Cellulolytic enzymes behavior in delignified green coconut residues and enzymatic hydrolysis with enzyme recovery

Abstract

Lignocellulosic bioconversion to obtain fermentable sugars often requires high enzyme dosages, increasing the total production cost. This study investigated the adsorption, desorption, and recycling of cellulases in enzymatic hydrolysis experiments using pretreated green coconut shell as substrate. The green coconut shell (GCS) was subjected to different pretreatments including dilute acid, alkaline, and two-stage acid-alkaline pretreatments. Adsorption and desorption studies involving cellulases from Trichoderma reesei ATCC 26921 and Cellic Ctec2 (10 FPU/g, initial dosage) with 5% solid loading showed that alkaline and two-stage acid-alkaline pretreatments were more suitable for enzyme recycling, because they showed lower values of cellulase adsorption capacity (48 % and 69 %) and higher values of cellulase recovery by desorption without Tween 80 addition (reaching 50 % using two-stage acid-alkaline pretreated GCS). Cellulases bound to the solid residue and dissolved in the supernatant after enzymatic hydrolysis can be reused for a new enzymatic hydrolysis process without compromising the sugar yield results. Using GCS as a substrate, the addition of solid residue and the supernatant from the previous step of adsorption of cellulases achieved a satisfactory sugar yield g/g (73.0 % for LCM1 and 60.0 % for LCM3) using less enzyme (just using recycled enzyme with no new enzyme added to the system) than the control case. Thus, it was possible to recycle the cellulases in two successive hydrolysis cycles with reduced enzyme load to achieve the same reducing sugar yields (up to 84 %), enabling cheaper and more efficient hydrolysis of lignocellulosic biomass.