PO05 | INFLUENCE OF SALAMI GRIND SIZE ON HIGH-PRESSURE PROCESSING EFFICACY AGAINST LISTERIA INNOCUA AND SALMONELLA SPP.

Silvia Vianello, Mattia Ramini, Alfonso Rosamilia, Lucia Buratti, Sara Castagnini, Maria Francesca Pelliconi, Nica De Prisco, Lia Bardasi | Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia-Romagna “Bruno Ubertini”, Bologna, Italy.

Purpose. High-pressure processing (HPP) is a non-thermal technology used to enhance microbiological safety while preserving the organoleptic characteristics of food products. However, its antimicrobial efficacy may be influenced by microorganism-related, technological and product-related factors. This study aimed to evaluate the influence of salami grind size on HPP efficacy against Listeria innocua and Salmonella spp..

Methods. Three meat batters differing only in grind size were used for salami production: 4 mm (A), 6 mm (B) and 8 mm (C). A challenge test was performed in accordance with ISO 20976-2:2022. Each raw batter was divided into two batches and artificially inoculated with 1% (v/w) of a multi-strain cocktail of L. innocua (surrogate for L. monocytogenes) and Salmonella spp., respectively (initial target concentration of 10⁶ CFU/g). Salami were ripened for 23 days and subsequently subjected to HPP (593 MPa, 290 s). For each batch, three samples were analyzed before stuffing (T0) and at the end of fermentation (T1), while ten samples were analyzed at the end of ripening (Tend) and after HPP treatment (THPP). At each sampling point, pH and water activity (a_w) were measured and counts of L. innocua and Salmonella spp. were determined. Microbiological results were expressed as CFU/g and converted to log₁₀ CFU/g. Samples yielding counts below the detection limit (<10 CFU/g) were further analyzed qualitatively according to ISO 11290-1:2017 and ISO 6579-1:2017. For statistical purposes, log₁₀ reductions were calculated as the difference between the mean log₁₀ concentration at T0 and the mean log₁₀ concentration at T1, Tend and THPP, rather than using the worst-case approach described in ISO 20976-2:2022. Differences in pathogen reductions among formulations were evaluated by analysis of variance (ANOVA).

Results. Overall, mean pH and a_w values decreased during processing. Mean pH decreased from 5.68, 5.59 and 5.71 at T0 to 4.64, 4.67 and 4.60 at T1 in formulations A, B, and C, respectively, reaching 4.57, 4.73, and 4.76 at Tend. Mean a_w decreased from 0.96 at T0 to 0.94 in formulation A and 0.95 in formulations B and C at T1 and further decreased to 0.91 in formulations A and C and 0.92 in formulation B at Tend. The initial inoculum levels ranged from 7.10 to 7.30 log₁₀ CFU/g for L. innocua and from 6.88 to 6.99 log₁₀ CFU/g for Salmonella spp.. For L. innocua, the greatest reduction at T1 was observed in formulation A (1.33 log₁₀ CFU/g). At Tend, reductions were comparable among formulations (2.78-3.01 log₁₀ CFU/g). At THPP, formulation B showed the highest overall reduction (4.61 log₁₀ CFU/g; p < 0.05). For Salmonella spp., reductions at T1 were limited (0.41-0.70 log₁₀ CFU/g). At Tend, formulation A showed the highest reduction (3.52 log₁₀ CFU/g). At THPP, reductions were similar among formulations, with the microorganism still detectable but below the limit of quantification (<10 CFU/g).

Conclusions. This preliminary study indicates that salami grind size under the tested conditions had a minor impact on pathogen inactivation. Although a significantly higher reduction of L. innocua was observed in formulation B after HPP; this difference may be partially attributable to the slightly higher a_w at Tend rather than to grind size alone. The treatment showed substantial efficacy across all formulations, especially against Salmonella spp.. These results support the robustness of HPP validation across different salami grind sizes, while further investigations will evaluate additional intrinsic factors affecting HPP efficacy.