P10 | Experimental evaluation of the growth of Listeria monocytogenes in dry-aged beef: comparison with the ComBase predictive model

E. Zanato¹, G. Polizzi¹, L. Prandini¹, F. Savini¹, V. Indio¹, A. De Cesare¹, A. Seguino¹, G. Merialdi², L. Bardasi², S. Vianello², M. Ramini², A. Serraino¹. | ¹ Dipartimento di Medicina Veterinaria, Alma Mater Studiorum Università di Bologna, Ozzano dell’Emilia (BO); ²Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia Romagna, Bologna, Italy

Purpose. The dry aging process for beef involves aging the meat in controlled environmental conditions of temperature, ventilation, and relative humidity inside refrigerated cabinets. The use of microbiological predictive models has shown that the ambient temperatures used in the dry-aging process, combined with the intrinsic characteristics of the meat (pH and aw), can allow for the growth of Listeria monocytogenes on beef. EFSA itself, in one of its opinions, confirmed this thesis, but recommended further investigations to validate the data from the predictive models. However, in contrast to these predictions, some challenge test studies conducted on beef under different aging conditions report a reduction in the pathogen during the process. The objective of this study is to compare the data obtained from a challenge test conducted to evaluate the behavior of L. monocytogenes in dry-aged beef with the predictive data obtained using the ComBase predictive model. Methods. Three batches of beef loins were inoculated with three different strains of L. monocytogenes. The extrinsic ripening parameters were set at a temperature of 1±2°C, humidity of 78±5%, and ventilation of 2.5 m/s in the Stagionello® Meat Curing Device. The process lasted 60 days; pH and temperature were continuously monitored during the process; aw was measured in the meat at time 0, 14, 30, 45, and 60 days; For the purpose of growth modeling, the aw data calculated assuming a constant decrease between one sample and the next was used. The data recorded by the ripening chamber, along with the aw obtained at the time points, were entered into the ComBase software, reporting the average data measured every 4 hours for the simulation of growth conditions (Base Growth) and subsequently under non-thermal survival conditions (Non-Thermal Survival) when the surface aw had decreased to a level <0.92. Results. From the analyzes conducted at the end of the process, an average reduction of the pathogen of 0.55 log CFU/g was observed. The ComBase model, set to the Growth condition, predicted an average growth of 3.12 log CFU/g, highlighting a difference compared to the experimental data; The combined use of the two models (Growth + Non-Thermal Survival) provided a prediction that more closely resembled the actual data, but still overestimated, predicting an average growth of 2.85 log CFU/g compared to the actual growth. Conclusions. The results suggest that for a correct predictive assessment of microbiological risk in dry-aged meat, some correction or caution factors need to be introduced: The sampling methods for measuring aw can significantly influence the result; It is frequently assumed that the surface pH of meat is equal to the deep pH. Ventilation is recognized as a critical factor in the microbiological control of dry-aged meat, and it appears to play a decisive role in reducing Listeria monocytogenes during the dry-aging process of beef; The effect of ventilation cannot be estimated with current predictive models, nor can the competitive effect of the microflora present, and therefore specific predictive models should be developed for dry-aged meat.