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
- 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.
- Test media 2, containing cheese whey, shows inadequate acid development, indicating the probable presence of bacteriophage in the cheese plant.
