Single Cell Oil: new generation biodiesel and bioproducts starting from biomass

Single cell oil (SCO) represents an innovative and versatile platform to produce a wide range of added value bioproducts. From an industrial point of view, SCO is a promising alternative of vegetable oils and fossil-derived fuels and chemicals. SCO is produced via fermentation by oleaginous yeasts. The key strategy necessary to make economically sustainable this process is the use of second-generation sugars, obtained from the hydrolysis of cellulose and hemicellulose of residual or dedicated lignocellulosic biomasses. Among lignocellulosic crops, Arundo donax L. was defined as a promising grass in the biorefinery field. The present study was focused on two main goals: the first one was the investigation of sustainable homogeneous and heterogeneous catalysts for the biomass hydrolysis in order to produce glucose and xylose, by using microwaves as heating system; the second one was the fermentation of lignocellulosic hydrolysate into SCO by oleaginous yeast Lypomyces starkeyi. From an industrial point of view, the innovative aspect of this study was the fermentation of hydrolysates without any detoxification steps. The quantitative conversion of hemicellulose into xylose was performed by optimizing both homogeneous and heterogeneous catalysis. The cellulosic fraction remained in the solid residue recovered at the end of the first step was then hydrolyzed by testing FeCl3 or the enzymatic mixture Ctec2, obtaining an overall yield for both approaches of about 40-50 %, expressed as g glucose/g glucan in the starting biomass. The biological conversion of second-generation sugars into oil reached the yield of 20 wt% respect to consumed sugars and an overall yield of 10 wt% respect to the starting lignocellulosic biomass.