Simultaneous Biological Pretreatment and Saccharification of Rice Straw by Ligninolytic Enzymes from Panus neostrigosus I9 and Commercial Cellulase.

Ariyah Terasawat,Sivawan Phoolphundh

doi:10.3390/jof7100853

Abstract

The utilization of rice straw for biofuel production is limited by its composition. The pretreatment process is required to improve the enzymatic accessibility of polysaccharides in the biomass prior to enzymatic saccharification. In this study, simultaneous biological pretreatment and saccharification (SPS) of rice straw starting from laccase production by Panus neostrigosus I9 was operated in a 2-L fermenter. It was found that fungal physiology was strongly influenced by the agitation, and that the highest laccase production was obtained at an agitation speed of 750 rpm (209.96 ± 0.34 U/L). The dilution rate of 0.05 h−1 was set in continuous fermentation which resulted in laccase activity of 678.49 ± 20.39 U/L, approximately three times higher than that in batch culture. Response surface methodology (RSM) was applied to achieve the condition for maximum percentage of delignification. The maximum percentage of delignification of 45.55% was accomplished after pretreatment of rice straw with laccase enzyme 39.40 U/g rice straw at 43.70 °C for 11.19 h. Reducing sugar of 3.85 ± 0.15 g/L was obtained from the digested rice straw in a SPS reactor, while non-pretreated rice straw gave only 1.13 ± 0.10 g/L within 12 h of incubation. The results indicated that simultaneous biological pretreatment and saccharification (SPS) of rice straw by laccase helped to improve the accessibility of cellulose by cellulolytic enzymes.

Highlights

Thailand has a variety of lignocellulosic biomasses, with rice straw being the most abundant agricultural waste
The utilization of rice straw for biofuel production is limited by its composition [1], as it consists of cross-linked polymers of cellulose, hemicellulose, and lignin
Total carbohydrate was depleted after 60 h of cultivation, while laccase activity was detected from 20 h of cultivation and maintained high activity until 80 h of cultivation (Figure 1)

Summary

Introduction

Thailand has a variety of lignocellulosic biomasses, with rice straw being the most abundant agricultural waste. The utilization of rice straw for biofuel production is limited by its composition [1], as it consists of cross-linked polymers of cellulose, hemicellulose, and lignin. These structures provide impermeability and resistance to oxidative stress and microbial attack [2]. The optimized operating parameters can reduce the pretreatment time and increase the yield of monomeric sugar at minimal cost. Among these organisms, filamentous fungi and especially white rot basidiomycetes are the most efficient lignin degraders [8]

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