Optimisation of alkaline pretreatment of spent coffee grounds for microbial oil production by Cryptococcus curvatus.

In a world of finite resources, the transition to a sustainable post-fossil resources economy is essential. Within this concept, spent coffee grounds (SCGs) could be used for the production of bio-based chemicals, biopolymers and value-added products. Lipids and phenolics were initially extracted from SCGs. Alkaline pretreatment of the remaining SCGs solids has been optimised in this study via Central Composite Design to maximise lignin removal and overall sugar to polysaccharide conversion yield. The optimal SCGs pretreatment conditions were 0.06% (w/v) NaOH and 99.5 °C resulting in 35.7% lignin removal at 60 min pretreatment duration with low glucan and hemicellulose losses (ca. 2.5%). Enzymatic hydrolysis of the remaining SCGs alkaline pretreated solids resulted in 79.4% glucan, 74.5% mannan and 54.8% hemicellulose hydrolysis yield. The SCGs hydrolysate was used as fermentation feedstock in bioreactor cultures of Cryptococcus curvatus resulting in 36.1 g/L microbial oil with 0.25 g/g yield and 0.41 g/(L∙h) productivity. The total dry weight reached 62.7 g/L corresponding to 57.5% (w/w) intracellular lipid content. The microbial oil was rich in oleic acid (55.6%) followed by palmitic acid (18.9%) and stearic acid (14.0%). The proposed process led to the production of 7.81 g microbial oil per 100 g antioxidant- and oil-free SCGs. • Antioxidant- and oil-free SCGs were efficiently used for microbial oil production. • Optimal SCGs pretreatment conditions were 0.06% (w/v) NaOH and 99.5 °C. • Lignin removal of 35.7% with low glucan and hemicellulose losses was achieved. • Fermentation of SCGs hydrolysate led to 57.5% (w/w) intracellular lipid content. • 7.81 g microbial oil obtained per 100 g antioxidant and oil-free SCGs. [ABSTRACT FROM AUTHOR]