Geagley Lab provides dairy oversight, ensures industry makes the grade

The Michigan Department of Agriculture’s Geagley Laboratory in East Lansing is a busy place.

It is Michigan’s only state lab for testing processed dairy products, and without it, Michigan would not meet the requirements of the Grade “A” Pasteurized Milk Ordinance and, therefore, could not ship milk interstate.

“We could not survive without the inspection service MDA provides both on farm and in the lab,” says Gary Trimner, director of member services for the Michigan Milk Producers Association. “We’d be out of business without question. In our two plants, the vast majority [of products] flow outside of the state, supplying the world market.”

Key Points

• All Grade A dairy plants are tested four times every six months.

• Products must be tested within 48 hours of being collected.

• Some of the tests are for antibiotics, pasteurization and somatic cell count.


As directed by the PMO, milk products produced at every Grade A dairy plant in the state are tested four times in a six-month period. MDA dairy inspectors collect whole containers of every processed product a plant produces — from skim milk and yogurt to cottage cheese and chocolate milk.

“Some of the smaller plants have only a few products, but the larger plants, like Country Fresh in Grand Rapids, have 30 or more,” says Bonnie Moon, MDA microbiology manager at the lab.

Products must be tested within 48 hours from the time they are taken from the plant. In total, it takes about a week to sample, test and incubate the products, and read the results.

Each week about 150 milk products are tested at the lab for antibiotics, correct pasteurization, somatic cell count, coliform (E. coli) and the Standard Plate Count (bacteria). In 2009, the Geagley lab analyzed 5,308 milk and milk product samples.

“The plate count is not exactly a plate count any more,” says Jayshree Patel, lead microbiologist, who has worked in the lab for more than nine years with microbiologist Brian Rizzi.

Patel says the plate count, which used a petri dish, was replaced with a more efficient film test. “Two years ago we went to the film, and in the past several years have gone from a staff of five to two and a half people.”

Weekly system

MDA dairy inspectors collect the containers of milk products normally bound for consumers and deliver them to the lab on Tuesdays or Wednesdays, which are considered receiving days. Everything is labeled so that samples can be tracked to the original container. Over the next two days, the samples are set up, and by week’s end, results are read before the next batch arrives.

Samples are diluted, and in the case of dense dairy products, like cheese and cottage cheese, the samples go into a unit called the “Stomacher,” which heats the samples and crushes them into a liquid form.

Each sample, mixed with a particular activator to show contaminates, has the date it was collected, time, temperature and container size recorded.

Testing for bacteria takes the longest, about 48 hours, while the specialized coliform test takes between 22 and 26 hours.

While the samples are incubating, the other tests are performed.

The staff uses dyes and a microscope to obtain the somatic cell count, and test for the enzyme phosphatase, which indicates the presence of raw milk and
under-pasteurization.

The antibiotic test exposes the product to bacteria and heat. A color change indicates the lack of bacteria.

“We know that antibiotics kill bacteria, so that’s an indicator that there is something in the product,” Rizzi explains. “Other things can produce that result, though, like sanitizer. But if bacteria are killed, we need to act quickly and test further.”

Patel says the lab has had only one positive test for antibiotics in at least 20 years. “A positive test would institute an immediate recall of that product.”

Once the samples are incubated, Rizzi and Patel count the number of bacteria, which are now clearly visible on the film. Each product has a tolerance. If it exceeds threshold, “we report those results to the inspectors, who can then take the report to the plant for follow-up or corrective action,” Patel explains.

According to Moon, it’s the daily sampling and surveillance that affords Michigan residents a quick, coordinated response when food emergencies occur. 

Quality assurance

While the Michigan Department of Agriculture state lab serves as a critical food safety check, the dairy plants themselves also check milk. Every tanker, before milk is unloaded, is tested for drug residue and other milk components (at the plant’s discretion).

Laboratory staff are called industry milk analysts, and MDA evaluates and approves all 190 of them. MDA also evaluates 35 industry drug residue screening sites and nine certified laboratories. The commercial dairy industry, under the supervision of MDA, also collects and analyzes samples of milk from each dairy farm monthly for temperature, bacteria counts, somatic cell counts and drug residues.


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test-ready: Dairy products are all labeled before they are sampled so that test results can be matched with the original container.

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QUALITY ASSURANCE: MDA lead microbiologist Jayshree Patel and microbiologist Brian Rizzi perform tests on more than 150 milk products that are delivered to the lab by MDA dairy inspectors each week.

This article published in the July, 2010 edition of MICHIGAN FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.