Pulsed Electric Field Treatment Promotes Lipid Extraction on Fresh Oleaginous Yeast Saitozyma podzolica DSM 27192
This study reports on the use of pulsed electric field (PEF) as a pre treatment step to enhance lipid extraction yield using extraction with ethanol hexane blend on fresh oleaginous yeast Saitozyma podzolica. The yeasts were cultivated on nitrogen depleted condition and had a lipid content of 26.4 4.6% of dry weight. PEF treatment was applied on the yeast suspension either directly after harvesting (unwashed route) or after a washing step (washed route) which induced a reduction of conductivity by a factor eight. In both cases, cell concentration was 20 g of biomass per liter of suspension. In the unwashed route, the lipid extraction efficiency increased from 7% (untreated) to 54% thanks to PEF treatment. In case an additional washing step was added after PEF treatment, up to 81% of the lipid content could be recovered. The washed route was even more efficient since lipid extraction yields increased from 26% (untreated) to 99% of total lipid. The energy input for the PEF treatment never exceeded 150 kJ per liter of initial suspension. The best lipid recovery scenario was obtained using pulses of 1 ms, an electric field of 40 kV/cm and it required slightly less than 11 MJ/kgLIPID. This amount of energy can be further reduced by at least a factor five by optimizing the treatment and especially by increasing the concentration of the treated biomass. The process can be easily up scaled and does not require any expensive handling of the biomass such as freezing or freeze drying. These findings demonstrate the potential benefit of PEF treatment in the downstream processing of oleaginous yeast. From a basic research point of view, the influence of conductivity on PEF energy requirements and extraction yields was examined, and results suggest a higher efficiency of PEF treatment in terms of energy when treatment is performed at lower conductivity. Graphical Abstract Pulsed electric field treatment performed on fresh yeast biomass induced permeabilisation of cells and greatly improved the yields of subsequent lipid extraction using ethanol and hexane.
Frontiers in Bioengineering and Biotechnology