Abstract
Microbial growth on meat to unacceptable levels contributes significantly to change meat structure, color and flavor and to cause meat spoilage. The types of microorganisms initially present in meat depend on several factors and multiple sources of contamination can be identified. The aims of this study were to evaluate the microbial diversity in beefsteaks before and after aerobic storage at 4°C and to investigate the sources of microbial contamination by examining the microbiota of carcasses wherefrom the steaks originated and of the processing environment where the beef was handled. Carcass, environmental (processing plant) and meat samples were analyzed by culture-independent high-throughput sequencing of 16S rRNA gene amplicons. The microbiota of carcass swabs was very complex, including more than 600 operational taxonomic units (OTUs) belonging to 15 different phyla. A significant association was found between beef microbiota and specific beef cuts (P<0.01) indicating that different cuts of the same carcass can influence the microbial contamination of beef. Despite the initially high complexity of the carcass microbiota, the steaks after aerobic storage at 4°C showed a dramatic decrease in microbial complexity. Pseudomonas sp. and Brochothrix thermosphacta were the main contaminants, and Acinetobacter, Psychrobacter and Enterobacteriaceae were also found. Comparing the relative abundance of OTUs in the different samples it was shown that abundant OTUs in beefsteaks after storage occurred in the corresponding carcass. However, the abundance of these same OTUs clearly increased in environmental samples taken in the processing plant suggesting that spoilage-associated microbial species originate from carcasses, they are carried to the processing environment where the meat is handled and there they become a resident microbiota. Such microbiota is then further spread on meat when it is handled and it represents the starting microbial association wherefrom the most efficiently growing microbial species take over during storage and can cause spoilage.
Highlights
Owing to abundance of nutrients and high water activity, fresh meat can be colonized by different types of microorganisms
In order to understand which microbial species can contribute to spoilage and what their sources are, it would be important to understand the composition of the microbiota of beef before and after spoilage and to match the members of the microbiota with the microbial populations that are found on carcasses or handling tools and surfaces along the meat chain
Partial 16S rRNA gene sequencing was obtained from DNA directly extracted from environmental swabs as well as beef samples and 16S amplicon pyrosequencing was performed on with a 454 technology
Summary
Owing to abundance of nutrients and high water activity, fresh meat can be colonized by different types of microorganisms. Microbial growth on meat to unacceptable levels contributes significantly to change meat structure, color and flavor and to cause meat spoilage. The initial microbial load of meat depends on the physiological status of the animal at slaughter, the spread of contamination in abattoirs and during processing, while temperature and other conditions during distribution and storage can influence the rate of spoilage [3,4]. In order to understand which microbial species can contribute to spoilage and what their sources are, it would be important to understand the composition of the microbiota of beef before and after spoilage and to match the members of the microbiota with the microbial populations that are found on carcasses or handling tools and surfaces along the meat chain. Recent applications of high-throughput sequencing (HTS) in foods have proved useful for a quantitative in depth assessment of the changes in microbial populations during food production or storage [20,21]
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