Lab Lemco

Abstract: Factorial experiments, empirical model building and response surface analysis were used to optimize media composition and fermentation conditions for the propagation of Lactobacillus sakei, a species used as a starter in the manufacture of fermented sausages. Yeast extract, Lab-Lemco and, to a minor extent, Bacteriological peptone were found to be good sources of peptides and growth factors for L. sakei, while tryptone had a negative effect. Tween 80 had a more complex effect. A new buffered medium, PLY1, with low content of Yeast extract, Lab Lemco and Bacteriological peptone (3 g/l), was developed and compared favourably to the nutrient rich and expensive MRS medium for the growth of five strains of mesophilic lactobacilli (two L. sakei, two Lactobacillus curvatus and a Lactobacillus plantarum). The effect of temperature and pH on the maximum specific growth rate of two L. sakei in PLY1 was modeled in stirred fermenters and the two strains were found to have different behaviours in response to these factors. PLY1 may provide a valuable alternative to expensive media routinely used for propagation of mesophilic lactobacilli.

Abstract: The sulfite tolerance of meat yeasts was shown to be determined by pH, sulfite concentration, substrate availability, and the composition of the preincubation medium. Acetaldehyde production by Candida norvegica was sulfite-induced and occurred during the exponential growth phase in sulfited (500 micrograms SO2 ml-1) lab lemco glucose broth cultures buffered at pH 5, 6, or 7. Growth at pH 4, however, was inhibited by sulfite. Acetaldehyde production occurred in sulfited medium containing fructose or ethanol but not lactate nor a range of other assimilable substrates. A non-acetaldehyde-producing yeast, Candida vini, grew in sulfited (500 micrograms SO2 ml-1) lab lemco broth containing glucose or lactate buffered at pH 6 or 7 but not at pH 4 or 5.