Monoethylenic fatty acids

TABLE 1. Principal n-3 Fatty Acids, Saturated, and Monoethylenic Fatty Acid Isomers (w/w%) in Triacylglycerols and Wax Esters of Copepods and Commercial Oils of Pelagic Species of North Atlantic Fish Likely to be Consuming Copepods. 

The R-500 has an atypically high proportion of 20 1 n-7, but some other 6. campestris cultivars (cv. Polar and cv. Span) seem to have had proportions of 7 or 8% of 20 1 n-7 in total 20 1 (Hougen and Wasowicz, 1979). There may be other factors such as maturity of seed which also require investigation, as they affect fatty acid composition (Izzo et a/., 1979) or distribution (Harris and Norton, 1979), but it seems that the LEAR varieties wih a low erucic acid content have Cig, C20 and C22 monoethylenic fatty acids dominated by the "n-9" isomers, with 4-6% of monoethylenic "n-7" acid in the Cie chain length, and lesser proportions in the C20 and C22 chain lengths. These n-7 isomer details are similar to the scanty information available for other vegetable oils. 

The monoethylenic fatty acids are composed mainly of palmitoleic acid (16 1 -7), oleic acid (18 1 n-9) and its isomer cw-vaccenic acid (18 1 n-1). These are often accompanied by large amounts of (20 1 n-9) and (22 1 n-9). 

One attempt to classify fish fats (Lambertsen, 1978) is exemplified in Table 10.5. The percentages of as few as eight fatty acids of marine oils and lipids add up to about 80% of those present at 2-3% or more. Nutritionists may request 18 0, 18 2, 18 3 and 20 4, so 12 fatty acids have also been employed. Compared to lard, beef or sheep fats (see above), fish oils are considered highly unsaturated. One of the common trading standards of fish oils is the iodine value (IV). The iodine values of the monoethylenic fatty acids are 90 for 18 1 and 420 for 20 5n-3. Because of the extreme differences in IV for the typical two types of acids in Table 10.5, it was possible (Ackman, 1966) to develop an empirical formula percent polyunsaturated fatty acids = 10.7 + 0.337 (iodine value of oil—100). Table 10.6 shows the applicability of this formula. Since one of the objectives of the preparation of encapsulated fish oil products is to deliver 20 5n-3 and 22 6n-3 (Ackman et al., 1989 Sagredos, 1992), the iodine value is an easily utilized index of the suitability of raw materials for this or other uses. 

Figure 10.4 Comparison of origins of C16-C22 monoethylenic fatty acids in a marine Canadian Pacific herring (Clupea pallasii) and a freshwater alewife (Canadian Great Lakes Alosa pseudoharengus). Adapted from Ackman (1982).

A method for the complete structural analysis of complex mixrnres of methyl esters of saturated and un-samrated fatty acids has been performed by 2-D TLC. Adsorbent silica gel impregnated with a 10% solution of dodecane was used for the first direction with acetonitrile-acetone (1 1, v/v) as eluent. The silica gel for the second direction was impregnated with a 20% AgNOs and dipropyl ether-hexane (2 3, v/v) was used as eluent. In this way, complete separation of a standard mixture of the methyl esters of six saturated, nine monoethylenic, and three polyenic esters were achieved. 

The minor fatty acids of two LEAR oils (B. napus cv. Tower and 6. campes-tris cv. Candle) are listed in Table IV with the exception of some of the monoethylenic isomer details which will be found in Tables V and VI. The minor fatty acid details were compared for a HEAR (cv. Target) and a LEAR (cv. Tower) and it was concluded that the odd-chain, /so, anteiso, and c/s and trans 15 1 n-10 fatty acids had not been modified by the genetic manipulation necessary to change HEAR varieties to LEAR varieties (Sebedio and Ackman, 1979). This finding applied to both B. napus (cv. Tower) and 6. campestris (cv. Candle) oils (Ackman and Sebedio, 1979). 

The picolinyl ester of a mono-acetylenic fatty acid gave a spectrum which resembled that from its monoethylenic analogue except that there was a gap of 24 amu for fragmentations on either side of the triple bond [172], A series of di-acetylenic fatty acids gave spectra which were rather complex, but the terminal triple bond generally exhibited a fragmentation with a gap of 24 amu [174],... 

Upon expression the seeds yield about 50% (by weight) of a liquid wax composed of high molecular weight C20 and C22 esters of straight long-chain, monounsaturated fatty acids and alcohols (up to 85% of the oil), including monoethylenic acids composed mainly of eicosenoic acid (34%) and docose-noic acid (14%) alcohols, including eicose-nol (22%) and docosenol (21%) trace amounts of oleic and palmitoleic acids. 

---