Abstract
BackgroundThe use of lignocellulosic constituents in biotechnological processes requires a selective separation of the main fractions (cellulose, hemicellulose and lignin). During diluted acid hydrolysis for hemicellulose extraction, several toxic compounds are formed by the degradation of sugars and lignin, which have ability to inhibit microbial metabolism. Thus, the use of a detoxification step represents an important aspect to be considered for the improvement of fermentation processes from hydrolysates. In this paper, we evaluated the application of Advanced Oxidative Processes (AOPs) for the detoxification of rice straw hemicellulosic hydrolysate with the goal of improving ethanol bioproduction by Pichia stipitis yeast. Aiming to reduce the toxicity of the hemicellulosic hydrolysate, different treatment conditions were analyzed. The treatments were carried out according to a Taguchi L16 orthogonal array to evaluate the influence of Fe+2, H2O2, UV, O3 and pH on the concentration of aromatic compounds and the fermentative process.ResultsThe results showed that the AOPs were able to remove aromatic compounds (furan and phenolic compounds derived from lignin) without affecting the sugar concentration in the hydrolysate. Ozonation in alkaline medium (pH 8) in the presence of H2O2 (treatment A3) or UV radiation (treatment A5) were the most effective for hydrolysate detoxification and had a positive effect on increasing the yeast fermentability of rice straw hemicellulose hydrolysate. Under these conditions, the higher removal of total phenols (above 40%), low molecular weight phenolic compounds (above 95%) and furans (above 52%) were observed. In addition, the ethanol volumetric productivity by P. stipitis was increased in approximately twice in relation the untreated hydrolysate.ConclusionThese results demonstrate that AOPs are a promising methods to reduce toxicity and improve the fermentability of lignocellulosic hydrolysates.
Highlights
The use of lignocellulosic constituents in biotechnological processes requires a selective separation of the main fractions
Many of the detoxification methods based on physical, chemical and biological processes can result in a considerable reduction to the sugar concentration; these sugars losses are undesirable for fermentation purposes [18,19,20,21]
The Rice Straw Hemicellulosic Hydrolysate (RSHH) contained approximately 2 g/L acetic acid, whose origin is attributed to the acetyl groups present in the hemicellulose polymers that are released during hydrolysis
Summary
The use of lignocellulosic constituents in biotechnological processes requires a selective separation of the main fractions (cellulose, hemicellulose and lignin). Several methods have been proposed to reduce the concentration of toxic compounds to levels that would not inhibit the fermentation process [7,8,9] These methods can be divided into the following three main groups: biological, physical and chemical. The main chemical detoxification methods employed in hydrolysates treatment are based on the addition of reductive substances and pH modification. Many of the detoxification methods based on physical, chemical and biological processes can result in a considerable reduction to the sugar concentration; these sugars losses are undesirable for fermentation purposes [18,19,20,21]
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