Enzymatic hydrolysis and liquefaction of the residual almond hull solids (RAHS) after sugar extraction were studied. The hydrolysis performance of three different enzymes (Cellic CTec2, Viscozyme L and Pectinex Ultra SPL) were investigated. The ability of Aspergillus awamori and Aspergillus oryzae in utilizing the hydrolysate was evaluated. In 50 mL Falcon tubes, the combination of 200 \(\:{\upmu\:}\) L/g RAHS of Cellic Ctec2 and 60 \(\:{\upmu\:}\) L/g RAHS of Viscozyme L enzymes resulted in the optimal performance, with total sugar yield of 47.21%, total fiber conversion of 86.01%, and liquefaction efficiency of 51.61%. Applying these optimal conditions in 250 mL glass bottles resulted in higher liquefaction efficiency of 72.53%, while total fiber conversion was same as that in Falcon tubes. Through a combination of sugar extraction and subsequent enzymatic hydrolysis, a total of 0.55 g of sugars could be released per gram of almond hulls (dry basis, d.b.). The cultivation of Aspergillus awamori and Aspergillus oryzae in hydrolysate for five days produced uniform fungal pellets, with biomass yields of 0.89 g total suspended solids (TSS)/g sugar and 0.43 g TSS/g sugar, respectively. Both fungal strains were able to utilize sugars in the hydrolysate, including galacturonic acid. This research demonstrates that enzymatic hydrolysis of RAHS enables the recovery of additional sugars from almond hulls, thereby increasing the yield of fungal biomass and improving the overall utilization of almond hulls.
