Effect of light intensity on beta-carotene production and extraction by Dunaliella salina in two-phase bioreactors
ABSTRACT Application of two-phase bioreactors is a useful technique for improvement of the productivity of fermentations. Fermentative extraction of the products in situ is performed in this technique. The effect of light intensity on the extraction of beta-carotene from Dunaliella salina, in the fermentative extraction, has been investigated. Three different average light exposures were applied: 1.5 x 10(-8) (low), 2.7 x 10(-8) (intermediate) and 4.5 x 10(-8) (high) micromol s(-1) per cell. Results show that beta-carotene content of the cells increases by increasing the light exposure. Increase in the beta-carotene content of the cells is not necessarily coupled with an increase in the volumetric production of beta-carotene. Final volumetric production is about the same for the three bioreactors. beta-Carotene extraction rate is enhanced by the increase in the light exposure. The results suggest that extraction rate is related to beta-carotene content of the cells and is not essentially related to the volumetric production of beta-carotene. Although the effectiveness of extraction with respect to the light input is comparable for all light intensities applied, increasing the light input per cell leads to a higher volumetric extraction rate. Moreover, extracted beta-carotene stays very pure even so the extraction increased by the increase of light intensity.
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ABSTRACT: Full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3665214/ Green microalgae for several decades have been produced for commercial exploitation, with applications ranging from health food for human consumption, aquaculture and animal feed, to coloring agents, cosmetics and others. Several products from green algae which are used today consist of secondary metabolites that can be extracted from the algal biomass. The best known examples are the carotenoids astaxanthin and β-carotene, which are used as coloring agents and for health-promoting purposes. Many species of green algae are able to produce valuable metabolites for different uses; examples are antioxidants, several different carotenoids, polyunsaturated fatty acids, vitamins, anticancer and antiviral drugs. In many cases, these substances are secondary metabolites that are produced when the algae are exposed to stress conditions linked to nutrient deprivation, light intensity, temperature, salinity and pH. In other cases, the metabolites have been detected in algae grown under optimal conditions, and little is known about optimization of the production of each product, or the effects of stress conditions on their production. Some green algae have shown the ability to produce significant amounts of hydrogen gas during sulfur deprivation, a process which is currently studied extensively worldwide. At the moment, the majority of research in this field has focused on the model organism, Chlamydomonas reinhardtii, but other species of green algae also have this ability. Currently there is little information available regarding the possibility for producing hydrogen and other valuable metabolites in the same process. This study aims to explore which stress conditions are known to induce the production of different valuable products in comparison to stress reactions leading to hydrogen production. Wild type species of green microalgae with known ability to produce high amounts of certain valuable metabolites are listed and linked to species with ability to produce hydrogen during general anaerobic conditions, and during sulfur deprivation. Species used today for commercial purposes are also described. This information is analyzed in order to form a basis for selection of wild type species for a future multi-step process, where hydrogen production from solar energy is combined with the production of valuable metabolites and other commercial uses of the algal biomass.Critical Reviews in Biotechnology 07/2012; 33(2). DOI:10.3109/07388551.2012.681625 · 7.84 Impact Factor
- Planta Medica 07/2012; 78(11). DOI:10.1055/s-0032-1320483 · 2.34 Impact Factor
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ABSTRACT: Microalgal biotechnology has been commercially viable for several decades, but only for a restricted range of applications (Benemann et al. 1987). Owing to the relatively high capital cost of microalgal production systems, successful applications have generally focussed either upon niche areas in which both modern agriculture and microbial fermentation systems lack a competitive advantage or upon unique microalgal products, for which no competition exists. Although the largest existing algae farms are still for health food production (e.g. Spirulina production in China) and natural products (e.g. Dunaliella in Australia for β-carotene), those undergoing the most rapid expansion are currently aimed at biofuel production and associated R&D. The microalgal industry is growing rapidly, and while microalgal biofuel technologies generally remain in the basic and applied R&D stage (IEA 2011a), commercial-scale facilities are starting to come online. For photoautotrophic production, these include Sapphire Energy’s 120ha (300ac) Integrated Algal Biorefinery (IABR) facility currently under construction in New Mexico, USA (Sapphire 2011; US D.O.E. Energy Efficiency & Renewable Energy 2011), while Solazyme’s factories have focused on heterotrophic conversion of sugars to oils and other products (Solazyme 2011; Dillon 2011).Microalgal Biotechnology: Integration and Economy, Edited by Clemens Posten, Christian Walter, 12/2012: chapter Microalgal production systems: Global impact of industry scale-up: pages 267-306; Walter De Gruyter., ISBN: 9783110298277