Supplementatie van autotrofe microalgen aan het voeder van leghennen om eieren aan te rijken met langketen omega-3 vetzuren

The health benefits related to omega-3 polyunsaturated fatty acids (n-3 PUFA), and more specifically the long chain (LC) n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are generally recognized. Since the conversion of the shorter chain n-3 PUFA α-linolenic acid (ALA) to the n-3 LC-PUFA EPA and DHA is rather limited, the direct intake of EPA and DHA is of great importance. However, the daily intake of these n-3 LC-PUFA is below the daily recommended intake of 250 mg EPA+DHA, due to the inadequate consumption of food products naturally rich in n-3 LC-PUFA, such as fatty fish. In this context, enrichment of commonly consumed foods with n-3 LC-PUFA can raise the intake of these fatty acids to the recommended level. Eggs, for example, are generally consumed and form an integral part of the diet, all over the world. Furthermore, the n-3 PUFA profile can easily be modified by supplementation of different n-3 PUFA sources to the diet of the laying hens. Fish oil, as n-3 LC-PUFA source, can, for example, be supplemented to the diet of the laying hens to enrich eggs with n-3 LC-PUFA. However, because of the declining fish stocks and the off-flavours present in the eggs, alternative n-3 LC-PUFA sources must be found. Microalgae can be very promising since the n-3 LC-PUFA present in fish originate from microalgae. Research has already been performed on the supplementation of heterotrophic microalgae (i.e. they obtain their nutrients and energy from organic compounds which are produced by other organisms, via fermentation processes). However, from a sustainability viewpoint, it would be more interesting to use autotrophic microalgae (i.e. they use light and CO2 to form their biomass) as alternative n-3 LC-PUFA source to enrich eggs with n-3 LC-PUFA. The global aim of this doctoral work was therefore to study the supplementation of autotrophic microalgae to the diet of laying hens to enrich eggs with n-3 LC-PUFA. First of all, it was shown that the supplementation of different microalgal species (Phaeodactylum tricornutum, Nannochloropsis oculata, Isochrysis galbana and Chlorella fusca), leads to different n-3 LC-PUFA enrichment efficiencies in the egg yolk, due to the different n-3 PUFA profiles and the different bioaccessibility of the n-3 PUFA. ALA rich sources, such as Chlorella, lead to the lowest n-3 LC-PUFA enrichment efficiency since the conversion of ALA to n-3 LC-PUFA is rather limited. n-3 LC-PUFA rich sources such as Phaeodactylum, Isochrysis and Nannochloropsis lead to significantly higher n-3 LC-PUFA enrichment efficiencies. However, the enrichment efficiency when using Nannochloropsis is drastically lower in comparison with Phaeodactylum and Isochrysis. Nannochloropsis contains a cell wall, which is very hard to digest and thus may lead to a lower bioaccessibility of the n-3 PUFA compared to the other autotrophic microalgal species Isochrysis and Phaeodactylum, which do not contain a (rigid) cell wall. This was confirmed by comparing the n-3 LC-PUFA enrichment efficiency obtained by supplementation of Nannochloropsis to the diet of the laying hens in either intact or disrupted form. The disrupted form, with a higher bioaccessibility of the n-3 PUFA, lead to significant higher n-3 LC-PUFA enrichment efficiencies compared to the intact form. The n-3 LC-PUFA profile, on the other hand, has less influence on the n-3 LC-PUFA enrichment efficiency since no difference was observed between the disrupted form of Nannochloropsis (EPA sources) and Isochrysis (DHA source). Not only different microalgal species lead to different n-3 LC-PUFA enrichment efficiencies, but also the supplementation dose has a significant impact. An increase in enrichment efficiency, obtained by supplementation of Isochrysis to the diet of the laying hens, was observed until a supplementation dose of 120 mg n-3 PUFA per 100 g feed but at higher n-3 PUFA doses, a decrease in enrichment efficiency was observed. Thus, 120 mg n-3 PUFA per 100 g feed is the most appropriate supplementation dose. Furthermore, it was observed that the enrichment of n-3 LC-PUFA in the egg yolk is a gradual process, with the maximal enrichment after 14 days of supplementation. In addition to the enrichment of n-3 LC-PUFA in the egg yolk by supplementation of autotrophic microalgal species to the diet of the laying hens, changes in the egg yolk color were also observed, due to carotenoid enrichment in the egg yolk. This could lead to additional benefits such as a higher protection of the n-3 LC-PUFA against oxidation due to the antioxidative nature of several carotenoids. However, since the yolk color is an important quality parameter, it should remain within the range of consumer acceptability. To evaluate the n-3 LC-PUFA enrichment efficiency obtained by the supplementation of commercial n-3 PUFA sources (flaxseed, fish oil and a commercially available heterotrophic microalgal species, i.e. Schizochytrium ) compared to autotrophic microalgae, a comparative study was conducted. Isochrysis was selected as the most optimal microalgal species to use since it leads to the highest n-3 LC-PUFA enrichment efficiency while still retaining an acceptable yolk color. The four n-3 PUFA sources were supplemented in the same n-3 PUFA supplementation dose: 120 mg n-3 PUFA per 100 g feed. This study showed that next to the n-3 PUFA profile also the bioaccessibility of the n-3 PUFA plays an important role. Fish oil (as EPA and DHA source) leads to the highest n-3 LC-PUFA enrichment efficiency compared to the other n-3 PUFA sources. This suggested a higher bioaccessibility of the n-3 PUFA supplemented as oil compared to n-3 PUFA supplemented as biomass. The difference in enrichment efficiency between the other three n-3 PUFA sources, supplemented as biomass, can be explained by the difference in n-3 PUFA profile. Higher ratios of ALA+SDA (with a rather inefficient conversion to DHA) to n-3 LC-PUFA lead to lower n-3 LC-PUFA enrichment efficiencies. Taken all results together, autotrophic microalgae could serve as n-3 LC-PUFA source to enrich eggs with these fatty acids. However, the n-3 PUFA profile and n-3 PUFA bioaccessibilitiy of the microalgal species should be taken into account. Evaluating the economical aspect of the n-3 PUFA enriched eggs obtained by supplementation of autotrophic microalgae, it was concluded that the cost is too high due to the high cost price of the autotrophic microalgal biomass compared to the already available n-3 PUFA sources such as flaxseed, fish oil or heterotrophic microalgal species. Several organizations, microalgal producers and researchers however predict a decrease of the production cost in the near future, which will make it possible to compete with the currently commercially available n-3 PUFA sources. Next to this, additional benefits could be related to the supplementation of autotrophic microalgae to the diet of the laying hens such as for example the additional health benefits and higher oxidative stability of the n-3 LC-PUFA related to the enrichment of carotenoids.status: publishe