Milking microalga Dunaliella salina for β‐carotene production in two‐phase bioreactors

Abstract

A new method was developed for production of beta-carotene from Dunaliella salina. Cells were grown in low light intensity and then transferred to a production bioreactor illuminated at a higher light intensity. It was a two-phase bioreactor consisting of an aqueous and a biocompatible organic phase. Mixing of the cells and extraction were performed by recirculation of the organic phase. Two experiments were performed. In the first experiment, bioreactors were operated at two different solvent recirculation rates of 150 and 200 mL min(-1). The beta-carotene extraction rate increased significantly at the higher recirculation rate, without exerting any influence on cell number and viability. A second experiment was carried out at a recirculation rate (200 mL min(-1)) appropriate for the study of long-term production of beta-carotene. The results show that D. salina at high light intensity remained viable for a long period (>47 days) in the presence of a biocompatible organic phase; however, cell growth was very slow. beta-Carotene could be continuously extracted to the organic phase; the cells continued to produce beta-carotene and the extracted molecules were continuously reproduced. As a result, beta-carotene was continuously removed ("milked") from the cells. beta-Carotene extraction efficiency in this system was >55%, and productivity was 2.45 mg m(-2) day(-1), much higher than that of commercial plants.

Converted carotenoid production in Dunaliella salina by using cyclization inhibitors 2-methylimidazole and 3-amino-1,2,4-triazole

“…(0.51 pg/cell) by Del Campo et al (2000). In order to evaluate and use D. salina efficiently for lutein production, a two-phase system focusing on biomass production in the first stage and lutein accumulation in the second would be a valuable approach, as previously successfully applied for β-carotene production in D. bardawil by Ben-Amotz et al (1995) and Hejazi et al (2004).…”

Non-destructive oil extraction from Botryococcus braunii (Chlorophyta)

“…Spirulina, Dunaliella and Nannochloropsis) and also the halophilic bacterium Halomonas elongata have been tested for the potential of non-destructive extraction of high value products or biofuel (Sauer and Galinski 1998;Hejazi et al 2004;Eroglu and Melis 2010;Sim et al 2001;An et al 2004). For instance, milking yields for β-carotene from D. salina by (Hejazi et al 2004) were up to 55 % of β-carotene with a productivity of 0.06 mg L…”

“…A major drawback in the efforts to use algae, as well as any other oilproducing plants as sources of renewable energy, is that current harvesting and post harvesting techniques are expensive and require a high energy input (Moheimani et al 2011). Microalgal triglycerides, the main source of algal oils for biofuels, are secondary metabolites and are mainly produced when microalgae growth is limited (Ratledge and Kristiansen 2001;Hejazi et al 2004). …”

“…A particular innovative suggestion that addresses a number of the cultivation and associated cost problems with algal biofuel production is the concept of 'milking' or the 'non-destructive' oil extraction of the external hydrocarbons or oil from microalgae (Frenz et al 1989;Hejazi et al 2004). …”

Paving the Road to Algal Biofuels with the Development of a Genetic Infrastructure

“…Not only do microalgae fully address each of the disadvantages of land-based biofuel crops, but they also are amenable to genetic engineering for the enhanced biosynthesis of a wide range of advanced biofuels and high-value added products. Currently, three fundamental objectives remain critical to the implementation of economically-and technologically-feasible algal biofuel production: [1] increase of biological productivity through species selection and genetic engineering as well as optimization of culture conditions; [2] development of low-cost vessels for cultivation, whether they be closed photobioreactors or open pond systems; and [3] improvement of inexpensive downstream processing techniques for algal biomass, including harvesting, dewatering, and extraction of biofuel metabolites (Hejazi et al, 2004a;Shelef et al, 1984;Danquah et al, 2009). As with many novel sources of bioenergy, the complexity of the microalgal biofuel production process calls for a multidisciplinary approach in which biotechnological progress will be accompanied by advances in process engineering.…”