الفهرس 
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Abstract
Summary
Thyme “Thymus vulgaris L.” leaves, Lemongrass “Cymbopogon citratus” and carrot seeds “Daucus carota” were purchase from the local market (haraz store, Cairo, Egypt), Stachys “Stachys aegyptiaca Pers.” was collected from Bani Sweif governorate, Egypt. The leaves were separated from the branches and the air-dried leaves were stored in a polyethylene bag. Sunflower oil without added antioxidants were kindly supplied from ARMA (10th of Ramadan city, Egypt). Butylated hydroxytoluene (BHT) was purchased from Merck (Darmstadt, Germany). Sugar, mustard flour, white pepper, eggs, lemon and salt were purchased from local market, Giza, Egypt. The minced meat was purchase from the local market (Giza, Egypt).
Extraction of essential oils was performed by two methods (hydrodistillation and supercritical CO2).
Mayonnaise was treated with adding different concentrations of essential oils (200, 400 and600 ppm), also beef burgers was treated by adding the same concentrations of essential oils as compared with the synthetic antioxidant such as TBHQ at 200 ppm. The present study aimed to investigate the antioxidant and antimicrobial effect of essential oils and determining its efficiency in some food products (mayonnaise and beef burgers).
The obtained results could be summarized as follow:
I- Chemical, antioxidant and antimicrobial evaluation of selected essential oils: -
1- Data showed that yield percentage and physicochemical properties of essential oils as affected by the method of extraction. The highest values of yields were found in supercritical CO2 more than the essential oil extracted by hydrodistillation in all samples. The highest yield was for stachys extracted by supercritical CO2 and the lowest yield was for lemongrass extracted by hydrodistillation.
2- Results revealed that the main components in hydrodistillation EOs were (β-bisabolene and carotol), (β-elemenone and isojasmone), (limonene and α- citral) and thymol in carrot seed, stachys, lemongrass and thyme, respectively, however in supercritical CO2 EOs (β-bisabolene, α-bisabolene and carotol), (β-elemenone and D-carvone), (limonene and α- citral) and thymol were the main component in carrot seed, stachys, lemongrass and thyme, respectively.
3- Results cleared that the antioxidant activity of hydrodistilled essential oils were determined by DPPH method showed significant between essential oils in antioxidant activity and in IC50, due to the differentiation in chemical composition and active component of each essential oil, by increasing the concentration of essential oil the antioxidant increases. The best essential oilextracted by hydrodistillation was thyme then lemongrass followed by stachys at concentration 500 ppm being 86.90, 82.28 and 75.53%, respectively. It wasfound that TBHQ had the best result in IC50 because it had the lowest value then BHT and tocopherol and the best essential oil was thyme 64.97, 102.65, 148.93 and 182.46 ppm. Thyme essential oil extracted by SC-CO2 was the best in results in comparison with other essential oils and the lowest essential oil in antioxidant was carrot seed being 87.91 and 67.40%, respectively. The results showed that the antioxidant activity of essential oils increases with the increase of concentration.
4- Results indicated that TBHQ exhibits the highest antioxidant activity (1.32) compared to the sunflower oil samples under investigation at 200 ppm but at 500 ppm thyme and Stachys essential oils had higher antioxidant activity than BHT at 200 ppm. At the level of 500 ppm, thyme and stachys essential oils deserve special attention because they were more effective than BHT at the level of 200 ppm in delaying oxidation, and oxidative stability was directly proportional to the increase in the concentration of thyme and stachys essential oils.
5- Results demonstrated that all of the essential oils extracted by hydrodistillation showed an inhibitory effect against all the test microorganisms and the inhibition zones ranged from 0.00 to 58 mm. Among the studied essential oils, the highest antimicrobial activity against Pseudomonas aeruginosa was found in lemongrass EO with a zone diameter of 58 mm, followed by thyme EO with a zone diameter of 52 mm against Candida albicans, and the lowest activity was found in carrot seed EO with a zone diameter of 0.00 against Aspergillus flavus and Candida albicans. In general, the results, indicated that thyme EO is the best essential oil against all types of microorganisms followed by lemongrass EO and the lowest value was found in carrot seed EO and in comparison, with synthetic preservatives.
