Figure 3.1. Culture Activity Test

This section is adapted from two reports prepared by: Mark Mitchell (1995), Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, Ontario

Figure 3.1. Culture activity test: example.

Conditions

Culture Lactococcus lactis subsp. lactis

Lactococcus lactis subsp. cremoris

Temperature 37 C

Inoculum 2% of mother culture prepared with 10% reconstituted skim milk powder.

Test media 1 10% skim milk powder, low heat, antibiotic free.

Test media 2 Same as one with 1% cheese whey.

Results

Titratable acidity after 4 hours:

Treatment 1 0.34%

Treatment 2 0.25%

pH versus time

Time 0 1 2 3 4 5 6 7 8 9
Skim powder 6.62 6.59 6.5 6.4 6.15 5.74 5.39 5.08 4.92 4.87
Skim with whey 6.61 6.57 6.5 6.42 6.35 6.31 6.3 6.3 6.29 6.29

Interpretation

  1. Test media 1 shows normal growth. 0.34% acidity after 4 h with a 2% inoculum is adequate for most types of cheese. pH versus time plot is typical, reaching pH 5.2 between 6 and 7 hours.
  2. Test media 2, containing cheese whey, shows inadequate acid development, indicating the probable presence of bacteriophage in the cheese plant.

 pH vs Time