الفهرس 
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Abstract
A total of 100 fresh and chilled beef burger samples were collected from different butchers’ shops and refrigerators of hypermarkets in Assiut city were examined. The sensory evaluation of the examined chilled samples has low scores of sensory attributes, less than the fresh ones obtained from butchers’ shops with highly significant difference between them in pH (6.0 ± 0.3 and 5.8 ± 0.23, respectively) but no significant difference between mean values (p > 0.05) of TBA 0.22 and 0.25 (mg/kg) in fresh and chilled samples, respectively.
The microbiological evaluation of previously collected samples revealed that the fresh burger highly contaminated with aerobic mesophilic bacteria than chilled ones (8.5×〖10〗^7±4.4×〖10〗^7, and 4.5×〖10〗^7±1.4×〖10〗^7 (cfu/g), respectively) while, there is a significant difference in total yeast and mold count between them, with incidence of 82 % and 88%, with mean values 1.1×10⁴± 2.1 ×10³ and 3.9×10⁴±1.2 ×10⁴ in fresh and chilled samples, respectively.
In concern to isolation of salmonella spp., which considered one of the most important food-born pathogens, it was isolated in fresh burger in 22% (11/50), while higher incidence 26% (13/50) in chilled samples and examined serologically and that revealed 8%, 7%, 3%, 2%, 2%, 1% and 1% of the examined samples were contaminated with S. Enteritidis, S. Typhimurium, S. tsevie, S. rissen, S. Infantis, S. chester and S. montevideo, respectively.
In the present study, the antimicrobial properties of some natural compounds (cinnamon, clove, ginger and oregano EOs), nisin and different concentrations of combination were studied in vitro. Three out of them (CEO, ClEO and OEO) showed antibacterial activity against S. Typhimurium (NCTC12023), as confirmed by well` diffusion method, while GEO give no inhibition zones with any concentrations; only with pure oil (8 mm). The most effective oil from them with lowest concentration were CEO with MIC (0.625%) and MLC were 1.25%.
The active phenolic compounds of CEO were studied using GC/MS analyses. It was found that CEO contained 39 components while the main four ones were, (E) Cinnamaldehyde (19.85%), Eugenol (19.25%), Cinnamaldehyde propylene glycol acetal (16.5%) and Benzyl alcohol (13.44%).
In addition, the antibacterial activity of combination between CEO and nisin was studied using agar well diffusion method. Results revealed that the MIC of N +CEO were (0.0075% + 0.15%) with inhibition zone (11 mm) and MLC of N +CEO were (0.015% + 0.3%) with inhibition zone (15 mm).
Nisin and CEO were the most effective and alternative natural antimicrobials against S. Typhimurium (NCTC12023). But, to enhancement the antibacterial activity of nisin and overcome the hydrophobic properties of EO, they were converted to nano-materials using different techniques.
The mean droplet diameter of CNE was 81.35±18.75 nm with PDI of 0.399 and of NNP was 15.69±3.11 nm with PDI of 0.257 and that indicated the stability of fabricated nano-materials. The TEM revealed a successful preparation of nanoparticles. Obviously, NNPs is separated, spherical shape particles with average size 9.23± 2.78 while, CNE, showed separate nano-micelles with average size 56.74±12.33 nm. The particles obtained are well dispersed with no significant of agglomeration or aggregation and perfect stability also, the FTIR was analysed. The cytotoxicity effect of fabricated nano-materials on Vero cell line was studied and clarified that the cytotoxicity effect of NNP and CNE were 87.2% and 85.15%, respectively at 100 (µg/ml) concentration.
The antibacterial activity of CNE and NNP against S. Typhimurium were determined and the result of MICs of them were 0.3% and 0.0065%, respectively and their combination, were NNP (0.003) + CNE (0.15) %.
The in-vivo study summarized that efficacy effect of different treatments showed 100% reduction for S. Typhimurium at 3rd day except the nisin; CEO free at MIC1; its combination and CNE at MIC 1 (0.3%).
The sensory properties of different treated burger samples during cold storage (4ºC) were enhanced by using different preservatives with different concentrations compared to the untreated (control) samples after 5 days of the storage period with significant difference (P-Value <0.05) by both concentrations of CNE. Control samples were started to be unaccepted with appearing rancid odour at 7th day and spoiled with off odour at 9th day of storage period, while at both CEO concentrations, the panellist could smell only the strong cinnamon odour until 12th day of storage, which disappeared in CNE. Samples with free nisin, had acceptable sensory score just until 5th day then spoiled at 9th day (as control). On the other hand, the other treated samples showed no signs of spoilage until the end of experiment with accepted sensory evaluation.
Moreover, during storage, pH values increased slightly and the rise became more obvious for control, reaching to 6.3 on 7th day of the storage then spoiled. For samples incorporated with CNE (MIC2), NNPs (MIC1 and MIC2) and combination of (CNE+NNP MIC2) which maintained accepted pH (5.9, 5.2, 5.0 and 5.35 at 12th day, respectively) of meat up to 12th day of the storage.
In line with the pH findings, TBA data showed a progressive rise in TBA values across all samples that were analysed, suggesting that the oxidative breakdown of beef burger lipid happened throughout storage time, particularly in control groups rather than the combination. The strongest antioxidant activity over the storage duration was indicated by NNP (MIC2) recording the lowest TBA-Values, prolonging the period of acceptability until the seventh day. Additionally, combinations of our nanomaterials demonstrated TBA values that were lower to free ones.
Regarding various treatments, the antibacterial effectiveness of a free (nisin + CEO) or nanomaterials (NNP+ CNE) combination demonstrated a potential impact on the APC and overall yeast and mould count. Concerning MIC2, NNP (0.006) + CNE (0.3%) concentration showed the best decrease rates of 52.10 and 42.79% for APC and total yeast and mould count, respectively.
Consequently, these results offer intriguing information that may help in the prevention of microbial spread in food and can be applied on an industrial scale as a unique technique to enhance burger safety and quality during refrigeration.