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  • Senexin A Plant tissues were thought to be natural sources

    2024-06-08

    Plant tissues were thought to be natural sources containing different types of antioxidant compounds (tocopherols, ascorbic acid, carotenoids, and phenolic compounds). As a general classification, antioxidants were grouped as vitamins (ascorbic acid, tocopherols), carotenoids (condensed tannins, xanthophylls and carotenes), flavonoids (flavones, isoflavınes, flavonols, flavanols, flavanones), phenolic acids (hydroxyl-benzoic Senexin A and hydroxyl-cinnamic acid), phenolic alcohols, stilbenes, lignans, tannins, sulfur containing antioxidants and neoformed compounds (melanoidins) (Table 1). Tocopherols, as one of the first identified antioxidants, were firstly used to prevent lipid oxidation (Smith et al., 1945), and then to prevent the oxidative destruction of carotenes due to their chain breaking activity. Their antioxidant mechanism could be summarized as: they are able to quench lipid radicals and regenerate lipid molecules followed by producing a tocopheryl semiquinone radical that may form a molecule of stable tocopheryl quinone and a regenerated tocopherol molecule (Nimse & Pal, 2015). Nuts, vegetable oils, herbs and spices were discovered as natural sources of tocopherols (Das Gupta and Suh, 2016, Demo et al., 1998). Their structures were described as a polar chromanol head group with an isoprenoid-derived hydrophobic tail. The number and substation of methyl groups attached to chromanol ring determined the types of tocopherols (α-, β-, γ-, or δ-) (Cahoon et al., 2003). There has been widespread confusion concerning their relative antioxidant potential. In vivo studies have shown that their antioxidant potential was in the order of α>β>γ>δ, while in vitro studies have reported in reverse order. Many factors such as radical types, solvent types, temperature, light, another substances in the system must be considered to solve the confusion in all in vivo and in vitro studies (Shahidi & Ambigaipalan, 2015). The detailed information about tocopherols and tocotrienols in plants has been compiled in a recent review (Saini & Keum, 2016). As another fat-soluble antioxidant, carotenoids (xanthophylls and carotenes) containing 40-carbon terpenoids with a basic structural unit isoprene (Table 1) emerged as a lipid oxidation inhibitor by quenching singlet oxygen (Burton & Ingold, 1984). Then it was understood that they were potential scavenger of reactive oxygen species (Fiedor & Burda, 2014). It was demonstrated that β-carotene, α-carotene, lycopene, lutein and cryptoxanthin constituted of almost 90% of the carotenoids in human diet (Gerster, 1997, Rao and Rao, 2007). Green leafy vegetables, carrot, tomato and cereals were found as the most common carotenoid sources (Müller, Caris-Veyrat, Lowe, & Böhm, 2016) and especially tomato, among them, have been taken attention with its high lycopene content (Toor & Savage, 2005). It was reported that lycopene, the open-chain isomer of β-carotene (Table 1), showed the greatest quenching ability, such that is double of β-carotene ability (Di Mascio, Kaiser, & Sies, 1989). Recent developments about carotenoids, their chemistry, occurrences, biological activities in detail were discussed in a review conducted by Saini, Nile, and Park (2015). Ascorbic acid, also known as vitamin C, was defined as one of the most crucial antioxidant compounds for humans. Although vitamin C was developed as a potential scurvy inhibitor, then its antioxidant activity as a reducing agent was also noticed (Bielski, Richter, & Chan, 1975). Unlike other low-molecular-weight antioxidants, ascorbic acid differed from others as a radical chain terminator by transformation to non-toxic and non-radical products (Davey et al., 2000). It was emphasized that ascorbic acid, as a mildly electronegative compound (Table 1), was able to donate electrons to a wide variety of substrates such as superoxide radical anion, hydrogen peroxide, hydroxyl radical, singlet oxygen and reactive nitrogen oxide (Carocho and Ferreira, 2013, Davey et al., 2000). It is, however, a very unstable compound and easily degraded. Therefore, encapsulation methods were used as a promising alternative to overcome the instability problems of ascorbic acid (Comunian et al., 2013). Indeed, it was discovered that ascorbic acid involved in the regeneration processes of the lipophilic and membrane-associated tocopherols (Davey et al., 2000). Most of fruits and vegetables especially citrus fruits, red pepper came to the fore as vitamin C sources.