Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Spectrophotometric And Chromatographic Determination Of Antioxidant Capacity İn Some Plant Samples

Excessive amounts of free radicals that are produced from various metabolic reactions in the organism and are highly reactive due to their unpaired electrons cause significant damage in tissues, organs and physiological systems. The organism has developed a great many defence mechanisms for restricting this damage, and the food-ingested C and E vitamins, selenium, -carotene, lycopene, lutein and other carotenoids act as antioxidants aiding this defence. Flavonoids as secondary plant metabolites and terpenoids may be considered as additional defense elements. This signifies the importance for human health of the antioxidant-rich fruits and vegetables as well as of traditionally used medicinal plants also bearing these antioxidants. In recent years, studies focusing on therapeutic plants and the active principles isolated from them have intensified.

In this study, it has been aimed to identify the essential compounds having antioxidant properties contained in a number of food and medicinal plants such as sage, lady’s mantle, yarrow, dill, linden, nettle, thyme, celery leaves, parsley, oregano and mint, and to determine the total antioxidant capacity caused by these compounds.

The study consists of three parts. For determining total antioxidant capacity, the cupric ion reducing antioxidant capacity assay (abbreviated as the CUPRAC method) that is low cost, easily applied, and rapid, utilizing the copper(II)-neocuproine (2,9-dimethyl-1,10-phenanthroline) reagent was used, and the results were compared to those found by the ABTS/persulfate assay, the widely used method for antioxidant capacity measurement. For identification and individual quantitation of basic species giving rise to antioxidant capacity, the HPLC (High Performance Liquid Chromatography) method that has also found wide use in the identification of various antioxidant compounds was selected.

If all the antioxidants in a plant extract are identified, then the theoretically expected total antioxidant capacity can be calculated by multiplying the concentration of each antioxidant with its TEAC (trolox equivalent antioxidant capacity) coefficient and summing up the described products. In case when all the antioxidants were successfully identified, from the HPLC chromatogram, then the so calculated theoretically expected capacity should be in accord with the experimentally found antioxidant capacity.

The theoretically calculated-with the aid of HPLC-capacity values of the tested plant samples compensated for the experimentally found CUPRAC capacities at the following percentages: nettle extract 82 %, different hydrolyzates of parsley 60-77 %, mint extract 63 %, oregano extract 61 %, and different hydrolyzates of celery leaves 41-57 %. It was thought that unestimated species in the chromatograms were responsible for this case.

The order of plant samples with respect to CUPRAC total antioxidant capacity was: lady’s mantle > thyme > linden > oregano > sage > mint > yarrow > celery leaves > dill nettle > parsley.

SAYIK Aysema,

Danışman : Prof. Dr. Ayşe S. YUSUFOĞLU

Anabilim Dalı : Kimya

Programı (Varsa) : Organik Kimya

Mezuniyet Yılı : 2007

Tez Savunma Jürisi : Prof. Dr. Ayşe S. YUSUFOĞLU (Danışman)

Prof. Dr. Süleyman TANYOLAÇ

Prof. Dr. Refiye YANARDAĞ

Prof. Dr. Nüket ÖCAL

Doç. Dr. Zuhal TURGUT