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Putting Food Microbiology Under the Microscope

microbiological testing methods

Humans around the world consume nearly 37.5 billion pounds of food every day. But as the global demand for food increases, so does the risk of contamination during food production, processing, and distribution cycles.

Food safety is a top priority for all food ingredient and finished goods manufacturers, so it’s critical that they’re able to confirm if a product is safe to consume, what its shelf life date is, and at what point it becomes a contamination risk.

Enter the food microbiologist. Today, we’re speaking with our own Dr. Yuwei Hu to shed some light on what food microbiologists do and why their work is so important.

What led you to become a microbiologist?

It all started with one cup of yogurt. I had the opportunity to learn how to make yogurt when I was a freshman at Huazhong Agricultural University in Wuhan, China and it made me curious to learn how good bacteria played a role in making the foods that I love.

Tell us about your background in microbiology and your career journey.

In 2000, I started my master’s degree study at Huazhong Agricultural University with a focus on food microbiology that allowed me to study both good and bad microorganisms. From 2003-2007, I completed my Ph.D. studies at Cornell University and my focus evolved to include food pathogens such as Listeria monocytogenes and Salmonella.

I joined Medallion Labs in 2007 as a Senior Scientist on their Global Food Safety Team where I supported the international dairy and meat businesses with environmental monitoring programs, food safety risk assessments, spoilage control, and challenge studies. I also developed detection methods for probiotics and lactic acid bacteria (patented), rapid pathogen detection methods, and whole genome sequencing.

Since 2016, I have been Medallion Labs’ Microbiological Expert, focusing on microbiological testing methods, challenge studies, shelf-life studies, and lethality assessments.

What is a challenge study?

The food industry routinely uses challenge studies to decide whether a specific food requires time-temperature control for safety or if it is suitably formulated. A microbial challenge study is used to simulate what happens to a food product during processing, distribution, and shelf life if the food product is contaminated. A proper microbiological challenge study inoculates selected microorganisms in a food or formulation to determine if the organisms would present a potential health hazard or spoilage risk.

What are the benefits of conducting a challenge study?

Knowing when to perform a challenge study, how to design and conduct such a study, as well as, how to interpret the results allows food processors to understand their product’s quality, stability, and safety in addition to assuring that they meet regulatory mandates or established finished-product specifications.

That information allows stakeholders to make informed decisions that comply with food safety standards and minimize the risk of potential foodborne outbreaks and/or product recalls.

Challenge studies can also lead to reduced product hold while testing, longer shelf life, less aged-product write-off, higher production efficiency, and avoidance of costly recalls.


Our testing services can help you ensure brand standards and regulatory compliance for your product.Contact us to get started.

What is lethality processing validation and how is it different from a challenge study?

Lethality processing validation supports a challenge study by providing scientifically valid evidence of the process and parameters used to achieve the stated microbiological destruction of a target microorganism.

What product(s) or ingredient(s) should manufacturers consider for challenge studies?

Any product or ingredient that might support the growth of microorganisms during manufacturing, processing, or distribution environments. They should also consider how shelf life might lead to a foodborne disease outbreak and/or food quality concerns.

What are some of the most commonly conducted challenge studies?

Foodborne pathogen challenge studies include, but are not limited to, Listeria monocytogenes, Salmonella, Staphylococcus aureus, E.coli O157, and Bacillus cereus. We also see many spoilage microorganism challenge studies which focus on yeast, mold, and lactic acid bacteria.

What are some reliable regulatory references that can help determine if the challenge study testing at Medallion Labs meets regulatory criteria for a product?

The National Advisory Committee on the Microbiological Criteria for Foods (NACMCF) is an impartial organization that provides scientific advice and guidance to federal agencies such as the United States Department of Agriculture (USDA) and Food and Drug Administration (FDA), among others.

Does Medallion offer inoculation services on-site during production or only for samples submitted to the lab?

We can provide both services, though we may recommend one over the other based on unique factors like the setting for on-site inoculation, timelines, etc.

What has been your most impactful challenge study to date? What was the outcome?

Our expert lethality processing team once inoculated over 30,000 pounds of pizza snack products to validate fryers and help make ready-to-eat pizza snack products comply with both FDA and USDA food safety standards. This study successfully opened a new market channel for our client’s pizza snack brand.

What is your favorite part of conducting challenge studies?

Killing all the bad microorganisms. 🙂


Food microbiologists are helping to improve the food industry’s safety and standards through proper testing and challenge studies at every stage of the production cycle. To learn more about Medallion Labs and our customizable solutions for challenge studies and lethality validation, connect with us today.

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