br Introduction The term antioxidant derives

Introduction The term antioxidant derives from the prevention of the oxygen consumption. In the late of 19th centuries, antioxidants were generally used in industrial processes such as against to metal corrosion, vulcanization of rubber. Later on, the use of antioxidants to prevent the rancidity causing by oxidation of unsaturated more became prevalent (French et al., 1935, Smith et al., 1945, Stirton et al., 1945). They were thought as food additives to conserve the nutritive value of food by preventing carotenes, various fat-soluble vitamins and essential fatty acids against oxidation. Number of antioxidant substances were discovered and isolated from natural sources such as herbs, spices, vegetables, and fruits. Then, researchers identified some antioxidants such as vitamin E, vitamin C in blood and urine, and realized their importance in biochemical processes (Jacob, 1996, Kadin and Osadca, 1959, Tappel and Zalkin, 1959). Later on, it was noticed that antioxidants inhibited the oxidation processes and prevented oxidative stress related diseases (e.g. atherosclerosis, certain cancers, type 2 diabetes, cardiovascular diseases, chronic inflammation, stroke and septic shock, aging); and therefore they have come into prominence with their crucial roles not only in foods but also in the human body. Quantification and activity determination of antioxidants has also been an area of interest for decades among food scientists. Many different analytical methods with diverse extraction procedures have been developed to date (Oroian & Escriche, 2015). A timeline about the major developments and milestones on the research on food antioxidants is given in Fig. 1. A simple search of Web of Science database using the keywords “Antioxidants”, “Antioxidants and Assay”, “Antioxidant and Health”, and “Antioxidant Content” indicates thousands of published articles appeared in peer-reviewed journals (Fig. 2). According to data from Web of Science, the researches investigating food antioxidants, which especially provide health benefits beyond preservative effects, are on the rise. Obviously, there is a growing interest in improving the knowledge on the antioxidant content of foods, and their physiological effects in the human body. This paper provides a comprehensive review of antioxidants covering the occurrence and roles of antioxidants in foods, analytical methods for the determination of total antioxidant capacity of foods, and the physiological effects of antioxidants. Each of these topics is discussed in details in the following sub-sections.
Antioxidants in food Dietary antioxidants have important roles in food or in human body by counteracting oxidation processes and preventing the chronic diseases related to oxidative stress. These compounds exert their activity by several mechanisms: (i) free radical quencher, (ii) singlet oxygen scavengers, or (iii) chelators of metal ions catalyzing the oxidative reactions (Shahidi, Janitha, & Wanasundara, 1992). Over the course of seventy years, there have been several studies that enlighten the antioxidant profiles of different foods and their antioxidant potential. As a historical view, after discovering of antioxidants to prevent the rancidity causing by the oxidation of unsaturated fats, a number of antioxidant substances have been discovered and isolated from natural sources such as herbs, spices, vegetables (Anglin, Mahon, & Chapman, 1956). Some synthetic antioxidants substituted to phenols and aromatic amines such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) were developed in some research laboratories (Kraybill et al., 1949). These compounds or their combinations were found safe and effective in retarding rancidity in chips, nuts, and chicken fat (Dugan et al., 1950, Kraybill and Dugan, 1954). However, the concern about their toxicity and higher costs together with the consumer preference with regard to food additive safety created a need to identify the natural sources having antioxidant potential (Moure et al., 2001, Ulland et al., 1973).