Bioconversion of Agro-Residues into Microbial Oil-Based Oleochemicals Employing Packed Bed Bioreactor

Lignocellulosic waste-streams are resources worth investigating to produce value-added bioproducts due to their low-cost, renewability, versatility, and abundance. This study evaluated five Zygomycota strains as potential oleaginous microorganisms for direct bioconversion of cakes derived from the vegetable-oil-milling industry into microbial oil. Solid-state fermentation (SSF) conditions in tray bioreactors revealed that temperature, moisture content, and substrate affected lipid production and fatty acids composition. Employing SSF, under optimal conditions (30 °C, 65% initial moisture content), and substrate supplementation with nitrogen sources increased lipid productivity 1.1-fold on palm kernel cake (PKC) substrate. Supplementation strategies using glycerol, molasses, or mineral solution did nοt favor lipid production. When cotton seed cake (CoSC) was applied, C. echinulata was able to produce 304.1 mg/gfs of biomass with a lipid content of 40.2% (w/w) in tray bioreactors. Scaling-up SSF using CoSC in packed bed reactors led to the highest biomass production (320.5 mg/gfs), while lipids production was unaffected. Then, microbial oil was enzymatically converted into polyol esters achieving the highest conversion yield of 80% after 2 h. Physicochemical properties of polyol esters demonstrated their potential utilization as biolubricants. The present study showed the perspective of bioconverting industrial side streams into microbial oil and a route for sustainable synthesis of oleochemicals.