Erucic acid digestibility

Wiseman (1986) reported a reduction in digestibility and in available energy of up to 30% due to oxidation of fat as a result of overheating during processing. A number of naturally occurring fatty acids can also adversely affect overall fat utilization. Two such components are erucic acid present in rapeseed oils and some other Brassica spp., and the cyclopropenoid fatty acids present in cottonseed. 

When Carroll (1958) fed fatty acids as the methyl or ethyl esters, these esters were more efficiently absorbed than the free fatty acids by the rat. However, for fatty acids in the form of triglycerides (TG) the effect was opposite for saturated and monounsaturated fatty acids. A saturated TG was less digestible than the fatty acid itself, while a TG composed of a monounsaturated fatty acid was absorbed better than its free fatty acid (Carroll and Richards, 1958). Triglyceride fatty acids also influence absorption, particularly with the poorly digested fatty acids. For example, the absorption coefficient of erucic acid was increased from 72% when fed as ethyl erucate to 80% when ethyl erucate was mixed with soybean oil (Ziemlanski et al., 1973a). Even the absorption of 22 1 in HEAR oil was improved by mixing... 

Finally, it seems clear that the poor digestibility of HEAR oil in the rat can be attributed to the 22 1 content of the oil (Table I). In these HEAR oils, 22 1 comprised 40-50% of the fatty acids. This is in marked contrast to the newly developed low erucic acid rapeseed (LEAR) oils (<5% 22 1 by definition) which are well digested by rats with a digestibility of 96% which is equal to that of peanut oil (Rocquelin and Leclerc, 1969). 

Erucic (22 1 n-9) and gandoic (20 1 n-9) acids proved to be slightly more digestible when present in small amounts, such as in LEAR oils, than when present at higher concentrations such as in HEAR oils. A digestibility of 91 % was recorded for erucic acid in LEAR oil that contained only 1.9% of this acid, whereas a HEAR oil with 45% erucic acid showed a digestibility of 73% for this acid (Rocquelin and Leclerc, 1969). 

The influence of other fatty acids in the dietary fat on the accumulation of the cardiac TG was also investigated. It is evident from the results presented in Table V, that neither 18 2, 18 3, nor saturated fatty acids affect the erucic acid induced accumulation of cardiac TG in the rat. The digestibility of erucic acid was not significantly different between each of these diets in the three studies reported in Table V. It may therefore be concluded that erucic acid, once absorbed, will accumulate in the heart in the form of TG quite independent of the concentration of other fatty acids. 

Experiments in which rats were fed diets containing similar levels of erucic (c/s 22 1 n-9) and brassidic (trans 22 1 n-9) acids, show that the c/s-docosenoic acid isomer is more cardiopathogenic than the trans isomer (Astorg and Levillain, 1979). However, the cis isomer may be much better absorbed than the trans isomer, as indicated by their respective digestibility coefficients. Rocquelin et al. (1975) found that the trans isomer was less digestible (46%) than the cis isomer (83%), and this was shown by the fact that the rat hearts contained 1 mg/g of the trans isomer and 18 mg/g of the... 

---