The Use of Green Solvent to Extract Carotenoids from Dried Algal Biomass: A Comparison Study

  • Farah Abuhantash

Student thesis: Master's Thesis

Abstract

Microalgae are a promising sustainable source of different bioactive compounds, such as natural carotenoids which accumulate at different concentrations in different microalgal species. This includes the accumulation of β-carotene and astaxanthin known to be high value product (HVPs) within the cell while growing. Dunaliella salina is a common marine microalga which can accumulate up to 14% of its weight as β-carotene. The large-scale production and extraction of HVPs has gained a lot of interest recently for commercial and industrial applications. Although conventional extractions using organic solvents are simple, their use results in poor selectivity and purity, high solvent consumption, lengthy extraction runs and negative environmental impact. Due to such limitations and impacts, scientists are now investigating innovative extraction techniques known as green techniques. Advancements in the search of environmentally friendly extraction techniques are aimed at using alternative green solvents such as supercritical and subcritical fluids, ionic liquids and deep eutectic solvents. In this study, the use of supercritical CO2 (scCO2) and ionic liquids (ILs) are investigated, and their performances are compared to that of the conventional extractions. The potential of using a modified and combined solvent is also examined. Extractions were carried out from a dried biomass of D.Salina grown at two different salinities, thus having different initial carotenoid contents. To the best of our knowledge, a direct comparison study of scCO2and IL extraction techniques or combined use for carotenoids extraction from dry D.Salina biomass has yet not been investigated. In this thesis work, ethanol, hexane and acetone were tested in the conventional organic extractions at two different temperatures (40 and 50oC) for two different extraction periods (6 and 24hrs) from two different biomass grown in two different salinities (15 and 20% salinities). The best solvent, in terms of capability to efficiently extract carotenoids at specified conditions, was selected as basis of calculation. Three different ILs, namely 1-Ethyl-3methylimidazolium [Emim], 1-Butyl-3methylimidazolium [Bmim] and 1-Hexyl-3methylimidazolium tetrafluoroborate [Hmim][BF4] were examined at (50 and 60oC) for 6hrs extraction. The use of scCO2 was investigated in the range of (200–400bar), (40–60°C) temperatures for 30min period of extraction from 15% grown salinity biomass. The study is also extended to test the use of IL as a co-solvent in the scCO2 extraction. Results indicated that hexane is the best conventional solvent with 721µg/ml concentration, and the effectiveness of ethanol is just 4% lower than hexane when tested at different extraction conditions. On the other hand, [Bmim][BF4] had the highest extraction efficiency when compared to [Emim] and [Hmim][BF4]. However, its performance of ILwas low when compared to hexane and did not exceed 10% extraction yield. Nonetheless, an addition of 1:1 w/w ethanol to [Bmim][BF4] resulted in 6 folds increase when compared to pure [Bmim][BF4]. When scCO2 extraction was tested, the highest yield was found to be only 6% at 400 bars and 60°C with 2.75ml/min flow rate. However, the addition of 5% [Bmim][BF4] increased the yield by 2 folds and significantly lowered the optimal operating conditions to 200 bars and 40oC. With [Bmim][BF4] being insoluble in scCO2, the resulting extract was solvent free and did not go any further purifications. In summary, this study shows the possibility of β-carotene extraction from dried D.Salina biomass using ILs and scCO2. The addition of a small volume of ethanol to ILs can enhance the extraction yield as it lowered the IL's viscosity, hence diffusivity and the addition of IL to scCO2 extraction, can also increase the extraction yield as it aids in swelling the cells, hence enhance the scCO2 diffusivity.
Date of AwardMay 2021
Original languageAmerican English

Keywords

  • Microalgae
  • Dunaliella salina
  • carotenoids
  • conventional extraction
  • green chemistry
  • green extraction
  • supercritical extraction
  • ionic liquids.

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