Production of Fermentable Sugars from Organosolv Pretreated Cassava Peels

Afolake Atinuke Olanbiwoninu,Sunday Ayodele Odunfa

doi:10.4236/aim.2015.52012

Afolake Atinuke Olanbiwoninu, Sunday Ayodele Odunfa

Open Access

https://doi.org/10.4236/aim.2015.52012

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Abstract

Cassava peels are rich in lignocellulolytic materials which are not readily amenable to enzymatic hydrolysis; hence, there is a need for a suitable pretreatment method that will support enzymatic hydrolysis. This study was designed to investigate lignocellulolytic organisms that would effectively support the bioconversion of organosolv pretreated cassava peels to fermentable sugars. Decaying cassava peels were collected into sterile bottles and microorganisms isolated, characterized and screened for lignocellulolytic enzymes production. Optimum temperature, pH and nutrient sources for enzyme production were determined. Organosolv pretreatment was carried out using methanol with varied concentration of catalyst (0.01 - 3 M), reaction time (15 - 60 min) and substrate size. Crude enzymes (cellulase and xylanase) from the isolates were added to the pretreated peels and bioconversion was monitored by measuring the concentration of reducing sugar and calculating the percentage peel hydrolysis. The fermentable sugars produced were quantified using gas chromatography. Pseudomonas fluorescens and Aspergillus terreus were isolated. P. fluorescens produces 2.8 u/mL of crude enzymes optimally at 50°C and pH 8 while A. terreus produces 3.4 u/mL optimally at 40°C, pH 6. Both isolates utilizes CarboxyMethylCellulose (CMC) and yeast extract as their best carbon and nitrogen sources. Highest percentage of peel hydrolysis was 67% for P. fluorescens at 0.01 M and 0.05 M for A. terreus (94%). Highest concentration of fermentable sugar was produced by A. terreus crude enzyme (331.79 mg/L glucose, 45.3 mg/L rhamnose and 46.52 mg/L xylose). P. fluorescens and A. terreus effectively supported the bioconversion of organosolv pretreated cassava peels to fermentable sugars.

Highlights

Cassava peels are the main by-product from processing tuberous roots of cassava for human consumption
The lignocellulolytic properties of cassava peels enhance its usefulness as a source of fermentable sugars after bioconversion
The peel is made up of cellulose, hemicelluloses and lignin but the structures of these materials are complex with recalcitrant and heterogeneous characteristics and are highly resistant to enzymatic hydrolysis; there is a need to pretreat the peels thereby making the enzymes amenable to the sugars embedded in the cellulose and hemicelluloses component of the peel [3]

Summary

Introduction

Cassava peels are the main by-product from processing tuberous roots of cassava for human consumption. Cassava peels have been evaluated as a feedstuff for animals [1], for the production of biogas, biofuels and ethanol and as substrates for microbial protein enrichment [2]. The lignocellulolytic properties of cassava peels enhance its usefulness as a source of fermentable sugars after bioconversion. The peel is made up of cellulose, hemicelluloses and lignin but the structures of these materials are complex with recalcitrant and heterogeneous characteristics and are highly resistant to enzymatic hydrolysis; there is a need to pretreat the peels thereby making the enzymes amenable to the sugars embedded in the cellulose and hemicelluloses component of the peel [3]. Pretreatment is an important step for the bioconversion of lignocellulosic biomass. Many methods have been developed for pretreating lignocellulosic biomass but only few are promising for industrial purposes [5]

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