Feasibility of raw glycerol conversion into single cell oil by zygomycetes under non-aseptic conditions.

The use of plant oils as feedstock for the biodiesel manufacture has many drawbacks, thus, the interest has turned to single cell oil (SCO) as an alternative. However, the production of SCO is still too expensive, mainly due to the low oil productivity and the high cost of medium sterilization required. In this work raw glycerol was converted into SCO by oleaginous Zygomycetes under non-aseptic conditions on selective (i.e., containing essential oils and/or antibiotics) nitrogen limited media. The obtained data showed that although bacterial populations inhibited the fungal growth, lipid accumulation remained unaffected by the presence of bacteria in the growth medium compared to control experiments (conducted under aseptic conditions). Therefore, a two-stage process was developed in which growth was performed under aseptic conditions (1st stage) followed by lipid accumulation performed under non-aseptic conditions (2nd stage) in the presence of thyme essential oil as an antibacterial agent. Large amounts of lipids were accumulated inside the mycelia, yielding around 13% wt/wt of oil per glycerol consumed.