because they were found at less than 0.01%. 

In agreement with Barron et al. (117) trans- accenic acid was taken into account, because it was found at 1.9% in the fatty acids analysis of the total TG fraction. The aforementioned study detected 116 TG molecular species instead of their 181, because they only considered 14 fatty acids for the calculation of the composition due to the lower sensitivity of their GLC analysis. 

The oil yields and fatty acid compositions given in the table are typical values, and can vary widely. The quality of an oil is determined principally by its fatty acid analysis. Structures of the fatty acids are shown in Table 3.1 (see page 38). 

Meyer-Rochow, V.B. and Pyle, C.A. (1980). Fatty acid analysis of lens and retina of two Antarctic fish and of the head and body of the antarctic amphipod Orchomene plebs. Comparative Biochemistry and Physiology 65B, 395-398. 

Borga, P Nilsson, M., and Tunlid, A. (1994). Bacterial communities in peat in relation to botanical composition as revealed by phospholipid fatty-acid analysis. Soil Biol. Biochem. 26, 841-848. 

The methyl esters obtained are readily analysed qualitatively and quantitatively by gas chromatography, and the data obtained allow detection of sophistication. In the literature there is a wealth of fatty acid analysis data on virgin olive oils, all constantly reporting almost the same qualitative composition. However, what is surprising is the systematic attitude of so many researchers not reporting the presence of vaccenic acid, 11 -ds-octadecenoic acid, an isomer of oleic acid. The presence of this positional isomer of oleic acids was first described in olive oil by Tulloch and Craig (1964). 

Fatty acid analysis of a fat is nowadays a relatively routine analytical operation. After methylation of the fat using reaction with boron trifluoride/methanol, boron trichloride/methanol, methanolic hydrogen chloride solution, diazomethane or, if free fatty acids are not present, alkaline catalysts such as sodium methoxide/methanol, the prepared methyl esters are then analysed by GC on a polar column such as CpSil 88, BPX70 or SP2340. The high polarity of the column is necessary to separate the saturated and unsaturated fatty acids fully. The fatty acid composition of a milk fat sample is thus relatively easily obtained, and was therefore one of the first techniques investigated for authentication purposes. 

Sterol analysis, fatty acid analysis of the whole fat and of the acids at the 2-position, and triglycerides by GC, can be very useful in determining adulteration of and by animal fats. In the future HPLC of triglycerides is likely to provide an even better method for some purposes, but much more data need to be collected before this can be evaluated. 

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