Associative Growth of Lactococcus lactis and Leuconostoc mesenteroides Strains in Milk

¹ Institut National de la Recherche Agronomique, Unité de Recherches Laitiéres, 78352 Jouy-en-Josas Cedex, France

The associative growth of a proteinase-positive strain of Lactococcus lactis ssp. lactis CNRZ 1076 and Leuconostoc mesenteroides ssp. mesenteroides UM10 in reconstituted skim milk was studied in detail. The maximum population and the growth rate of Lc. lactis CNRZ 1076 were not affected by the association between strains. The growth rate of Leuc. mesenteroides UM10 was lower in mixed-strain cultures than in pure culture (0.40 vs. 0.63/h, respectively), and the maximum population was 10-fold lower. Acidification was essentially due to the action of Lc. lactis CNRZ 1076, and the acidification rate in mixed-strain cultures and in pure cultures were comparable except when the percentage of Lc. lactis cells was lower than 12%. Inhibition of Leuc. mesenteroides growth was less when the percentage of Lc. lactis cells was lower in the inoculum. Inhibition was almost suppressed when reconstituted skim milk was supplemented with amino acids, Mn²⁺, and Mg²⁺. Twenty-four paired associative cultures of 3 Lc. lactis strains and 8 Leuc. mesenteroides strains in reconstituted skim milk confirmed that competition between the two species for nitrogenous nutrients is a common feature of mixed-strain cultures, regardless of the subspecies of Leuc. mesenteroides or Lc. lactis strains used.

Key Words: Leuconostoc mesenteroides • Lactococcus lactis • mixed-strain culture • milk

Submitted on May 24, 1996
Accepted on February 3, 1997