Combined Fungal and Mild Acid Pretreatment of Glycyrrhiza uralensis Residue for Enhancing Enzymatic Hydrolysis and Oil Production

The feasibility of the combination of fungal with mild acid pretreatments of Glycyrrhiza uralensis residue (GUR) for enzymatic hydrolysis and oil production was studied. Combined pretreatment with Phanerochaete chrysosporium and 2.5% sulfuric acid was shown to be more effective than the acid-only pretreatment. Subsequently, the residue obtained from acid hydrolysis was subjected to enzymatic hydrolysis to generate fermentable sugars for oil production by Chlorella protothecoides. The reducing sugar yield of enzyme hydrolysate from co-treated GUR was 1.08- to 1.71-fold higher than that obtained from acid-treated GUR under the same conditions. The highest cell dry and oil yield from co-treated GUR reached 4.16 and 1.66 g/L dry weight, respectively, values which were 2.1- and 3.32-fold higher than those using glucose as a carbon source. This study suggested that combined pretreatment with P. chrysosporium and 2.5% sulfuric acid is an effective strategy for enhancing enzymatic hydrolysis and microalgal oil production from GUR.