Team:Manchester/Burtscheese

We have visited a local cheese maker Claire Burt to get to know about the cheese making process and cheesemaker’s perspective about our idea.
We found that the commercial cheese making process is very sensitive and needs to be highly controlled.
Claire explained to us that the major sources of Listeria contamination are various surfaces or water used in the process. That suggested us that having a cell-free or an isolated-cell test would be more convenient than a biosensor integrated into the product.

On the 5th of June, we were kindly invited to ‘Burt’s Cheese’ in Cheshire. The owner, Claire Burt, was generous enough to give us a full demonstration of the cheese making process where we learned the importance of pH and temperature control in cheese manufacture. With this data, we were able to amend our current cheese making protocol to fit better for a soft, white mould cheese. Our original cheese making protocol did not use any other live culture besides our E. coli but Claire advised us to include other cultures. These other cultures are used to produce flavors and/or CO2 in cheese with eyes. This meant we now needed to control for pH and temperature more strictly. For example, culture must be added at 17°C and increased slowly to 30℃ rather than simply heating to 32°C. We were also informed that it was important to check the pH of the milk is as close to 6.74 as possible for an optimal batch.

Claire Burt also gave us a good insight into the hygiene practices she must adhere to ensure her cheese is safe. For example, Claire uses an ozone producing machine in order to control phage contamination. There is also a strict hygiene checkpoint at which hairnets, lab coats and shoes are changed to minimise the introduction of outside contaminants. We discovered where and how any foodborne pathogens can enter the process. Of particular concern to Mrs. Burt was the hygiene quality of the large metal vat that the farm used to store pasteurised milk. She also stated that Listeria, when present, is often on surfaces and within the water. In addition to this, we learnt that small-scale cheese producers often only send swab samples to labs every 3 months due to the high costs associated with testing. An outbreak of Listeria can be extremely damaging within this space of time. For example, a recent L. monocytogenes outbreak in South Africa lasted 15 months, infecting over 1000 and killing over 200 people. (Blomfield, 2018)

From our visit we decided that, seeing as Listeria monocytogenes contamination was possible at the first stage of processing (the storage vat) we should integrate our biosensor into the cheese itself. Rather than developing the sensor in an external Escherichia coli bacterium, we made the milestone choice to integrate the E. coli into the cheese starter culture. In doing this, the bacterium will always be detecting L. monocytogenes, drastically reducing the time the pathogen spends in the food. Claire Burt also prompted us to research the pathogen detection market to see if we could produce our biosensor as a cheaper alternative to lab grade testing for smaller producers.