Food for Thought: Filtration frustration? We have the answer

Quality control (QC) microbiology testing is a vital step in the production process – if there’s an issue with your product, it’s the lab that will most likely identify the cause.

In beverage production, the QC microbiology lab is where spoilage microorganisms are detected, contaminations are discovered and where water testing is conducted.

New Food heard in a previous interview with Sartorius’ Tricia Vail that due to beverages not being sterile, they might contain spoilage microbes that can potentially make them unsafe to consume.

In this latest interview with the company, we spoke to Juliane Grossmann and Olivier Guenec to learn more about one of the most popular methods for microbiological QC testing, including how to overcome current challenges.

Q: What is the most popular method for microbiological QC testing in the beverage industry and how does it work?

JG: A common testing method used in the beverage industry is filtration by means of membrane filtration. This allows technicians to concentrate very large volumes (from 100ml up to one litre) of liquid samples. The size of the sample is a huge benefit for the beverage sector. In comparison, the food testing arena is mostly not filterable and requires many manipulations to determine if there are any spoilage microorganisms present.

This membrane filter is normally a cellulose nitrate or mixed cellulose ester with different coloured membrane filter and pore sizes, depending on the microbes you are searching for.

A membrane filter of the appropriate pore size is placed in a filter holder, and the sample is then filtered. In this process, microorganisms in the test sample are retained on the filter surface by the screening action of the membrane filter.

Growth inhibitors can be removed by flushing the membrane with sterile buffered solution after filtration. Afterwards, the membrane filter is placed on a culture medium and incubated.

Several days later, technicians can examine the filters and count the colonies that have developed on the membrane filter surface during incubation.

OG: It can take anywhere from 24 hours to seven days for results; it depends on the type of microorganisms.

You cannot send your product to your customers before obtaining results of the necessary contamination control because it’s forbidden to have certain bacteria in your samples such as E. coli.

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