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.

Food Sampling & Analysis - IX

Requirements and Considerations before Sampling

The following questions are some of the frequently asked questions before you go for a sampling work, which may be intended for regulatory requirements or company quality assurance or any other relevant requirements as we discuss in the previous articles. The purpose and the frequency is basically come with the planning, but when you decide the sampling plan, it is mandatory to reassure that you are doing the right thing. Thus it is very good practice to keep a check list and to follow some of the requirements given below as guide lines to get ready for a sampling expedition.

Does the person taking the sample properly authorized?

Food Authorities must ensure that the officers that they authorize to carry out food standards enforcement possess suitable qualifications, and that they have evidence of experience and competency to carry out the duties assigned to them; for example, records of qualifications, details of accompanied sampling visits and formal appraisals.

When official sampling of foodstuffs for food standards purposes is undertaken, authorized officers must additionally be trained in the appropriate techniques and be competent to carry out sampling duties. Sampling under the provisions of food legislations and the code of practice should only be undertaken by officers who meet the appropriate requirements stipulated in the code. The authorization and qualification of officers are often questioned at the beginning of a court case.

Does the type of samples that are to be taken known?

The Food Safety (Sampling and Qualifications) Regulations require authorized officers who procure samples under the Act, and who consider that the samples should be analyzed as a formal sample, to divide the sample into three parts.

A decision needs to be made whether to take a formal or an informal sample and, in the former case, whether a single part sample is necessary or appropriate and whether the containers of food samples should be opened or not. If no formal proceedings are likely to arise, then the use of a simple informal sample will probably suffice. In this case, the sample is taken as a single item or serving, with no formal requirements on the division of the sample. This is often taken as an unopened container of the food and labeled to identify its status as a sample.

The type of food involved may also affect the way in which the sample is taken, particularly samples taken under the provisions of regulations that have their own sampling provisions, as listed in the schedule to the Food Safety Regulations. For example, specific guidance is given on how to sample peanuts for aflatoxins and whole frozen chickens for extraneous water content.

Are there any legal, official or product specific sampling procedures that need to be considered before taking food samples?

Most of the Food Safety Regulations contain the basic legal provisions relating to the sampling of foods. That specifies the detailed requirements for the manner of procuring samples and the method of dealing with them. This includes their division into parts, the persons to whom parts must be provided and the notices to be given. However, the sampling, storage and analysis of some food products, analytes and even packaging materials are often controlled by specific legislation that contains its own detailed provisions which may override these general considerations. Examples include: caseins and caseinates; coffee extracts and chicory extracts; condensed and dried milk; specified sugar products; wine and spirit drinks; dairy products (e.g. extraneous water); bottled waters; poultry meat standards (e.g. water content); fishery products (e.g. chemical checks); veterinary residues in animal products; pesticides in crops, foods and feeding stuffs; nitrates; aflatoxins; ochratoxin A; lead; cadmium; mercury; 3-monochloropropane-1, 2-diol (3-MCPD); dioxins; plastic materials and articles in contact with food and mineral hydrocarbons.

The sampling procedures of the Code, however, do not have to be adhered to in the following circumstances:

Complaint food samples that are submitted by consumers or other agencies;

Food samples that are submitted to the Public Analyst or Food Examiner solely for monitoring or surveillance purposes, where there is no intention at the time of sampling that any formal enforcement action will ensue from the result;

Food samples submitted for expert opinion (e.g. foreign body identification) rather than for analysis or examination;

Food samples taken as evidence in their own right (e.g. for use-by date offences);

Samples taken under the provisions of regulations that have their own detailed sampling provisions listed in the Schedule to the food safety regulations in the concerning country.

Do you know how many, and how much sample will be needed?

The Code of Practice Guidance indicates that the quantity and nature of any sample should be such as to enable the required analysis to be made. The nature of the samples that are appropriate will depend on the purpose for which the analysis is undertaken. The quantity will vary according to the product and the type of analysis to be carried out. The Public Analyst/Sampling Specialist/Food Analyst should be consulted in case of doubt. This question of how much sample to take is regularly asked of Public Analysts. Generally, if each part of a formal sample is about 300 - 500 grams then this should be sufficient for analysis. In the case of spirits for alcohol content taken from licensed premises, the equivalent of a double shot from an optic (50ml) for each part of the sample will usually suffice although more may be required for other analysis. Again some regulations give guidance on the minimum weight of final samples.

