Fatty acids double bond contents

Proton chemical shift data from nuclear magnetic resonance has historically not been very informative because the methylene groups in the hydrocarbon chain are not easily differentiated. However, this can be turned to advantage if a polar group is present on the side chain causing the shift of adjacent hydrogens downfteld. High resolution C-nmr has been able to determine position and stereochemistry of double bonds in the fatty acid chain (62). Broad band nmr has also been shown useful for determination of soHd fat content. 

Parodi (1976) determined the distribution of double bonds in cis and trans octadecenoic fatty acids from milk fat and bovine adipose tissue. About 95% of the 18 1 is the cis-9 isomer. Parodi detected the cis-12, -13, and -14 isomers, fatty acids not observed by Hay and Morrison (1970). The 18 1 content of Australian butterfat has varied throughout the season from 17.3 to 24.9 M%, with isolated trans unsaturation from 4.3 to 7.6 M%,... 

Catalytic hydrogenation of vegetable oils is widely used to form harder fats and to decrease the content of polyunsaturated fatty acyl groups. The products have a greatly increased resistance to rancidity. However, they also contain fats with trans double bonds as well as isomers with double bonds in unusual positions.251 253 Such compounds may interfere with normal fatty acid metabolism and also appear to affect serum lipoprotein levels adversely. Trans fatty acids are present in some foods. One hundred grams of butter contain 4-8 g, but hydrogenated fats often contain much more. It has been estimated that in the United States trans fatty acids account for 6-8% of total dietary fat.253... 

This unit defines three different tests that are used to evaluate lipid systems. The first two, i.e., iodine value (IV see Basic Protocol I) and saponification value (SV see Basic Protocol 2), are used to determine the level of unsaturation and the relative size (chain length) of the fatty acids in the system, respectively. The free fatty acid (FFA) analysis (see Basic Protocol 3) is self-explanatory. Each of these analyses provides a specific set of information about the lipid system. The IV and SV provide relative information this means that the data obtained are compared to the same data from other, defined lipid systems. In mixed triacylglyceride systems there is no absolute IV that indicates the exact number of double bonds or SV that indicates the exact chain length. The data from the FFA analysis is an absolute value however, the meaning of the value is not absolute. As a quality indicator, ranges of FFA content are used and the amount that can be tolerated is product and/or process dependent. 

Miwa and Yamamoto (31) described a simple and rapid method with high accuracy and reliability for the determination of C8 0-C22 6 fatty acids, which occur in esterified forms in dietary fats and oils and in living cells [the biological effects of routinely consumed fats and oils are of wide interest because of their impact on human health and nutrition (28,29), in particular, the ratio of cu-3 polyunsaturated fatty acid to w-6 polyunsaturated fatty acids (w-3/cu-6) seems to be associated with atherosclerosis and breast and colon cancers (30)]. They report improved separation of 29 saturated and mono- and polyunsaturated fatty acids (C8-C22), including cis-trans isomers and double-bond positional isomers, as hydrazides formed by direct derivatization with 2-nitrophenylhydrazine hydrochloride (2-NPH HC1) of saponified samples without extraction. The column consisted of a J sphere ODS-M 80 column (particle size 4 /xm, 250 X 4.6-mm ID), packed closely with spherical silica encapsulated to reach a carbon content of about 14% with end-capped octadecyl-bonded-spherical silica (ODS), maintained at 50°C. The solvent system was acetonitrile-water (86 14, v/v) maintained at pH 4-5 by adding 0.1 M hydrochloric acid with a flow rate of 2.0 ml/min. Separation was performed within only 22 min by a simple isocratic elution (Fig. 6). The resolution of double-bond positional isomers, such as y-linolenic ( >-6) and a-linolenic acid ( >-3) hydrazides and w-9, >-12, and >-15 eicosenoic acid hydrazides was achieved by use of this column. 

Cold properties of biodiesel are highly correlated to the fatty acid composition. Biodiesel with a high content of saturated fatty acids, such as that from palm oil and coconut oil, possesses poor cold flow properties. On the other hand, biodiesel with a high content of unsaturated fatty acids possesses better flow properties at lower temperatures. However, biodiesel from highly unsaturated fatty acids with more than two double bonds has combustion problems. Therefore, in some countries, the content of highly unsaturated fatty acid methyl esters in biodiesel is kept low (5). 

For the study of the physical and chemical properties of triply unsaturated fatty acids and for the comparison with y-linolenoic acid [6Z,9Z.12Z)-6,9,l2-octadeca-trienoic acid] coworkers of the Unilever Research Centre in Vlaardingen (Netherlands) synthesized some methyl esters of ( ,Z,Z)-trisunsaturated fatty acids 73). For the preparation of the esters of (2E,9Z, 12Z)-2,9,12-octadecatrienoic acid and of (2 ,11Z,14Z)-2,11,14-eicosatrienoic acid (68 a and b) they used the Wittig reaction to introduce the ( )-2-double bond into the starting diunsaturated aldehyde. Reduction of the acid chlorides of (7Z,10Z)-7,10-hexadecadienoie acid and of linolenoic acid (65a and b) with lithium tri-tert-butoxyaluminium hydride affords the corresponding aldehydes 66 a and b which can be olefinated with the stable ylide 67 to methyl ( ,Z,Z)-alkatrienoates 68a, b with a (Z)-2-isomer content of 4.6%73) (Scheme 13). 

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