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Chemical characterization and spectroscopic analysis of the solubilization products from wheat straw produced by Streptomyces strains grown in solid-state fermentation

Departamento de Microbiología y Parasitología, Universidad de Alcalá de Henares, 28871 Alcalá de Henares, Madrid, Spain
Department of Biological and Chemical Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK

Author for correspondence: M. E. Arias. Tel: +91 885 4633. Fax: +91 885 4623.

ABSTRACT

The effects of two extraction procedures on the yield and properties of APPL (acid-precipitable polymeric lignin, or solubilized lignocellulose) produced by four streptomycetes during growth in solid-state fermentation were examined. When APPL was extracted with NaOH (0.1 M) rather than distilled water, yields increased threefold, with Streptomyces chattanoogensis exhibiting maximum solubilization levels [163 mg product (g straw)^-1]. Alterations in the characteristics of APPL obtained during extraction with NaOH were detected using cross-polarization and magic-angle spinning (CPMAS) ¹³C NMR and IR spectroscopy and by GC-MS analysis after CuO oxidation, with the most significant changes detected in the cinnamic acid and lignin moieties. When APPL was extracted with NaOH, ester links between hemicellulose and lignin and between hemicellulose and cinnamic acid were cleaved, resulting in a decrease in the alkyl and carbonyl groups attached to lignin, enabling greater solubilization. Yields of APPL extracted with water were lower, but spectral characterization of this APPL suggested a possible role for actinomycete peroxidases and phenolic acid esterases in lignin solubilization. For industrial solubilization of lignocellulose, a possible role for the application of streptomycetes, or their enzymes, in alkali extraction is suggested as a means of increasing solubilization levels.