Laboratory testing in a dairy plant is primarily divided into ingredients, in-process product, finished product, environmental testing and equipment start-up. All of these categories can be evaluated for quality and safety targets. Chemical-based testing for animal drug residues, aflatoxins, allergens and equipment start-ups are routine in the industry. Microbial testing has regulatory benchmarks (standard plate count and coliform levels) that provide some standardization, but additional microbial testing by the U.S. dairy industry is anything but standardized.

While the Food and Drug Administration has not provided final direction for environmental microbial testing as per the Food Safety Modernization Act, it should be standard practice to collect weekly environmental swabs for the presence of Listeria species in wet areas and Salmonellaspecies in dry areas of the processing plant.

Testing protocols

Frequency and location should be based on an initial intense environmental monitoring of all areas of the plant weekly over a month with sample location rotation and frequencies established from the result of the intense month-long sampling. Environmental result trending should be used to adjust the initial sample location rotation and frequency. Positive environmental sample results should increase sampling frequency until the root cause is addressed, then sampling frequency should be reduced to the trending-justified levels.

Ingredients should not require microbial sampling upon receipt if the dairy plant received Certificates of Analysis and operates an effective supplier management program. Raw milk received in farm or over-the-road tankers should be routinely sampled to establish a microbial profile.

In-process product also needs to be sampled and tested after major processing steps, while frequency at each sampling location should be a minimum of once per product run to establish microbial profiles unique to each sampling location.

Finally, finished products microbial sampling frequency should be the minimum required to meet customer demands and/or company-established targets with the result used to establish microbial profiling for each specific product.  


Metagenomics holds promise

A new concept called “metagenomics” is being evaluated in university laboratories and some food plants. Testing results identify the collective microbial population contained in a sample. This new concept in mapping microbial patterns for ingredients, in-process product and finished product use microarray trays that have the capability of identifying many different bacteria at the same time from the same sample. While the current cost today prevents widespread usage, in the future microarray results will be like “words” telling dairy plants if their operations meet multiple microbial targets, if the variances in sampling results are normal or excessive and the location of microbial problems.

The microbial testing of samples taken by dairy plants today ensures ingredients meet specifications, processing is under control and finished products meet quality, shelf-life and safety requirements. This is dependent on defining normal versus excessive test result variations through the use of statistical process control, establishing sampling programs with the correct sampling locations, sampling frequencies and testing methodologies.

With the use of metagenomics technology, the microarray results are “sentences” and become a valuable tool for dairy plants to quickly identify root-cause solutions to microbial problems. Only through evaluation of new microbial testing methodologies, updated sampling systems and the use of statistical process control can the dairy industry consistently deliver nutritious, wholesome and safe dairy products to consumers.

I want to give a special “thank you” to Marie Yeung and Dr. Raul Cano at California Polytechnic State University, San Luis Obispo, and Wendy Warren at Aegis Food Testing Laboratories, North Sioux City, S.D., for sharing technical information and pictorial diagrams.

For additional information on dairy testing, contact me and review the Center for Food Safety and Regulatory Solutions website,