Mortierella alpina, an oleaginous fungus, has been shown to be a potential source for arachidonic acid (ARA) production. The recovery of intracellular lipids from M. alpina is an important step for the downstream bioprocessing, and green extraction techniques with a focus on being efficient and eco-friendly have drawn much attention. In this study, different cell disruption techniques (mechanical: high-speed homogenization 10,000 rpm, ultrasonication 20 kHz, high-pressure process (HPP) 200–600 MPa; non- mechanical: acid treatment HCl) were investigated for lipid recovery from M. alpina, and process parameters (A. temperature, B. pressure, C. cosolvent ratio) of supercritical carbon dioxide (SC-CO2) lipid extraction were studied by applying response surface methodology (RSM). Compared with Soxhlet extraction as a control group (100%), high-speed homogenization has the highest lipid recovery (115.40%) among mechanical disruption techniques. Besides, there was no significant difference between high-speed homogenization and 1 M HCl treatment (115.55%) in lipid recovery. However, lipid recovery decreased to 107.36% as the concentration of acid was increased to 3 M, and acid treatment showed a negative effect on the ARA ratio. In HPP treatment, the highest lipid recovery (104.81%) was obtained at 400 MPa, 1 time of treatment and water medium. In the response surface model of SC-CO2 extraction, results showed the major influence of the process parameters to lipid recovery was pressure, and there are interaction effects of AC (temperature and cosolvent ratio) and BC (pressure and cosolvent ratio). Lipid recovery of SC-CO2 extraction reached 92.86% at 201 bar, 58.9 °C and cosolvent ratio 1:15. The microbial lipid recovery process of this study could be used as a reference and an eco-friendly alternative for the future downstream bioprocessing of ARA production by M. alpina.
Arachidonic acid (ARA), an important polyunsaturated fatty acid (PUFA), acts as a precursor for eicosanoid hormones, such as prostaglandins, leukotrienes and other biological substances in human and animal bodies. Mortierella alpina is considered to be a potential strain for ARA production. Using agricultural waste as a substrate for microbial fermentation could achieve biorefinery concepts, and sea water utilization of the cultivation process could help to conserve fresh water resources. The objectives of this study were to find a potential M. alpina strain for ARA production, to investigate the tolerance of salinity and to evaluate the feasibility of the taro waste hydrolysate for M. alpina cultivation. The result showed that M. alpina FU30797 had the highest lipid content (25.97%) and ARA ratio (34.60%) among three strains. Furthermore, there was no significant difference between 0 and 10 g/L of sea salt solution on the biomass concentration and lipid content of M. alpina FU30797. The acidic hydrolysate and enzymatic hydrolysate of taro peel waste (TPW) were both utilized as culture substrates by M. alpina FU30797; however, the substrate up-take rate and lipid content in the TPW enzymatic hydrolysate cultivation were 292.33 mg/L-h and 30.68%, respectively, which are higher than those in acidic hydrolysate cultivation, and the ARA ratio was 33.05% in the enzymatic hydrolysate cultivation. From fed-batch cultivation in the bioreactor, the lipid content and ARA ratio reached 36.97% and 46.04%, respectively. In summary, the results from this project could potentially provide useful information for developing the PUFA-ARA bioprocess by using M. alpina.
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