Romanian Biotechnological Letters Vol. 18, No. 6, 2013 Copyright © 2013 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER Romanian Biotechnological Letters, Vol. 18, No. 6, 2013 8873 Alcoholic fermentation by yeast immobilized on maize stem disks filled with Ca-alginate Received for publication, January 15, 2013 Accepted, October 2, 2013 RADOJKA RAZMOVSKI*, VESNA VUČUROVIĆ Faculty of Technology, University of Novi Sad, Boulevard Cara Lazara 1, 21000 Novi Sad, Republic of Serbia, * corresponding author:Tel.: +38121485376, fax: +38121450413, E-mail address: razmovski@tf.uns.ac.rs Abstract The bioethanol production from sugar beet thick juice using whole cells of Saccharomyces cerevisiae immobilized by two new combined strategies of yeast natural adhesion onto the maize stem ground tissue (MSGT) disks and Ca-alginate entrapment was examined in order to improve process efficiency through use of mechanically resistant and physically stable biocatalyst. The first strategy involves the development of immobilized biocatalyst in the form of MSGT discs overlaid with Ca- alginate (IB 1 ), while in the second strategy the MSGT discs were filled with Ca-alginate (IB 2 ). The IB 1 was physically unstable and inconvenient for repeated batch or continuous processes. In contrast, the IB 2 showed high mechanical strength, high cells retention and fermentative activity during four successive cycles without any significant decrease in ethanol production. The average ethanol concentration, productivity and yield during repeated fermentation of sugar beet thick juice (initial sugar of 150 g/l) by IB 2 were 69.18 g/l, 1.44 g/lh and 0.473 g/g (92.6% of the theoretical), respectively. The repeated batch fermentation by IB 2 is useful for reducing the cost of bio-ethanol production due to the savings in time and energy for inoculum preparation, easier ethanol recovery, and lower need for the utilization of costly centrifuges for yeast separation. Keywords: bioethanol; fermentation; Saccharomyces cerevisiae; immobilization; sugar beet thick juice Introduction During the recent years, fermentative production of ethanol from renewable resources has received attention due to the increasing petroleum shortage [1]. Generally, bioethanol is produced from sugar-based feedstock (sugar cane, sugar beet, molasses, cane juice, beet juice), starch-based feedstock (corn, potato, rice, triticale etc.) and cellulosic (bagasse and wood) resources. In particular, sugar-based feedstock contains readily available fermentable sugars and can be an ideal substrate for ethanol production by direct fermentation without need for previous hydrolysis [2]. Owing to the surplus of sugar on the World Market, the European Union (EU) decided to reduce economic support for refined sugar by about a third, in order to prevent export of excess sugar to non-EU markets. Because of this, many sugar producers in Europe are considering to adapt to a combined sugar-ethanol plant in order to achieve increased profitability and fuel efficiency in the sugar beet processing by using its by- products for ethanol production [3]. In this context, the overall ethanol production from different intermediate products (raw juice, thin juice, thick juice) and by-product (molasses) of the sugar beet processing is very important, especially the assessment of them as the most suitable substrate for ethanol production. Because of the large amount of fermentable sugars (approx. 55-65%) accompanied by profuse mineral elements and storability, thick juice was found to be an excellent feedstock for ethanol production [4].