Where the samples are pre-packed, and in relatively small containers, e.g. 250 grams, and they are not to be opened, then ideally at least 6 or 9 items should be taken as the sample and divided into the three representative final parts, with two or three food containers in each part. Generally, one sample of a specific food is taken and divided into three final parts of the sample. On some occasions multiple samples are taken e.g. to check whether the nutrition declarations on a ready meal are “typically” low by purchasing from different shops or different batches of production.

Are the correct labels, forms and paperwork, equipment, containers, utensils, and official seals available?

Each Authority should ideally have a defined system for the administration of samples. This will normally include the use of appropriately designed record forms, sample labels and laboratory submission sheets. Self-duplicating forms provide a useful means of keeping an exact record of all data. On taking a formal sample for analysis, the three final parts of the sample will need to be labeled with the name of the food, the name of the sampling officer, the name of the authority, the place, date and time of sampling and an identification number. They will also need to be placed in suitable containers and secured with a tamper evident seal. Sufficient labels, forms, containers and seals will need to be taken to the point at which the sampling is to be carried out.

Consideration also needs to be given to the correct container for the sample type. The code of practice Guidance indicates that samples of food which are not pre-packed or opened cans or packets of food should first be placed in clean, dry, leak-proof containers such as wide mouthed glass or plastic jars, stainless steel metal cans or disposable food quality plastic bags. Jars, bottles or cans should be suitably closed. Disposable food-quality plastic bags should be sealed securely after filling so that they cannot leak or become contaminated during normal handling. Samples of alcoholic drinks should be placed in glass bottles of appropriate size which have leak-proof caps and do not absorb alcohols.

The code of practice guidance indicates that the contained final parts should each be secured with a tamper evident seal. It is often useful to place the parts of the sample in a second container, such as a plastic bag, which should be sealed in such a way as to ensure that the sample cannot be tampered with, without being obvious. As the sample to be taken is not always known before going out on inspections, it may be necessary to take a selection of sample containers. It is good practice to place all sampling materials, labels etc into a sampling kit that is re-stocked after use. This gives an image of a professional approach to sampling to the seller/owner of the food.

Items and sampling equipment that may be useful when taking samples include: chopping board, can opener, knife, plastic bags, scissors, spoons, jars (note: glass is not often allowed in factories), gum tape, corkscrew, plastic gloves, ladle, protective clothing, cold box. Whatever equipment is used, it is important to ensure that it is appropriately maintained.

Is any specialized sampling equipment needed for the products concerned?

In some instances more specialized equipment might be needed to carry out the sampling and could include items such as a sampling spear, thief (specific piece of sampling equipment), temperature-monitoring device, scales, and weights. Equipment such as food processor or mincer may occasionally be useful, although it is more usual for any blending to be left to the food analyst. A camera is a useful piece of equipment for recording both the premises and details of the samples taken when appropriate.

British Standards and ISO standards contain many specifications of items of equipment those are useful during sampling, including cheese borers, dippers, and sampling spears. Some standards also specify appropriate ways of sampling for unusual shapes, e.g. round cheeses. Consideration needs to be given to the type of sample to be taken prior to setting out, to ensure that the appropriate equipment is available. It might also be necessary to take another person along to help carry out the sampling, especially if a large bulk of sample is to be taken or sub-sampled, or if there are health and safety implications, e.g. sampling from large volumes of liquid in vats, or food in silos.

Must the food sample be taken during normal working hours?

Entry into food premises, within a permitted area, may be demanded during reasonable hours, which usually means during the normal business hours of the premises in question. However, working hours within the food industry vary greatly and may not coincide with the normal hours of work. Sampling visits should therefore be planned as part of the inspection programme and timed having regard to all relevant and available information, including hours of operation, hours at which certain foods may be handled and any seasonal factors. It is desirable to sample at different times of the day at manufacturing and packing premises to ensure that samples are obtained from beginning and ends of batches etc., whether during the process of a single inspection, or by timetabling subsequent inspections differently. It is also important that food businesses are aware that they may be inspected and samples taken at any time during their working hours. You may need to consider the availability of appropriate secure storage facilities for any samples obtained outside of normal office hours.

