Effect of Microwave-Assisted Pretreatment Conditions on Hemicellulose Conversion and Enzymatic Hydrolysis of Norway Spru
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Effect of Microwave-Assisted Pretreatment Conditions on Hemicellulose Conversion and Enzymatic Hydrolysis of Norway Spruce S. Kuittinen 1 & Y. Puentes Rodriguez 1 & M. Yang 1 & M. Keinänen 2 & O. Pastinen 3 & M. Siika-aho 4 & O. Turunen 3 & A. Pappinen 1
# Springer Science+Business Media New York 2015
Abstract The present study investigated the ability of pressurized microwave pretreatment to convert softwood lignocellulose to fermentable monosaccharides. Norway spruce lignocellulose was subjected to microwave pretreatment (600 and 1200 W) under high pressure at different temperatures. Microwave pretreatment at mild acid concentrations (0.05– 0.1 % H2SO4), temperatures of 170 and 200 °C, and a very short incubation time (5 min) released 84–100 % of hemicellulosic monosaccharides (mannose, galactose, and xylose). In addition, minimal amounts of degradation products (5-(hydroxymethyl)-2-furaldehyde, levulinic acid) were formed. The highest yield of fermentable sugars was 75 %, after both the pressurized microwave pretreatment with conditions 0.05 % H2SO4/600 W/200 °C/5 min and enzymatic hydrolysis with 20 FPU Celluclast 1.5 L, 400 nkat of Novozyme 188, and polyethyleneglycol (PEG) 4000 (0.3 g/ g of pretreated material). Results showed that already 0.05 % H2SO4 used in microwave pretreatment could effectively liberate hemicellulose monosaccharides without serious monosaccharide degradation and form a basis for enzymatic hydrolysis.
* S. Kuittinen [email protected] 1
Faculty of Science and Forestry, School of Forest Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland
2
Department of Biology, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland
3
Department of Biotechnology and Chemical Technology, School of Chemical Technology, Aalto University, P.O. Box 16100, 00076 Aalto, Finland
4
VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 Espoo, Finland
Keywords Microwaves . Softwood . Norway spruce . Lignocellulose . Pretreatment . Hemicellulose
Introduction Softwoods are widespread in Nordic areas, and these species have several advantages for effective bioconversion such as remarkable amount of hemicellulose sugars, which could be used in biorefining [1]. In contrast to pentose sugars derived from hemicellulose of hardwoods and herbaceous plants, the hemicellulose fraction in softwood species has high hexose carbohydrate content and is thus easier to utilize directly in fermentation [1]. The highly recalcitrant structure of lignocellulosic biomass, composed of hemicellulose, cellulose, and lignin, makes it crucial to find an effective pretreatment to alter the hemicellulosic and cellulosic fractions [2]. Several chemical, physical, and biological pretreatment techniques or combinations of them have been presented, but only a few have proved to be both effective and suitable for larger-scale use, especially for recalcitrant softwood species [2–7]. Currently, steam pretreatment or steam explosion techniques are considered
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