Grape marc as a source of carbohydrates for bioethanol: Chemical composition, pre-treatment and saccharification Kendall R. Corbin a , Yves S.Y. Hsieh a , Natalie S. Betts a , Caitlin S. Byrt a,b , Marilyn Henderson a , Jozsef Stork c , Seth DeBolt c , Geoffrey B. Fincher a , Rachel A. Burton a,⇑ a The Australian Research Council Centre of Excellence in Plant Cell Walls, School of Agriculture, Food and Wine, University of Adelaide, Waite Campus, Glen Osmond, South Australia 5064, Australia b The Australian Research Council Centre of Excellence in Plant Energy Biology, University of Adelaide, Waite Campus, Glen Osmond, South Australia 5064, Australia c Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, United States highlights  The chemical composition of white and red grape marc was determined.  Marc carbohydrates were characterized using enzyme digests, HPLC and MALDI-TOF-MS.  Dilute acid pre-treatments liberated glucose more efficiently than thermal treatments.  White marc contains 40% fermentable water-soluble carbohydrates.  Theoretical ethanol yields were calculated based on chemical composition. article info Article history: Received 10 April 2015 Received in revised form 4 June 2015 Accepted 5 June 2015 Available online 11 June 2015 Keywords: Bioethanol Grape marc Polysaccharide Pre-treatment Saccharification abstract Global grape production could generate up to 13 Mt/yr of wasted biomass. The compositions of Cabernet Sauvignon (red marc) and Sauvignon Blanc (white marc) were analyzed with a view to using marc as raw material for biofuel production. On a dry weight basis, 31–54% w/w of the grape marc consisted of car- bohydrate, of which 47–80% was soluble in aqueous media. Ethanol insoluble residues consisted mainly of polyphenols, pectic polysaccharides, heteroxylans and cellulose. Acid and thermal pre-treatments were investigated for their effects on subsequent cellulose saccharification. A 0.5 M sulfuric acid pre-treatment yielded a 10% increase in the amount of liberated glucose after enzymatic saccharification. The theoretical amount of bioethanol that could be produced by fermentation of grape marc was up to 400 L/t. However, bioethanol from only soluble carbohydrates could yield 270 L/t, leaving a polyphenol enriched fraction that may be used in animal feed or as fertilizer. Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved. 1. Introduction The carbohydrates in plant biomass can be used as a raw mate- rial for producing liquid biofuels and valuable biochemicals. However, plant material is heterogeneous and recalcitrant to degradation. Further, the carbohydrates may take a variety of chemical forms, including polysaccharides, oligosaccharides, monosaccharides, or form glyco-conjugates like glycoproteins and glycolipids. To overcome the structural complexity of plant biomass, research has focused on modifying plants to make the carbohydrates more available (Abramson et al., 2010). Alternatively, physical or chemical pre-treatments combined with enzymatic hydrolysis have been used to facilitate the liberation of fermentable sugars (Mosier et al., 2005). However, these additional processing steps are energetically and financially costly, and potentially create bottlenecks in large scale production (Klein-Marcuschamer et al., 2012). Thus the need to identify dedi- cated biomass sources that are structurally favorable in their http://dx.doi.org/10.1016/j.biortech.2015.06.030 0960-8524/Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved. Abbreviations: A:X, arabinose:xylose ratio; AIR, alcohol-insoluble residue; Ara, arabinose; ASE, accelerated solvent extractor; CDTA, cyclohexane-1,2-diamine tetraacetate; Fuc, fucose; Gal, galactose; GalA, galacturonic acid; Glc, glucose; GlcA, glucuronic acid; HILIC, hydrophilic interaction chromatography; HMF, 5-(hydroxymethyl)furfural; HPLC, high-performance liquid chromatography; Man, mannose; mol%, relative percent molarity; MS, mass spectrometry; Na 2 CO 3 , sodium carbonate; NCPs, noncellulosic polysaccharides; Rha, rhamnose; WSC, water soluble carbohydrates; Xyl, xylose. ⇑ Corresponding author. Tel.: +61 8 8313 7296; fax: +61 8 8313 7116. E-mail address: Rachel.burton@adelaide.edu.au (R.A. Burton). Bioresource Technology 193 (2015) 76–83 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech