Background. Food borne illnesses caused by known pathogens such as Salmonella sp., E. coli, and Listeria monocytogenes (Listeria) are prevalent enough to warrant studies on how to protect both the food supply and consumers from contamination. The results of some of these studies suggest that various herbs and spices have antimicrobial activities against bacteria. Nutmeg in particular has a specific antimicrobial activity against Listeria , Gram-positive bacteria responsible for causing an infectious disease called listeriosis. Unfortunately, studies of the combination of nutmeg and Listeria have focused on idealized growth media such as Tryptone Soy Agar and Broth (TSA and TSB) or other standardized media. Objectives . To fully understand the dynamics of bacterial activity that causes the illness it is important to explore its behavior in more realistic growth media, such as food models. Food models should represent the complexity of a regular meal while being simple enough that confounding factors can be minimized. This study sought to profile the effects of nutmeg oil on the growth of Listeria in chicken broth as the food model within a range of incubation temperatures. Methods. The antimicrobial effects of nutmeg oil on Listeria was determined at three different temperatures and four different concentrations. 0.5 ml of 18-hour culture of Listeria in 5 mL BHI broth was inoculated into 4.5 mL BHI broth and the corresponding amount of nutmeg oil was added to reach final concentrations of 0.0625%, 0.125%, 0.25% and 0.5%. After 24 hours of incubation at refrigerator temperature (6°C), ambient temperature (21 degrees C) and 35 degrees C, 100 µL of the dilutions were then plated out in triplicates onto BHI agar to obtain a measurable number of CFU/ml. Colonies were then counted, documented and analyzed using two-way ANOVA with Bonferroni post-hoc analysis. Results . There was a significant interaction effect between nutmeg oil concentration and incubation temperature in the effectiveness of nutmeg oil as an antimicrobial agent against Listeria (p<0.0001). Increasing nutmeg oil concentration results in a significant increase in antimicrobial activity against Listeria (p<0.0001). Incubation temperature is also a significant factor in inhibiting microbial growth (p<0.0001). Conclusions. Along with results from other studies, this study supports the idea that antimicrobial activity of herbs and spices depends not only on the type of antimicrobial used, but also on the environment in which the pathogen of interest is being cultivated.
|Advisor:||Kirk, Elizabeth A.|
|Commitee:||Lund, Kaleb C., Spicer, Diane|
|Department:||Department of Nutrition|
|School Location:||United States -- Washington|
|Source:||MAI 51/01M(E), Masters Abstracts International|
|Subjects:||Food Science, Microbiology, Nutrition|
|Keywords:||Antimicrobial activity, Growth temperature, Incubation temperature, Listeria, Monocytogenes, Nutmeg essential oil|
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