Carbon Dioxide Production by Leuconostoc mesenteroides Grown in Single and Mixed Culture with Lactococcus lactis in Skimmed Milk

Lactic acid bacteria are now used extensively as and aroma of the fermented product but also on the starter cultures in the dairy industry and therefore the texture of blue cheese. optimization of growth conditions appears to be essential The shift in metabolic pathways in response to for successful industrial applications. Furthermore, environmental conditions is well documented in the studying the effects of some environmental parameters on literature in the case of homofermentative species [13], growth kinetics should provide useful information but little information is available about the behavior of concerning the physiology of the microorganisms [1-3]. heterofermentative species such as Leuconostoc Strains belonging to the species Lactococcus lactis and mesenteroides. The quantitative aspects and kinetics of Leuconostoc sp. are the most important organism in the evolved CO in mixed culture of Leuconostocmanufacture of these products at a moderate temperature Lactococcus under different culturing conditions have [4]. Mixed cultures of these bacteria are commonly used been fairly studied [14]. In point of view of the recent as a starter in manufacture of cheese and fermented milk report demonstrating the importance of evolved CO to the texture of dairy products, a study of this matter starter cultures that have been selected for their seemed appropriate. performance during milk fermentation and product The present study was undertaken to determine formation. whether Leuconostoc mesenteroides plays a role in Leuconostoc strains grow associatively with acid carbon dioxide production in pure and mixed culture producing Lactococcus strains and are employed for their with Lactococcus lactis in milk. technological properties (mainly aroma and texture). The associative growth between these two groups of bacteria MATERIALS AND METHODS has been studied with respect to citrate metabolism and aroma formation and has been described as a synergistic Bacterial strains: Leuconostoc mesenteroides subsp. functional relationship. Thus attention has been devoted dextranicum (L4), Leuconostoc mesenteroides subsp. to the growth rate, acid production and final population mesenteroides (19D) and Lactococcus lactis subsp. of these bacteria, which also reflect the interactions lactis (SLO ), which is known for its proteolytic activity, occurring in mixed strain cultures of Leuconostoc and were obtained from Laboratoire de MicrobilogieLactococcus [5, 6]. biotechnologie, ENSBANA, Dijon, France. The identity The importance of Leuconostoc sp. in dairy of species was confirmed by the use of physiological, fermentation is related to their ability to produce carbon biochemical and sugar test by API 50 CHL system dioxide from lactose and citrate. Various methods have according to the manufacturer’s instructions (API been used to measure CO production by microorganisms System, Bio-Merieux France) [15-17]. 2 [7-11]. Holmes et al. [12] demonstrated that cell extract of The strains were stored as frozen stock at 20°C Lactococcus lactis and Lactobacillus enhanced gas in fortified skimmed milk (10% skim milk, 0.25% production of Leuconostoc mesenteroides subsp. yeast extract, 0.5 % glucose) containing 30% glycerol as the ratio of CO is critical as it affects not only the flavor 2