Optimization of media and fermentation conditions for the growth of Lactobacillus sakei

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 con-tent 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 Lac-tobacillus 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 valu-able alternative to expensive media routinely used for propagation of mesophilic lacto-bacilli. Key words: fermented sausages, starters, media, Lactobacillus sakei