الفهرس 
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Abstract
This study was conducted to asses in details the antioxidant percentages and antioxidant activity in three categories of herbs and medicinal plants.
And also studied the content of phenolic compounds in these plant samples .In addition ,the present study was carried out to evaluate the antioxidant activity of these plants by different methods .Furthermore ,the different forms of phenolic compounds and their composition was studied. Finally, the possibility to use these plant samples and their extracts as sources for natural antioxidants in food technology applications was studied .The results could be summarized as follows:
1-Samples sources:-
In this thesis, three categories of herbs and medicinal plants were obtained from Egypt, Germany and Sudan locations, plants were as follow:-
The Egyptian samples namely: coriander seeds (Coriandrum sativum); dill (Anethum graveolens) seeds; sage (Salvia officinalis) and marjoram (Origanum majorana) were obtained from the Egyptian market.
German herbs samples namely : rosemary (Rosmarinus officinalis L), basil (Ocimum basilicum) and thyme (Thymus officinalis L.) were bought from the German market.
Sudanese samples were kindly given by Department of Food Science and Technology, Sudan University of Science and Technology, Khartoum, Sudan. Sudanes samples namely: (Guiera senegalensis leaves (GSL); Guiera senegalensis roots (GSR); Salvadora persica park (SPP); Salvadora persica leaves (SPL); Combretum. cordofanum leaves (CCL); and Sclerocarya birrea leaves (SCL) .
2-Total phenolic and total flavonoid content of investigated plant material:-
Samples were studied for the effect of different solvents and tow extraction techniques on total phenolic compounds. The solvents used in this study were (methanol, water ,60 % aqueous methanol ,80% aqueous methanol ,acetone and ethyl acetate ) .The extraction techniques used were manually liquid extraction and Accelerated Solvent Extraction method(ASE) .The results showed that all examined samples had sensible amount of total phenolic compounds and for the most of used solvent and material ASE solvent extraction had higher content of total phenolic content compared with manually solvent extraction .The extraction efficiency of solvents on total phenolic compound content, the aqueous methanol solutions were found to be more suitable solvents for phenolic compound extraction in all investigated samples compared with other solvent used. Data cleared that, ASE extraction method on total phenolic compounds extraction of Egyptian samples , the aqueous methanolic solution 80% have the highest yield of phenolic compounds in both coriander and dill whereas both methanol and 60% aqueous methanol presented the highest yield of phenolic content in marjoram and sage, respectively. Total phenolic content of sage was the highest among the investigated samples, it ranged from 81.4 to107 mg of gallic acid equivalents/g total extractable .The content of total phenolic compound of German samples extracted by ASE methods. phenoilc compound content were :129.3 ; 97.8; and 130.4 mg GAE/g for rosemary, basil, and thyme, respectively.
Methanolic extracts of Sudanese plant materials obtained either by manually liquid extraction or by accelerated solvent extraction (ASE) examined for their content of phenolic compounds. The total amount of phenolic compounds ranged from 52.6 to 166.7 mg GAE/100 g of sample material for the manually liquid extraction and from 53.1 to 169.3 mg GAE/100 g for extraction by ASE. The content of total flavonoid also determined, The results cleared that the flavonoids content did not depend on total phenolic content in the samples however basil and Guiera senegalensis leaves (GSL) had the highest content of total flavonoid for German samples and Sudanese samples, respectively. The content of total flavonoids of German herbs was in rosemary 27.38 CE mg/g, basil 61.39 CE mg/g, thyme 24.17 CE mg/g. Total flavonoids content in Sudanese samples followed this order, GSL> CCL > GSR> SCL> SPL > SPP.
3-Antioxidant activity measurement:-
In this work, the antioxidant activity for investigated samples solvent extracts was examined with different methods namely :DPPH radical scavenging activity; ß-carotene bleaching method ; Cupric ion reducing antioxidant capacity (CUPRAC) method ; Degree of polymerization assay ; Determination retarding of photosensibiled oxidation reaction activity; Lipoxygenase inhibition activity.)
3.1- DPPH radical scavenging activity:-
In DPPH radical scavenging activity method, rosemary had the highest activity among German samples for all used solvent and sage had this order also for Egyptian samples, at the same time all other samples showed a remarkable activity. The results demonstrated that, the scavenging effect of solvent extracts on DPPH radical were related to the amount of phenolic compounds in the extracts. The antioxidant activity of methanolic extracts of Sudanese plant materials determined by the DPPH method revealed that the ASE extracts had higher antioxidant activity on DPPH than those for manually extracts except in SPL , and CCL had the highest antioxidant activity.
3.2- ß-carotene bleaching method:-
In ß-carotene bleaching methods ,the ethyl acetate of sage had the highest activity among other Egyptian samples and acetone extract of basil had this order for German samples. The results did not appeared any relation between the content of phenolic compounds of extract and the antioxidant activity by this method. Methanolic extracts of Sudanese plant materials were remarkable effective in inhibiting the co-oxidation of ß-carotene by linoleic acid in the order GSL > SCL > GSR > CCL > SPP > SPL.
3.3- Degree of polymerization:-
Degree of polymerization of German samples ranged between 3.10 to 8.23 monomer unites of catechin per polymer of phenolic compounds ,the highest degree of polymerizytion was recorded in basil. In Sudanese plants , degree of polymerization ranged between 2.78 to 59.63 monomer unites of catechin per polymer of phenolic compounds.the highest degree of polymerization was for Sclerocarya birrea leaves( SCL).
