Hypotonic osmotic shock treatment to enhance lipid and protein recoveries from concentrated saltwater Nannochloropsis slurries

The effect of cell disruption on the extraction of oil and protein from concentrated microalgae slurries

“…N.gaditana strain (SAG 2.99) was acquired from the Culture Collection Centre at Georg-August-Universität Göttingen (SAG, Germany). After inoculation into a modified 3f medium on synthetic seawater in a bubble-column photobioreactor with 25 L working volume, the culture was cultivated with permanent white illumination (daily step increase from 120 to 370 μmol m -2 s -1 ) and continuous CO2-enriched aeration (air flow rate of 0.15 vvm and a CO2-to-air ratio of 1/100 v/v) for 18 days as previously described (Halim et al, 2020). Nitrogen in the medium was depleted on day 10 of cultivation.…”

“…Microalgal metabolites are intracellular in nature and can generally only be made accessible after liberation from cell-wall encapsulation. (Halim et al, 2019b;Halim et al, 2020). Microalgal cell walls are comprised of multilayered biopolymers that confer the cells with formidable defence against external processing (Baudelet et al, 2017;Canelli et al, 2021;Scholz et al, 2014).…”

“…We have previously reported the use of autolytic incubation and hypotonic osmotic shocks as novel preparatory steps to weaken Nannochloropsis biomass in a concentrated slurry state (10 -30 wt% biomass) and enhance product recoveries without drying (Halim et al, 2019a;Halim et al, 2019b;Halim et al, 2020;Halim et al, 2016). Even though they had different mechanisms, both pretreatments were shown to be highly effective in catalysing cell-wall/cell membrane degradation and rendering the Nannochloropsis biomass more susceptible to subsequent mechanical or chemical disruption steps.…”

“…In the case of hypotonic osmotic shock, the structural integrity of the biomass was compromised via the delivery of a reverse osmotic gradient which resulted in the net diffusion of water into the cells, the build-up of internal pressure and the progressive damage to cell membrane (Halim et al, 2020). Reverse osmotic gradient was generated by freshwater washing (and reconstitution) of the slurry.…”

“…Reverse osmotic gradient was generated by freshwater washing (and reconstitution) of the slurry. When subjected to subsequent disruptions (by HPH), the washed slurries resulted in 2x the level of cell disruption of the untreated slurries (Halim et al, 2020). We have yet to directly compare the performance of autolytic incubation and hypotonic osmotic shock within the same study.…”