Milking of microalgae revisited

Dunaliella salina is een groene alg die in staat is om grote hoeveelheden bètacaroteen te produceren als hij gestrest wordt. Een nieuw proces dat is voorgesteld, is om dez alg continu te kweken in een gesloten fotobioreactor en gelijktijdig de carotenoïden uit de biomassa te extraheren. Voor deze extractie wordt een tweefase-systeem toegepast, met dodecaan als biocompatibele organische fase. Het idee hierachter was dat de cellen hun carotenoïden aan de organische fase afstaan en tegelijkertijd nieuwe carotenoïden produceren om hun voorraad op te vullen. Echter, hoe het mechanisme achter dit proces precies werkte was nog onbekend. Om het mogelijk te maken het voorgestelde tweefase systeem te optimaliseren is het nodig om het mechanisme achter de extractie precies te begrijpen. Bovendien, zodra het mechanisme bekend en beheersbaar is, kan het tweefase-syteem worden toegepast ook op andere microalgen, zoals bijvoorbeeld voor de productie van biodiesel

Phase toxicity of dodecane on the microalga Dunaliella salina

In the so-called milking process of Dunaliella salina carotenoids are extracted and simultaneously produced by the culture, whilst the biomass concentration remains constant. Different theories exist about the extraction mechanisms although none have been proven yet. In this research, direct contact between dodecane and cells during the extraction process was studied microscopically and effects of direct contact were determined during in situ extraction experiments. Our results showed that water– solvent interphase contact resulted in cell death. This cell death and consequent cell rupture resulted in the release and concomitant extraction of the carotenoids. Furthermore, it has been suggested to add a small amount of dichloromethane to the biocompatible dodecane to create an organic phase with more extraction capacity. Our results showed that the addition of dichloromethane resulted in increased cell death and consequently the extraction rate increased. The improved solubility of carotenoids in an organic phase with dichloromethane did not significantly increase the extraction rate

Pro’s en contra’s van rijden op dieselolie uit algen

Het wegtransport slorpt bijna een kwart van al onze energie op. Om dit aandeel te verduurzamen is een keuze voor dieselolie uit algen uit energetisch oogpunt een zinnige optie. Vergeleken met elektrische auto's is er sprake van aanzienlijke efficiencywinst. Wel vergt de algenkweek veel ruimte. Zelfs als de huidige auto's vier keer zo efficiënt worden is hiervoor nog steeds een oppervlakte ter grootte van de Provincie Groningen nodig

Mechanism of extraction of Beta-Carotene from microalga Dunaliellea salina in two-phase bioreactors

We show that it is possible to extract beta-carotene selectively from Dunaliella salina in two-phase bioreactors. The cells continue to produce beta-carotene and the extracted part is substituted by newly produced molecules. This process is called "milking." We performed several experiments to understand the exact mechanism of the extraction process. The results show that direct contact between the cells and the biocompatible organic solvent was not a requirement for the extraction but it accelerated the extraction. Electron microscopy photographs showed an undulated shape of the cell membrane and a space between the cell and the chloroplast membranes in the cells growing in the presence of dodecane (a biocompatible solvent). Extra-chloroplast beta-carotene globules located in the space between the cell and the chloroplast membranes were observed in these cells as well. It was shown that dodecane was taken up by the cells. The concentration of dodecane in the cells was about 13 pg.cll(-1). It can be concluded that dodecane uptake by the cells is responsible for the morphological changes in the cells and leads to more activity in the cell membrane. The results suggest two possible modes of extraction. One of the mechanisms is transport of the globules from the chloroplast to the space between the cell and the chloroplast membranes and subsequently from there to the outside by exocytosis. Another possible mode for the extraction could be release of beta-carotene from the globules as a result of alterations in the membrane in response to the uptake of dodecane. beta-Carotene molecules diffuse from the chloroplast to the space between the cell and the chloroplast membranes and from there to the medium either by diffusion or by exocytosis after accumulation in the vesicles. (C) 2004 Wiley Periodicals, Inc

Use of methylene blue uptake for assessing cell viability of colony-forming microalgae

During the past few years, interest in microalgae has grown, mainly because of their potential for biofuel production. Botryococcus braunii, a green microalga that can accumulate more than half of its dry weight as hydrocarbons, is one of the most important examples. This microorganism grows in colonies and there has been no reliable viability protocol reported for this species as yet. Knowing the number of dead cells in cultures is essential for the development of efficient bioprocesses such as non-destructive extraction procedures (“milking”) to obtain lipid soluble substances from microalgal biomass. Our study presents a simple colorimetric method to determine the proportion of living to dead cells in cultures, based on the uptake of methylene blue in solution by dead B. braunii cells. The main parameters influencing this process were investigated and used to develop a protocol. This technique was validated using flow cytometry and Neochloris oleoabundans, and appears not to be limited to use with B. braunii

Continuous production of carotenoids from Dunaliella salina

During the in situ extraction of ß-carotene from Dunaliella salina, the causal relationship between carotenoid extraction and cell death indicated that cell growth and cell death should be at equilibrium for a continuous in situ extraction process. In a flat-panel photobioreactor that was operated as a turbidostat cell numbers of stressed cells were kept constant while attaining a continuous well-defined light-stress. In this way it was possible to study the balance between cell growth and cell death and determine whether both could be increased to reach higher volumetric productivities of carotenoids. In the two-phase system a volumetric productivity of 8.3 mg ß-carotene LRV-1 d-1 was obtained. In situ extraction contributed only partly to this productivity. The major part came from net production of carotenoid-rich biomass, due to a high growth rate of the cells and subsequent dilution of the reactor. To reach equilibrium between cell growth and cell death, sparging rates of dodecane could have been increased. However, already at the applied sparging rate of 286 Ldod LRV-1 min-1 emulsion formation of the dodecane in the aqueous phase appeared. In a turbidostat without in situ extraction a volumetric productivity of 13.5 mg ß-carotene LRV-1 d-1 was reached, solely based on the continuous production of carotenoid-rich biomass

Microalgen: het groene goud van de toekomst? : grootschalige duurzame kweek van microalgen voor de productie van bulkgrondstoffen

De kweek van microalgen kan een belangrijke rol spelen in milieuvriendelijke productie van grondstoffen voor biodiesel. Daarnaast leveren algen tal van andere nuttige stoffen voor de levensmiddelen- en chemische industrie. Dit boekje brengt de huidige stand van zaken omtrent algenkweek in kaart. Daarnaast analyseert het de mogelijkheden van economisch rendabele algenkweek op grote schaal voor de winning van waardevolle producten en de rol die het Wagenings algencentrum, AlgaePARC, daarin gaat vervullen