Microbial oil produced from the fermentation of microwave-depolymerised rapeseed meal

Rapeseed meal is high in protein and carbohydrate and is a promising feedstock for microbial valorisation, however, the fibrous structure is difficult to breakdown and involves multiple chemical and enzymatic steps to release a fermentable hydrolysate. In this investigation an innovative pre-treatment of rapeseed meal was demonstrated, involving a one-step process using microwave heating and no additional chemicals or enzymes. 57% of the biomass was solubilised over just a few minutes with minimal energy input. The hydrolysate contained a mixture of monosaccharides, oligosaccharides and micronutrients. To ferment this material the oleaginous yeast Metschnikowia pulcherrima was selected and was able to metabolise the material including some of the oligosaccharides of approximately DP8 and below, producing a lipid that was highly monounsaturated. On the laboratory scale 11% lipid could be achieved from the rapeseed meal alone, with a lipid profile akin to palm oil. On the addition of glycerol to increase the C:N ratio, over 16 g/L of yeast was achieved with lipid content of 38% w/w. To demonstrate the scalability of the microbial process, the fermentation was demonstrated on depolymerised rapeseed meal with glycerol, in a 30 L pilot scale fermenter, yielding 12 g/L of yeast with 22% w/w lipid over 120 h. While the lipid production needs to be further optimized on this scale, the use of rapeseed meal as a feedstock, coupled with a one-step microwave process that does not need additional pre- and post-processing stages, is an exciting route to potential commercially viable microbial oils.