6- Results demonstrated that all of the essential oils extracted by supercritical CO2 showed an inhibitory effect against all the test microorganisms and the inhibition zones ranged from 6.00 to 53 mm. Among the essential oils studied, the highest antimicrobial activity against Pseudomonas aeruginosa was found in lemongrass EO with a zone diameter of 53 mm, followed by thyme EO with a zone diameter of 50 mm against Candida albicans and Pseudomonas aeruginosa, however, the lowest activity was found in carrot seed EO with a zone diameter of 0.00 against Aspergillus flavus and Candida albicans. In general, the results, indicated that thyme EO is the best essential oil against all types of microorganisms followed by lemongrass EO and the lowest value was found in carrot seed EO and in comparison, with synthetic preservatives.
II- Evaluation of essential oils in food products: -
A- mayonnaise
1- Findings demonstrated that the low acidity in crude oil is a good physico-chemical indicator for crude oil. Acidity of oils should not exceed 5%. According to this view, sunflower seed oil was an edible oil. The peroxide value of sunflower seed oil was 6.6 meq O2/kg, indicating that the tested vegetable oil was fresh and suitable for mayonnaise production.
2- Results showed that at the end of the storage period, mayonnaise sample with added hydro-distilled stachys essential oil had the lowest acidity of 0.485; however, there was no significant difference between control (+) sample and samples with added essential oils.
3- Data suggested that between various concentrations of essential oils in comparison with control sample (without any antioxidant), in the last week, concentration of 600 ppm for all essential oils were the best treatment and had significant difference in antioxidant activity in comparison with synthetic antioxidant of 200 ppm TBHQ except carrot seed essential oil, it had no positive effect. In short, all concentrations of essential oils had an antioxidant activity similar to synthetic antioxidant of TBHQ at concentration of 200 ppm for inhibition of secondary products except carrot seed essential oil.
4- Data indicated that control mayonnaise and mayonnaise treated with essential oils at zero time were contained lower total bacterial counts (TBC) with values range from 2.302 to 2.315 log cfu/g. The current results reveal that the TBC of control mayonnaise increased through storage being 2.315, 4.431 and 5.732 log cfu/g, respectively. Data revealed that TBC values for all investigated samples increased through storage period. On the other side, it could be noticed that increasing the essential oils concentration in mayonnaise samples decreased the TBC except carrot essential oil had the same trend as control sample. Mayonnaise prepared with thyme and stachys at concentration 600 ppm had the lowest TBC than experimental mayonnaise and the sample with TBHQ.
5- Data showed that the growth rate of mold and yeast at mayonnaise prepared with the different concentrations of essential oils was lower than that recorded in control mayonnaise. On the other hand, mayonnaise made from higher concentration of essential oils was less contaminated than lower concentrations of essential oils. from a microbiological safety point of view, it is generally recommended that mayonnaise made with essential oils reduce the risk from microorganisms. The mayonnaise prepared from thyme, stachys or lemongrass EOs extracted by hydrodistillation and supercritical CO2 at 600 ppm had great effect for lowering the gross rate of mold and yeast.
6- The results of statistical analysis of sensory evaluation of prepared mayonnaise using different concentrations of essential oils indicated that mayonnaise samples prepared by add different concentrations of essential oils showed no significant (P >0.05) effect on appearance property in the first day of storage. On the other hand, the color attribute of mayonnaise samples prepared by add were less significantly with increased the concentration of EOs than control sample. Meanwhile, samples prepared with added thyme 200 and 400 ppm and stachys 200 ppm essential oils extracted by hydrodistillation and samples prepared by supercritical CO2 thyme oil at 200 ppm recorded higher significant score in taste (8.1, 8.1, 8.0 and 8.0) and overall acceptability (7.6, 7.6, 7.3 and 7.3) than other samples at the third week of storage. Results of appearance indicated that the addition of hydrodistilled thyme, stachys and lemongrass EOs at 200, 400 and 600 ppm and supercritical CO2 thyme at 200 and 400 ppm gave a better rating scores in the mayonnaise samples under study than control samples.
