IFR researchers have demonstrated a potential new way of preventing spoilage in cheese

Tuesday 24 August 2010

Late-blowing in cheese is a significant problem, especially in the manufacture of hard or semi-hard cheeses. Spoilage and loss of product contributes to wastage in the food chain and decreases efficiency.

The problem is caused by contamination of the cheese-making process by Clostridium tyrobutyricum bacteria, which are found naturally in soil, silage, hay and milk. Even small amounts of the bacteria alter the fermentation, causing an excess build-up of CO2 and the production of butyric acid, which gives a rancid taste. Steps must be taken to eliminate the problem, especially as the spores of the bacteria are heat-resistant and can survive pasteurisation.

Funded by the Biotechnology and Biological Sciences Research Council (BBSRC), researchers at IFR have identified and characterised a naturally occurring microorganism that specifically attacks C. tyrobutyricum. Bacteriophages are viruses that infect bacteria, and their use to control food spoilage bacteria has been investigated previously by many research groups, including at the IFR.

In research published in the journal Applied and Environmental Microbiology, Melinda Mayer, Arjan Narbad and colleagues demonstrate the potential use of this bacteriophage for controlling C. tyrobutyricum. The bacteriophage produces a protein, called an endolysin, which recognises C. tyrobutyricum and breaks open its cells. The group sequenced the genome of the bacteriophage and identified the gene encoding the endolysin. Cloning this gene into E. coli allowed them to produce the endolysin protein to assess its ability to control C. tyrobutyricum levels.

The endolysin effectively reduced levels of C. tyrobutyricum in laboratory trials as well as in milk. Significantly the endolysin showed strong specificity for C. tyrobutyricum, which is important as any potential ways of controlling C. tyrobutyricum in cheese production must not interfere with the bacteria that ferment the cheese. This specificity could also mean that the endolysin could form the basis of a detection system.

To develop this further the researchers are expressing the endolysin in Lactococcus lactis, the bacterium involved in the cheese fermentation process. This will ensure that the endolysin can be produced in situ during cheese production. The technology will then be taken forward into trials to test how well it performs during cheese production.

Reference: Genomic sequence and characterisation of the virulent 1 bacteriophage ΦCTP1 from Clostridium tyrobutyricum and heterologous expression of its endolysin. Melinda J. Mayer et al.. Appl. Environ. Microbiol. doi:10.1128/AEM.00989-10

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