Robert M. Kerr

Food and Agricultural Products Center

When a company sends a sample to an outside lab for microbiological, chemical or another type of analysis, the lab returns the information on a Certificate of Analysis (COA).  Have you ever been sent a COA, and wondered what all the information means?  Well, I hope to take a few minutes to explain some of the common elements of a COA.

 

A COA is issued by laboratories to provide their customers with all the information pertaining to the sample submitted.  If when reading a COA you can’t find a piece of information, or do not understand, do not hesitate to call the lab.  There should be a telephone, email, website or customer service contact information on the COA.

 

Additionally, a food company may require a COA for each lot of incoming raw material to be used in food production.  The COA serves as the guarantee the raw material meets the specifications defined by the manufacturing company and agreed to by the company purchasing the material.  This type of COA may be generated by the manufacturing company’s on-site lab, or by a contracted third party.

 

COA vs. Specification

A common misunderstanding is the difference between a COA and a specification.  A COA provides data for a specific sample.  A specification provides the acceptable range.  For example, the specification for fat content of a product would be a minimum of 2% and a maximum of 4%.  If the COA shows the fat content of Sample A to be 3%, the sample meets the specification.  However, if the COA shows the fat content of Sample B is 4.2%, the sample does not meet specification due to high fat content.  A specification also can be a maximum or minimum only.  For example, the specification for a product could be ≥ 2% fat content (or 2% minimum fat content).  If that were the case, both samples measuring 3% and 4.2% meet the specification.

 

Sample Information

The COA should contain the name of the sample or material tested with an identification number or lot number.  The date of analysis commonly will be included, and for tests which take several days to complete, the date may be the date the results are issued.  There can be many other relevant details to include with the sample identification specific to the type of test that was performed, the specification for the product, the results and the method followed.

 

Lab Accreditation

Food safety audit codes may require the outside lab you contract with to be accredited.  This means the laboratory has implemented its own quality management system and has completed an audit to prove it.  A common example is ISO 17025, and they should be able to provide you with a current certificate for your records.  Along with the certificate will be the lab’s scope of certification, which details which methods are covered under the system audit.  It is important to look at the scope of certification to see if the test you are asking them to conduct is listed in the scope.  Be sure to keep the current certificate on file, because they have an expiration date.

 

Microbiology

There are different methods of finding how many bacteria are present in a sample, as well as different methods for different types of bacteria.  A common unit of measurement for microorganisms is reported on a COA is colony forming units per gram (cfu/g) for food samples.  This count can be measured by looking at a petri dish and counting the visible colonies of microorganisms that have grown under ideal conditions.  To grow these colonies, a portion of the food sample is diluted with sterile liquid and placed in the petri dish.  For example, the lab technician will weigh 10 grams of the sample and mix it with 90 milliliters of liquid, diluting it 10 times.   If, at this point, the sample is placed in the petri dish and only one colony forming unit is observed, the result will be reported as 10 cfu/g.  If there are five colonies observed, the result will be reported as 50 cfu/g, and if no colonies are observed the result will be reported as <10 cfu/g.  The <10 cfu/g does not equate to a negative or zero result because the sample was diluted in the first step.  The original dilution can be further diluted 100 or 1,000 times in order to find the optimum dilution to count the colonies.

 

Water Activity vs. Moisture

Moisture is typically reported as a percentage of the material.  It is found by recording the weight before the test is performed and calculating the loss of weight after the method is completed.  Water activity, on the other hand, is a measure of water is available for use in a material by microorganisms.  There is a certain water activity level that inhibits the growth of microorganisms, and that level differs for each type of microorganism.  Water activity (A^w) is measured on a scale of 0 to 1, with 1 being pure water.  Sugar, salt and other ingredients, along with processing methods, are things that can reduce the water activity of a food below certain points at which different microorganisms are unable to grow.

 

Quantitative vs. Qualitative

Qualitative results will not be a measurement, rather they will be the absence or presence of a characteristic.  For example, a product specification may state the material is “free of rancid odors.”  As the odor is not measured and is an organoleptic characteristic, the qualitative result is the product is either “free of rancid odors” or “rancid odors were detected.”  Another common example of qualitative results is if a food sample is Salmonella “positive” or “negative.”  One of the official methods to test for the presence or absence of Salmonella uses a specific indicator rather than a number to obtain results.  The basis for this is the fact that it doesn’t matter if there are 10 or 1,000 Salmonella colony forming units in the sample, the sample is considered contaminated.  Quantitative results, on the other hand, can be counted or measured.  For example, a product may have a weight specification to meet the labeled weight of 25 lbs.  Also, the product may have a dimensional specification for it to be 6.0 inches wide and 5 inches tall, ± 0.3 inches. 

 

Is that result good or bad?

Except for the positive presence of a pathogen in a food sample or food contact surface, the answer to that question is for your company to decide.  The answer is based on food safety legislation, customer requirements and/or your company’s specification.  The best practice is to develop a table that will outline what is acceptable and what is not acceptable before the sample is sent to the lab, and the lab can help you with that task, as well.

 

Remember, all COA’s are not created equal.  The information they contain will vary by type of product, individual company or lab conducting the analysis.  If you would like to ask me a question about a COA, email stephanie.baker10@okstate.edu.