Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 9 Eicosenoid isomers in partially hydrogenated menhaden oil. (From Ref. 18.)
trans Fatty acids are formed by some bacteria primarily under anaerobic conditions
[25]. It is believed that the formation of trans fatty acids in bacterial cell
membranes is an adaptation response to decrease membrane fluidity, perhaps as a
reaction to elevated temperature or stress from solvents or other lipophilic compounds
that affect membrane fluidity (4-chlorophenol).
Not all bacteria produce appreciable levels of trans fatty acids. The transproducing
bacteria are predominantly gram negative and produce trans fatty acids
under anaerobic conditions. The predominant formation of trans is via double-bond
migration and isomerization, although some bacteria appear to be capable of isomerization
without bond migration. The action of bacteria in the anaerobic rumen
results in biohydrogenation of fatty acids and results in trans fatty acid formation in
dairy fats (2–6% of total fatty acids). The double bond positions of the trans acids
in dairy fats are predominantly in the �11 position, with smaller amounts in �9,
�10, �13, and �14 positions [26].
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