Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/16/2009
Publication Date: 4/1/2009
Citation: Ukuku, D.O., Zhang, H.Q., Huang, L. 2009. Growth parameters of escherichia coli O157:H7, salmonella and listeria monocytogenes and aerobic mesophilic bacteria of apple cider amended with nisin-EDTA. Foodborne Pathogens and Disease. 6(4):487-494. Interpretive Summary: The most important growth parameters in bacterial life cycle are the time it takes bacteria to adjust to new environment (lag phase) and the time it takes the bacteria to multiply (growth rate). In this study, we investigated the effect of food additives (nisin, Ethylenediamine Tetraacetic Acid (EDTA) and its combination (nisin + EDTA)) on growth parameters of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella spp in sterile and non sterile apple cider. Only nisin extended the lag phase for native microflora of apple cider and also, killed the inoculated populations of Listeria monocytogenes. EDTA or nisin alone did not extend the lag phase or reduce the growth rate for Escherichia coli O157:H7, Salmonella spp and the native microflora in apple cider. The native bacteria of non sterile apple cider extended the lag phase of Listeria monocytogenes and Salmonella cells therefore growth rate could not be calculated with the exception of E. coli O157:H7 cells. This means that E. coli O157:H7 cells strive better in apple cider than Listeria monocytogenes and Salmonella cells. However, a combination of nisin and EDTA killed approximately 99.9% of the native bacteria while the inoculated populations of all bacteria were below detection in apple cider. This study suggests that addition of nisin-EDTA combination will kill most of the bacteria in unpasteurized apple cider to enhance the bacterial safety of the juice.
Technical Abstract: The effect of nisin (0 or 300 IU), Ethylenediamine Tetraacetic Acid (EDTA, 20 mM) and (nisin 300 IU+ EDTA 20 mM) on growth parameters; including lag period (LP) and growth rate (GR) of Escherichia coli O157:H7, L. monocytogenes and Salmonella spp. in the presence or absence of aerobic mesophilic bacteria of apple cider during storage at 5 C for 15 days or 23 C for 16 h was investigated. The growth data were analyzed and fitted to the modified Gompertz model. The LP values for aerobic mesophilic bacteria of apple cider (control) and those amended with EDTA and nisin during storage at 5 C were 1.61, 1.76 and 5.45 d, respectively. In apple cider stored at 23 C for 16 h, the LP values were 3.24, 3.56 and 5.85 h, respectively. The LP for E. coli O157:H7 determined in the presence of aerobic mesophilic bacteria of apple cider stored at 23 C for 16 h was 1.48 h while populations for L. monocytogenes and Salmonella declined. In sterile apple cider left at 23 C for 16 h, the LP values for E. coli O157:H7, Salmonella and L. monocytogenes averaged 2.74, 2.37 and 3.16 h, respectively. The GR values for these pathogens were 0.402, 0.260 and 0.187 log (cfu/ml)/h, respectively. Addition of nisin and EDTA combination caused a decline in lag phase duration and the growth curve for all pathogens tested were not estimated with the modified Gompertz model.