Helena L. Fernandes

Supercritical CO2 extraction of carotenoids and other lipids from Chlorella vulgaris

Freeze-dried samples of the microalga Chlorella vulgaris were submitted to supercritical CO2 at temperatures of 40 and 55 °C and pressures up to 35.0 MPa. This study was carried out on whole and crushed algae. The extraction yields of carotenoids and other lipids were low in the former case and improved significantly in the latter one. Extraction yields of carotenoids and other lipids increased with pressure. The fraction of carotenoids in the oil was also greater at higher pressures. On the other hand, supercritical CO2 extraction of carotenoids compared favourably with hexane and acetone extractions.

Evolution of pigment composition in Chlorella vulgaris

The onset of carotenogenesis in Chlorella vulgaris and the change in nature and concentration of pigments with time was studied. The succession of pigments observed was interpreted in terms of relative efficiencies of carotenoid interconversion pathways, and this might be used to monitor the progress of the carotenogenic process. This work is relevant to the use of dry Chlorella biomass, as a naturally encapsulated form of a natural colouring ingredient, in animal feed.

Microporous Hollow Fibres for Carbon Dioxide Absorption: Mass Transfer Model Fitting and the Supplying of Carbon Dioxide to Microalgal Cultures

A method of supplying to photosynthetic algal cultures was devel- CO 2 oped based on mass transfer measurements of through microporous hydro- CO 2 phobic hollow -bres for various gas and liquid Now rates. A mathematical model was derived to describe the mass transfer. The designed hollow -bre module led to overall mass transfer coefficient values ranging from 1E26 ) 10~3 to 2E64 ) 10~3 cm s~1. Higher efficiencies of the transmission were obtained CO 2 at high liquid Now rates and low gas Now rates. The use of microporous hydro- phobic hollow -bres enabled an enhancement of the carbon dioxide transfer per area of membrane surface by a factor of 10, in comparison to operation with silicone tubing. The hollow -bre module was operated in an external bypass to a 1d m 3microalgae culture vessel. In this system the algal growth pattern was similar to that obtained with a control culture where was bubbled. CO 2 However, the dissolved oxygen concentration was always lower in the vessel in which was supplied by the module. 1998 SCI. CO 2 ( J. Chem. T echnol. Biotechnol. 71 ,6 1 E70 (1998)

Temperature profiles of cellular growth and exopolysaccharide synthesis by Botryococus braunii Kütz. UC 58

Temperature profiles (range 20–33 °C) were obtained for growth and exopolysaccharide (EPS) biosynthesis of the microalga Botryococcus braunii strain UC 58 under photoautotrophic conditions. The maximum temperature for growth was 32 °C and the temperature dependence of the specific growth rate was described by the Hinshelwood equation based on the Arrhenius relationship. The optimal range of temperatures for growth and extracellular EPS synthesis (25–30 °C) concurred and production of 4.5–5 g l−1 of EPS was obtained routinely, leading to high broth viscosities. Below 23 °C EPS biosynthesis was negligible, although the specific growth rate maintained high values. At supraoptimal temperatures EPS biosynthesis decreased, accompanying the increase in doubling time.The polymers formed at temperatures within the optimal range for production, when dissolved in water, produced solutions (2 gl−1) with the highest viscosity, suggesting that their molecular weight showed the highest values. The degree of polymerization of the EPS synthesized at suboptimal and supraoptimal temperatures was significantly below the values within the optimal range.

Eicosapentaenoic acid-rich biomass production by the microalga Phaeodactylum tricornutum in a continuous-flow reactor

The marine diatom Phaeodactylum tricornutum Bohlin is a potential source of the pharmaceutically valuable w3 polyunsaturated fatty acid eicosapentaenoic acid (EPA). The results of indoor continuous growth of Phaeodactylum tricornutum Bohlin are reported. The relationships between dilution rate (D), nitrate concentration and chemical composition were studied. Higher biomass and lipid productivities were obtained at low D values. EPA was found to be an intermediate metabolite and the best productivity (6 mg 1-r day-r) was achieved for D values ranging from 0.32 to 0.50 day-‘. Under optimum conditions, 84 and 1170, respectively, of total recovered EPA were present in monogalactosyldia~lglycerol (MGDG) and in triacylglycerol (TG) moieties, respectively. Recorded EPAI! and EPA/20,4 03 ratios for all tested dilution rates were among the highest values ever reported, showing EPA purification to be easier to perform from this starting material than from many others commonly in use. Copyright 0 1996 Elsevier Science Ltd.

Lipid production by Phaeodactylum tricornutum

The results of a three month investigation on the outdoor mass culture of Phaeodactylum tricornutum Bohlin are reported. Experiments carried out from January to March 1989 gave an average output rate of 4·0 g m−2 day−1 in ash-free dry weight (AFDW) basis for semicontinuous mode (days 0–74) and 2·0 g m−2 day−1 for batch mode (days 74–84). Eicosapentaenoic acid (20:5 ω3 EPA) was the predominant fatty acid synthesized by this diatom during semicontinuous growth constituting 3·9% of AFDW, yielding 0·15 g m−2 day−1. The content of EPA was decreased to 0·7% of AFDW during batch mode, 16:0 and 16:1 becoming the main fatty acids. The relationship between optical density and output productivity rate was studied. In the range studied, the lower the concentration the higher the productivity and the lower the lipid production rate. Several flocculant systems were tried and calcium hydroxide, Ca(OH)2, was found to be best at concentrations from 30 to 100 mg litre−1, in an apparently random way. The addition of chitosan did not improve the efficiency of flocculation.

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.

Rheological behaviour of the culture medium during growth of the microalga Botryococcus braunii

Abstract A non-axenic strain of the microalga Botryococcus braunii Kutzing, isolated from a small lake in Portugal, when cultured at 25°C in mineral medium and under continuous illumination, showed a poor production of hydrocarbons (5% of the dry biomass) but excreted remarkably high quantities of an exopolysaccharide (4–4·5 g litre −1 ) into the medium. The production of the soluble polysaccharide, which contains galactose, fucose and uronic acid residues, occurs mainly after the exponential phase of growth. The rheological properties of broth during growth were studied. The increase of polysaccharide concentration as a consequence of its continuous biosynthesis, changes the medium behaviour from Newtonian to non-Newtonian with a flow characterized by a power-law equation. This behaviour becomes Newtonian again, when the culture is maintained for a longer period of time.