Thesis: Aqueous Two-phase Systems (ATPS) for the extraction of b-carotene from the microalgae Dunaliella salina from saltworks in Sal Island in Cabo Verde.
Author: Neusa Fátima Lima Lopes Pinheiro
Directors: Mª Ángeles Sanromán Braga and Francisco Javier Deive Herva
The search for antioxidant molecules from natural raw materials is triggering a great deal of academic and industrial interest because of their social acceptance over conventional chemical synthesis. Among the possible sources, photosynthetic microorganisms, such as microalgae, are known to have different molecules with anti-inflammatory, anticarcinogenic, antimicrobial, antiviral and cardio-protective activities. Microalgae produce a wide range of natural products, including proteins, enzymes, bioactive compounds and carotenoids.
The unicellular green flagellate Dunaliella salina Teodoresco is the richest natural source of carotenoid β-carotene. All Dunaliella species synthesize carotenoids, although only D. salina is capable of storing β-carotene over 14% of its dry weight. Although some processes for the production of antioxidants have already been implemented at an industrial scale, the investigation of more sustainable alternatives for its extraction and purification is a prominent theme. Thus, the present work bets in the use of Aqueous Two-Phase Systems (ATPS) for the extraction of β-carotene from D. salina microalgae from saltworks in Cape Verde. Preliminary, two microalgal strains of D. salina were scaled up from laboratory to pilot plant bioreactors, and the biological process was modelled with logistic equations. Afterwards, a mapping of the solubility region for systems composed of the non-ionic surfactant Tergitol NP10 and sodium and potassium salts was performed, and the quality of the separation was initially traced by the determination of the tie-lines (TL). All the experimental data were suitably modelled by the empirical equations proposed by Merchuk, Othmer-Tobias and Bancroft, in order to verify the thermodynamic consistency of the obtained values. Then, the lytic effect of the components of the Aqueous Two-Phase Systems (ATPS) was studied by UV microscopy as a preliminary step of the extraction experiments. The first article with sodium salts was carried out because sodium is, at a first glance, the cation leading to the greatest ability to interact with water, but it was much less soluble, as checked experimentally. Hence, the application fo potassium salts turned out to be a more suitable option. In the light of the superiority of phosphate (PO43−) and citrate (C6H5O73−) as phase segregation agents, these potassium salts were selected to evaluate their capacity for β-carotene extraction. Given the superior specific growth rate of D. salina SM1A (Santa Maria1A), which is interesting for scaling-up the bioprocess at continuous bioreactor, Tergitol NP10-based ATPS was applied to implement a simultaneous lytic-extraction strategy in this biomass.
It becomes clear that the proposed integrated methodology based on Tergitol NP10 is advantageous regarding ultrasound-assisted technology, due to the latter entails higher energy costs. The viability of both the microalgal strain cultivation at bioreactor scale and the implementation of a combined lytic and extraction process was demonstrated.