Abstract
Brewer’s spent grain (BSG) is the main by-product of the beer brewing process. It has a huge potential as a feedstock for bio-based manufacturing processes to produce high-value bio-products, biofuels, and platform chemicals. For the valorisation of BSG in a biorefinery process, efficient fractionation and bio-conversion processes are required. The aim of our study was to develop a novel fractionation of BSG for the production of arabinose, arabino-xylooligomers, xylose, and bioethanol. A fractionation process including two-step acidic and enzymatic hydrolysis steps was investigated and optimised by a response surface methodology and a desirability function approach to fractionate the carbohydrate content of BSG. In the first acidic hydrolysis, high arabinose yield (76%) was achieved under the optimised conditions (90 °C, 1.85 w/w% sulphuric acid, 19.5 min) and an arabinose- and arabino-xylooligomer-rich supernatant was obtained. In the second acidic hydrolysis, the remaining xylan was solubilised (90% xylose yield) resulting in a xylose-rich hydrolysate. The last, enzymatic hydrolysis step resulted in a glucose-rich supernatant (46 g/L) under optimised conditions (15 w/w% solids loading, 0.04 g/g enzyme dosage). The glucose-rich fraction was successfully used for bioethanol production (72% ethanol yield by commercial baker’s yeast). The developed and optimised process offers an efficient way for the value-added utilisation of BSG. Based on the validated models, the amounts of the produced sugars, the composition of the sugar streams and solubilised oligo-saccharides are predictable and variable by changing the reaction conditions of the process.
Highlights
Brewer’s spent grain (BSG) is a by-product of the brewing industry
Concentrations of glucose, xylose, arabinose, ethanol, acetic acid, formic acid, 5hydroxymethyl-furfural (HMF), and furfural were quantified by high-performance liquid chromatography (HPLC) with refractive index detection
The aim of the first acidic treatment was to preferentially release arabinose from BSG, and retain the xylan and glucan part insoluble, resulting in a liquid fraction with arabinose as the main constituent and a solid fraction containing the main part of the initial xylan and glucan content of BSG
Summary
Brewer’s spent grain (BSG) is a by-product of the brewing industry. It is the solid residue of the mashing process, which contributes to 85% of the total by-product of the brewing [1]. BSG is a cheap raw material produced all year round in large quantities from small breweries to large ones [2]. BSG mainly consists of lignocellulose (cellulose, hemicellulose, and lignin), proteins, and minerals [1]. Due to its high moisture content, the transport and long-term storage of BSG are difficult [4]. Nowadays it is mainly used for feeding cattle in local farms [5]
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