pH – Food
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Shelf Stability1 |
Food – indicate if part of a meal, control, or follow up |
25 grams |
Sterile plastic sample bag with round wire closure |
Submission and Collection Notes
Test selection is completed by the laboratory and is based on the information provided on the requisition. Specific analyses may be requested using the ‘Comments’ section of the requisition.
Special Instructions
For sampling, follow the instructions found in Public Health Inspector’s Guide to Environmental Microbiology Laboratory Testing.
Shipping Instructions:
- Ship all foods in containers with hard walls and lids secured in the closed position.
- Shipping containers must be labelled with the submitting organization, unique identifier and contents e.g. FOOD SAMPLES on the outside of the container.
- DO NOT SHIP WITH CLINICAL SPECIMENS. Shipping containers used for food samples should be dedicated to food samples and not be used for other types of environmental samples.
- Ship dry foods and other shelf stable foods at ambient temperature in a closed container.
- Ship frozen foods in an insulated container with sufficient ice packs to maintain the frozen state.
- Ship perishable foods in an insulated container with sufficient cold packs to maintain a temperature as close to 4°C as possible. If ice is used, contain the ice in a manner that does not allow water contact with the samples.
- Submit all food samples to the laboratory as soon as possible.
Test Frequency and Turnaround Time (TAT)
The pH test is performed Monday to Saturday.
Turnaround time is up to 7 days.
The pH is a function of the hydrogen ion concentration in the food and is a measure of food acidity and alkalinity, which varies with food type. pH is measured on a scale of 1 to 14, with 7 being neutral, lower numbers indicating greater acidity and higher numbers indicating greater alkalinity. (Health Canada, MFHPB-03, modified)
Interpretation
The pH is just one factor that influences bacterial growth, and can interact with the following to inhibit growth of pathogens and other organisms: water activity (aw), salt, redox potential, preservatives and temperature. As the pH decreases, a lower temperature is needed to inactivate microbes. Foods with an equilibrium pH ≤ 3.7 will not support the growth of bacterial foodborne pathogens, regardless of the aw. However, if the pH of the food (jarred/canned products) is ≤ 4.6, microorganisms are inhibited providing the aw is ≤ 0.85. According to Public Health Ontario’s Home Canning Literature Review, June 2014, a hermetically sealed acidic canned or jarred food with an equilibrium pH ≤ 4.6 that has gone through sufficient heat treatment to eliminate vegetative microorganisms (bacteria, yeasts and molds), will not support the germination and growth of botulinum spores and production of the toxin.
Reporting
Results are reported to the submitting health unit as indicated on the requisition, when all analyses are completed.
Food samples that show the presence of bacteria capable of causing food-borne illness are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.
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