From paper mill waste to single cell oil: Enzymatic hydrolysis to sugars and their fermentation into microbial oil by the yeast Lipomyces starkeyi.

• The valorisation of industrial wastepaper was studied. • The glucose and xylose yields were both 95 mol% respect to glucan and xylan. • The sequential utilisation of glucose and xylose for lipid production was observed. • L. starkeyi converted undetoxified hydrolysate into oil with a yield of 20.2 wt%. • The lipid profile of the microbial oil was similar to those of typical vegetable oils. Single cell oil (SCO) represents an outstanding alternative to both fossil sources and vegetable oils from food crops waste. In this work, an innovative two-step process for the conversion of cellulosic paper mill waste into SCO was proposed and optimised. Hydrolysates containing glucose and xylose were produced by enzymatic hydrolysis of the untreated waste. Under the optimised reaction conditions (Cellic® CTec2 25 FPU/g glucan, 48 h, biomass loading 20 g/L), glucose and xylose yields of 95 mol% were reached. The undetoxified hydrolysate was adopted as substrate for a batch-mode fermentation by the oleaginous yeast Lipomyces starkeyi. Lipid yield, content for single cell, production and maximum oil productivity were 20.2 wt%, 37 wt%, 3.7 g/L and 2.0 g/L/d respectively. This new generation oil, obtained from a negative value industrial waste, represents a promising platform chemical for the production of biodiesel, biosurfactants, animal feed and biobased plastics. [ABSTRACT FROM AUTHOR]