Evaluation and comparison of antioxidant properties and total phenolic content of pomegranate (Punica granatum L.) peel and juice

Abstract

Pomegranate peel is currently a waste but contains valuable, rich with a diverse range of bioactive compounds. The objective of the present study was to assess the antioxidant properties by IC50 value and FRAP value, total phenolic content (TPC), total flavonoid content (TFC) and total anthocyanin content (TAC) of the peel (PP) and the juice (PJ) of local pomegranate cultivars, Nayana, Nimali and Kalpitya red. Antioxidant properties were tested by FRAP and DPPH assay. TPC was measured spectrophotometrically using the Folin Ciocalteu method and expressed as mg Gallic acid equivalents (GAE)/gram. TFC was evaluated by the aluminum chloride assay. TAC was detected by the vanillin assay. The TAC and TFC of PP of Nimali, Nayana and Kalpitya red cultivars were 22.12 ± 0.20, 49.05 ± 0.30 and 69.08 ± 0.57 mg catechin equivalents (CE)/g and 67.67 ± 0.59, 59.58 ± 0.85 and 75.99 ± 0.85 mg rutin equivalent (RE)/g respectively. The TAC of PJ ranged from 0.40 ± 0.01 to 2.82 ± 0.03 mg CE/g was nearly 60 times less than that of PP of the same cultivar. The TFC of PJ ranged from 0.39 ± 0.00 to 0.80 ± 0.00 mg RE/g was nearly 100 times less than that of PP. The TPC and FRAP values of PP of Nimali, Nayana and Kalpitya red cultivars were 469.67 ± 8.97, 413.92 ± 4.75 and 318.82 ± 4.66 mg GAE/g and 6690.00 ± 153.00, 4270.60 ± 83.00 and 4512.00 ± 14.00 μmol Fe2+/g respectively. The TPC of PJ varied from 0.87 ± 0.02 to 1.98 ± 0.04 mg GAE/g was nearly 300 times less than that of PP. The FRAP values of PJ ranged from 15.57 ± 0.36 to 40.18 ± 0.29 μmol Fe2+/g were nearly 200 times less than that of PP. The IC50 values of PP of Nimali, Nayana and Kalpitya red cultivars were found to be 14.20, 20.40 and 18.00 μg/mL respectively. The IC50 values of PJ were in the range of 915-3098 μg/mL, nearly 100 times higher than that of PP. The results revealed that PP contains exceptionally high TPC and antioxidant properties observed by IC50 and FRAP values with respect to PJ of the same cultivar. The PP of Nimali cultivar had the highest antioxidant properties and TPC. The PP of Kalpitiya red cultivar possessed the highest TFC and TAC. Thus, PP has a high potential to be utilized as a resource of bioactive compounds. The results proved that there is no correlation between phenolic compounds and the antioxidant properties. All the parameters tested were significantly different (p<0.05) among the cultivars.