Enzyme and Microbial Technology 32 (2003) 114–119 Immobilization of Saccharomyces cerevisiae on to acrylamide–sodium acrylate hydrogels for production of ethyl alcohol H. Nursevin Öztop a,∗ , A. Yasemin Öztop b , Erdener Karada ˘ g c , Yasemin I¸ sikver d , Dursun Saraydin d a Biochemistry Research Laboratory, Chemistry Department, Cumhuriyet University, Sivas 58140, Turkey b Department of Microbiology—Clinical Microbiology, Medicine Faculty, Cumhuriyet University, Sivas 58140, Turkey c Chemistry Department, Adnan Menderes University, Aydýn 09010, Turkey d Hydrogel Research Laboratory, Chemistry Department, Cumhuriyet University, Sivas 58140, Turkey Received 11 July 2001; received in revised form 19 September 2002; accepted 23 September 2002 Abstract Acrylamide/sodium acrylate (AAm/SA) copolymers, prepared by using various crosslinkers, were used in experiments on swelling, diffusion, immobilization of yeast cells (Saccharomyces cerevisiae) and production of ethyl alcohol. AAm/SA hydrogels were used for swelling and diffusion studies in the nutrient medium of the cells. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, diffusional exponent, network constant and diffusion coefficient of the hydrogel/penetrant systems were calculated and evaluated. Yeast cells were immobilized onto the hydrogels by adsorption method during multiplication and ethyl alcohol production of the hydrogels was investigated. Swelling of AAm increased with the addition of SA and ethyl alcohol production increased with increasing SA in the hydrogels. The best system for immobilization is found to be AAm/SA hydrogels containing N,N ′ -methylenebisacrylamide as crosslinker. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Acrylamide; Hydrogel; Immobilization; Saccharomyces cerevisiae; Ethyl alcohol; Sodium acrylate 1. Introduction In the conversion of sugars to ethanol, immobilized micro- bial cell systems offer advantages over cell suspension systems in terms of ethanol production and the stability of cell activity. Many support materials for cell immo- bilization have been reported including calcium alginate, -carrageenan gel, polyacrylamide and -alumina. The use of immobilized yeast cell system for alcoholic fermentation is an attractive and rapidly expanding research area be- cause of its additional technical and economical advantages compared with the free cell system [1–5]. Yeast cells have been reported to be immobilized on hydrogel carriers obtained by chemical initiation [6] or by -irradiation [4]. Hydrogels are polymeric networks, which absorb and retain water without dissolving. This property makes them interesting materials as carriers for immobi- lization of bioactive compounds as alternatives to others successfully used materials [7]. ∗ Corresponding author. Fax: +90-346-219-1186. E-mail address: oztop@cumhuriyet.edu.tr (H.N. Öztop). In our previous study, yeast cells were immobilized on to radiation synthesized HEMA/AAm and AAm/MA hydrogels and, used for the production of ethyl alcohol [8,9]. Currently, the immobilization of yeast cells onto acrylamide/sodium acrylate (AAm/SA) copolymers as a gel matrix and the production of ethyl alcohol were investigated. 2. Materials and methods Two hydrophilic monomers used in this study, namely, AAm, and SA were obtained from BDH (Poole, UK). Ammonium persulphate as initiator were obtained from Merck (Darmstadt, Germany). Trimethylolpropan triacry- late (T), 1,4-butandiol dimethacrylate (B), ethylene glycol dimethacrylate (E), N,N ′ -methylenebisacrylamide (N) as crosslinkers, N,N,N ′ ,N ′ -tetramethylenediamine (TEMED) as catalyst, yeast extract, pepton, malt extract, glucose, NH 4 Cl, NaCl, CaCl 2 , lactic acid, alcohol dehydrogenase, -NAD and Saccharomyces cerevisiae were obtained from Sigma (St. Louis, MO). Molasses was a gift from a Sugar Factory (Kayseri, Turkey). All chemicals were used as received. 0141-0229/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII:S0141-0229(02)00244-2