Should prior warning of attendance be given?

The powers of entry under the Act are extensive and officers may clearly enter either business or domestic premises (as long as, in the latter case, the dwelling is in the Authority’s own area and that 24 hours notice of intended entry is given to the occupier). Special circumstances apply to police and special premises to investigate complaints and carry out inspections. At the time of seeking entry, the officer may be required to produce an authenticated document that shows their authority in the case of official sampling by public health authorities. As a general rule, inspections shall be carried out without prior warning.  Circumstances will arise, however, when prior notification of a visit will be beneficial, for example when the food business is carrying out a particular operation (a small production run of a limited line, for example).

Does the Food Analyst need to know the sample is coming?

Whilst it is not essential to let the food analyst know in advance of every sample to be submitted, in the interests of efficiency and effectiveness it is important to let your analysts have a clear idea of the numbers and types of samples and when they may be expected. It would be prudent for any unusual demand or urgent requirements to be notified to the food analysts as soon as possible. The following are examples of particular instances when it is important to liaise with the food analyst before sampling and to give an accurate indication of the number of samples expected and when they are likely to be submitted:

In the case of the delivery of large numbers of samples, or where space in freezers will need to be allocated

Where samples need to be analyzed soon after receipt, such as fresh milk for compositional analysis, or foods with labile or evanescent analytes such as sulphite or vitamin C

Test for “previously frozen” must be made by prior arrangement because samples cannot be stored for long and because test chemicals in the laboratory have a limited shelf life and may need sourcing shortly before the samples are expected.

Is a plan for sampling in special circumstances, for example postal purchases, internet purchases and deliveries needed?

Special problems arise as a result of distance selling, and most of the codes of practice guidance include a section covering this area. This presents particular difficulties in sampling because a food can be ordered by telephone, from the Internet or from literature and the first possibility of sampling does not arise until the sample arrives at its destination. Consideration has to be given as to whether a divided sample is sensible or practical. For instance, if Scottish salmon were ordered by phone and delivered, consideration needs to be given as to whether it can be divided and whether a part of the sample can be returned to the seller. Also, what changes might take place to that part of the sample in transit. It might be concluded that division into three parts is not practical and a single part sample used. The Authority needs clearly to consider the arguments in the case of each food type and needs to be able to justify not dividing the sample in the event of a court case. However, where a sample can be divided and returned without fear of the part changing, e.g. vitamin tablets, it might be safer to return a part of the sample to the seller/owner, although it is advisable to discuss these arrangements with the seller/owner beforehand.

Is any specialized clothing required?

The Food Safety Act and Code of Practice requires authorities to provide officers with clean protective clothing including headgear consistent with good industry practice. It also requires officers to wear it, and to give details of their health status when requested to do so. Many companies will have their own hygiene requirements for entering food production areas and will normally provide sampling officers with the appropriate clothing. These often include overalls, hairnets, hats, overshoes, wellington boots, beard snoods etc. It is necessary to comply with the hygiene requirements of the company concerned and this often includes a signed declaration of the officer’s state of health.

For sampling in shops, the provision by the authority of clean white coats, white hat and disposable gloves is good practice. In certain instances personal protective equipment may be needed when sampling. For instance, when dealing with the cutting of meat, the use of protective clothing such as chain mail gloves might be necessary. Other protective items might include protective boots, ear defenders, safety goggles, blue plasters and a small first aid kit. The health and safety of sampling staff should be considered at all times and they should also comply with the hygiene requirements of any food company concerned.

Will the samples be purchased or taken?

It is for the authorized officer to decide, in accordance with the policy of their Food Authority, whether to purchase the sample, or if powers to take it should be exercised. Officers have the power to:

Purchase a sample of any food, or any substance capable of being used in the preparation of food (e.g. food additives);

Take a sample of any food which; appears to be intended for sale, or to have been sold, for human consumption, or they find on, or in, any premises which they are authorized to enter.

Take a sample from any food source, or a sample of any contact material (e.g. plastic packaging), which is found on, or in, any such premises;

Take a sample of any article or substance which is found on, or in, any such premises and which the officer has reason to believe may be required as evidence in proceedings under any provisions of the Act or of regulations or orders made under it.

