Research review paper Fermentation of lactose to bio-ethanol by yeasts as part of integrated solutions for the valorisation of cheese whey Pedro M.R. Guimarães, José A. Teixeira, Lucília Domingues ⁎ IBB—Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal abstract article info Article history: Received 15 June 2009 Received in revised form 3 February 2010 Accepted 4 February 2010 Available online 11 February 2010 Keywords: Lactose fermentation Cheese whey Bio-ethanol Yeast Kluyveromyces Recombinant S. cerevisiae Cheese whey, the main dairy by-product, is increasingly recognized as a source of many bioactive valuable compounds. Nevertheless, the most abundant component in whey is lactose (ca. 5% w/v), which represents a significant environmental problem. Due to the large lactose surplus generated, its conversion to bio-ethanol has long been considered as a possible solution for whey bioremediation. In this review, fermentation of lactose to ethanol is discussed, focusing on wild lactose-fermenting yeasts, particularly Kluyveromyces marxianus, and recombinant Saccharomyces cerevisiae strains. The early efforts in the screening and characterization of the fermentation properties of wild lactose-consuming yeasts are reviewed. Furthermore, emphasis is given on the latter advances in engineering S. cerevisiae strains for efficient whey-to-ethanol bioprocesses. Examples of industrial implementation are briefly discussed, illustrating the viability of whey-to-ethanol systems. Current developments on strain engineering together with the growing market for biofuels will likely boost the industrial interest in such processes. © 2010 Elsevier Inc. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 2. Whey utilization/valorisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 3. Fermentation of lactose to ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 3.1. Kluyveromyces spp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 3.2. C. pseudotropicalis (C. kefyr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 3.3. Saccharomyces cerevisiae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 3.4. Industrial production of ethanol from whey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 1. Introduction Cheese whey is a by-product of dairy industries, particularly the watery portion that is formed during the coagulation of milk casein in cheese making or in casein manufacture. Whey is produced in large amounts and has a high polluting load, therefore representing a significant environmental problem. On the other hand, however, whey retains much of the milk nutrients, including functional proteins and peptides, lipids, lactose, minerals and vitamins and therefore has a vast potential as a source of added value compounds, challenging the industry to face whey surplus as a resource and not only as a waste problem. The utilization of whey has been a challenge since man started making cheese. As cheese production increased, the volume of whey also grew and many cheese factories were built near waterways so that most of the whey was diverted to these streams or rivers (Kosikowski, 1979). Modern times brought the awareness of the polluting problem that whey represents and the consequent regulations prohibiting its dumping into waterways and even into municipal sewage systems, whose conventional treatments are not appropriate to sufficiently reduce whey polluting load (Kosikowski, 1979). Whey represents about 85–95% of the milk volume and retains 55% of milk nutrients. Among the most abundant of these nutrients are Biotechnology Advances 28 (2010) 375–384 ⁎ Corresponding author. Tel.: + 351 253 604 400; fax: + 351 253 678 986. E-mail address: luciliad@deb.uminho.pt (L. Domingues). 0734-9750/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.biotechadv.2010.02.002 Contents lists available at ScienceDirect Biotechnology Advances journal homepage: www.elsevier.com/locate/biotechadv