Flaxseed triacylglycerols

Wanasundara et al. (1999) reported that neutral lipids (acylglycerols and fatty acids) constitute 96% of the total lipid in flaxseed, whereas polar lipids (glycolipids and phospholipids) account for 1.4%. Stenberg et al. (2005) observed similar findings except that less phospholipid was detected. Froment et al. (1999) discussed the effects of cultivar, location, and late harvest on phospholipid content. Neutral lipid fraction of flaxseed meal was 95-98% triacylglycerols (TAG) and thus accounts for the predominant lipid in flaxseed (Oomah et al., 1996). 

ALA is found in plant chloroplast membranes, animal tissues, zooplankton, phytoplankton, and marine species. In plants, ALA is found in leaves, mainly in glycolipids and in triacylglycerols in certain seed oils (rapeseed, flaxseed, per-illa seed, chia seed), beans (soybeans, navy beans), and nuts (walnuts) (2,3). 

The characteristic fatty acid patterns of plant triacylglycerols are to some extent under genetic control (see Section VI). In addition, environmental factors may modify the basic patterns, the extent of modification depending on the species. Thus the seed oils of plants grown in cool climates tend to be more unsaturated than those grown in warm climates (Hitchcock and Nichols, 1971). The chief influence seems to be on the characteristic fatty acid of the seed, so that for example in flaxseed oil there is a marked decline in the proportion of linolenic acid between 10° and 30°C and a corresponding increase in the proportion of its precursor, oleic acid (Canvin, 1965). Similarly, the proportion of linoleic acid in sunflower seed oil steadily declines between 10° and 30°C, to be replaced by oleic acid. Yet the linoleic content of safflower and the ricinoleic acid of castor are unaffected by the same variation in temperature (Canvin, 1965). All rules have exceptions, and the experiments of Appelqvist (1975) showed that different lines of zero-erucic acid rape could respond differently to the same climatic variations. 

According to Oomah et al. (1996), extraction of residual oil from commercially available flaxseed meal with hexane alone resulted in a higher oil recovery than methanol/hexane or methanol-ammonia-water/hexane. However, it should be noted that their starting material was meal and not seeds of flax. Analysis of the extracted lipids from the meal showed (Table 3) that hexane preferentially extracted the neutral lipids primarily composed of triacylglycerols (TAG). Neutral lipid fraction of oil extracted with methanol/hexane solvent system contained more monoacylglycerols (MAG), diacylglycerols (DAG) and free fatty acids (FFA) than the lipids extracted by other solvent systems (Table 3). Methanol/hexane solvent system extracted more polar lipids than methanol-water-am-monia/hexane system and this lipid fraction was composed mainly of phosphotidylcholine (PC). Polar lipids of methanol-ammonia-water/hexane extracted lipids contained also phosphotidylethanolamine (PE), lysophosphatidylcholine (LPC) and some unidentified compounds. 

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