Enhanced ethanol production from sugarcane juice by galactose adaptation of a newly isolated thermotolerant strain of Pichia kudriavzevii Sandeep Singh Dhaliwal a , Harinder Singh Oberoi a,⇑ , Simranjeet Kaur Sandhu a , Dhiraj Nanda b , Dinesh Kumar b , Satinder Kaur Uppal c a Central Institute of Post Harvest Engineering and Technology, Ludhiana 141 004, India b National Bureau of Animal Genetic Resources, Karnal, India c Department of Plant Breeding and Genetics, Punjab Agricultural University, Ludhiana 141 004, India article info Article history: Received 28 November 2010 Received in revised form 1 February 2011 Accepted 4 February 2011 Available online 12 March 2011 Keywords: Ethanol productivity Galactose adaptation Pichia kudriavzevii Sugar cane juice Thermotolerance abstract The thermotolerant yeast strain isolated from sugarcane juice through enrichment technique was identified as a strain of Pichia kudriavzevii (Issatchenkia orientalis) through molecular characterization. The P. kudriavzevii cells adapted to galactose medium produced about 30% more ethanol from sugarcane juice than the non-adapted cells. The recycled cells could be used for four successive cycles without a significant drop in ethanol production. Fermentation in a laboratory fermenter with galactose adapted P. kudriavzevii cells at 40 °C resulted in an ethanol concentration and productivity of 71.9 g L À1 and 4.0 g L À1 h À1 , respectively from sugarcane juice composed of about 14% (w/v) sucrose, 2% (w/v) glucose and 1% (w/v) fructose. In addition to ethanol, 3.30 g L À1 arabitol and 4.19 g L À1 glycerol were also produced, whereas sorbitol and xylitol were not formed during fermentation. Use of galactose adapted P. kudriavzevii cells for ethanol production from sugarcane juice holds potential for scale-up studies. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Energy crisis and environmental pollution from the use of fossil fuels has become a serious global threat. Thus, we need to move towards a sustainable development path and explore the use of biofuel as cheaper and cleaner alternate to fossil fuels. Sugarcane (Saccharum officinarum) is a high biomass tropical crop and contains about 12–17% total sugars, of which 90% is sucrose (Wheals et al., 1999). Sugar concentration in cane juice depends upon the variety, maturity and the time of harvest. Sugarcane juice normally has sufficient organic nutrients and minerals in addition to fermentable sugars, and thus could be considered as an ideal substrate for ethanol production. Ethanol from sugarcane juice is being produced commercially in Brazil (Moreira, 2000). India is the second largest producer of sugarcane after Brazil. As per the available statistics, the current sugarcane production and productivity in India are 350 million tones and 66.9 tons per hectare, respectively and the entire crop in India is used for sugar production. Every ton of sugarcane yields 740 kg of juice (135 kg sucrose and 605 kg water) and 130 kg of dry baggase (da Rosa, 2005). Although, there is no data available on the quantity of rotten, damaged and shriveled canes produced annually in India, we feel that such canes can be segregated and used for ethanol production for use as biofuel. In India, ethanol is produced from molasses, but limited availability and alternative uses of molasses has led to search for alternative substrates. In absence of a com- mercially feasible technology for ethanol production from lignocel- lulosic biomass, and limited availability of food grains to meet the food needs of growing population in India; ethanol production from sugarcane juice seems to be the only promising alternative for use as biofuel. In countries like India, ethanol production from sugarcane juice will help improve the socio-economic condition of the farmers who are currently supplying sugarcane at a lower price to sugar mills and have to wait for a long period to get their returns. Glucose is the preferred carbon source and consumption of other sugars takes place during glucose repression. Glucose enters the glycolytic pathway directly; it is utilized by yeast cells in pref- erence to other sugars such as galactose that requires conversion to glycolytic pathway intermediates prior to use (Barnett, 1976). However, cell adaptation leads to changes in the regulation mechanism in the cells. The yeast cells adapted to galactose medium showed higher rates of glucose uptake than those under derepressing conditions (Ernandez et al., 1992). Galactose adaptation of cells helped in simultaneous uptake of galactose and other sugars like glucose and fructose in high cell density fermentation (Ernandez et al., 1992). The utilization of galactose 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.02.015 ⇑ Corresponding author. Tel.: +91 161 2313126; fax: +91 161 2308670. E-mail address: hari_manu@yahoo.com (H.S. Oberoi). Bioresource Technology 102 (2011) 5968–5975 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech