Food Sampling & Analysis - X

Requirements and Considerations at Sampling

There are various requirements to be fulfilled by the sampling specialist while collecting samples. Some of these requirements are mandatory regulatory requirements while others are voluntary and there are different set of procedures to be followed to eliminate cross contamination and to eliminate sample errors. Following are some of these requirements which you can use as guidelines while you are collecting samples as accompany worker or as a public health authority. It is more important to understand the role that you have to follow otherwise your sample will not give the correct answers while risking the loss of materials and time as well as the credibility of the organization.

Personal Conduct

Clean, well maintained protective clothing, hair and beard restraints, and use of sterile gloves are important elements of the food safety activity. Sampling specialists must not carry out sampling when suffering from temporary illnesses or injury (e.g., cold, flu, open cuts or sores), or diagnosed with communicable disease (e.g., Hepatitis A). Officers performing sampling of prepared food or fresh fruit and vegetables and not following good hygienic practices and aseptic techniques could contaminate the product or be perceived as a potential source of contamination. Before sampling, use all precautionary measures (e.g., use white hard hats in addition to hair nets) that the facility may have in place. Wash hands before, and after sampling as well as after breaks, use of washrooms, and any time when a potential source of cross-contamination has been touched. Discard disposable equipment in proper garbage receptacles.

Sampling Procedures

Each sample that an inspector submits for government laboratory analysis is considered to be an official sample. All samples should be representative of the lot. Appropriate measures should be taken to ensure that samples are not compromised during its handling, storage and transport to the laboratory. If samples are improperly collected, mishandled, transported and/or are not representative of the sampled lot, the laboratory results may be inaccurate and inconclusive.

Sampling Equipment

When drawing samples, ensure there is no potential for cross-contamination from equipment, material and apparatus. For aseptic sampling for microbiological testing, make arrangements with accredited laboratory personnel or contact your supplier for the supply of sterile equipment and sterile material.

Sample Containers

For all sampling purposes, use clean, dry and leak proof containers where the capacity is adequate for the desired sample unit. For microbiological sampling use sterile bags

Instruments for opening food packages

Sterile scissors or knives are needed to open large packages for microbiological sampling purposes.

Sampling devices

For all sampling purposes, use appropriate, clean and dry sampling devices. When sampling for microbiological purposes, sterile scoops, spoons, triers or forks must be used for collecting sample units.

Sterile disposable gloves

Use prepackaged sterile disposable gloves that do not contain talcum powder. The talcum powder may interfere with the chemical and microbiological laboratory testing.

Shipping containers and packaging material

Use an insulated container of sufficient capacity. Use appropriate packing materials such as scrunched up newspaper, shredded paper, styro-foam nuggets, bubble-wrap or any other suitable material needed to secure samples within the shipping container.

Coolants

Use plastic containers filled with refrigerant or well frozen ice packs in plastic bags to keep sample units cool. Dry ice is needed to keep frozen samples in a frozen state.

Other equipment

Bring the following supplies that may be used for sample collection or for marking samples: 

1. Document holder, 
2. Sanitized thermometer, 
3. Flashlight, 
4. Markers, 
5. Rubber band,  
6. Masking tape.

Choosing the samples

Sampling should be carried out in such a way that the samples represent the lot. Random samples, representative of the lot, must be taken from various locations (top, middle and bottom). Open, broken or damaged containers must not be sampled. For microbiological sampling purposes, sampling technician should not sample products that are past the "use by" date or the "best before" date. Also, samples should be collected in such a way that they can be tested before the "use by" or "best before" date. If at all possible, the inspector should collect samples that are five (5) days before their "best before" date. This ensures that the samples collected represent an accurate profile of the product, as retailers should not be selling products that are past the "best before" or "use by" date.

When sampling at wholesalers, packing or processing establishments, choose product that would normally be offered for sale. Do not collect produce directly from the processing and packing line or from cull bins because the product has not gone through all of the establishment's preparation and packing steps.

Sample size

The size of the sample is indicated in the specifications for each sampling plan and depends on the laboratory tests to be performed. If the sample taken is due to a consumer complaint or investigation, consult the labs regarding how much sample they require to perform the analysis. Consumer complaints may have limited amount of sample available, which will dictate how many analyses can be performed.

Sampling for Pesticide Residues, Chemical Contaminants, Food Additives, Preservatives and Treatments

The sample size should consist of at least one kilogram of edible portion of produce or as otherwise indicated in the sampling plan. Insufficient sample size may prevent Laboratory to perform all analytical tests and therefore maybe rejected by Laboratory as unfit sample. In this case the inspector and Area Fresh Fruit and Vegetables Program Specialist will be notified with a request to re-sample and resubmit.

Sampling for Irradiation

The sample size is indicated in the sampling plan. For example: the 2014-2015 sampling plan requires the collection of five avocados, ten mangoes and five papayas. The samples for irradiation can be taken from the same container.

Sampling for Microbiology

The sample size is indicated in the sampling plan. For example, the 2014-2015 sampling plan for domestic fresh fruit calls for: one melon or five (5) prepackaged products weighing at least a total of 750 grams. For bulk products, five (5) sample units weighing at least 150 grams each will be randomly collected. Do not combine any of the sample units into one single sample. Keep the five sample units separate.

Steps for Sample Collection

General procedures

1. Only trained sampling technicians should collect samples, otherwise be under the supervision of or be assisted by a trained sampling technician.
2. Wear clean and protective clothing, hair and beard net to minimize the risk of compromising the sample.
3. Sampling should be done in a clean area to minimize the risk of contamination.
4. Samples should be taken randomly, i.e., minimum of three containers from various locations (top, middle and bottom).
5. When sampling master containers, choose a minimum of three master containers at random; and, from each container, randomly choose a package.
6. Do not overfill the sample container or permit punctures by wire closure.
7. Sample containers must be securely sealed after filling so that they cannot leak or become contaminated during normal handling. It is a good practice to place one bag inside another (double thickness) to maintain container integrity.
8. The packaging of the samples should be done directly at the site of sampling to avoid the possibility of contamination.
9. Samples must be well packaged to maintain their integrity.
10. Consumer-sized prepackaged products should not be opened. They should be submitted as one, in tact, sample unit.

Specific procedures

Sample Collection for Pesticide Residues, Chemical Contaminants, Food Additives, Preservatives and Irradiation

1. Except for specific product like potatoes, the product should be wrapped in aluminum foil, and placed in a polyethylene bag (4 mm or thicker). It is necessary to wrap the product in aluminum foil immediately because the polyethylene might interfere with the integrity of the sample.
2. Do not place potatoes directly in a polyethylene bag. Wrap them in aluminum foil and place them in a paper bag or another type of bag that will permit air circulation.
3. While sampling for food additives and preservatives (e.g. sulphites) use sterile disposable gloves that do not contain talcum powder. The talcum powder may interfere with laboratory testing. Due to the high transferability of sulphites, the sampling technician should change non-talcum gloves in between samples.
4. For other types of chemical sampling, if gloves are used, the use of non talcum powder gloves must be ensured.

Sample Collection for Microbiology

Special care should be taken by sampling technician while sampling fresh fruit and vegetables for microbiological testing. Whenever possible, submit samples to the laboratory in the original unopened containers. If a prepackaged product is sampled, ensure that the container will not become damaged during transportation. For example, some samples, such as sprouts, come in plastic consumer containers, often arrive at the Laboratory cracked and /or with loose lids. Ensure that the plastic containers are well padded and protected during shipment. If the product within a container is too large for submission, a representative portion of the product must be sampled and transferred to a sterile sample container (e.g. Whirlpack bags) under aseptic conditions.

Sampling technician should bring enough sterile equipment to collect the appropriate number of samples. Use sterile disposable gloves that do not contain talcum powder. The talcum powder may interfere with laboratory testing. The gloves must be put on using aseptic techniques. Do not reuse gloves. Change gloves when taking sub-samples. Contact with surfaces other than those of the product itself should be avoided. Place the product immediately in the sample container using the sampling equipment. If product falls outside of the sample container, do not place it back in the container. If a bag is used as a sample container, do not blow into the bag to open it, as you may contaminate the bag.

Marking of the samples

Immediately identify each sample unit with a label or a strip of masking tape to mark the outside of the sample bag. Each sample or sub-sample must be labelled with the sample identification number, the sub-sample identification number and any other information that will help to match the Sampling Report to the proper sample. The marking must be legible and permanent. Do not use a felt pen on plastic sample containers because the ink might penetrate the container.

Storage and transportation of samples

General procedures

Storage and transportation of the laboratory samples must be carried out in conditions that avoid compromising the integrity of the product. The procedures described below should be followed:

1. Deliver samples to the laboratory promptly. Microbiological samples should be collected and sent to laboratories at the beginning of the week so that the laboratories would have enough time to analyse them.
2. If there is a holiday during the week (i.e., National Day, Remembrance Day, Easter, Christmas, etc.) consult with laboratory staff to determine when it is appropriate to send samples.
3. If samples are not shipped immediately, they should be stored in either a refrigerator or freezer, as appropriate.
4. Transport frozen or refrigerated samples in insulated shipping containers of rigid construction so that they will arrive at the laboratory in good condition.
5. The size of the shipping container should be sufficient to hold the samples and ice packs to be shipped.
6. Use clean, dry and sanitized shipping containers, coolers and sanitized ice packs. The packing materials also have to be clean, dry and sanitary.
7. Samples must be separate from each other during storage and transportation to the laboratory. This separation is particularly important for samples with dusty residues or containing volatile analytes.
8. Samples known, or thought, to bear such residues should be double sealed in polyethylene or nylon bags.
9. Samples should be packed tightly to prevent shifting within the shipping container but not so tight that the samples may be compromised during transport. To achieve properly secured samples, use scrunched up newspaper, shredded paper, styrofoam nuggets, bubblewrap, or other suitable packaging material.
10. During summer months, prior to use, place shipping containers in a freezer long enough to chill them thoroughly. Include more ice packs in hot weather. A check should be made, using a thermometer, to verify the internal cooler temperature.

Transportation of Refrigerated Samples

Transport samples in a shipping container with suitable refrigerant capable of maintaining the samples at a temperature between 0 and 7°C. Coolant material, i.e. ice packs, should not be placed directly on the samples. A layer of packaging material can be used to avoid direct contact between the samples and the coolant material in order to prevent freezing. For very large coolers, ice packs around the sides of the cooler or in between samples may be necessary to ensure consistent and adequate refrigeration.

Transportation of Frozen Samples

Surround frozen samples with dry ice wrapped in paper to avoid contact between samples and the dry ice. Sufficient dry ice must be used to keep the product frozen. Clearly label on the outside of the box that the box contains dry ice.

Shipping Temperature of the Samples

Temperature abuse may compromise the integrity of the sample. For microbiological testing, it may result in the replication or death of the targeted microorganism to be tested, and may render analytical results invalid.

Shipping Temperature of Samples for Pesticide residues, chemical contaminants, food additives, preservatives and treatments:

Samples should be maintained at a temperature that prevents product deterioration before it reaches the laboratory. If the product is highly perishable or in an advanced stage of maturity, the product must be frozen in order to prevent further deterioration.

Shipping Temperature of Samples for Irradiation Analysis:

Samples should be maintained at a temperature that prevents product deterioration and should be refrigerated. Do not freeze samples, even if the product is highly perishable or in an advanced stage of maturity.

Shipping Temperature of Samples for Microbiology Analysis

Samples should be maintained at a temperature that prevents product deterioration and ensures sample integrity upon arrival to Laboratory. All samples should be refrigerated prior to shipping (e.g., refrigerate tomatoes, peppers or other products to bring their temperature between 0 and 7°C prior to shipping them to the laboratory). Do not freeze samples, even if the product is highly perishable, susceptible to chilling injury and/or in an advanced stage of maturity. The laboratory may refuse to analyze any samples that they deem compromised, and/or samples that they believe to have been stored at inappropriate temperatures during shipment. The upper temperature limit for samples upon the arrival at Laboratory for microbiological analysis is 7°C. Samples that arrive at the laboratory with a temperature above 7°C will not be analyzed.

Shipping the Samples

Before placing samples in a shipping container, ensure that each sample is properly identified with a sample number. Place the sampling report(s) in a sealed envelope outside of the shipping container or in a separate plastic bag inside of the shipping container.

Ensure that the shipping container is properly labeled and sealed. Mark on the shipping container the following statement: "Perishable, Handle With Care, Dry Ice (if applicable)." Advise the carrier of the requirement for refrigeration and of the presence of dry ice, if used. Samples should be shipped within a reasonable time. Samples for microbiology analysis should be shipped as soon as possible. Any delay in transporting the sample should be avoided. If the samples are to be delivered during a weekend and there is no one at the laboratory to receive them, it is advisable to keep the samples under appropriate storage temperature at the work site, and ship them on an early day in the week, rather than shipping the samples over the weekend. If there is a holiday during the week (i.e., National Day, Remembrance Day, Easter, Christmas, etc.) consult with laboratory staff to determine when it is appropriate to send samples.