| Abstract
| - The activities of the oxygen radical scavenging enzymes [glutathione-peroxidase (GSH-POD),superoxide dismutase (SOD), and guaiacol peroxidase (G-POD)], hydrogen peroxide scavengingenzymes in the ascorbate-glutathione cycle [ascorbate peroxidase (AsA-POD), monodehydroascorbatereductase (MDAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR)], thenonenzyme components [ascorbate (AsA), dehydroascorbate (DHAsA), glutathione (GSH), andoxidized glutathione (GSSG)], and their antioxidant capacity [oxygen radical absorbance capacity(ORAC)] were measured in the juice of six different thornless blackberry (Rubus sp.) cultivars. The‘Hull Thornless' cultivar contained the highest levels, whereas ‘Black Satin' consistently had thelowest activities for all the enzymes tested in this study. ORAC values were also the highest in‘Hull Thornless' and lowest in ‘Black Satin'. The highest levels of AsA and DHAsA were in the juiceof ‘Hull Thornless' blackberries with 1.09 and 0.15 μmol/g fresh wt, respectively. ‘Hull Thornless'also had the highest ratio of AsA/DHAsA among the six blackberry cultivars studied. The‘Smoothstem' cultivar contained the lowest amounts of AsA and DHAsA. ‘Hull Thornless' had thehighest GSH content with 78.7 nmol/g fresh wt, while ‘Chester Thornless' contained the largestamount of GSSG. The highest GSH/GSSG ratio was 4.90 which was seen in the ‘Hull Thornless'cultivar. The correlation coefficient between ORAC values and AsA/DHAsA ratios was as high as0.972. A correlation (r = 0.901) was also detected between ORAC values and GSH content. Theantioxidant activity in blackberry juice was positively correlated to the activities of most antioxidantenzymes (r = 0.902 with SOD; r = 0.858 with GSH-POD; r = 0.896 with ASA-POD; and r = 0.862with GR). Keywords: Antioxidant; free radicals; oxygen scavenging enzymes; blackberry
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