Transportation and  storage of samples until analysis

As a general rule, food samples should always be trans-ported and stored in exactly the same way and under the same conditions as the food is transported and stored until marketed. The guidelines below should be followed to ensure the integrity of the product until the time of analysis:

Foods with low water activity

Foods with low water activity (dehydrated, dried or concentrated), which are microbiologically stable, may be transported and stored at room temperature, although they should be protected against moisture.

Frozen foods

Frozen foods should be transported and kept frozen until the time of analysis. The Compendium  recommends storage at minus 20ºC. ISO 7218:2007 recommends minus 15°C, preferably minus 18°C. The transportation should be carried out using Styrofoam boxes with dry ice taking certain precautions and care: the product should not come into contact with the dry ice since the absorption of CO₂ may change the pH. If the lid does not make the packaging air-tight and gas-proof and/or if the packaging is gas-permeable and/or becomes fragile or brittle at low temperatures, a secondary packaging should be used. Generally, wrapping in thick paper or paperboard is sufficient to avoid this problem. Labels and tags used to identify the samples should be waterproof, smudge-proof and fade-proof to avoid the loss of important data.

Refrigerated foods

Refrigerated foods should be transported and kept under refrigeration from the moment they are collected until the time of analysis. The Compendium  recommends, as a general rule, that these samples be transported and stored at a temperature between 0 and 4.4°C, with a maximum time interval of 36 hours between sampling and analysis. The ISO 7218:2007 recommends that this kind of food sample be transported at a temperature between 1ºC and 8°C, stored at 3 ± 2ºC with a maximum interval of 36 h between sampling and analysis (24 h in the case of highly perishable samples). In case it is impossible to perform the analysis within the maximum time interval stipulated, the samples should be frozen and kept under the same conditions as those described for frozen samples (minus 15ºC, preferably minus 18ºC), provided freezing does not interfere with recovery of the target microorganism(s). The  Compendium  recommends that transportation be carried out using Styrofoam boxes containing ice. The Compendium further recommends the use of reusable gel ice packs, to avoid liquid from accumulating inside the boxes. If gel ice is not available, common ice may be used, provided it is pre-packed in plastic bags. Tightly closed styrofoam boxes, with ample space inside for ice, in amounts suf-ficient enough to cover all sample-containing flasks, can keep the samples at appropriate refrigeration temperatures for up to 48 hours in most situations. As a general rule, these samples should not be frozen, and for that reason, the use of dry ice inside the styrofoam boxes is not recommended. If the transport of the samples requires a prolonged period of time, making the use of dry ice necessary, the sample packages should not come into direct contact with the dry ice packs, to avoid freezing. Labels and tags used to identify the samples should be waterproof, smudge-proof and fade-proof to avoid losing important data.

Commercially sterile foods in sealed packages

Commercially sterile foods in sealed packages under normal circumstances may be transported and stored at room temperature, and should be protected against exposure to temperatures above 40°C. Samples of bottled carbonated soft drinks, sold at room temperature, may also be transported and stored under these same conditions. Blown packages should be placed inside plastic bags due to the danger of leakage of materials of high microbiological risk. Transportation and storage can be carried out under refrigeration, to prevent explosion. However, if there is any suspicion of spoilage caused by thermophilic bacteria, refrigeration is not indicated. Thermophilic vegetative cells usually die under the effect of cold and sporulation is not com-mon in canned products.

Water samples

For water samples Chapter 60 of the 4th Edition of the Compendium recommends that bottled water in its original, sealed packaging may be transported and stored at room temperature, without the need of refrigeration. Water contained in opened packages or water samples transferred to other containers should be transported and stored under refrigeration (temperature not specified). The samples should be analyzed within an interval of preferably 8 h, but may not exceed 24 h.

For other types of water, part 9060B of the 21st Edition of the  Standard Methods for the Examination of Water and Wastewater provides the following guidelines:

Drinking water for compliance purposes: preferably hold samples at temperatures below 10°C during tran-sit to the laboratory. Analyze samples on day of receipt whenever possible and refrigerate overnight if arrival is too late for processing on same day. Do not exceed 30 h holding time from collection to analysis for coliform bacteria. Do not exceed 8 h holding time for hetero-trophic plate counts. Nonpotable water for compliance purposes: hold source water, stream pollution, recreational water, and wastewater samples at temperatures below 10°C, during a maximum transport time of 6 h. Refrigerate these samples upon receipt in the laboratory and process within 2 h. When transport conditions necessitate delays longer than 6 h in delivery of samples, consider using either field laboratory facilities located at the site of collection or delayed incubation procedures. Other water types for noncompliance purposes: hold samples at temperatures below 10°C during transport and until time of analysis. Do not exceed 24 h holding time.

References

SILVA, N.D .; TANIWAKI, M.H. ; JUNQUEIRA, V.C.A.;  SILVEIRA, N.F.A. , NASCIMENTO , M.D.D. and GOMES ,R.A.R .(2013) . MICROBIOLOGICAL EXAMINATION METHODS OF FOOD AND WATE A Laboratory Manual . Institute of Food Technology – ITAL, Campinas, SP, Brazil.