367 Bulletin UASVM Agriculture, 67(2)/2010 Print ISSN 1843-5246; Electronic ISSN 1843-5386 Monitoring a Biotechnological Process in a Biofermentor to Obtain a Dairy Product Using Brewer’s Yeasts Adriana PĂUCEAN 1) , Dan VODNAR 2) , Elena MUDURA 1) , Mirela JIMBOREAN 1) , Carmen SOCACIU 2) , Dorina BRĂTFĂLEAN 3) University of Agricultural Sciences and Veterinary Medicine, Faculty of Agriculture, Mănăstur Street 3-5, 400372, Cluj-Napoca, Romania 1) Department of Food Science and Technology, apaucean@yahoo.com 2) Department of Chemistry and Biochemistry 3) University Babes-Bolyai, Faculty of Chemistry and Chemical Engineering, Arany Janos Street 11,400028, Cluj-Napoca, Romania Abstract. Dairy products may go beyond the borders of nutritional value and become functional products if the fermentation process is performed in the best available manner. Our study monitories the process parameters and their variation during the fermentation time of milk incubated with a complex mixture of microorganisms formed by: a lactic culture, kefir-yeast culture and brewer’s yeasts sampled from the secondary fermentation of beer. The study was realized using a Tryton- Pierre Guerin Technologies biofermentor. The results were correlated with the development dynamics of lactic bacteria and yeasts population during 24 hr of fermentation. The pH level variation is typical for kefir-like products. The oxygen content during fermentation is a competitive factor for the two species of microorganisms featuring in our research: Lactococcus lactis and Saccharomyces cerevisiae. In this situation the semi-anaerobic environment insures the fastest rate of acidification for milk and the Saccharomyces cerevisiae yeasts did not display a fermentation metabolism but maintain their viability. Keywords: fermented milk product, Saccharomyces cerevisiae, process parameters. INTRODUCTION Fermented milk products are very popular all over the world, due to both their pleasant flavor and the potential to preserve and even improve good health (Farnworth, 2004). The correlation between the consumption of yogurt and kefir and the overall health of the digestive, circulatory, and immune systems is among the main reasons for which consumers all over the world have become increasingly interested in these foods (Adolfsson, 2004). On the other hand, yeasts, due to their complex and harmonious chemical composition, are capable to insure the right amount of nutrients with high energetic and nutritional value, and in certain case a certain therapeutic value (Ferreira et al., 2010). Brewer’s yeast obtained as a byproduct of beer fermentation, due to the strict hygienic conditions maintained in breweries and to the use of malt worth, which insures good nutrition for the yeast, is the best functional yeast which can be used (Mussatto, 2009). Research has shown that the malt wort biosynthesizes greater quantities of vitamins and biologically active substances than other culture environments (Talbott et al., 2007). From the nutritional point of view, brewer’s yeast possesses valuable concentrations of proteins and vitamins (Webb, 2006). Through the usage of select starter cultures whose metabolism can be coordinated through the size of the inoculators and the setting of physical and chemical activity conditions, one guarantees reproducible processes which result in the manufacturing of