Effect of antimicrobials as ingredients of pork bologna for Listeria monocytogenes control during storage at 4 or 10 °C

Sodium or potassium lactate and sodium diacetate are currently included as ingredients in meat products for control of Listeria monocytogenes contamination during storage. This study compared the antilisterial activity of sodium lactate (SL), sodium diacetate (SD) and glucono-delta-lactone (GDL) used as single or combined ingredients at various levels in pork bologna stored under refrigeration (4 °C) or at a mildly abusive temperature (10 °C). Moreover, treatments were evaluated for their influence on the microflora of the product. Inoculated (3-4 log cfu/cm2; 10-strain composite of L. monocytogenes) bologna slices were vacuum-packaged, and stored at 4 °C or at 10 °C. Absence of the above antimicrobials from the formulation allowed increases of L. monocytogenes to 8.3 log cfu/cm2 in 10-20 days and 8.8 log cfu/cm2 in 8-12 days at 4 and 10 °C, respectively. Modelling of L. monocytogenes growth as a function of time, indicated that the treatment that resulted in the lowest maximum specific growth rate (μmax) was the combination of 1.8% SL with 0.25% SD (0.009 and 0.084 day−1 at 4 and 10 °C, respectively), followed by the combination of 1.8% SL with 0.125% SD and 0.125% GDL (0.039 and 0.210 day−1 at 4 and 10 °C, respectively); the μmax of control treatments was 0.609 day−1 at 4 °C and 1.34 day−1 at 10 °C. Lactic acid bacteria (LAB) were the most prominent spoilage organisms isolated from the product. The combination of 1.8% SL with 0.25% SD seemed to be the treatment that controlled growth of LAB more effectively at 4 °C, while at 10 °C their growth was inhibited more effectively by 0.125% GDL. These findings indicated that meat processors need to select the most effective combination and concentration of these preservatives to achieve safety as well as the shelf-life necessary for these products.