Aims: To determine the effects of supplemented copper (Cu2+) on growth and viability of strains used as starters and adjunct cultures for Emmental cheese manufacture.
Methods and results: Thirteen strains belonging to Lactobacillus delbrueckii, Lactobacillus helveticus, Lactobacillus rhamnosus, Streptococcus thermophilus or Propionibacterium freudenreichii species were exposed to various copper concentrations in the proper growth medium at relevant growth temperatures, and the effects of supplemented copper on bacterial growth and cell viability were determined by optical density and pH measurements, also by platings. Among the species considered, L. delbrueckii was the most copper resistant and S. thermophilus the most sensitive to copper. Anaerobic conditions increased this sensitivity significantly. There was also a considerable amount of variation in copper resistance at strain level.
Conclusions: Copper resistance is both a species- and strain-dependent property and may reflect variability in copper-binding capacities by cell wall components among species and strains. In addition, the chemical state of copper may be involved.
Significance and impact of the study: This study revealed that copper resistance is a highly variable property among starter and adjunct strains, and this variability should be considered when strains are selected for Emmental cheese manufacture.