Increasing the shelf life of the product is considered a challenge facing meat product manufacturers,
especially products with a short shelf life such as sausage. Therefore, the use of natural agents during processing
could have important good health and economic feedback. In this concern, two experiments were designed, the
first one was achieved in vitro to study the antibiotics sensitivity of Listeria monocytogenes ATCC7644 for
sixteen different antibiotics. L. monocytogenes was resistant to five antibiotics belonging to four groups of
antibiotics penicillin, cephalosporin, macrolide, and tetracycline. After that, the effect of oils and aqueous,
ethanolic and methanolic extracts of three medicinal plants (ginger, lemongrass, thyme) as effective agents for
these bacteria to select the more potent as antibacterial agent against L. monocytogenes bacteria in the processed
sausage. The results showed that the ethanolic extract of ginger is the most effective in inhibiting the tested
bacteria compared to the other extracts .Also, the lowest inhibitory concentration (MIC) of the extract was 5000
mgL-1
. In the next experiment, fresh beef sausage was prepared and inoculated with of L. monocytogenes then,
treated with MIC of ginger ethanolic extract compared to chemical preservatives (sodium benzoate, sodium
nitrate, potassium sorbate, sodium propionate) and kept for 21 days to estimate the periodical changes in the
different microbial groups. Total count of aerobic bacteria and coliforms besides the survived L. monocytogenes
cells were recorded the obtained data found that all numbers gradually decreased to reach the minimum after 21
days of preservation, In contrast with yeasts and fungi, which increased their number to reach the maximum
after 21 days. Moreover, after 21 days the corruptions indicators (pH, thiobarbituric acid (TBA), protein
content) in sausage inoculated with L. monocytogenes were estimated. The results showed that there were no
significant differences in the pH values between all treatments, moreover, treating sausage with ethanolic ginger
extract reduced the TBA and protein content compared to the other treatments. |
