Study of the growth rate of Saccharomyces cerevisiae strains using wheat starch granules as support for yeast immobilization monitoring by sedimentation/steric field-flow fractionation Lambros Farmakis a, * , John Kapolos b , Athanasia Koliadima a , George Karaiskakis a a Department of Chemistry, University of Patras, 26504-GR Rio-Patras, Greece b Department of Agricultural Products Technology, Technological Educational Institute of Kalamata, 24100 Kalamata, Hellas, Greece Received 5 September 2006; accepted 2 January 2007 Abstract The efficiency and the effectiveness of wheat starch granules as a support for the immobilization of the alcohol resistant psychrophilic yeast Saccharomyces cerevisiae strain AXAZ-1 was studied. The growth rate of these cells in the presence or the absence of the support in the culture medium was investigated by the technique of sedimentation/steric field-flow fractionation (Sd/StFFF). An abrupt increase of biomass productivity in less required time was observed in the case of the presence of wheat starch granules in the culture medium. The results indicate that wheat starch granules might be a good medium for yeast cell culture and bioreactor formation. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Yeast immobilization; Yeast cells proliferation; Biocatalysts; Wheat starch; Field flow fractionation 1. Introduction In industrial fermentation processes, such as baking, wine making, brewing as well as potable and fuel grade alcohol production, yeasts are added as promoters. The most widely used yeasts in food industry are the related species and strains of Saccharomyses cerevisiae. Yeasts can be added either as free or as immobilized cells on suitable supports. Ca-alginate, j-carageenan, agar, pectic acid (Colagrande, Silva, & Fumi, 1994), glass bed, delignifed cellulosie (Bardi & Koutinas, 1994), gluten pellets (Bardi, Bakoyianis, Koutinas, & Kanellaki, 1996) and inor- ganic supports such as mineral kissiris (Bakoyianis, Kane- llaki, Kalliafas, & Koutinas, 1992) and c-aloumina (Loukatos et al., 2000), are used during the last three dec- ades as substrates for yeast strains immobilization. Cell immobilization in alcoholic fermentation is a rap- idly expanding research area because of its attractive tech- nical and economic advantages compared to the conventional free cell system (Margaritis & Merchant, 1984; Stewart & Russell, 1986). Immobilization supports suitable for the wine industry have to meet additional pre- requisites such as food-grade purity, low cost, abundance, non-degradable nature and suitable for low-temperature fermentation. Although many immobilization supports have been proposed for use in wine making, industrial application of the technology is still uncertain. Many sup- port systems such as inorganic materials or alginates were considered inappropriate for wine making and were there- fore eventually abandoned (Kourkoutas, Kanellaki, Kouti- nas, & Tzia, 2005). Cell immobilization has a number of technical and eco- nomical advantages over free cell systems. Improvements in maximum growth rate and productivity in biomass production using orange peel as promoter were observed in batch aerobic fermentation (Plessas, Kourkoutas, 0963-9969/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2007.01.009 * Corresponding author. Tel./fax: +30 2610997144. E-mail address: LFarmakis@chemistry.upatras.gr (L. Farmakis). www.elsevier.com/locate/foodres Food Research International 40 (2007) 717–724