Development and Acid Formation of Lactococci at Technically Significant Temperatures: Comparative Analysis

Mesophilic lactococci strains of Lactococcus lactis subsp. lactis and Lactococcus cremoris are part of many fermented dairy products, including cheeses. As a rule, they serve as the main acid agents in bacterial starter cultures. Throughout all technological stages of cheese production, these microorganisms encounter various factors that affect their growth and metabolism. Despite its widespread industrial use and accumulated scientific knowledge, the question still remains of how lactococci behave during production. This article provides a comparative assessment of temperature-related development processes and acid formation in lactococci Lactococcus lactis subsp. lactis and Lactococcus cremoris. The strains showed no differences in culture development rate or acid-forming activity under optimal thermostating conditions during the deep liquidphase cultivation in milk. These variables were measured by the increase in titratable acidity (°T) and the decrease in active acidity (pH). The lactococci developed and metabolized carbohydrates at (10 ± 1) °C, which allowed for acid formation processes during the cheese ripening stage. Both strains showed significant psychrotrophy. Their development and metabolism were interrupted at (4 ± 1) °C, which made it possible to avoid the risk of reducing the storage capacity of fermented dairy products under the effect of lactococci starter. The greatest risks of using Lactococcus cremoris starter cultures were associated with their low thermal stability, which made the strains sensitive to temperatures above (40 ± 1) °C.