In this study, inocula of identified strains of Staph. aureus, Listeria monocytogenes, E. coli O157:H7 and Salmonella sp. were added individually to manufactured sausage to evaluate the effect of different treatments on behavior of pathogens in fermented and non-fermented sausage. Fermented sausage was inoculated with activated starter containing Lactococcus lactis and Lactobacillus plantarum while, non-fermented sausage was treated by adding the minimum inhibitory concentration (MIC) of either cumin or marjoram essential oils. Survival of pathogens and microbiological, chemical and organoleptic evaluations were carried out at different intervals during 60 days. Coliform bacteria completely disappeared after 7 days for all starter treatments while it disappeared for all cumin or marjoram treatments after 15 days. Starter treatments had a slight higher proteolytic bacterial count than control while essential oils treatments were lower than control treatments. Both starter and essential oils treatments containing various pathogens recorded the rapid decrement in nitrite content and the lowest increment level of total volatile nitrogen (TVN) as compared to negative or positive control. On the other hand, using lactic acid bacteria or essential oils of cumin and marjoram showed the highest reduction level and the lowest counts of Staph. aureus, L. monocytogenes, E. coli O157:H7 and Salmonella sp. than positive control. In addition, decreasing of the pathogens counts began on the 3rd day of storage, while positive control of all pathogens showed a slight decrease in number of pathogens and then increased by increasing the storage period. Moreover, starter treatments were more constant treatments and showed maximum organoleptic scores as compared to negative and positive controls while cumin followed by marjoram treatments recorded the lowest decrement rate in overall scores than that of negative and positive controls.
Key words: Pathogenic bacteria, lactic acid bacteria, essential oil, cumin, marjoram,
survival of pathogens, organoleptic evaluation. |