It may be beneficial for a sample to be obtained by ‘test purchase’ (i.e. by buying an item of food as an ordinary purchaser without first announcing your identity as an authorized officer to the seller).

Reference

http://multimedia.food.gov.uk/multimedia/pdfs/samplingguidancepart2.pdf 

Food Sampling & Analysis - VIII

Preparation of food Samples for Laboratory Analysis

Across the world, food safety testing has become a growing concern as more and more contamination scares arise. Melamine in milk products, carbendazim in orange juice, fish tainted with PCBs, mercury-tainted milk powder and food supplements containing unauthorized food ingredients are just a few of the most recent alerts and scandals. In response to the increase of foodborne illness, regulatory authorities continue to prescribe methods for food testing, making it even more important for laboratories to apply appropriate quality control procedures to ensure safe products from “farm to fork.” Because of the increased regulation for food safety, laboratories must be diligent when selecting their means of analyzing for contaminants or other harmful substances. Sample preparation is perhaps the most important step in the analysis because it can affect the analyte concentration and the cleanliness of the sample prior to further analysis. The proper sample preparation technique must be selected to ensure a reliable downstream analysis. 

In order to achieve the most reliable analysis of chemical hazards, the analyst must first consider how the sample preparation step will affect the instrumental analysis. Food matrices are notoriously complicated because they contain components such as carbohydrates, lipids and proteins. It has been estimated that about 30 percent of analytical errors originate from the sample preparation step, making it even more important that the technique chosen is reliable and repeatable. Whenever possible, official analytical methods provided by international organizations should be followed. However, it is sometimes necessary for a laboratory to create its own documented in-house method. In this case, the analyst will need to determine the most appropriate preparation technique for the samples at hand.

Once we have selected a sample that represents the properties of the whole population, we must prepare it for analysis in the laboratory. The preparation of a sample for analysis must be done very carefully in order to make accurate and precise measurements. Once a sample preparation technique is chosen, the laboratory must validate the procedure to prove that the chosen method is reliable and fit-for-purpose, which can be done by participating in proficiency testing/inter-laboratory comparison programmes. Participation in at least one proficiency test/inter-laboratory comparison is required in order to achieve and/or maintain accreditation according to ISO/IEC 17025:2005. Traditionally in food safety testing laboratories, liquid-liquid extraction (LLE) has been the most popular sample preparation choice. LLE relies upon the partitioning of analytes and interfering compounds into immiscible organic and aqueous layers. During the separation of organic and aqueous solvents, it is sometimes impossible to avoid the formation of emulsions that make it difficult to collect the layer that contains the target analytes, and the repeatability and accuracy of the method can be compromised. Two of the more rapidly growing sample preparation techniques are QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) and solid phase extraction (SPE).

Preparation of Homogeneous Samples

The food material within the sample selected from the population is usually heterogeneous, i.e., its properties vary from one location to another. Sample heterogeneity may either be caused by variations in the properties of different units within the sample (inter-unit variation) and/or it may be caused by variations within the individual units in the sample (intra-unit variation). The units in the sample could be apples, potatoes, bottles of ketchup, containers of milk etc. An example of inter-unit variation would be a box of oranges, some of good quality and some of bad quality. An example of intra-unit variation would be an individual orange, whose skin has different properties than its flesh. For this reason it is usually necessary to make samples homogeneous before they are analyzed, otherwise it would be difficult to select a representative laboratory sample from the sample. A number of mechanical devices have been developed for homogenizing foods, and the type used depends on the properties of the food being analyzed (e.g., solid, semi-solid, liquid). Homogenization can be achieved using mechanical devices (e.g., grinders, mixers, slicers and blenders), enzymatic methods (e.g., proteases, cellulases, lipases) or chemical methods (e.g., strong acids, strong bases and detergents).

Reducing Sample Size

Once the sample has been made homogeneous, a small more manageable portion is selected for analysis. This is usually referred to as a laboratory sample, and ideally it will have properties which are representative of the population from which it was originally selected. Sampling plans often define the method for reducing the size of a sample in order to obtain reliable and repeatable results.

