The Effects of Alkaline Pretreatment on Agricultural Biomasses (Corn Cob and Sweet Sorghum Bagasse) and Their Hydrolysis by a Termite-Derived Enzyme Cocktail

Mpho S Mafa,Abhishek Bhattacharya,Samkelo Malgas,Konanani Rashamuse,Brett I Pletschke

doi:10.3390/agronomy10081211

Abstract

Sweet sorghum bagasse (SSB) and corncob (CC) have been identified as promising feedstocks for the production of second-generation biofuels and other value-added chemicals. In this study, lime (Ca(OH)2) and NaOH pretreatment efficacy for decreasing recalcitrance from SSB and CC was investigated, and subsequently, the pretreated biomass was subjected to the hydrolytic action of an in-house formulated holocellulolytic enzyme cocktail (HEC-H). Compositional analysis revealed that SSB contained 29.34% lignin, 17.75% cellulose and 16.28% hemicellulose, while CC consisted of 22.51% lignin, 23.58% cellulose and 33.34% hemicellulose. Alkaline pretreatment was more effective in pretreating CC biomass compared to the SSB biomass. Both Ca(OH)2 and NaOH pretreatment removed lignin from the CC biomass, while only NaOH removed lignin from the SSB biomass. Biomass compositional analysis revealed that these agricultural feedstocks differed in their chemical composition because the CC biomass contained mainly hemicellulose (33–35%), while SSB biomass consisted mainly of cellulose (17–24%). The alkaline pretreated SSB and CC samples were subjected to the hydrolytic action of the holocellulolytic enzyme cocktail, formulated with termite derived multifunctional enzymes (referred to as MFE-5E, MFE-5H and MFE-45) and exoglucanase (Exg-D). The HEC-H hydrolysed NaOH pretreated SSB and CC more effectively than Ca(OH)2 pretreated feedstocks, revealing that NaOH was a more effective pretreatment. In conclusion, the HEC-H cocktail efficiently hydrolysed alkaline pretreated agricultural feedstocks, particularly those which are hemicellulose- and amorphous cellulose-rich, such as CC, making it attractive for use in the bioconversion process in the biorefinery industry.

Highlights

Agricultural feedstocks such as sweet sorghum bagasse (SSB) and corncob (CC) have been identified as promising alternatives for the production of second-generation biofuels and other value-added chemicals [1,2,3]
The spectrum of the Ca(OH)2 beechwood xylan and xyloglucan, respectively. These findings demonstrate that multifunctional enzymes (MFEs)-5E had a pretreated SSB and CC biomass samples had a broad and higher intensity peak starting from 1640 cm−1, higher propensity to hydrolyse amorphous cellulose followed by various xylan substrates and reaching a maximum at 1410 cm−1 and ending at 1370 cm−1 (Figure 2)
Biomass compositional analysis revealed that these agricultural feedstocks differed in their chemical composition because the CC biomass contained hemicellulose

Summary

Introduction

Agricultural feedstocks such as sweet sorghum bagasse (SSB) and corncob (CC) have been identified as promising alternatives for the production of second-generation biofuels and other value-added chemicals [1,2,3]. These feedstocks consist of polysaccharides (cellulose and hemicellulose). The cellulose consists of glucose moieties linked by β-1,4-glycosidic bonds, which forms crystalline cellulose that is recalcitrant to enzymatic hydrolytic activity, and amorphous cellulose that is hydrolysed by cellulases. To achieve efficient feedstock hydrolysis, the lignin is removed from the feedstock through chemical, physical, or biological pretreatments

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