The effect of pH and extraction time on total phenolic content and antioxidant properties of coloured water extracts from Brassica Oleracea

Red cabbage (Brassica oleracea) is a rich source of phenolic content including colour pigments and have also high antioxidant capacities. The amounts of their phenolic substances and antioxidant activities change depending on the extraction conditions (pH, time, solvent, etc.). In this work, the coloured water extract was obtained from red cabbage at different pH values (pH 4-10) for both an hour and 24 hours. The extracts were evaluated regarding total phenolic contents and antioxidant activities. The results showed that the total phenolic content of red cabbage extracts in all extraction conditions ranged from 4.93±0.20 to 7.59±1.22 mg GAE/g fw. The highest total phenolic contents (7.59±1.22 mg GAE/g fw) were obtained from red cabbage at 24 h and pH=6. On the other hand, the red cabbage extracts have high DPPH (IC50 values ranged from 0.21±0.06 to 0.94±0.03 mg/mL) and ABTS (IC50 values ranged from 0.29±0.01 to 0.46±0.05 mg/mL) activities at all pH values and times. The extract obtained from red cabbage at 1 h and pH=7 exhibited the strongest DPPH activity with the IC50 values of 0.21±0.06 mg/mL, it showed the best ABTS activity with the IC50 values of 0.29±0.01 mg/mL at 1 h and pH=5 and 8.