Preventing Changes in Sample

Once we have selected our sample we have to ensure that it does not undergo any significant changes in its properties from the moment of sampling to the time when the actual analysis is carried out, e.g., enzymatic, chemical, microbial or physical changes. There are a number of ways these changes can be prevented.

Enzymatic Inactivation – Many foods contain active enzymes they can cause changes in the properties of the food prior to analysis, e.g., proteases, cellulases, lipases, etc. If the action of one of these enzymes alters the characteristics of the compound being analyzed then it will lead to erroneous data and it should therefore be inactivated or eliminated. Freezing, drying, heat treatment and chemical preservatives (or a combination) are often used to control enzyme activity, with the method used depending on the type of food being analyzed and the purpose of the analysis.

Lipid Protection – Unsaturated lipids may be altered by various oxidation reactions. Exposure to light, elevated temperatures, oxygen or pro-oxidants can increase the rate at which these reactions proceed. Consequently, it is usually necessary to store samples that have high unsaturated lipid contents under nitrogen or some other inert gas, in dark rooms or covered bottles and in refrigerated temperatures. Providing that they do not interfere with the analysis antioxidants may be added to retard oxidation.

Microbial Growth and Contamination – Microorganisms are present naturally in many foods and if they are not controlled they can alter the composition of the sample to be analyzed. Freezing, drying, heat treatment and chemical preservatives (or a combination) are often used to control the growth of microbes in foods.

Physical Changes – A number of physical changes may occur in a sample, e.g., water may be lost due to evaporation or gained due to condensation; fat or ice may melt or crystallize; structural properties may be disturbed. Physical changes can be minimized by controlling the temperature of the sample, and the forces that it experiences.

Sample Identification

Laboratory samples should always be labeled carefully so that if any problem develops its origin can easily be identified. The information used to identify a sample includes:

1. Sample description;
2. Time sample was taken;
3. Location sample was taken from;
4. Person who took the sample, and;
5. Method used to select the sample; 

The analyst should always keep a detailed notebook clearly documenting the sample selection and preparation procedures performed and recording the results of any analytical procedures carried out on each sample. Each sample should be marked with a code on its label that can be correlated to the notebook. Thus if any problem arises, it can easily be identified.

Reference

http://www.sepscience.com/Sectors/Food/Articles/415-/The-Importance-of-Sample-Preparation-in-Food-Analysis

http://people.umass.edu/~mcclemen/581Sampling.html

Food Sampling & Analysis - VII

Food Sampling

Food sampling concerns the selection of the individual units of foods, food products or bulk foodstuffs from the food supply or source, whether it be market place, manufacturing outlet, field or from the homes of the members of the study population. The selection and collection of items of foods defined in number, size and nature to represent the food under consideration. The sampling plan must be in line with physical operation of removal of items from lots or fields or large loads (e.g. ships) with the consolidation and reduction of the collected items to form the portion for the planned analysis.

The official sampling procedure is intended to provide a sample, which is representative of the consignment or lot from which it is drawn. The sample is analyzed to determine the content of some compositional characteristic or the presence of a contaminant. The analysis result is then compared with a declared level (e.g. crude protein) or a minimum or maximum specification (e.g. additives, moisture, etc.) or in the case of a contaminant a maximum permitted level. In certain circumstances, official tolerances (or limits of error) are prescribed and are taken into account when determining compliance with a declared level. Analysis of the properties of a food material depends on the successful completion of a number of different steps: planning (identifying the most appropriate analytical procedure), sample selection, sample preparation, performance of analytical procedure, statistical analysis of measurements, and data reporting. 

Sample Selection

A food analyst often has to determine the characteristics of a large quantity of food material, such as the contents of a truck arriving at a factory, a days worth of production, or the products stored in a warehouse. Ideally, the analyst would like to analyze every part of the material to obtain an accurate measure of the property of interest, but in most cases this is practically impossible. Many analytical techniques destroy the food and so there would be nothing left to sell if it were all analyzed. Another problem is that many analytical techniques are time consuming, expensive or labor intensive and so it is not economically feasible to analyze large amounts of material. It is therefore normal practice to select a fraction of the whole material for analysis, and to assume that its properties are representative of the whole material. Selection of an appropriate fraction of the whole material is one of the most important stages of food analysis procedures, and can lead to large errors when not carried out correctly.

