Detoxification of Corncob Acid Hydrolysate with SAA Pretreatment and Xylitol Production by ImmobilizedCandida tropicalis

Li-Hong Deng,Yun Liu,Yong Tang

doi:10.1155/2014/214632

Abstract

Xylitol fermentation production from corncob acid hydrolysate has become an attractive and promising process. However, corncob acid hydrolysate cannot be directly used as fermentation substrate owing to various inhibitors. In this work, soaking in aqueous ammonia (SAA) pretreatment was employed to reduce the inhibitors in acid hydrolysate. After detoxification, the corncob acid hydrolysate was fermented by immobilized Candida tropicalis cell to produce xylitol. Results revealed that SAA pretreatment showed high delignification and efficient removal of acetyl group compounds without effect on cellulose and xylan content. Acetic acid was completely removed, and the content of phenolic compounds was reduced by 80%. Furthermore, kinetic behaviors of xylitol production by immobilized C. tropicalis cell were elucidated from corncob acid hydrolysate detoxified with SAA pretreatment and two-step adsorption method, respectively. The immobilized C. tropicalis cell showed higher productivity efficiency using the corncob acid hydrolysate as fermentation substrate after detoxification with SAA pretreatment than by two-step adsorption method in the five successive batch fermentation rounds. After the fifth round fermentation, about 60 g xylitol/L fermentation substrate was obtained for SAA pretreatment detoxification, while about 30 g xylitol/L fermentation substrate was obtained for two-step adsorption detoxification.

Highlights

Increasing attention has been paid on xylitol production from corncob hydrolysate in China because corncob is widely distributed in northern, central, and southern China with more than 40 million tons annually [1]
The contents of cellulose and xylan increased for the corncob detoxified by soaking in aqueous ammonia (SAA) pretreatment, and 90–97% cellulose was obtained for SAA pretreatment, which is in good agreement with the results in literature [18]
SAA pretreatment of corncob is a novel strategy to reduce the inhibitors formation with merits of high delignification and efficient removal of acetyl group bounded to oligomer with high recoveries of cellulose and xylan

Summary

Introduction

Increasing attention has been paid on xylitol production from corncob hydrolysate in China because corncob is widely distributed in northern, central, and southern China with more than 40 million tons annually [1]. Fermentation production of xylitol from corncob acid hydrolysate is an attractive and promising alternative owing to environmentally friendly merit [2]. Acid hydrolysis corncob cannot be directly used as fermentation substrate owing to various inhibitors, which would inhibit microbial growth and enzyme activity. Among these inhibitors, acetic acid and phenolic and furfural compounds are predominant. Duarte et al [6] reported that phenolic and furfural compounds had strongly detrimental effect on specific growth rate of microorganism and biomass productivity.

Methods

Results

Conclusion