Summary
Background
Shelf-life of beef can be extended for relatively long periods of time under chilled vacuum packaged conditions.Under low oxygen atmospheres, specific microbial populations tend to predominate, including lactic acid bacteria. Other bacteria, such as enterobacteriaceae, may also contribute to spoilage.
Over the course of chilled storage, lactoc acid bacteria and other contaminants may grow to levels that contribute to unacceptable odours and flavours. The types and levels of spoilage bacteria can also shift as a result of repackaging vacuum packaged meat.Exporters of high quality, vacuum packaged primals observe that these products have a shelf-life as long as 75-100 days when stored in the range of -1 to 3ºC.However, the industry does not know the specific factors that influence this extended shelf-life. Consequently, the industry is not able to implement science-based controls to predict the desired level of product quality and safety.We have observed that growth rates of microbial communities, such as those on agars that isolate total aerobic and lactic agar bacteria, differ among like products produced at different abattoirs. In addition, different products within the same abattoir show similar bacterial growth rates.
The purpose of this project was to determine if there is a correlation between the type of bacterial community and/or individual species, and the growth rate observed on total viable count and lactic acid bacteria agars.
Objectives
The objectives of this project were to:define the microbial community profile of vacuum-packaged beef primals by terminal restriction fragment length polymorphism (t-RFLP)
determine the species of bacterial communities in beef primals showing high, medium and low TVC and LAB growth rates
Results
The research presented in this report builds on information produced in MLA project A.MFS.0147 "Ensuring the quality of exported meat primals using a predictive tool for specific spoilage organisms." This earlier study defined growth kinetics of two common microbial parameters of meat quality, Total Viable Count and Lactic Acid Bacteria. While each of these tests have long historical use and are primary tests for domesticand international market standards, they measure changes in a group of bacteria and not at the species level.
In the previous project, we described the effect of storage temperature on changes in total viable count and lactic acid bacteria levels of beef primals, produced predictive models for the viability of total viable count and lactic acid bacteria, and then validated model predictions against observations of total viable count and lactic acid bacteria levels in primals from six Australian export abattoirs stored at -0.5⁰C for 30 weeks. This study showed that bacterial communities at the six abattoirs were different, that communities varied over storage time, and that there were different bacteria on cube roll compared to striploin. However, differences did not appear to be associated with highly unique genera or species, indicating that the factors influencing different growth rates of TVC and LAB may lie at the strain level.
To test this hypothesis, strains from different abattoirs should be analysed for temperature and pH growth/no-growth boundaries, production of growth-limiting factors (e.g. types and levels of organic acids, quorum factors, bacteriocins) and for rates of utilising meat-based nutrients.