It is convenient to define some terms used to describe the characteristics of a material whose properties are going to be analyzed.

Population – The whole of the material whose properties we are trying to obtain an estimate of is usually referred to as the population.

Sample – Only a fraction of the population is usually selected for analysis, which is referred to as the sample. The sample may be comprised of one or more sub-samples selected from different regions within the population.

Laboratory Sample – The sample may be too large to conveniently analyze using a laboratory procedure and so only a fraction of it is actually used in the final laboratory analysis. This fraction is usually referred to as the laboratory sample.

Sampling Plans

To ensure that the estimated value obtained from the laboratory sample is a good representation of the true values of the population and it is necessary to develop a sampling plan. A sampling plan should be a clearly written document that contains precise details that an analyst uses to decide the sample size, the locations from which the sample should be selected, the method used to collect the sample, and the method used to preserve them prior to analysis. It should also stipulate the required documentation of procedures carried out during the sampling process. The choice of a particular sampling plan depends on the purpose of the analysis, the property to be measured, the nature of the total population and of the individual samples, and the type of analytical technique used to characterize the samples. For certain products and types of populations sampling plans have already been developed and documented by various organizations which authorize official methods, e.g., the Association of Official Analytical Chemists (AOAC).

The primary objective of sample selection is to ensure that the properties of the laboratory sample are representative of the properties of the population, otherwise erroneous results will be obtained. Selection of a limited number of samples for analysis is of great benefit because it allows a reduction in time, expense and personnel required to carry out the analytical procedure, while still providing useful information about the properties of the population. Nevertheless, one must always be aware that analysis of a limited number of samples can only give an estimate of the true value of the whole population.

Purpose of Analysis

The first thing to decide when choosing a suitable sampling plan is the purpose of the analysis. Samples are analyzed for a number of different reasons in the food industry and this affects the type of sampling plan used:

Official samples – Samples may be selected for official or legal requirements by government laboratories. These samples are analyzed to ensure that manufacturers are supplying safe foods that meet legal and labeling requirements. An officially sanctioned sampling plan and analytical protocol is often required for this type of analysis.

Raw materials – Raw materials are often analyzed before acceptance by a factory, or before use in a particular manufacturing process, to ensure that they are of an appropriate quality.

Process control samples – A food is often analyzed during processing to ensure that the process is operating in an efficient manner. Thus if a problem develops during processing it can be quickly detected and the process adjusted so that the properties of the sample are not adversely effected. Techniques used to monitor process control must be capable of producing precise results in a short time. Manufacturers can either use analytical techniques that measure the properties of foods on-line, or they can select and remove samples and test them in a quality assurance laboratory.

Finished products – Samples of the final product are usually selected and tested to ensure that the food is safe, meets legal and labeling requirements, and is of a high and consistent quality. Officially sanctioned methods are often used for determining nutritional labeling.

Research and Development – Samples are analyzed by food scientists involved in fundamental research or in product development. In many situations it is not necessary to use a sampling plan in R&D because only small amounts of materials with well-defined properties are analyzed.

Nature of Measured Property

Once the reason for carrying out the analysis has been established it is necessary to clearly specify the particular property that is going to be measured, e.g., color, weight, presence of extraneous matter, fat content or microbial count. The properties of foods can usually be classified as either attributes or variables. 

Attribute – An attribute is something that a product either does or does not have, e.g., it does or does not contain a piece of glass, or it is or is not spoilt.

Variable – A variable is some property that can be measured on a continuous scale, such as the weight, fat content or moisture content of a material. Variable sampling usually requires less samples than attribute sampling.

The type of property measured also determines the seriousness of the outcome if the properties of the laboratory sample do not represent those of the population. For example, if the property measured is the presence of a harmful substance (such as bacteria, glass or toxic chemicals), then the seriousness of the outcome if a mistake is made in the sampling is much greater than if the property measured is a quality parameter (such as color or texture). Consequently, the sampling plan has to be much more rigorous for detection of potentially harmful substances than for quantification of quality parameters.

