UVM Theses and Dissertations
Format:
Print
Author:
Coale, Katherine
Dept./Program:
Nutrition and Food Sciences
Year:
2014
Degree:
M.S.
Abstract:
This study analyzed the anti-listerial potential of the microbial communities found on the surface of soft-ripened, raw milk cheeses. The current literature shows that the use of surface smear bacteria with anti-listerial capabilities has the potential to become a food safety tool. While these studies indicate that certain organisms are effective against Listeria monocytogenes, no one organism or consortium oforganisms have demonstrated anti-listerial properties strong enough to be used alone as a food safety measure.
The experimental cheeses were inoculated with a 6-strain cocktail of L. monocytogenes at a level of l00cfu/cm² to mimic the European Union's limit for L. monocytogenes levels in a food at the time of consumption. The growth of L. monocytogenes was enumerated over 60-days of cheese aging, a time period mandated by the United Stated Code of Federal Regulations for raw milk cheeses. The cheeses were aged according to the manufacturer's specifications and surface isolates were analyzed for a molecular profile to further describe the microbial community. Over the 60-day aging period levels of L. monocytogenes never dropped below 100cfu/cm² and this was consistent across 3 independent trials. As such, the microbial community on the surface of the experimental soft-ripened, raw milk cheese does not provide sufficient inhibition of L. monocytogenes to promote food safety.
During this study the interaction between L. monocytogenes and the spoilage microorganism, Pseudomonas spp., was also investigated. L. monocytogenes and Pseudomonas spp. grown in isolation and co-culture were analyzed. Analysis via zones of inhibition was performed for both organisms and revealed no visible inhibition. However, enumeration of the both organisms grown alone and in co-culture revealed a statistically significant increase in population levels for the organisms grown alone. This suggests a potential, although small, inhibitory relationship between L. monocytogenes and Pseudomonas spp.
The results of this study show that for soft-ripened raw milk cheese, the microbial community does not demonstrate anti-listerial effects strong enough to be used as a food safety tool. The safety of these varieties of cheese must be achieved through other strategies including microbial testing across the cheesemaking continuum and adherence to strict microbiological criteria.
The experimental cheeses were inoculated with a 6-strain cocktail of L. monocytogenes at a level of l00cfu/cm² to mimic the European Union's limit for L. monocytogenes levels in a food at the time of consumption. The growth of L. monocytogenes was enumerated over 60-days of cheese aging, a time period mandated by the United Stated Code of Federal Regulations for raw milk cheeses. The cheeses were aged according to the manufacturer's specifications and surface isolates were analyzed for a molecular profile to further describe the microbial community. Over the 60-day aging period levels of L. monocytogenes never dropped below 100cfu/cm² and this was consistent across 3 independent trials. As such, the microbial community on the surface of the experimental soft-ripened, raw milk cheese does not provide sufficient inhibition of L. monocytogenes to promote food safety.
During this study the interaction between L. monocytogenes and the spoilage microorganism, Pseudomonas spp., was also investigated. L. monocytogenes and Pseudomonas spp. grown in isolation and co-culture were analyzed. Analysis via zones of inhibition was performed for both organisms and revealed no visible inhibition. However, enumeration of the both organisms grown alone and in co-culture revealed a statistically significant increase in population levels for the organisms grown alone. This suggests a potential, although small, inhibitory relationship between L. monocytogenes and Pseudomonas spp.
The results of this study show that for soft-ripened raw milk cheese, the microbial community does not demonstrate anti-listerial effects strong enough to be used as a food safety tool. The safety of these varieties of cheese must be achieved through other strategies including microbial testing across the cheesemaking continuum and adherence to strict microbiological criteria.