P09 | Influence of sampling depth on pH and aw in beef during dry aging for 45 days

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

Purpose. The dry-aged beef market is constantly growing and has recently found an official regulatory definition in Delegated Regulation (EU) 2024/1141, which also outlines its production hygiene requirements; However, several aspects remain underexplored, as highlighted by the EFSA scientific opinion (2023). As of today, the available literature data indicate the inability of many pathogenic microorganisms to multiply or a reduction in their counts during dry aging, with the only exceptions being Listeria monocytogenes and Yersinia enterocolitica. Regarding L. monocytogenes, published studies report conflicting data between the actual behavior observed in experimental inoculation tests and the data obtained with predictive models published by EFSA. There is a notable difference in the water activity (aw) and pH data reported by different authors. The aim of this study is to evaluate whether sampling methods influence the pH and aw data obtained from dry-cured meat and, consequently, the results of predictive models. Methods. Three batches of beef round were dry-aged in a dedicated device (Stagionello® Meat Curing Device) with the following parameters: Temperature 1±2°C, relative humidity 78±7%, air velocity 2.5 m/s. Sampling was performed on the meat before the aging process began and every 15 days for up to 45 days. The pH was determined according to ISO 2917:1999 using a Delta-OHM HD 2105.2 insertion probe for deep measurements (20 mm) and by a destructive method exclusively on the surface layer (5 mm) with a pH meter pH510, Instrument XS, 1.1. Sampling for aw measurement was performed by taking a core sample only from the surface area (8 mm), to an intermediate depth (15 mm), and to the greatest depth (20 mm). The water activity (aw) was measured in accordance with ISO 18787:2017 using an Aqualab 4TE hygrometer. Results. The data show a progressive divergence between pH and aw values as a function of depth and aging time. Regarding pH, a slight and constant reduction is observed in the surface portion, from 5.40±0.04 to 5.37±0.05 between T0 and T45 (-0.6%), indicating an initial acidification process due to oxidative phenomena and surface microbial activity. Conversely, at depth, a constant increase in pH is observed, from 5.60±0.16 to 5.95±0.02 (+6.2%), suggesting the activation of endogenous proteolytic processes with the formation of basic compounds. The AW follows a similar trend: At T45, the surface portion underwent a net decrease from 0.9925±0.003 to 0.9191±0.001 (-7.4%), demonstrating the significant dehydration of the crust; The intermediate layer shows a more moderate reduction from 0.9925±0.002 to 0.9604±0.005 (-3.2%), while at depth the loss is minimal, from 0.9926±0.003 to 0.9693±0.005 (-2.3%). Conclusions. The non-homogeneity of the observed values highlights the importance of specifying the sampling depth in experimental studies and predictive models of microbial growth. The stratified approach adopted in this study provides a solid and reproducible methodological basis, useful for future challenge tests on Listeria monocytogenes or other pathogens, contributing to a more accurate understanding of microbial behavior in relation to dry aging.