Tris–sucrose buffer system: a new specially designed medium for extracellular invertase production by immobilized cells of isolated yeast Cryptococcus laurentii MT-61 Mehmet Nuri Aydogan & Mesut Taskin & Ozden Canli & Nazli Pinar Arslan & Serkan Ortucu Received: 3 January 2012 / Accepted: 12 May 2013 / Published online: 31 May 2013 # Institute of Microbiology, Academy of Sciences of the Czech Republic, v.v.i. 2013 Abstract The aims of the present study were to isolate new yeasts with high extracellular (exo) invertase activity and to investigate the usability of buffer systems as invertase pro- duction media by immobilized yeast cells. Among 70 yeast isolates, Cryptococcus laurentii MT-61 had the highest exo- invertase activity. Immobilization of yeast cells was performed using sodium alginate. Higher exo-invertase ac- tivity for immobilized cells was achieved in tris–sucrose buffer system (TSBS) compared to sodium acetate buffer system and potassium phosphate buffer system. TSBS was prepared by dissolving 30 g of sucrose in 1 L of tris buffer solution. The optimum pH, temperature, and incubation time for invertase production with immobilized cells were determined as 8.0, 35 °C and 36 h in TSBS, respectively. Under optimized conditions, maximum exo-invertase activ- ity was found to be 28.4 U/mL in sterile and nonsterile TSBS. Immobilized cells could be reused in 14 and 12 successive cycles in sterile and nonsterile TSBS without any loss in the maximum invertase activity, respectively. This is the first report which showed that immobilized microbial cells could be used as a biocatalyst for exo- invertase production in buffer system. As an additional contribution, a new yeast strain with high invertase activity was isolated. Introduction Invertase is an enzyme (β-D-fructofuranoside fructohydrolase, β-fructofuranosidase, sucrase, invertin, saccharase; EC 3.2.1.26) used to produce noncrystallisable sugar syrup from sucrose. The hydrolysis of sucrose, which yields glucose and fructose at equimolar concentrations known as invert syrup, is catalyzed by invertase enzyme. The invert syrup is widely used in food and beverage industries as a humectant in the manufac- ture of soft-centered candies and fondants, noncrystallizing creams, jams, artificial honey, and in confectionery industry to a lesser extent in the industrial production of liquid sugar (Kotwal and Shankar 2009; Safarik et al. 2009). Fermentative production of invertase has been performed with free or immobilized cells of fungi (yeasts and molds) and bacteria (Tanaka et al. 2000; Rubio et al. 2002; Rubio and Navarro 2006; Vasquez-Bahena et al. 2006; Alegre et al. 2009; Canli et al. 2011). Invertase has been studied, especially in yeasts such as Saccharomyces cerevisiae, Candida utilis, Schwanniomyces occidentalis, and Rhodotorula glutinis (Fontana et al. 1992; Costaglioli et al. 1997; Belcarz et al. 2002; Rubio et al. 2002). Although various microorganisms have been used for invertase production as mentioned above, the potential of yeast Cryptococcus laurentii to produce invertase has not been stud- ied in detail. There is only one report on the invertase-producing ability of free cells of C. laurentii (Dudikova et al. 2007). On the other hand, there is no study on invertase production with the immobilized cells of this yeast species. M. N. Aydogan : O. Canli Department of Biology, Science Faculty, Ataturk University, Erzurum, Turkey M. Taskin (*) Department of Molecular Biology and Genetics, Science Faculty, Ataturk University, Erzurum, Turkey e-mail: mesuttaskin61@hotmail.com N. P. Arslan Institute of Natural and Applied Sciences, Ataturk University, Erzurum, Turkey S. Ortucu Department of Molecular Biology and Genetics, Science Faculty, Erzurum Technical University, Erzurum, Turkey Folia Microbiol (2014) 59:9–16 DOI 10.1007/s12223-013-0258-2 A.3