الفهرس 
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Abstract
The use of selected plant leaves as a natural source of phytochemicals with its biological activity such as (phenolic compounds and dietary fibers) was carried out. Chemical, physical, microbial and sensory properties of these ingredients and the application of their use in meat products were also detected and followed the effect of their addition on the quality meat products (beef burger and meat-rice kofta).
Lipid oxidation and microbial proliferation are the major factors of lossing in meat. The use of natural antimicrobial and antioxidant compounds is important not only in the preservation of food, but also safe for human consumption. Recently, investigation of natural plant products for discovering active compounds has also developed in finding natural occurring antioxidant and antimicrobial agents for using in food to replace synthetic additives due to their carcinogenicity. Among the plants rich in antioxidant and antimicrobial compounds, the pomegranate leaves extract (PLE), guava leaves extract (GLE) or green garlic leave extract (GGLE), were examined in the recent study. The present results can be summarized as follows:
Firstly: Bioactive substances, antibacterial and antioxidant activities of pomegranate leaves extract, guava leaves extract or green garlic leaves extract:
1. Proximate composition and extraction ratio of PLE, GLE or GGLE:
Pomegranate leaves, guava leaves extract or green garlic leaves contained 13.12, 50.47, 18.64%; 6.50, 4.36, 14.17%; 1.14, 5.84, 2.74%; 3.35, 5.27, 7.09%; 64.67, 22.72, 55.18% of moisture, protein, fat, ash and carbohydrates (on fresh weight basis) respectively, while after extraction, pomegranate leaves provided higher ratio (26%) than that of GL (20%) or GGL (14%).
2. HPLC analysis of PLE, GLE or GGLE:
The predominant compound in case of PLE and GLE was gallic acid with the values of 3743.09 and 2576.49 μg/g, respectively. Rosmarinic came in the second order (2173 μg/g) for PLE sample, while cateachin was the corresponding one in case of GLE sample (889.72 μg/g). But, GGLE had 90.39 μg/g of ferulic acid as a predominant phenolic compound, in addition to 50.85 μg/g of apigenin-7-glucoside as in the second order.
In the third order, various samples showed caffeic and vanillic acids in (PLE), qurecetin in (GLE) and gallic acid in (GGLE) within moderate values of (479.65, 209.91), (297.29) and (37.78) μg/g, respectively.
3. In-vitro antioxidant activity of PLE, GLE or GGLE:
A. DPPH radical scavenging assay:
- DPPH inhibition % indicates that, none of GLE and GGLE treated samples evolution showed activity as strong as the PLE (92.0%) at 200 ppm concentration.
- The scavenging ability of PLE increased from 56.61to 92.00 % at 200 ppm, indicating that it has generally better scavenging ability even than that of BHT (88.45%).
- DPPH of GLE increased from 43.00 to 79.71%, while such value increased from 4.61 to 14.12 % in GGLE, at 400 ppm, respectively. The DPPH scavenging activities of PLE, GLE or GGLE were dose dependent.
B. Scavenging activity of ABTS• + free radical:
- Results showed a dose dependent scavenging ABTS• + radical cation.
- The scavenging ability of PLE was 94.54 %, which was more than that of BHT (91.00%) at 200 ppm, indicating had better scavenging ability. ABTS of GLE was 82.10%, while the ABTS value of GGLE was 14.12 % at 400 ppm, respectively.
4. Total phenolic content (TPC):
- PLE was too rich with polyphenols in terms of TPC, values were 27.84, 17.43 and 10.45 (mg GAE/g) for PLE followed by GLE then GGLE, respectively.
5. Total flavonoid content (TFC):
- The PLE exhibited the highest level of TFC (70.65 mg CE/g) as compared with GLE (59.76 mg CE/g) and GGLE (5.56 mg CE/g).
6. In-vitro antimicrobial activity of PLE, GLE or GGLE:
- Antibacterial activity of PLE, GLE or GGLE were tested by agar diffusion method against seven pathogenic bacteria (Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa and Yersinia enterocolitica); which were selected on the basis of the size of the halo formed and their possible occurrence in food products.
- Antimicrobial results using the agar diffusion assay clearly indicate that, PLE, GLE or GGLE show promising in-vitro activities against many food-borne pathogens and spoilage microorganisms. All tested microorganisms (Gram-positive, Gram-negative bacteria) were susceptible to the action of PLE, GLE or GGLE, with a range of inhibition zone diameter values from 11 to 20 mm/sample.
- The obtained results revealed that PLE recorded a large inhibition zones against tested bacteria ranging from 17 - 20 mm. Similarly, GLE indicated a large inhibition zones against tested bacteria ranging from 13-18 mm, while GGLE showed a lower inhibition zones against tested bacteria ranging from 11-17 mm.
Secondly: Utilization of PLE, GLE or GGLE in food system:
1. Application of PLE, GLE or GGLE to beef burger:
- The proximate analysis of fresh beef burger that contained values for moisture, protein, fat, ash, and a carbohydrate was 60.42, 18.65, 17.28, 1.18 and 2.47%, respectively (on wet basis).
