Preparation of kenaf stem hemicellulosic hydrolysate and its fermentability in microbial production of xylitol by Escherichia coliBL21

Siti Syazwani Mohd Shah,Kheng Oon Low,Abdullah Amru Indera Luthfi,Jamaliah Md Jahim,Shuhaida Harun,Shareena Fairuz Abdul Manaf,Rosli Md Illias

doi:10.1038/s41598-019-40807-z

Siti Syazwani Mohd Shah, Kheng Oon Low + Show 5 more

Open Access

https://doi.org/10.1038/s41598-019-40807-z

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Abstract

Kenaf (Hibiscus cannabinus L.), a potential fibre crop with a desirably high growth rate, could serve as a sustainable feedstock in the production of xylitol. In this work, the extraction of soluble products of kenaf through dilute nitric-acid hydrolysis was elucidated with respect to three parameters, namely temperature, residence time, and acid concentration. The study will assist in evaluating the performance in terms of xylose recovery. The result point out that the maximum xylose yield of 30.7 g per 100 g of dry kenaf was attained from 2% (v/v) HNO3 at 130 °C for 60 min. The detoxified hydrolysate was incorporated as the primary carbon source for subsequent fermentation by recombinant Escherichia coli and the performance of strain on five different semi-synthetic media on xylitol production were evaluated herein. Among these media, batch cultivation in a basal salt medium (BSM) afforded the highest xylitol yield of 0.35 g/g based on xylose consumption, which corresponded to 92.8% substrate utilization after 38 h. Subsequently, fermentation by E. coli in the xylose-based kenaf hydrolysate supplemented with BSM resulting in 6.8 g/L xylitol which corresponding to xylitol yield of 0.38 g/g. These findings suggested that the use of kenaf as the fermentation feedstock could be advantageous for the development of sustainable xylitol production.

Highlights

Xylitol is a non-fermentable pentahydroxy sugar-alcohol found in some fruits and vegetables including mushrooms, lettuces, berries and corns[1,2]
A handful of research work has been dedicated to direct utilization of crop biomass for xylitol production to replace the use of the costlier commercial sugar as the main carbon source
The abundance of genomic information associated with Escherichia coli (E. coli) has allowed the engineering of biosynthetic pathways for valuable xylitol production[11]

Summary

Introduction

Xylitol is a non-fermentable pentahydroxy sugar-alcohol found in some fruits and vegetables including mushrooms, lettuces, berries and corns[1,2]. Paidimuddala and Gummadi[15] asserted that the use of hydrolysates from biomass could afford the maximum xylitol yields of 0.30–0.32 g/g, under aerobic conditions These agricultural residues consist of three major components: cellulose, lignin, and hemicellulose. Kenaf captures greenhouse gas at a significantly high rate This is mainly because kenaf has much higher photosynthesis rate compared to some other conventional trees and could contribute to the pursuit of global sustainable development[19]. This third world fiber crop (i.e. after wood and bamboo) is endowed with inherent pest-resistant properties and a high growth rate of 180–220 kg per hectare, making it a favourable choice for cultivation as a major industrial crop in the future[20,21]. It has been found that the attainment of a high-yield conversion of xylan necessitates the pretreatment under only mild conditions to prevent substantial depolymerization of cellulose[30]

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