Predictive model for spoilage in vacuum packed primals

Summary

​Background
The shelf-life of beef and lamb 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, LAB 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.
Currently, 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.
An approach to solving this problem is predictive modelling. This strategy defines parameters that influence the desired attributes, condenses this knowledge into a simple tool and provides proactive risk management for the Australian meat industry.
An example of this approach and positive impact is the MLA Refrigeration Index for Escherichia coli.
Purpose and Description
The purpose of this project was to produce knowledge that will underpin a predictive model for the spoilage of vacuum packaged meat primals. 
To achieve this goal, the dominant bacterial species that impact meat quality under vacuum packaged conditions were defined, including those species that emerge after opening and repackaging primal cuts.
Growth kinetics of the identified specific spoilage organisms - SSO - were measured over -1 to 10ºC and then the kinetic parameters translated into a secondary predictive model.  This model was validated against measurements of microbial and quality changes in an Australian-USA commercial cold chain, in collaboration with Food Science Australia and consultants in the USA.
Objectives
The objectives of the project were to:define the dominant microbial species that contribute to spoilage of vacuum packaged primals, including species in the original packaged primals and those that emerge after opening and repackaging, these studies will validate the species that affect spoilage and those which will be targeted for model developmentProduce a predictive model for the growth of SSO in vacuum packaged primalsValidate the predictive model against commercial product data, these data sets and the time-temperature profiles will be used to compare model predictions to observations, models will be adjusted accordingly
Conclusions
There were seven genera identified as dominant in the clone libraries of vacuum packaged beef striploins. These werePseudomonasClostridiumCarnobacteriumLactococcusBrochothrixLactobacillus Buttiauxella
Sequences aligning with Serratia spp. and Leuconostoc spp. were also large proportions of the clone library results.
There was no significant difference between the microbial communities as a result of storage temperature or the source abattoir from which the meat was collected. The atmosphere of storage had a significant effect on the composition of the microbial community.
A predictive model was produced to estimate total viable count and lactic acid bacteria levels on vacuum-packaged beef primals from -1.5 to 7ºC. The model forms were very similar and are:total viable count = square root of the specific growth rate = 0.112 x temperature (ºC) + 0.089lactic acid bacteria = square root of the specific growth rate = 0.111 x temperature (ºC) + 0.089