- Control sample had always higher deteriorated effect in its chemical, sensorial, microbiological and color stability when compared with PLE, GLE or GGLE treated samples (2%).
- Results also reveal that, the lowest significant (P<0.05) incremental rate of all quality deteriorations during refrigerated storage at 4°C was recorded in burger sample formulated with 2% PLE.
- The exogenous application of powdered extract of PLE, GLE or GGLE added with 2% showed potential for enhancing the color, lipid stability, sensory qualities and microbial status, while maintained the chemical indices, and extended the shelf life of beef burger during refrigerated storage at 4°C to 8, 10 and 12 day, respectively vs. 6 days for control sample.
- Among the positive effects of these compounds (PLE, GLE or GGLE) on beef burger characteristics are retarding lipid oxidation, color loss, off-odor formation and microbial growth occurring during refrigerated storage and may offer a promising choice in food safety and preservation.
- Cooking characteristics of the prepared beef burger with the addition of PLE, GLE or GGLE were improved and were gradually decreased the shrinkage% from its maximum value in control (6.55%) to be 3.45, 3.61 or 3.74 using GL, GGL or PL extracts, respectively. Minimal cooking loss% (2.08) was recorded in PLE 2% sample, while the highest one % (3.75-3.88) was recorded in treated samples with GGL extract.
- A positive influence in cooking yield was obtained by the addition of GGL, GL or PL extracts as it increased from 63.67% for control sample to be 74.05 % for the PL (2%) extract. A storage for 12 day, caused decreasing in cooking yield with the same pattern of different samples (minimal cooking yield was noted for control followed by GGL, GL or PL samples, respectively).
2. Processing of meat-rice kofta with adding PL, GL or GGL powders:
- The proximate chemical composition of various treated meat–rice kofta containing 45.95, 18.05, 9.62, 3.12 and 23.26% as moisture, protein, fat, ash and carbohydrate on wet basis, respectively.
- The investigated sensorial scores were significantly (P< 0.05) decreased in all samples by increasing refrigerated storage time, probably due to microbial effect, lipid oxidation and protein degradation. The results also clearly showed that control sample developed discoloration, sliminess and off-odors after 6 days of storage, whereas treated samples with PL, GL or GGL powders showed only minor color change, rotten odors and sliminess after 8, 10 and 12 days, respectively.
- Incremental pattern was observed in TVBN, TBARS and pH values in meat-rice kofta during cold storage, the addition of PLP, GLP or GGLP kept the TVBN, TBARS and pH values at the lowest values as compared with control.
- Total bacterial count of different prepared meat-rice kofta ranged between 4.8×105 to 8.5×105 cfu/g at the beginning of refrigerated storage. Total bacterial count of prepared meat-rice kofta sample without adding PLP, GLP or GGLP was progressively increased over storage period from 7.4×105 cfu/g at zero time reached 9.7×105, 9×105, 8.3×105 and 7.6×105 cfu/g after 3, 6, 9 and 12 day of refrigerated storage, respectively.
- On the other hand, the other treated meat-rice kofta, which contained different ratios of PLP, GLP or GGLP (3, 5 or 10%) showed a progressive reduction in total bacterial counts over time of refrigerated storage; while total viable counts of prepared samples contained 10% of PLP, GLP or GGLP were 7.1×105, 6.3×105 and 7×105 cfu/g after 12 day of storage, respectively.
- Psychrotrophic bacterial and enterobacteriaceae were minimized during storage period in all meat-rice kofta containing different ratios of PLP, GLP or GGLP in comparison to untreated one.
- The positive effects of these compounds (PLP, GLP or GGLP) on meat-rice kofta characteristics were retarding each of lipid oxidation, color loss, off-odor formation and microbial growth that occurring during refrigerated storage and may offer a promising choice in food safety and preservation.
- Cooking characteristics of the prepared meat-rice kofta having PL, GL or GGL powders were significantly (p < 0.05) improved. Addition of PL, GL or GGL powders were able to gradually decrease the shrinkage from its maximum value in control (7.55%) to be 3.74% using PL powder added to kofta.
- Cooking loss of treated meat-rice kofta with GGLP, GLP or PLP showed less cooking loss% compared to control sample at zero time as well as after storage for 12 day. At zero time, maximum cooking loss was found in control sample (32.27%), while addition of 10% PL powder decreased cooking loss to be 28.11%.
- A positive influence in cooking yield was obtained by the addition of GGL, GL or PL powders, it increased from 77.40% (control sample) reaching 83.25% (10% PL powder).
Conclusion
It could be concluded that the Egyptian local plants; i.e. tested PL, GL or GGL either extracts or powders may be potential sources of bioactive phytochemicals that possess a natural antioxidant and antimicrobial compounds for using in food to replace synthetic additives.
This study demonstrates the potential use of PL, GL or GGL extracts or powders to improve the microbial quality, retard lipid oxidation, maintain the good color and quality indices for extending the shelf-life of some food products (treated beef burger, meat-rice kofta) during cold storage at (4˚C) to be a good replacers of synthetic antimicrobials and antioxidants that widly use in meat products.