antioxidant properties of extract 'sboswellia serrata oleo-gum resin in soyabean oil

introduction:frankincense is a natural oleo-gum-resin which is obtained through slits made in the trunks of trees of the genus boswellia (family burseraceae). the genus boswellia is approximately represented by 43 different trees and shrubs distributed mostly in the india, arabian peninsula, and east africa (mothana et al.2011). trees from the genus boswellia (burseraceae) are traditionally used as a medicine, a fumigant, in various cosmetic formulations and in aromatherapy in several countries around the world.frankincense therapeutic effect significantly depends on the amount of oleoresin. these effects include anti-inflammatory, hepatoprotective, anticancerous, anti-hiv, anti-microbial, antifungal, anti-ulcerous, gastroprotective, hypoglycemic andantihyperlipidemic properties (aman et al. 2009; al-harrasi and al-saidi, 2008; khadem et al. 2009 and shah et al.2009). lipids are susceptible to oxidation on storage and frying processes. characteristic changes associated with oxidative deterioration include development of unpleasant tastes and odors as well as changes in color, specific gravity, viscosity and solubility.lipid peroxidation is one of the major agents of deterioration for vegetable oils, fats and other food systems (iqbal and bhanger, 2007). during oxidation hydroperoxides are formed which again break down to form products like alcohols, aldehydes, ketones and hydrocarbons, which possesses offensive off flavors (grace roy et al.2010).in order to inhibit oxidation, synthetic antioxidants, such as bha (butylated hydroxyanisole), bht (butylated hydroxyanisole) and tbhq ter-butyl hydroquinone have been added to foods but there is concern about the use of these compounds due to their reported adverse effects on health. this has led to an increasing trend in the search and replace of these synthetic antioxidants with natural ones such as phenolic compounds (mariod et al. 2006).antioxidants affect the process of lipid oxidation at different stages due to differences in their mode of action. because of the complexity of the oxidation process itself,the diversity of the substrates and the active species involved, the application of different test methods is necessary in the evaluation of antioxidants. the aim ofthisstudy was to evaluatethe antioxidantproperties of various solvent extractsand essential oil offrankincense(boswellia serrata)and evaluation ofitsantioxidant activityinsoybeanoil. materials and methods: in this study, the dried powder of b.serrata (25g) was extracted overnight in 250 ml each of methanol, ethanol and acetone respectively, in a mechanical shakerat room temperature and each extract was filtered with whatman no. 1 filter paper. the filtrates obtained from methanol, ethanol and acetone extractions were evaporated at 40 °c in a rotary evaporator. the content of phenolic compounds was measured by folin–ciocalteu, briefly 20 µl of extract solution were mixed with 1.16 ml distilled water and 100 µl of folin–ciocalteu reagent, followed by addition of 300 µl of na2co3 solution (20%) after 8 minutes. subsequently, the mixture was incubated at oven at 40 °c for 30 minutes and its absorbance was measured at 760 nm. the ability of extracts to scavenge dpph radicals was determined according to the method of blois (1958). briefly, 1 ml of a 0.1 mm methanolic solution of dpph was mixed with 3 ml of extract solution in methanol (containing 100–1000 μg/ml). the mixture was then vortexed and left for 30 min at room temperature in the dark. the absorbance was measured at 517 nm. the percentageof the dpph radical scavenging was calculated using the equation given below: % inhibition of dpph radical= ( abr - aar ) / aar×100 where abr is the absorbance before reaction and aar is theabsorbance after reaction has taken place. the molecule 1, 1-diphenyl-2-picrylhydrazyl (a,a-diphenyl-bpicrylhydrazyl dpph) is characterized as a stable free radical by virtue of the delocalisation of the spare electron over the molecule as a whole, so that the molecule does not dimerize, as would be the case with most other free radicals (nur alam et al., 2013).next, oxidative stabilityand antioxidant activity of methanol extract concentrations (200, 500, 800, 1000 ppm) with the synthetic antioxidant tbhq (100 ppm) were evaluated in soybean oil without antioxidants (63 ˚c, 12 days). results and discussion: the extract significantly (p0.05) suppressed the formation of peroxides and thiobarbituric acid-reactive substances (tbars) during accelerated oxidation, even at a level of 200 ppm. based on the obtained results, the methanolic extract at 1000 ppm had the highest antioxidant activity among other extracts and inhibits the peroxide value and the index of thiobarbituric acid, but it coulden't compete with the synthetic antioxidant tbhq. results showed that, boswellia serrata was found as a potential source of natural antioxidants due to its marked antioxidant activity.