Survival of Salmonella in chocolate
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Rønsbo, Mie Hvillum1, Forfatter
Haxgart, Sine Nygaard1, Forfatter
Knøchel, Susanne1, Vejleder
Sandris Nielsen, Dennis1, Vejleder
Heimdal, Hanne1, Vejleder
1Det Biovidenskabelige Fakultet, København, Danmark
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 Abstract: Outbreaks caused by Salmonella have been linked to a number of food products with low water activity (aw) including chocolate. Low concentrations of Salmonella in chocolate (as low as 0.005 – 0.025 CFU/g) have been found to be the reason for illness. This study evaluated the survival of Salmonella in chocolate. This was done in corporation with the major Danish chocolate manufacturer Toms Gruppen A/S. Toms Gruppen A/S have food safety as main priority and therefore they want to act pro-active to secure their products. The survival of Salmonella typhimurium C5 and S. typhimurium C5¿rpoS during storage for 5 months was examined in white, milk, 57%, and 72% chocolate, respectively. Further these strains were examined at room temperature and 10°C, respectively. The survival of S. typhimurium 365, S. oranienburg and S. nigeria was examined in milk and 72% chocolate, respectively, and at room temperature and at 10°C, respectively. Further, the survival of S. typhimurium C5 and S. typhimurium C5¿rpoS during conchingof 72% chocolate (conched and not conched chocolate) at 75°C for 22 hours was investigated. To quantify the number of viable cells during storage and conching a method was developed for isolating cells from chocolate and subsequently purification of RNA. Finally, the water content and aw were measured for the four chocolates. The greatest relative log reduction was observed in white and milk chocolates. These types of chocolate were found to have the highest water content and the lowest aw compared to 57% and 72% chocolate, respectively. The greatest log reduction was approximately 2 log and was found for S. typhimurium C5 and S. typhimurium C5¿rpoS in white and milk chocolate after storage at room temperature. The lowest reduction observed was approximately 0.5 log and was found for all five Salmonella strains stored at 10°C. The survival curves showed the tendency of similar relative log reduction the five Salmonella strains. The survival of Salmonella was found to be correlated with water content and aw of the chocolates. In addition, a difference in log reduction was observed between storage at room temperature and at 10°C with the latter being the least inhibiting. The investigations on the survival of Salmonella during conching showed a reduction of 3 log when Salmonella was inoculated into 72% chocolate (approximately 2•10^7 CFU/g) and heat treated at 75°C for 22 hours. The inactivation curves of Salmonella during conching showed an initial decrease followed by tailing indicating greater persistence of Salmonella. In addition to the storage experiment, the water content and aw of chocolate was found to influence the survival on Salmonella during conching.The method of quantification by Real-Time PCR was only partly developed in the course of this work. The method was used to show that Salmonella was found to survive in the chocolate. It was not possible to quantify the number of surviving Salmonella cells in the chocolate from the data obtained. However, it was possible to isolate RNA from Salmonella artificially inoculated into chocolate. It was found that PCR inhibiting substances can be avoided by 100 fold dilutions of the samples. Further, the genes 16S rRNA and invA was found not to be an appropriate choice for measuring RNA activity of Salmonella in chocolate.
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 Type: Speciale
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Sprog: English - eng
 Datoer: 2009
 Sider: 149 pages
 Publiceringsinfo: København, Danmark : Institut for Fødevarevidenskab
 Indholdsfortegnelse: -
 Note: Food Science and Technology, Food Science and Technology
 Type: Speciale
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