Astaxanthin production by
microalgae - applications in fish
Aquaflow Technical Leaflet 2003-131
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
Commercially-
available astaxanthin is produced by chemical synthesis and new
‘natural’ alternatives are sought, in part due to current growing
concern on food safety and synthetic pigment issues. Among these sources,
the microalgae Haematococcus
pluvialis has
promising potential, although
pigment production from this microalgal species poses several problems. 1)
The microalgae has a slow growth rate and 2) astaxanthin is a secondary
product that accumulates when cell growth has stopped and the microalgae is
in a cell phase called aplanospore, similar to a resistant phase. At this
stage, H. pluvialis has a very rigid cell wall, restricting pigment
extraction and assimilation when ingested by fish.
The
objectives of this project were to optimise culture conditions in order to
stimulate microalgae biomass production and to perform a thorough analysis
of the factors that induce and favour astaxanthin synthesis and
accumulation. These were achieved by the following:
Culture
conditions and media optimisation: by optimising each component separately
in a semi-continuous culture system. This media, called OHM (Optimal Haematococcus
Medium) has proven to be very effective, as high daily cell
productivity has been obtained with these culture conditions, which cannot
be maintained by means of traditional formulations.
Factors
inducing astaxanthin synthesis and accumulation: light intensity and
nutrient deficiencies are the main factors involved in astaxanthin
accumulation during the aplanospore phase. However their relative importance
is a subject of controversy. Nitrogen shortage in the culture media is the
main agent responsible for regulating pigment synthesis by the microalgae.
Cultures kept at high light intensities consume nitrogen more quickly;
therefore, astaxanthin synthesis begins sooner and accumulates in greater
quantities.
Maximising
astaxanthin production: From 1) and 2) above, a 2-stage production system
was designed to maximise biomass and pigment production. During the first
stage, biomass is obtained by the semi-continuous production of green
vegetative cells. In the second phase, astaxanthin is produced from H. pluvialis reared at high light intensities in batch culture. The
residual nitrogen consumption from the semi-continuous culture causes the
cells to enter the aplanospore phase, thus initiating astaxanthin synthesis.
Scale-up
version to pre-industrial level of the production system: Flat
photobioreactors with a 100 l culture capacity were used to induce
astaxanthin synthesis by the two phases described above. The results from
this pilot trial were similar to those obtained under experimental
conditions.
Digestibility
improvement and ornamental fish pigmentation trials: Previous studies
reported that the addition of nitrogen to astaxanthin-rich cultures induced
aplanospore germination and caused partial cell wall degradation, allowing
astaxanthin extraction. The pigment digestibility and retention were tested
in ornamental fish (Carassius auratus).
Aplanospore germination induction improved biomass digestibility and the
retention of the natural pigment retention was greater than control cultures
supplemented with synthetic astaxanthin.
The
innovations provided by this research have lead to a culture system for H
.pluvialis, allowing biomass productivity and astaxanthin accumulation
at high concentrations.
For more information:
Dr.
Jaime Fábregas
Departamento de Microbiología,
Facultad de Farmacia
Universidad de Santiago de Compostela
15782 Santiago de Compostela - Spain
Tel.: +34 981 59 22 10; Fax: +34 981 59 22 10
E-mail:
fabregas@usc.es