Lipid production through the single-step microwave hydrolysis of macroalgae using the oleaginous yeast Metschnikowia pulcherrima

Macroalgae (seaweeds) represent an emerging resource for food and the production of commodity and specialty chemicals. In this study, a single-step microwave process was used to depolymerise a range of macroalgae native to the United Kingdom, producing a growth medium suitable for microbial fermentation. The medium contained a range of mono- and polysaccharides as well as macro- and micronutrients that could be metabolised by the oleaginous yeast Metschnikowia pulcherrima. Among twelve macroalgae species, the brown seaweeds exhibited the highest fermentation potential, especially the kelp Saccharina latissima. Applying a portfolio of ten native M. pulcherrima strains, yeast growth kinetics, as well as production of lipids and 2-phenylethanol were examined, with productivity and growth rate being strain dependent. On the 2 L scale, 6.9 g L-1 yeast biomass - a yield of 0.14 g g(-1) with respect to the supplied macroalgae - containing 37.2% (w/w) lipid was achieved through utilisation of the proteins, mono- and polysaccharides from S. latissima, with no additional enzymes. In addition, the yeast degraded a range of fermentation inhibitors released upon microwave processing at high temperatures and long holding times. As macroalgae can be cultured to food grade, this system offers a novel, potentially low-cost route to edible microbial oils as well as a renewable feedstock for oleochemicals.