Synergy between chemical and biological catalysis for new generation oil production according to the biorefinery perspective

Single cell oil (SCO) represents an innovative and versatile industrial platform to produce a wide range of added-value bioproducts such as biodiesel, bioplastics and biosurfactants. SCO is produced by oleaginous yeasts able to accumulate up to 70% of their dry cell weight as triacylglycerols (TAG). In order to make economically sustainable this process, second generation (2G) sugars, obtained from residual or dedicated lignocellulosic biomasses, must be used as fermentative substrate. 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 is 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 is the optimization of lignocellulosic hydrolysate fermentation into SCO by oleaginous yeast Lypomyces starkeyi and the transesterification of TGA into fatty acid methyl esters (FAMEs). 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 dilute H2SO4 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 2G sugars into oil reached the yield of 18 wt%, very close to the theoretical one (20 wt%).