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    • Furthermore because most of foods and beverages

    2023-09-18

    Furthermore, because most of foods and beverages have been consumed after processing, researchers have focused on the effects of processing (e.g. blanching, cooking, drying, cooling, freezing, high-pressure treatment, pulsed electric field) on total antioxidant capacity of foods. In general, there was a misunderstanding that food processing, especially thermal treatments, caused decrease in nutritional value of vegetables and fruits. For example, Wu et al. (2004) showed that cooking caused decrease in antioxidant capacity of some types of foods such as broccoli and carrots. However, Dewanto, Wu, Adom, and Liu (2002) reported that thermal treatment enhanced the antioxidant potential of tomatoes by increasing the bioaccessible part of antioxidant compounds such as lycopene despite the loss in vitamin C content. Similarly, another research group showed that the thermal process enhanced the total phenolic content and antioxidant capacity of agro-industrial waste (Vodnar et al., 2017). It is worth to say that thermal processing disrupts the cell membranes and cell walls leading to releasing the phytochemicals bound to food matrices. Nayak, Liu, and Tang (2015) also reviewed comprehensively the effects of food processing on phenolic antioxidants of fruits, vegetables and grains. They concluded that optimization of thermal and non-thermal food processing operations had potential to retain phytochemicals in the processed foods.
    Measurement of antioxidant capacity Number of analytical methods have been developed for the determination of total antioxidant capacity of foods. Table 3 gives the principles of these antioxidant capacity measurement assays together with schematic representation of their mechanisms and their advantages/disadvantages. With discovering of antioxidants, it was thought that they prevented the rancidity by means of preventing the Oseltamivir phosphate of unsaturated fatty acids. Therefore, antioxidant capacity was previously measured by the rate of oxygen consumption, changing of the peroxide values or stability tests in fat containing system (Brand-Williams et al., 1995, Stirton et al., 1945). Later on, selective solvent extraction and steam distillation techniques were employed to separate antioxidant compounds in complex food products. In addition, ultraviolet spectra, gas chromatography and colorimetric techniques were used to identify and determine the quantity of each antioxidant present in the extracts (Stuckey & Osborne, 1965). In a study, a simplified colorimetric method was described for the rapid evaluation of antioxidants by following the oxidative destruction of carotene in diluted emulsion of an antioxidant, carotene and lipid (Marco, 1968). It was emphasized that antioxidants exert their activity (biologically or technologically) by interacting with oxidative free radicals. On this basis, a new colorimetric method with a non-biological, stable free radical called α,α-diphenyl-β-picrylhydrazyl (DPPH), which forms the basis of today's radical scavenging potential measurements, was described (Blois, 1958). In this method, the decrease in absorbance because of the reduction of DPPH radical by an antioxidant compound was monitored kinetically for a better understanding of antioxidant behavior (Table 3) (Sánchez-Moreno, Larrauri, & Saura-Calixto, 1998). It was emphasized that the DPPH method was not useful for measuring the antioxidant activity of plasma, because protein was precipitated in the alcoholic reaction medium (Magalhaes, Segundo, Reis, & Lima, 2008). By the way, researchers realized that human serum contained many different antioxidants including vitamin C, a-tocopherol, β-carotene, uric acid, bilirubin and albumin; and they counteracted with oxidative stress in the body. Because of the presence of many different antioxidants in serum and difficulty of measuring them separately, measurement methods to determine total antioxidant capacity of serum based on total reactive antioxidant potential (TRAP) via oxygen electrode (Wayner, Burton, Ingold, & Locke, 1985) or fluorescence properties of phycoerythrin (DeLange & Glazer, 1989) were discovered. It was reported that most of antioxidant tests examined the ability of a substance to scavenge the free radicals containing one or more unpaired electrons and produced in living organisms such as superoxide anion, hydroxyl, peroxyl and nitrite oxide (Halliwell, 1990, Halliwell et al., 1995). Peroxyl radicals as common free radicals produced in biological systems and their scavenging were extensively evaluated in most of assays (Sánchez-Moreno, 2002). In TRAP method, peroxyl radicals were generated by a water-soluble azo-initiator, such as 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), and the oxidation of oxidizable materials was monitored by measuring the oxygen consumed during the oxidative reaction (Table 3) (Sánchez-Moreno, 2002, Wayner et al., 1985).