In recent years a lot of attention has been paid to biofuel production and the transition from first to second
generation feedstocks, mainly from the perspective of reducing the use of fossil resources and avoiding competition with
the food chain. These lignocellulosic materials can be used for fermentative production of other biochemicals, building
blocks or biomaterials, making them attractive for a biobased economy. The many aspects that need to be considered for
process design and industrial implementation for second generation sugar syrup, from technical, cost and sustainability
perspective, are reviewed in this paper.
The major classes of lignocellulosics, being cereal residues, hardwood and softwood, their compositions, and the main
pretreatment methods, in view of efficiency in opening up the cell wall matrix and their potential to minimize the
production of inhibitors, are compared. Still, due to naturally present potentially inhibitory sugars, as well as the inevitable
production of some inhibitors in pretreatment, a detoxification step is likely necessary to prevent carry-over in the final
product. In-depth studies have generated a very detailed view on enzymes required to saccharify the pretreated
lignocellulosics efficiently, including the description of a new mechanism by the lytic polysaccharide monooxygenase.
The enzyme classification, specificity, and their limitations, either substrate, enzyme or process related, are reviewed.
Different ways to deal with minor impurities in the sugar syrup, from fermentation operational point of view, are
deliberated upon. Finally, economic analysis in combination with life cycle assessment to value sustainability aspects, is
discussed and shows the requirement for an integrated multidisciplinary approach to clear the way for production of
universally fermentable sugar syrup from lignocellulosics.