ADSA-ASAS 2006 Joint Meeting location:Minneapolis, MN-USA date:9-16 July 2006
Microbiological safety of Ragusano cheese through traditonal farmhouse manufacturing: a preliminary study
Ragusano is a pasta-filata cheese made from raw milk in the south-eastern region of Sicily (Italy). It is produced at the farmhouse level using traditional wooden tools and natural rennet, in the absence of a starter culture. The cheese manufacturing process involves two rounds of cooking, stretching of the overnight-ripened curd, moulding, brining and aging. Slight differences in the manufacturing process among producers lead to different flavor and texture of the final product.
In an attempt to define the key steps of the process that lead to a good cheese, we monitored the production of Ragusano in five farms of the Hyblean region of Sicily. During each of three subsequent days, two blocks of Ragusano were produced per farm, for an overall count of thirty blocks of cheese. Chemical and microbiological analysis were performed on milk, production intermediates and different sections of cheese aged for 2, 3 and 4 months.
Results point to the importance of the second cooking of the curd as a key step in establishing the necessary conditions for a fast acidification. In fact, in the only farm where this step takes place for 10 minutes only (as opposed to an average length of 150 minutes), acidification of the curd appears to be noticeably slower, with a concomitant higher susceptibility to contamination.
Manufacturing conditions proved to be very effective in causing death of the small number of Staphylococcus aureus cells found as natural contaminants of raw milk. No contaminations by Listeria monocytogenes, Salmonellae and Escherichia coli were detected at any stage of the process. On the other hand, after 2 months from manufacturing already, cheeses showed water activity (aw) levels which are hardly compatible with growth of the above mentioned pathogens, and which decreased further with subsequent aging.
Our results show that the cheese-making technology of Ragusano guarantees high levels of microbiological safety as long as good practices are mantained throughout the entire process. The high temperatures used for cooking and stretching the curd, fast acidification, low aw values and high salt content contribute to make Ragusano a hostile environment for the growth of pathogens.