3.4- Cupric ion reducing antioxidant capacity (CUPRAC) assay:-
For Cupric ion reducing antioxidant capacity (CUPRAC) assay .Data revealed that, the antioxidant activity of German herbs by CUPRAC method calculated as Torolox equivalent ,thyme had the most efficiency in cupric ion reducing antioxidant capacity among German samples that was 0.829 mg Torolox equivalent and also the same for C. cordofanum leaves (CCL) among Sudanese samples that had 1.636 mg Torolox equivalent .
3.5-Retarding of photosensibiled oxidation reaction activity:-
For retarding of photosensibiled oxidation reaction activity of examined samples, rosemary had the highest percent of photooxidation retardation in German samples. After 1 h of exposure of samples to the light in the presence of 1mg /ml of chlorophyll as sensitizer the herbs extracts showed higher activity. The percent of retardation of photooxidation in rosemary ranged between 11.59 and 41.72) at the used concentration of the extract. and Sclerocarya birrea leaves (SCL) was the highest among Sudanese samples .the inhibition perecent ranged from 30.24 to 41.19 % in SCL after 1 h of exposure to the light.
3.6-Lipoxygenase activity inhibition:-
For the effect of different concentration of methanolic extracts of samples on lipoxygenase activity inhibition, rosemary had the highest activity among German samples that was concentration dependant. The increase of the concentration from 0.2, 0.4 and 0.6 mg/ml for rosemary caused increase in the inhibition of lipoxygenase activity by 7.77%, 19.29% and 30.93% ,respectively. While Sudanese samples followed different manner for every sample with increasing the concentration, at the same time, all of them appeared remarkable inhibition activities that was the maximum for Guiera senegalensis roots (GSR) methanolc extract. The results suggest that all examined sample materials acts as potent antioxidant with different efficiency.
4-Phenolic compounds fractionation of Sudanese samples on Sephadex LH-20:-
Low pressure liquid chromatographic analysis using Sephadex LH-20 was another method carried out in this work in order to identify the main phenolic compounds in ethyl acetate extract of Sudanese samples. Then the UV absorption intensity of isolated fractions was measured spectrophotometry .The results indicated that the presence of the main groups of phenolic compounds in each sample. also antioxidant activity for Sudanese samples phenolic fractions was measured by DPPH method. The GSR fractions were the strongest of all collected fractions then the other fractions followed this order CCL˃ SPL˃ SPP ˃GSL ˃ SCL. The IC50 obtained were 0.93, 1.95, 4.32, 7.39, 8.25 and 11.46, respectively.
5- Identification of phenolic compound fractions in herbs and medicinal plants by HPLC analysis:-
The more detailed analysis of the nature of phenolic compounds of the investigated samples by HPLC provided information of their decomposition as well as their distribution. In this work, the different forms of phenolic compounds (free, insoluble bound and esterified phenolic compounds) were measured. The results indicated that , these plants are more suitable material for phenolic compounds extraction which present in different forms by suitable analysis procedure, and their composition was examined by HPLC method that indicated presence of highly active phenolic compound. Thus it is assumed that that composition of phenolic compounds might be one of the factors which explain their importance as antioxidants.
6- Stabilization of refined rapeseed oil during deep- frying by different plant samples:-
The technical application of natural antioxidant in food processing in this study was stabilization of refined rapeseed oil during deep –frying Stabilization of refined rapeseed oil during deep-frying treated with rosemary, sage and thyme was carried out . The addition of herbs to oil and storage of the mixture over a certain period of time resulted in the transfer of phenolic compounds from the herbs into the oil ,where they act as antioxidant to inhibit oxidation process and stabilized the frying oil and improve the sensory quality of French fries being fried . In this work the effect of extraction temperature, time and amount of plant material on the oxidation stability of rapeseed oil was studied
Different parameters for the assessment the quality of used frying oils were measured, those parameter were Oligomer triacylglycerides, Acid value, Tocopherols content,and Oxidation stability by Rancimat Test.
7-- Effect of Sudanese plant extracts on sunflower oil oxidation stored at 70°C:-
7.1- Peroxide value of sunflower oil oxidized at 70°C:-
The effect of methanolic extracts of Sudanese plant materials on the oxidative stability of sunflower oil during storage at 70°C was tested in the dark compared with control. The increase of the peroxide values (PVs) was markedly lower for the extracts in comparison to the control . Within 96 h of storage the control without extract reached a PV of 21.6 meq O2/kg. The best effect was shown by the extract from G. senegalensis (roots) for which after 96 h of storage only a PV of 4.6 meq O2/kg was found.
7.2-Oxidative stability of sunflower oil by Rancimat test :-
The influence of Sudanese plant extracts on the oxidative stability of sunflower oil tested with Rancimat measurement, the antioxidant effect of the examined plant extracts was only very small in comparison to the control. While the blank. showed an induction period of 2.4 h, the highest induction period was found for G. senegalensis (leaves) with 3.3 h.
Conclusion
The results concluded that:-
• The investigated herbs and spices are rich source of natural antioxidants.
• All investigated samples contain high levels of phenolic compounds these phenolic compounds work as antioxidants with different abilities,
• Different antioxidant activity determination methods should be used to evaluate the mechanism thereby these phenolic compounds inhibit or delay the oxidation reactions.
• More detailed characterisation of phenolics could be obtained from HPLC analysis.
• Different phenolics forms are presented in the investigated samples and can be isolated by alkaline hydrolysis procedure and these obtained forms have also antioxidant activity, these bioactive properties exerted by these forms could be applicable as a source of natural antioxidant.
• High quality rapeseed oil rich with natural antioxidant can be obtained if sage, rosemary or thyme added directly to oil then the lipid oxidation problems during deep frying might be eliminated.