Abstract
This study reports the use of hypotonic osmotic shock as a treatment step to enhance the recoveries of biofuel-convertible lipids and proteins from lipid-rich saltwater Nannochloropsis gaditana (N. gaditana) slurries (biomass content = ~140 mg biomass / g slurry, total lipid content = ~600 mg lipid /g biomass). The osmotic shock was induced through repeated washing of microalgal slurries with multiple batches of fresh water. Subjecting the slurries to 2 stages of freshwater washing resulted in a measurable damage to cell membranes (the uptake of membrane permeability marker increased by 6 folds), a partial loss of cell viability (only 64% of available cells were recoverable), and a minor release of free protein (~2 wt% of available protein) from the biomass into the interstitial space of the slurries. Hypotonic osmotic shock was revealed to be ineffective in rupturing N. gaditana slurries (only 13 ± 9% of available cells were ruptured after 2-stage washing) and, as such, had a limited prospect as a stand-alone cell disruption technology for the saltwater strain.The washing treatment, however, was found to be able to weaken the structural integrity of N. gaditana slurries and enhance the performance of subsequent mechanical or chemical cell disruption technologies when installed as a preparatory step. Applying the washing treatment prior to high-pressure homogenisation (HPH) and low-solvent-to-biomass ratio hexane extraction (hexane : slurry = 1:1 w/w) for the recovery of biofuel-convertible lipids increased the extent of cell rupture from 28 ± 8 to 46 ± 19% of available cells and more than doubled neutral lipid yield from 25.1 ± 2.0 to 64.6 ± 4.9 wt% of available neutral lipid. Initial analysis revealed that the washing treatment had a minimal energy cost (~6% of the total energy expenditure of downstream processing) and that its integration into HPH + hexane lipid recovery led to a 2.5 fold increase in the energy output of the biomass. Partnering the washing treatment with NaOH hydrolysis increased protein yield from 6.7 ± 2.4 to 31.9 ± 10.7 wt% of available protein.
Highlights
In recent years, microalgae have been shown to be a highly prom ising feedstock for sustainable biofuels and high-value bioproducts because of their high areal productivity and non-requirement for agricultural resources [1,2,3,4,5,6,7]
This study reports the use of hypotonic osmotic shock as a treatment step to process highly lipid-rich saltwater N. gaditana slurries (137.7 ± 12.6 mg biomass / g slurry, 607.0 ± 102.5 mg lipid /g biomass)
Sub jecting the slurries to 2 stages of freshwater washing damaged the cell membranes and resulted in a limited release of free protein into the supernatants (~2 wt% of available protein)
Summary
Microalgae have been shown to be a highly prom ising feedstock for sustainable biofuels and high-value bioproducts (e.g. chlorophyll, β-carotene, ω-3 fatty acids and protein) because of their high areal productivity and non-requirement for agricultural resources (e.g. arable land and freshwater for marine microalgae) [1,2,3,4,5,6,7] These products are intracellular in nature and can generally only be recovered after they have been liberated from the encapsulation of the cell walls [3,8,9,10,11]. For fresh water microalgal species, on the other hand, osmotic shock is carried out with a hypertonic shift, triggered by adding solutes (such as NaCl and sorbitol) to the culture medium. [22,23]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
