C: Food Chemistry Comprehensive Assessment of Antioxidant Activity of Essential Oils Kevin P. Anthony, Suziat A. Deolu-Sobogun, and Mahmoud A. Saleh Abstract: Essential oils have been studied for their unique ability to act as antioxidants. Antioxidant activities of 423 essential oils of 48 different botanical families were evaluated for their antioxidant activities as free radical scavenging agents using the 1,1-diphenyl-2-picrylhydrazyl method. Seventy-three oils showed 50% or more inhibition at a concentration of 1.25 mg/mL. The 73 most active oil samples were further evaluated for their scavenging activities using series of dilutions to estimate their EC 50 . The EC 50 of the 73 most active oils ranged from 4 to 2000 μg/mL. Oils having an EC 50 of less than 300 μg/mL (20 selected samples) were subjected to β -carotene bleaching antioxidant activity test and more detailed analysis including thin layer chromatography, gas chromatography/mass spectrometry, high performance liquid chromatography and bioautography. Essential oils of the botanical families Lamiaceae and Myrtaceae were the most effective antioxidants. Thymol and carvacrol were the major constituents in most of the essential oils of the family Lamiaceae and eugenol was the major terpene in all of the essential oils of the family Myrtaceae. Keywords: DPPH, food spices, Lamiaceae, Myrtaceae, oxidative damage, radical scavenging Practical Applications: Supplementation of food with spices containing essential oils may counteract and retard the process of oxidative damage, lipid oxidation and elevate antioxidant activity of the final product. Introduction Free radical mediated oxidation is an important biological pro- cess in all living organisms for energy production, but when the production of oxygen derived free radicals becomes overwhelmed, it triggers diseases (Nadkarni and D’Souza 1988). Reactive oxygen and nitrogen free radicals are produced during biological redox reactions and can be triggered by several environmental factors such as pollution, smoke, and sunlight. Electron acceptors, such as molecular oxygen and nitrogen, react easily with free radicals to become radicals themselves and are designated as reactive oxygen and nitrogen species (ROS/RNS), respectively. There is consid- erable evidence that these free radicals induce oxidative damage to biomolecules such as lipids, proteins and nucleic acids produc- ing oxidative stress. Oxidative stress may lead to atherosclerosis, ageing, cancer, diabetes mellitus, inflammation, and several non- transmissible degenerative diseases in humans (Wang and others 2008; Yuan and others 2008; Dhiman and others 2009; Lai and others 2010). ROS/RNS are normally detoxified by an efficient antioxidant system that includes enzymes such as superoxide dis- mutase, catalase, and glutathione peroxidases. However, when the defense system is not efficient enough, the cells can experience oxidative stresses which are associated with a variety of chronic diseases described above (Halliwell 1994; Aviram 2000). In addition to the health effects on humans in the form of ox- idative stress or oxidative damages, there are major concerns in food technology resulting from lipid oxidation, due to the forma- tion of oxidation products such as fatty acid hydroperoxides and secondary degradation products including acrolein and related un- MS 20111367 Submitted 11/12/2011, Accepted 5/4/2012. Authors are with Dept. of Chemistry, Texas Southern Univ., 3100 Cleburne Street, Houston, TX 77004, U.S.A. Direct inquiries to author Saleh (E-mail: saleh_ma@tsu.edu). saturated aldehydes and ketones (Saleh and others 1986). These autoxidation products of fats and oils are responsible for off-flavors with characteristic rancid odors and are responsible for the de- crease of both the nutritional quality and safety of foods (Hertog et al 1993). Antioxidants have the ability to protect cells from free radical damage and serve as chemopreventive agents by inhibit- ing the generation of free radicals and play an important role in neutralizing oxidative damage caused by these free radicals. Plants produce a wide variety of secondary products having strong antioxidant effects (Ruberto and others 2000; McGaw and others 2007; Lai and others 2010). Mata and others (2007) showed that some of the natural components such as the essential oils have potential for biological, antioxidant, therapeutic, and pharma- ceutical purposes. Several epidemiological studies (Stampfer and others 1993; Saija and others 1995; Yanagimoto and others 2002; Benedet and others 2007; Bounatirou and others 2007; Wei and Shibamoto 2007) have shown an association between a diet rich in fruit and vegetables and a decreased risk of cardiovascular diseases, stroke, and some forms of cancer. The use of naturally occurring antioxidants in daily life has been regarded as an effective way for promoting human health. There is a large pool of publications describing the antioxidant activity of essential oils, however they all present results of re- search that was performed on a small number of oils and at most an individual botanical family or related species. In addition, they tend to use different methods and different calibrations for the antioxidant activity making it very difficult to carry out a realistic comparison between different types and sources of essential oils for their antioxidant activity. Differences used in analytical meth- ods and measurement conditions can be responsible for reported variations in the antioxidant activity of same samples (MacDonald- Wicks and others 2006). Consequently, results on the antioxidant activity of essential oils from the same plant, which are reported in numerous studies, may vary greatly (Ruberto and others 2000; C  2012 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2012.02795.x Vol. 00, Nr. 0, 2012  Journal of Food Science C1 Further reproduction without permission is prohibited