الفهرس 
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Abstract
Food safety is one of the major challenges for the 21s century implying a significant redirection of food microbiologist efforts in many parts of the world toward the prevention of food-borne diseases. Great efforts are directed to implement antimicrobial strategies to overcome the contamination of meat and meat products with pathogenic microorganisms through its procession from farm to fork.
In the present study, 100 random samples of meat products represented by frozen minced beef, beef burger, beef sausage, and beef luncheon (25 samples each) were collected from different supermarkets in Sohag City, Egypt. The samples were tested for the presence of Staph. aureus, and E. coli. Some E. coli isolates were submitted for serological identification. Also, some obtained isolates of Staph. aureus were examined by PCR for virulence genes (icaA, hla, tst, and sea); and the virulence genes (yjaA, astA, eaeA, stx1, and stx2) were examined for the obtained isolates of E. coli. On the other hand, nano-emulsions of ORO and LGO were prepared and then characterized by Zeta sizer, FTIR, and TEM. The effect of OR and LG EOs and their nano-emulsions on the growth and multiplication of experimentally inoculated Staph. aureus and E. coli during storage of minced beef at 4°C was studied. Sensory evaluation and pH of the minced meat treated with the oils and NEs were estimated during storage. In addition, a homemade experiment was done over a short period of time to give a recommendation to the housewives on how and when to apply the OR, LG EOs, or their NE to meat products to decrease microbial contamination.
The obtained results revealed that 46 % of examined meat product samples were contaminated with Staph. aureus. The incidence of Staph. aureus was (11/25) 44%, (10/25) 40%, (10/25) 40%, and (15/25) 60% of examined minced beef, burger, sausage, and luncheon samples, respectively. The present study also declared that 31 (31%) out of 100 examined meat product samples were contaminated with E. coli in percentages of 32%, 28%, 48%, and 16% of the examined samples of minced meat, beef burger, sausage, and luncheon, respectively.
E. coli serotypes were isolated from minced beef, beef burger, sausage, and luncheon in various ratios as the following; O125 was found in 16.7% sausage; O114 was 40, 14.3, 33.3 and 50% of minced, beef burger, sausage and luncheon, respectively; O126 was 20 and 42.9 of minced and burger, respectively; O168 was 14.3% in burger; O119 was 14.3% in burger; O128 was 40% of minced beef; while O26 was 14.3 and 33.3% of burger and sausage, respectively.
Investigation of some Staph. aureus isolates (10 isolates) for the presence of virulence genes (icaA, hla, tst and sea) by PCR revealed that 3 (30%), 2 (20%), and 6 (60%) of the tested isolates harbored icaA, tst, and sea, respectively, while hla gene wasn’t found in any tested isolate. On the other hand, the virulence genes of E. coli isolates represented as eaeA gene was detected in 8 (100%) and yjaA gene was detected in 4 (50%) of the 8 tested E. coli isolates. Furthermore, stx1 was detected in 2 isolates in a percentage of 25%. But astA gene and stx2 gene could not be detected in any tested isolate.
The characterization of ORNE and LGNE by zeta-sizer showed that the Poly dispersity index was 0.319 and 0.245 with average dynamic size of 68.91±49.12 and 38.53±20.39 nm, respectively. However, TEM results revealed that the prepared OR NE had a droplet size 62.5 nm, while LG NE had a droplet size 43.5 nm. In addition, FTIR analysis of the prepared NEs suggested that there were changes occurred in the functional groups of EOs, which were due to NEs formation.
The MIC of OR and LG EOs and their NEs was determined against Staph. aureus and E. coli. Results showed that the MIC against Staph. aureus for oils and NEs was at concentrations of 0.5% and 1%. The inhibition zone was 8.3 ±1.2 and 9.5±0.5 mm for ORO, while for LGO was 14.2 ±1.8 and 16.8±1.3 mm, respectively. On the other hand, the zone of inhibition of Staph. aureus growth formed by ORNE was 9.73± 0.6 and 12.7±0.8 mm; and by LGNE was 16.9±1.7 and 20.4±0.9 mm at concentrations of 0.5% and 1%, respectively.
The MIC for oils and NEs against E. coli was at concentrations 1% and 1.5%. The zone of inhibition was 9.33±1.15 and 14.17±1.04 mm for ORO; and for LGO was 15.50 ±0.87 and19.33±1.15 mm, respectively. Meanwhile, the zone of inhibition of E. coli growth formed by ORNE was 11.33±1.15 and 15.50±1.32 mm at concentrations of 1% and 1.5%; and was 17.00 ±1.00 and 21.23±1.37 mm for LGNE, respectively.
The antibacterial activity of OR and LG EOs and their NEs was tested against Staph. aureus and E. coli experimentally inoculated in minced meat and stored at refrigeration temperature (4oC). The results showed a significant decrease (P<0.05) in Staph. aureus and E. coli count at 5th day of storage with the addition of EOs; and no count was detected in the 7th day of storage.
The count of Staph. aureus was clearly decreased on the 5th day and cannot be detected on 7th day of storage when ORNE was added at concentrations of 0.5% and 1%. However, LGNE at concentrations of 0.5% and 1% clearly decreased the count on 3rd day and cannot be detected since the 5th day of storage.
The count of E. coli was clearly decreased on the 5th day and cannot be detected at 7th day when ORNE was added at concentration of 1%. While, the count markedly decreased on 3rd day of storage and cannot be detected since 5th day when ORNE 1.5% or LGNE 1% was used. The addition of LGNE 1.5% leads E. coli cannot be detected since the 3rd day.
The sensory evaluation of minced meat stored at 4 ℃ with added different concentrations of OR and LG EOs or NEs revealed that minced meat acquired higher scores for appearance, odor, texture, and OAA than the control and showed highest significant (P<0.05) lowering effect on pH values compared to control samples.
The result of the mini-experiment for home application revealed that OR and LG EO and their NEs at a concentration (1%) significantly decrease Staph. aureus count at 4hr, 7hr and 24hr compared to the control. Also, E. coli count significantly decreased by the addition of OR and LG oils at 4hr, 7hr, and 24hr, and by using ORNE and LGNE the count significantly decreased at 4hr and 7hr; and could not be detected at 24 hr with reduction rate 100%.
The results emphasized that EOs and NEs had the ability to suppress microbial growth, extend the shelf-life, and exhibit desirable sensory attributes in minced beef.