The objectives of the present study were: (i) to record time-temperature data in the geometrical center (“coldest spots”) of different sizes and states (raw vs. frozen) of pork “gyros” during realistic cooking scenarios, (ii) to model the growth of Salmonella spp., Escherichia coli O157:H7, Staphylococcus aureus, Clostridium sporogenes (as a surrogate of Clostridiumbotulinum), and lactic acid bacteria (LAB) (dominant indigenous microbiota) as a function of temperature in the range likely occurring during roasting, using existing and newly fitted cardinal growth models and (iii) to evaluate the performance of these models (incorporating or not the Jameson effect) in simulating the growth of Salmonella spp. or C. sporogenes at different starting levels, in parallel to that of dominant microbiota, under commercial roasting scenarios of raw and frozen gyros. In frozen gyros, the residence of “coldest spots” within the dangerous temperature zone (4.4–60οC) was either non-existing (60 and 180 kg) or limited (30 kg) compared to raw gyros during the 8.5–11 h roasting. Regarding microbiological data, growth rate was increased from 10 °C to 40 °C for Salmonella spp. and E. coli O157: H7 or from 12 °C to 45 °C for C. sporogenes, while limited growth (Salmonella spp. and E. coli O157:H7), or inactivation (S. aureus) of pathogens was recorded during storage at 45 °C. Growth of S. aureus was observed only during storage at 40 °C. Primary modeling was performed by using the Baranyi model, while secondary cardinal models were adequately applied to describe growth rate as a function of temperature, according to the low RMSE values (0.017–0.050). Under the worst-case scenario (2-days roasting), Salmonella spp. growth was observed not only in raw gyros (ca. 2.5 log increase) but also in frozen (ca. 2.0 log increase). On the contrary, C. sporogenes growth potential was significantly lower, i.e., 0.5–1.0 log increase, suggesting a non-considerable risk of C. botulinum toxin production. A good agreement between simulated and observed growth of Salmonella spp. or C. sporogenes against LAB was indicated by the ASZ approach (Salmonella spp.: 83%; C. sporogenes: 84%; LAB: 81%). Overall, the developed secondary models may adequately predict the growth of Salmonella spp. or C. sporogenes against LAB under the examined contamination levels and roasting scenarios; however further testing of models applicability is prompted in relevant products i.e., gyros made of chicken, kebab, or döner.
Read full abstract