Determination of total phenolic content of raspberry and blackberry cultivars by immobilized horseradish peroxidase bioreactor

Raspberry and blackberry cultivars were assayed for total phenol content by enzymatic method using immobilized horseradish peroxidase (HRP). The HRP was immobilized on the styrene-divinylbenzene-polygluteraldehyde (STY-DVB-PGA) beads. Total phenol content determined by immobilized and free enzymatic methods was compared with those obtained by applying the Folin-Ciocalteu method. The total phenol content by immobilized HRP method ranged from 254 to 973 mg gallic acid equivalent (GAE) per 100 g fw as well as 105 to 435 mg ellagic acid equivalent (EAE) per 100 g fw in raspberry and blackberry cultivars. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical values were correlated with total phenol content in raspberry using immobilized enzymatic method as GAE (R2 = 0.7450, P = 0.05) and EAE (R2 = 0.7449, P = 0.05). All antioxidant activity values were highly correlated with total phenol content in blackberry using free and immobilized enzymatic methods as GAE (R2 = 0.9777 and 0.9223, P = 0.05 respectively) and EAE (R2 = 0.9979 and 0.9223, P = 0.05 respectively). A significant additivity was observed using individual phenolic compounds by immobilized enzymatic method as 95% (GAE) and 90% (EAE). These results show that the immobilized enzymatic assay can be applied to determine the total phenol content of berry fruits, which is more specific and not affected by interfering compounds.