Water Activity – Food
|Test Requested||Required Requisition(s)||Specimen Type||Minimum Volume||Collection Kit|
Food – indicate if part of a meal, control, or follow up
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.
For sampling, follow the instructions found in Public Health Inspector’s Guide to Environmental Microbiology Laboratory Testing.
- 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 water activity test is performed Monday to Saturday.
Turnaround time is up to 7 days.
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.
The availability of water for microbial, enzymatic or chemical activity determines the shelf life of foods. This water availability is determined using a water activity meter. Water activity (aw) is the ratio of water vapor pressure of the food substrate to the vapor pressure of pure water at the same temperature. Water activity is measured on a scale of 0 to 1; pure water has an aw of 1.00 and the aw of a completely dehydrated food is 0.00. (Health Canada, MFLP-66)
For most foods to be considered safe to store at room temperature, they should have an aw ≤ 0.85. Bacterial foodborne pathogens are inhibited at this aw; however, for those microorganisms that can cause spoilage (e.g., yeasts and moulds), the aw should be < 0.60 to prevent food spoilage by inhibiting growth of these organisms.