Growth and Activities of Lactococcus lactis in Milk Enriched with Low Mineral Retentate Powders

¹ Groupe de recherche sur les bactéries lactiques, Agriculture Canada, Food Research and Development Centre, 3600 Casavant Boulevard West, St-Hyacinthe, PQ, Canada J2S 8E3

The growth and activities of three strains of Lactococcus lactis ssp. cremoris (Wg2, E8, and HP) and their proteinase-negative variants were studied in skim milk enriched with three types of retentate powder. The performance of these strains in enriched milks was compared with that determined in reconstituted skim milk. Proteinase-positive strains of L. lactis ssp. cremoris exhibited higher maximum specific growth rates than protease-negative variants. Moreover, maximum specific growth rates of lactococci were lower in skim milk than in enriched milk with a high buffering capacity. The performance of proteinase-positive strains was better than that of proteinase-negative variants. Growth of proteinase-positive lactococci in milk media increased -amino groups as determined by the increase of equivalent glutamic acid concentration. Available -amino groups decreased with proteinase-negative variants. Proteinase-positive strain Wg2 exhibited the most proteolytic activity but showed the least specific overall productivity of lactic acid despite high biomass concentration in milk. Among proteinase-positive lactococci, strain E8 produced more lactic acid than other strains, and, among proteinase-negative variants, strain HP had the best specific overall productivity of lactic acid.

Key Words: Lactococcus • retentate powder • enriched milk

Submitted on December 9, 1991
Accepted on April 28, 1992