B- Beef burgers
7- data demonstrated that at any given time of refrigerated storage control sample exhibit significantly (P<0.05) higher pH values than treated samples, conversely thyme, stachys and lemongrass hydrodistilled essential oils treatment had the lowest increment pH during the course of refrigerated storage. Similar trend of pH changes had been observed in supercritical CO2 EOs. However, the lower pH values of treated burgers reflect antimicrobial properties of these essential oils
8- Results indicated that during cold storage there was an incremental pattern in TBARS values in different samples which indicated oxidation in beef burgers, with the control burger, oxidizing was most rapidly to the greatest extent as compared to samples treated with EOs except carrot essential oil was like control. It was clear from the same results that control and samples with carrot oil exhibited the highest (P<0.05) TBARS values initially and at any given time of refrigerated storage. Conversely, treated samples with thyme, stachys and lemongrass at 600 ppm had the greatest oxidative stability as shown by the consistently lower TBARS values.
9- Data demonstrated that at the end of sixth day of storage the control samples had TBARS value of 0.95 mg malonaldehyde (MDA)/kg, which was close to the maximal (0.9 mg MDA/kg) recommended limit by Egyptian Standards for meat products. beef burger samples treated with hydro-distilled thyme essential oil (600 ppm) which still acceptable until 12 days as indicated by their lower TBARS values (< 0.9 mg MDA/kg) however the supercritical thyme still acceptable until 9 days. The 600 mg essential oil/kg beef burger sample had almost the lowest malonaldehyde value at the end of 15 days of storage relative to all other treatments other than control-positive, which may be due to the strong antioxidant effects of the essential oil of stachys.
10- Results indicated that showed the time of cold storage increased the TVBN of all samples progressively increased with different rates depending on the nature of treatments. However, control samples showed the highest (P<0.05) incremental rate compared to other treatments and had TVBN value of 17.681 mgN/100gm at 6 days of cold storage, indicating 7 days shelf-life. However, the TVBN values above 20 mgN/100gm raw samples indicate spoilage of beef burger products as recommended by Egyptian Standards 2005. long shelf-life storage (15 days) was found with thyme, lemongrass and stachys at 600 ppm for both extraction methods.
11- The initial value of APC (day 0) for beef burger samples was 3.72 log CFU/gm, which was an indicator of good quality beef burgers.
12- The results showed that the total viable counts decreased during and at the end of the storage period due to a rise in the concentration of essential oil in beef burgers. The samples with 600 ppm EOs had the best effect on reducing the total viable count during storage. Samples treated with different concentrations of stachys essential oil extracted by hydrodistillation , showed a decrease in the amount of aerobic plate microorganisms compared to the miscible maximum of 6 log cfu/g, High concentrations of stachys are also more effective in reducing this number than lower concentrations when compared to control samples, however, lemongrass essential oil extracted by supercritical CO2 was the most effective, particularly at 9th and 12th days.
13- Data revealed that the increase of the concentration of essential oil also reduced the number of enterobacteriaceae, with 600 ppm of essential oil added to beef burgers had the lowest number of enterobacteriaceae compared to all other samples during storage. In addition, all samples with essential oils had a higher antimicrobial effect than control and the sample with 600 ppm essential had an even greater effect than control positive against enterobacteriaceae except carrot essential oil. This finding is due to the antibacterial activity of essential oils thyme, stachys and lemongrass against bacteria. Samples treated with different essential oil concentrations showed a decrease in the enterobacteriaceae count compared with control samples, especially at 9th and 12th day, and a higher concentration was more effective than a lower concentration in decreasing this count.
14- The results of mean values for perceived sensory scores of beef burgers indicated that there was a substantial difference between all samples in all sensory characteristics of all treatments at day 12. The best results were found in positive control samples and 600 ppm essential oil added to beef burgers except the carrot essential oil. At the 6th day of storage period, control samples began to spoil and appear rancid odor, while sensory properties were enhanced until the 12th day of storage period by using stachys oil. Samples containing 600 ppm of thyme, stachys and lemongrass oils also exhibited the highest improvement in sensory attributes. These results were applied to both extraction methods.
Conclusion
All essential oils under study except carrot seed essential oil had a great antioxidant and antimicrobial effect in food products (mayonnaise and beef burgers) compared to control negative sample or treated with synthetic preservatives as it decreases the formation of malonaldehyde and inhibit microbial growth at concentration 600 ppm. Stachys and thyme essential oil showed great antioxidant and antimicrobial effect.