ABSTRACT
Many studies have indicated that the consumption of foods from natural product sources (cereal, vegetables, fruits) can reduce the risk of chronic diseases in humans caused by oxidative stress, such as coronary heart disease (Bhupathiraju and Tucker, 2011; Dalen and Devries, 2014), diabetes (Salas-Salvadó et al., 2011; Singh et al., 2013; Esposito and Giugliano, 2014), cancer (Steinmetz and Potter, 1996; Research and Fund, 2007; Boivin et al., 2009), and neurodegenerative diseases (Alcalay et al., 2012; Otaegui-Arrazola et al., 2014). Natural products contain substances produced by a plant’s secondary metabolism and have antioxidant capabilities and the ability to overcome oxidative stress by neutralizing the overproduction of oxidant species (Dai and Mumper, 2010; Gülçin, 2012). Antioxidant activity can occur via several mechanisms, including free-radical scavenging; chelating pro-oxidative metals; quenching singlet oxygen and photosensitizers; and inactivating lipoxygenase, the enzyme responsible for lipid peroxidation (Choe and Min, 2009). The deterioration of foods is caused by lipid peroxidation, and some antioxidants, synthetic or naturally occurring, can be used as additives for food preservation (Niki, 1987; Niki et al., 2005). Phenolic compounds are the most common antioxidants that readily scavenge free radicals by donating hydrogen atoms. The antioxidant capability of phenol compounds involves donation of a phenolic hydrogen and the stabilization of the resulting antioxidant radical by electron delocalization by resonance throughout the
29.1 Introduction 547 29.1.1 Characteristics and Stability of DPPH 549 29.1.2 Reaction Mechanisms 551
29.2 Spectrophotometric Methods 551 29.3 Electron Spin Resonance Method 560 29.4 Electrochemical Methods 563 References 567
phenolic ring structure and/or intramolecular hydrogen bonding or by further oxidation (Frankel and Meyer, 2000; Choe and Min, 2009).
