3.5. Effect of onion solution on metal chelating activity of apple juice
Cooper chelating and ferric reducing activities are important indicators of the antioxidant capacities of natural products since they are closely related to suppression of oxyradical generation and the effects of oxidative damage (Sudha et al., 2011). To further examine the effects of heating and/or onion addition on the antioxidant capacity of apple juice, we measured ferric reducing and copper chelating activities. Heating itself did not affect ferric reducing and copper chelating activities (Fig. 5a and b). On the other hand, both heated and unheated apple juices supplemented with onion extract showed increased ferric reducing and copper chelating activities (Fig. 5a and b), suggesting that onion addition can increase ferric reducing and copper chelating activities in apple juice independent of heating. However, onion supplementation more effectively increased metal chelating activities in heated apple juice (Fig. 5a and b).