Accumulation of rumenic acid in eggs upon supplementation of laying hens’ diet with Ricinodendron heudelotii seed oil, a natural source of α-eleostearic acid

For several years, conjugated linoleic acids (CLA) and docosahexaenoic acid (DHA) have drawn the interest of scientists for their health benefits and their potential role as treatment against some health disorders such as cancer, diabetes and cardiovascular diseases. Among CLA, the isomer cis 9, trans 11 named rumenic acid (RA) has been particularly studied. However, it is found in small quantities in the human diet. Concerning DHA, which is known to play a major role in the brain and in many physiological functions, it needs to be provided by the food because it cannot be synthetized in sufficient amounts by humans. Many studies have investigated how to enrich food, and especially eggs, a common foodstuff, in DHA and, to a minor extent, in RA. Interestingly, it has been found that RA can be synthesised from α-eleostearic acid (α-ESA) in some animals, including the laying hen. α-ESA, a conjugated linolenic acid (CLnA), is found in significant amounts in the kernels of an African tree, the Ricinodendron heudelotii. The conversion of α-ESA in RA involves the action of an unknown enzyme with a Δ13-reductase activity. Regarding DHA, it can be enriched in eggs by feeding laying hens with flaxseeds or more efficiently with fish oil. In this master thesis, we wanted to investigate to what extent eggs could be enriched in RA. Another objective of this study is to demonstrate whether increasing amounts of α-ESA in the diets of laying hens could enhance the conversion of α-linolenic acid (ALA), the precursor of omega-3 anabolic processing, into DHA, thus allowing a higher amount of DHA in egg yolks. For this purpose, we fed laying hens with a staple feed enriched in flaxseeds (as a source of ALA). This staple feed was supplemented with three different levels (0%, 5% or 10%) of R. heudelotii oil. The results of this study show that an increasing amount of dietary α-ESA allows a higher content of RA in egg yolks. However, it does not seem that R. heudelotii oil induce a higher amount of DHA in the yolk. On the contrary, it even seems to reduce it slightly. However, the total amount of omega-3 fatty acids is higher in the “10% group” and to a lesser extent in the “5% group” compared to the control group. This significant amount of omega-3 in these groups is due to a high ALA content. The ratio between omega-6 and omega-3, even if increased in the 5% and 10% groups, is still in line with dietary recommendations (between 1/1 and 4/1). This research highlights the interest of using dietary CLnA to enrich egg yolks in RA. Feeding laying hens with 10% of R. heudelotii oil in addition to a staple feed enriched in flaxseeds allow the production of eggs containing 571 mg of RA and 81 mg of DHA.