Nature of Population

It is extremely important to clearly define the nature of the population from which samples are to be selected when deciding which type of sampling plan to use. Some of the important points to consider are:

1. A population may be either finite or infinite. A finite population is one that has a definite size, e.g., a truckload of apples, a tanker full of milk, or a vat full of oil. An infinite population is one that has no definite size, e.g., a conveyor belt that operates continuously, from which foods are selected periodically. Analysis of a finite population usually provides information about the properties of the population, whereas analysis of an infinite population usually provides information about the properties of the process. To facilitate the development of a sampling plan it is usually convenient to divide an "infinite" population into a number of finite populations, e.g., all the products produced by one shift of workers, or all the samples produced in one day.
2. A population may be either continuous or compartmentalized. A continuous population is one in which there is no physical separation between the different parts of the sample, e.g., liquid milk or oil stored in a tanker. A compartmentalized population is one that is split into a number of separate sub-units, e.g., boxes of potato chips in a truck, or bottles of tomato ketchup moving along a conveyor belt. The number and size of the individual sub-units determines the choice of a particular sampling plan.
3. A population may be either homogeneous or heterogeneous. A homogeneous population is one in which the properties of the individual samples are the same at every location within the material (e.g. a tanker of well stirred liquid oil), whereas a heterogeneous population is one in which the properties of the individual samples vary with location (e.g. a truck full of potatoes, some of which are bad). If the properties of a population were homogeneous then there would be no problem in selecting a sampling plan because every individual sample would be representative of the whole population. In practice, most populations are heterogeneous and so we must carefully select a number of individual samples from different locations within the population to obtain an indication of the properties of the total population.

Nature of Test Procedure

The nature of the procedure used to analyze the food may also determine the choice of a particular sampling plan, e.g., the speed, precision, accuracy and cost per analysis, or whether the technique is destructive or non-destructive. Obviously, it is more convenient to analyze the properties of many samples if the analytical technique used is capable of rapid, low cost, nondestructive and accurate measurements.

Developing a Sampling Plan

After considering the above factors one should be able to select or develop a sampling plan which is most suitable for a particular application. Different sampling plans have been designed to take into account differences in the types of samples and populations encountered, the information required and the analytical techniques  used. Some of the features that are commonly specified in official sampling plans are:

Sample size – The size of the sample selected for analysis largely depends on the expected variations in properties within a population, the seriousness of the outcome if a bad sample is not detected, the cost of analysis, and the type of analytical technique used. Given this information, it is often possible to use statistical techniques to design a sampling plan that specifies the minimum number of sub-samples that need to be analyzed to obtain an accurate representation of the population. Often the size of the sample is impractically large, and so a process known as sequential sampling is used. Here sub-samples selected from the population are examined sequentially until the results are sufficiently definite from a statistical viewpoint. For example, sub-samples are analyzed until the ratio of good ones to bad ones falls within some statistically predefined value that enables one to confidently reject or accept the population.

Sample location – In homogeneous populations it does not matter where the sample is taken from because all the sub-samples have the same properties. In heterogeneous populations the location from which the sub-samples are selected is extremely important. In random sampling the sub-samples are chosen randomly from any location within the material being tested. Random sampling is often preferred because it avoids human bias in selecting samples and because it facilitates the application of statistics. In systematic sampling the samples are drawn systematically with location or time, e.g., every 10th box in a truck may be analyzed, or a sample may be chosen from a conveyor belt every 1 minute. This type of sampling is often easy to implement, but it is important to be sure that there is not a correlation between the sampling rate and the sub-sample properties. In judgment sampling the sub-samples are drawn from the whole population using the judgment and experience of the analyst. This could be the easiest sub-sample to get to, such as the boxes of product nearest the door of a truck. Alternatively, the person who selects the sub-samples may have some experience about where the worst sub-samples are usually found, e.g., near the doors of a warehouse where the temperature control is not so good. It is not usually possible to apply proper statistical analysis to this type of sampling, since the sub-samples selected are not usually a good representation of the population.

Sample collection – Sample selection may either be carried out manually by a human being or by specialized mechanical sampling devices. Manual sampling may involve simply picking a sample from a conveyor belt or a truck, or using special cups or containers to collect samples from a tank or sack. The manner in which samples are selected is usually specified in sampling plans.