Biotechnology
in the reduction of thrombosis and heart diseases. They are also key elements in the development of brain and retina (Léger et al., 1994). In
this area, they can be used as ingredients in formulations of artificial
milk for preterm infants. According to a recent report (Cornet, 1998),
eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and arachidonic
acid (ARA), mainly sold as a form of triglycerides or ethyl esters, are
evaluated in the range of 2,400 to 60,000 francs per kilogramme.
To date, PUFAs are mainly obtained from fish oil, which is a relatively
cheap raw material. Nevertheless, microalgae can be considered as agood
alternative source of production as already suggested by Yongmanitchai
& Warcl ( 1989). Indeed, apart from PUFAs, many other metabolites of
high added value can be obtained from microalgae such as astaxanthine,
β-carotene or super-oxide dismutase (Vίlchez et al., 1997). Moreover,
contrary to fish oil, microalgae lipicls are free from cholesterol which
could be counterproductive for reducing blood lipid level (Cohen &
Cohen, 1991). A better production control could also limit the seasonal
variations which constitute an important drawback for industrial
productions (Robles Medina et al., 1995). Only inexpensive substrates
are required for PUFA production from microalgae: marine water, CO
2
,
minerals, and solar energy.
To be competitive with fish oil, microalgae lipid production has, however,
to be improved. First of all, a biomass productivity enhancement is
required by means of metabolism engineering, strain selection (Cohen,
1990), reactor design, light absorption and attenuation modelling
studies (Acién Fernândez et al., 1998). An improvement of the separation-purification processes is also required in order to provide pure
PUFAs. In this area, different purification methods already exist, from classical purification using urea inclusion (Cohen & Cohen, 1991) to more
sophisticated methods (Baudimant et al., 1998). Enzymatic PUFA
enrichment of the microalgae lipicl extracts is a good alternative allowing
the reduction of the number of purification steps. The use of biological
catalysts also reduces energy neecls and avoids the use of chemicals.
Moreover, the advantages of the use of lipases lay in their specificities.
The different strategies for the enzymatic enrichment of a particular
lipid fraction, from fish or vegetable oils, are shown on figure 1 ( Wanasundara & Shahidi, 1998; Huang et al., 1997). Different reactions can
be carried out: hydrolysis, esterification or transesterification (acidolysis
or alcoholysis) using lipases showing different specificities for or against
PUFAs. The tree fatty acid fraction obtained through hydrolysis of the
total lipid extract can be esterifiecl in orcler to provide PUFAs in a proper
form for their commercialisation. The partial phospholipids, glycolipids and triacylglycerides of the fraction obtained through hydrolysis
or alcoholysis can be esterified with exogenous free PUFAs to improve
enrichment.
Previously to enrichment of P. ententnm lipid extract, interesting for
its EPA and ARA contents, the purpose of this work is to study lipasecatalysed esterification of ptire ARA. First, through screenings, the
205
in the reduction of thrombosis and heart diseases. They are also key elements in the development of brain and retina (Léger et al., 1994). In
this area, they can be used as ingredients in formulations of artificial
milk for preterm infants. According to a recent report (Cornet, 1998),
eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and arachidonic
acid (ARA), mainly sold as a form of triglycerides or ethyl esters, are
evaluated in the range of 2,400 to 60,000 francs per kilogramme.
To date, PUFAs are mainly obtained from fish oil, which is a relatively
cheap raw material. Nevertheless, microalgae can be considered as agood
alternative source of production as already suggested by Yongmanitchai
& Warcl ( 1989). Indeed, apart from PUFAs, many other metabolites of
high added value can be obtained from microalgae such as astaxanthine,
β-carotene or super-oxide dismutase (Vίlchez et al., 1997). Moreover,
contrary to fish oil, microalgae lipicls are free from cholesterol which
could be counterproductive for reducing blood lipid level (Cohen &
Cohen, 1991). A better production control could also limit the seasonal
variations which constitute an important drawback for industrial
productions (Robles Medina et al., 1995). Only inexpensive substrates
are required for PUFA production from microalgae: marine water, CO
2
,
minerals, and solar energy.
To be competitive with fish oil, microalgae lipid production has, however,
to be improved. First of all, a biomass productivity enhancement is
required by means of metabolism engineering, strain selection (Cohen,
1990), reactor design, light absorption and attenuation modelling
studies (Acién Fernândez et al., 1998). An improvement of the separation-purification processes is also required in order to provide pure
PUFAs. In this area, different purification methods already exist, from classical purification using urea inclusion (Cohen & Cohen, 1991) to more
sophisticated methods (Baudimant et al., 1998). Enzymatic PUFA
enrichment of the microalgae lipicl extracts is a good alternative allowing
the reduction of the number of purification steps. The use of biological
catalysts also reduces energy neecls and avoids the use of chemicals.
Moreover, the advantages of the use of lipases lay in their specificities.
The different strategies for the enzymatic enrichment of a particular
lipid fraction, from fish or vegetable oils, are shown on figure 1 ( Wanasundara & Shahidi, 1998; Huang et al., 1997). Different reactions can
be carried out: hydrolysis, esterification or transesterification (acidolysis
or alcoholysis) using lipases showing different specificities for or against
PUFAs. The tree fatty acid fraction obtained through hydrolysis of the
total lipid extract can be esterifiecl in orcler to provide PUFAs in a proper
form for their commercialisation. The partial phospholipids, glycolipids and triacylglycerides of the fraction obtained through hydrolysis
or alcoholysis can be esterified with exogenous free PUFAs to improve
enrichment.
Previously to enrichment of P. ententnm lipid extract, interesting for
its EPA and ARA contents, the purpose of this work is to study lipasecatalysed esterification of ptire ARA. First, through screenings, the
205