Polyphenolic compounds are very important constituents because of their antioxidant activity in chelating redox-active metal ions, inactivating lipid free radical chains and preventing hydroperoxide conversion into reactive oxyradicals (Oliveira et al., 2009). An important function of phenolic acids is their action in plant defense mechanisms. Stress conditions such as excessive UV light, wounding or pathogen infection induces the biosynthesis of phenolic compounds. The phenylpropanoid pathway for the conversion of amino acid l-phenylalanine to trans-cinnamic acid by the PAL and the subsequent reactions producing new compounds such as chlorogenic acid, protocatechuic acid, caffeic acid and dicaffeoyltartaric acid are well known (Tomás-Barberán et al., 1997a and Tomás-Barberán et al., 1997b). In our study, the increased phenolic contents in wound tissue are associated with stimulated PAL activity from day 3 to day 12 after cut. The rapid increase of phenolic content from day 3 to day 9 in control should have benefited from consist higher PAL activity than in curing samples at the same period. The decreased gallic acid, chlorogenic acid and other phenolic on day 12 could be the result of higher browning and polymerization in control slices. The PPO activity curves, however, are matched well with total phenolic curves and individual phenolic profiles in the same tissue. An increase of the storage time and PPO activity has been reported in ‘Jonagored’ apple slices (Rocha & Morais, 2002). This could be due to the cutting-induced increase in synthesis or activity of PPO
Polyphenolic compounds are very important constituents because of their antioxidant activity in chelating redox-active metal ions, inactivating lipid free radical chains and preventing hydroperoxide conversion into reactive oxyradicals (Oliveira et al., 2009). An important function of phenolic acids is their action in plant defense mechanisms. Stress conditions such as excessive UV light, wounding or pathogen infection induces the biosynthesis of phenolic compounds. The phenylpropanoid pathway for the conversion of amino acid l-phenylalanine to trans-cinnamic acid by the PAL and the subsequent reactions producing new compounds such as chlorogenic acid, protocatechuic acid, caffeic acid and dicaffeoyltartaric acid are well known (Tomás-Barberán et al., 1997a and Tomás-Barberán et al., 1997b). In our study, the increased phenolic contents in wound tissue are associated with stimulated PAL activity from day 3 to day 12 after cut. The rapid increase of phenolic content from day 3 to day 9 in control should have benefited from consist higher PAL activity than in curing samples at the same period. The decreased gallic acid, chlorogenic acid and other phenolic on day 12 could be the result of higher browning and polymerization in control slices. The PPO activity curves, however, are matched well with total phenolic curves and individual phenolic profiles in the same tissue. An increase of the storage time and PPO activity has been reported in ‘Jonagored’ apple slices (Rocha & Morais, 2002). This could be due to the cutting-induced increase in synthesis or activity of PPO
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