Microwave-assisted FeCl3-catalysed hydrolysis of giant reed and cardoon cellulose followed by fermentation to single cell oil by Lipomyces starkeyi

This study investigated the microwave-assisted FeCl3-catalysed hydrolysis of giant reed (Arundo donax L.) and defatted cardoon (Cynara cardunculus L.) cellulose fractions to give glucose. Giant reed is a promising energy crops able to grow on marginal lands, while cardoon stalks are the crop residue in the production of vegetable oil. A preliminary acid pretreatment was adopted for giant reed, while steam-explosion pretreatment was performed on cardoon, both allowing a significant removal of xylan fractions. Under different reactions conditions the microwave-assisted FeCl3-catalysed hydrolysis converted the two pretreated feedstocks into glucose-rich hydrolysates which were employed as fermentation medium for the production of single cell oil (SCO) by the oleaginous yeast Lipomyces starkeyi DSM 70296. For giant reed, the low production of furanic compounds enabled the fermentation of undetoxified hydrolysates, while for cardoon the furfural removal was necessary before the fermentation step. After hydrolysis, for both hydrolysates the fermentation provided good lipid yields (~14 wt%) and oil content (~25 wt%). The SCO appears a valid candidate for the production of new generation biodiesel with good oxidative stability and cold flow properties. Moreover, it resulted very similar to palm and rapeseed oils, usually employed as a renewable source for the production of traditional biodiesel.