Insights into the hydrolysis of Eucalyptus dunnii bark by xylanolytic extracts of Pseudozyma sp.

Abstract

Transforming lignocellulosic biomass into C5 and C6 sugars suitable to produce biofuels, building blocks, and high-value-added compounds is a key aspect of sustainable strategies and is central to the biorefinery concept. Xylan is found acetylated and bound to cellulose and lignin forming an insoluble complex in nature, and its degradation involves a collection of enzymes acting together. To gain a better understanding of this process, the present study focuses on the elucidation of the main products resulting from the hydrolysis of delignified Eucalyptus dunnii bark by an enzymatic extract from Pseudozyma sp. with xylanase and acetylxylan esterase activities but no cellulase activity. Scanning electron microscopy (SEM) studies of the insoluble fraction after hydrolysis revealed cracking on the surface of the material. The enzymatic activity of the crude yeast extract was evidenced by TLC and HPLC analysis of the hydrolysate, which allowed us to detect xylose, acetylxylobiose, and acetic acid. Finally, the principal low molecular weight products obtained from this process were characterized by nuclear magnetic resonance (NMR) spectroscopy as xylose and 3-O-acetylxylobiose. Based on these spectroscopic and chromatographic results, it was possible to estimate a 4:1 ratio of xylose to 3-O-acetylxylobiose. These results highlight the importance of using an enzymatic system for effective xylan degradation.