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Byline: Roberto Carcoba (1), Carmen Pin (2), Ana Rodriguez (1) Keywords: Lactococcus lactis; Chemostat cultures; Lactose metabolism; Dilution rate; pH Abstract: Lactococcus lactis subsp. lactis IPLA 947 is a starter strain isolated from a Spanish farmhouse acid-coagulated cheese. To use this strain as starter culture in Afuega'l Pitu cheese manufacture, anaerobic lactose-limited chemostat cultures were used to optimise the active biomass production in a simple medium (BRFS). Growth, lactose consumption and metabolite production were measured at different pH values (5.5, 6.0 and 6.5) and dilution rates (0.06 to 0.96 h.sup.-1). The influence of both variables on the quoted parameters was described by means of mathematical models. These provided a satisfactory representation of the experimental data. The bacterial response surface showed a significant increase in the biomass when the pH increased and the dilution rate decreased. As dilution rate increased, biomass yield increased but only at the lowest pH. The lactose consumption and the ratio of metabolic end products were also influenced by both variables. As dilution rate decreased, the residual lactose decreased and increased amounts of metabolites other than lactate (acetate, formate, ethanol) were produced. The minimum lactose consumption was obtained at pH 5.5 and 0.96 h.sup.-1 dilution rate. A significant rise of acetate and formate levels occurred as pH increased. A maximum lactate level, along with an acetate, formate and ethanol production close to the minimum, was predicted by mathematical modelling at 0.5173 h.sup.-1 dilution rate and pH 6.054. Author Affiliation: (1) Instituto de Productos Lacteos de Asturias (IPLA-CSIC), Apdo. 85, 33300, Villaviciosa, Asturias, Spain (2) Institute of Food Research, Norwich Research Park, Norwich, NR4 7UA, UK Article History: Registration Date: 01/06/2004 Received Date: 28/01/2004 Online Date: 02/07/2004

Byline: Roberto Carcoba (1), Teresa Delgado (1), A. Rodriguez (1) Abstract: ssp. lactis IPLA947, L. lactis ssp. lactis biovar. diacetylactis IPLA838 and Leuconostoc citreum IPLA616 and designed for Afuega'l Pitu cheese manufacture from pasteurized milk was assayed in cow's and ewe's milk, and in mixtures containing 10% and 20% ewe's milk in cow's milk. The evolution of microbial counts, pH, titratable acidity, organic acids and volatile compounds production throughout the incubation period was determined. The use of ewe's milk as a culture medium increased the metabolic activity of the starter culture reflected in a higher lactose consumption, significantly higher acidity and some carbon source-derived organic acids and volatile compounds production, as well as in slightly higher starter strains growth, although the latter was not statistically significant. Thus, it is suggested that ewe's milk or mixtures of ewe's with cow's milk can be satisfactorily used in the manufacture of this traditional cheese. Author Affiliation: (1) Instituto de Productos Lacteos de Asturias (IPLA-CSIC), Carretera de Infiesto, s/n, E-33300 Villaviciosa, Asturias, Spain e-mail: anarguez@ipla.csic.es, ES Article note: Received: 27 August 1999