Review Protein extraction from biomass in a bioethanol refinery – Possible dietary applications: Use as animal feed and potential extension to human consumption Simone Chiesa, Edgard Gnansounou * Bioenergy and Energy Planning Research Group (BPE), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland article info Article history: Received 10 April 2010 Received in revised form 23 July 2010 Accepted 23 July 2010 Available online 6 August 2010 Keywords: Ethanol Protein Co-production Bio-refinery Human nutrition abstract The economy of the production of lignocellulosic ethanol could be supported by the simultaneous use of different components of the biomass other than sugars. Among these, protein is present at high concen- tration in leaves and is a candidate for different possible utilizations. Among dietary applications, plant protein may be used as animal feed and possibly extended to human consumption, in close similarity to leaf protein concentrates already proposed in the past. This would be especially beneficial for devel- oping countries. For this aim, protein quality plays a crucial role: separating only the noble fraction of protein in biomass and preserving its nutritional value, while simultaneously obtaining good yields and limiting drawbacks on other steps of the production chain is particularly challenging from a technical viewpoint. In this review, we compare the possible extraction of protein from dry biomass with the more commonly studied situation in which freshly harvested material is used, with special focus on dietary implications. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Improving the economy of ethanol production from lignocellu- losic biomass is a crucial factor which could give boost toward a concrete industrial implementation. A more rational utilization of the feedstocks, capable of taking advantage of different compo- nents present in the biomass other than fermentable sugars, could represent significant progress. This would contribute to give rise to a bio-refinery, in close similarity to the situation found in the petroleum industry. Products of special interest could originate not only from sugars not involved in the fermentation process, but also from other minor components of the biomass. In particular, proteins are present at variable concentrations according to the particular biomass and may reach values of 30% in the leaves of some species of plants (Nagy et al., 1978). Protein extraction from dry lignocellulosic feedstocks has started receiving attention only recently, often with the goal of producing high qual- ity animal feed. However, a similar process involving preparation of protein concentrates from freshly harvested leaves has been investigated for over 50 years, as proteins of outstanding quality may be adequate for human consumption, rather than being lim- ited in their use for animal. This operation would be particularly beneficial for developing countries which permanently face a pro- tein scarcity, as shown in Fig. 1 where national protein consump- tions are compared for a few industrialized and developing countries. In addition, co-production of ethanol and protein for hu- man nutrition would presumably positively impact the public opinion: the deleterious relationship of competition between bio- fuels and food that has been experienced in the past would be reversed. However, valorization of the protein fraction in a bio-refinery is challenging, as the use of dry biomass increases technical difficul- ties associated with the extraction. In particular, relatively harsh conditions may be required to obtain economically convenient protein yields; this may be in conflict with the preservation of the protein quality, both in term of amino acid profile and digest- ibility. The presence in the extract of antinutritional compounds with not yet completely clarified effects on human health should also be monitored and limited by appropriate processing. More- over, the extraction process should find its optimal collocation in the whole bioethanol production chain in order to avoid adverse effects on the other operations. In this review, after a brief survey of the role of dietary protein with special attention to its quality, we focus on the extraction and valorization of the protein fraction of lignocellulosic biomass with respect to a few selected possible uses, which include the produc- tion of animal feed. More in particular, we explore the possibility of extending the use as a source of protein in the human diet. For this aim, we compare the works performed in the past on the extrac- tion from fresh biomass with the more difficult situation found in a bioethanol refinery operating on dry feedstock. Several studies carried out in the last few years on protein valorization, especially for feed and food production, are reviewed with respect to their outcomes and potentialities. 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.07.125 * Corresponding author. Tel.: +41 21 693 0627; fax: +41 21 693 28 63. E-mail address: edgard.gnansounou@epfl.ch (E. Gnansounou). Bioresource Technology 102 (2011) 427–436 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech