Late-blowing defect.

The late-blowing defect in cheese is a significant problem, especially during the manufacture of hard or semi-hard cheeses. This defect is characterized by eyes, slits and cracks caused by the production of gas bubbles as well as abnormal cheese flavor from butyric acid. This defect can create considerable loss of product.

The problem is caused by contamination of the cheesemaking process by C. tyrobutyricum, found naturally in soil, silage, hay and milk. Researchers have identified and characterized a bacteriophage that specifically attacks C. tyrobutyricum. The bacteriophage produces a protein, an endolysin, which recognizes C. tyrobutyricum and breaks open its cells. The research group sequenced the genome of the bacteriophage and identified the gene encoding the endolysin. Cloning this gene into E. coli enabled the investigators to produce the endolysin protein so that they could assess its ability to control levels of C. tyrobutyricum. The endolysin reduced levels of C. tyrobutyricum in laboratory trials as well as in milk. The researchers are expressing the endolysin in L. lactis, the bacterium involved in the cheese fermentation process. This will ensure that the endolysin can be produced in situ during cheese production.

Contact: Arjan Narbad, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Phone: [phone]. Fax: [phone]. Email: [e-mail].