Total phenolic contents and antioxidant activities of pulp, seed and skin of 22 grape varieties (7 white and 15 red) grown in the Marmara region of Turkey were determined (common, registered or candidate cultivars). The total phenolic contents of grape pulp, seed and skin parts ranged from 9.26 to 62.29, from 162.29 to 326.18 and from 96.61 to 167.42 mg gallic acid equivalents/100 g fresh weight, respectively. Seasonal changes were noticeable in the total phenolic contents and antioxidant activities of different grape parts. The antioxidant activity of grape seeds of registered or candidate cultivars was the highest, followed by skins and pulps. The antioxidant activities of grape skins were higher in red varieties than in white varieties. The results indicated that registered and candidate red or white grape cultivars may have high amounts of phenolics and possess a superior antioxidant activity in comparison to popular cultivars, such as Bilecik İrikarası, Hamburg Misketi, Alfons and Isabella.
The main purpose of this study is to determine the contents of 3 major phenolic compounds (gallic acid, catechin, and epicatechin) in 22 different grape cultivars/hybrids obtained from 2 different breeding programs. Additionally, changes in these phenolic components in the grape leaves of some resistant/tolerant species were determined in relation to powdery and downy mildew diseases in viticulture. The skin, pulp, and seeds of grape berries were analysed over two years, while changes in the phenolic contents of grape leaves were determined before and after these diseases for two years. The major phenolic contents of new hybrids/cultivars were compared with those of popular cultivars in different parts of the grapes, and significant differences in phenolic contents were found among hybrids/cultivars and different grape parts. Variations in the contents of phenolics in grape seeds, skins, and pulp were high, but seeds contained higher levels of these phenolics than pulp and skin. Analyses of the relationship between two viticultural diseases and phenolic changes in resistant/tolerant cultivars in relation with the susceptible “Italia” cultivar revealed that an increase in the content of the phenolic compounds was found after powdery mildew disease. Hybrids/cultivars with high phenolic contents are recommended to develop new superior cultivars, which are resistant to grape fungal diseases, in breeding programs.
IntroductionIt is known that grapes are among the most important fruits for human health and their importance arises not only from nutritional value but also their natural phenolic compounds (Baydar, 2006a). Phenolic compounds are plant secondary metabolites that constitute one of the most common and widespread groups of substances in plants (Whiting, 2001). Plants need phenolic compounds for pigmentation, growth, reproduction, resistance to pathogens, and many other functions (Oksana et al., 2012). Plant phenolics are secondary metabolites that encompass several classes of structurally diverse natural products (Lattanzio et al., 2006). Secondary metabolites apparently act as defense (against herbivores, microbes, viruses, or competing plants) and signaling (to attract pollinating or seed-dispersing animals) compounds, as well as protecting the plant from ultraviolet radiation and oxidants (Swain, 1977;Kutchan, 2001). Phenolics are known to inhibit the feeding of many insects and have demonstrated toxicity (Grayer et al., 1992). The first stage of the defense mechanism of plants involves rapid
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