Metal chelating activityMetal chelating is one of the important antioxidant mechanisms which retard metal-catalyzed oxidation. In food systems, ferrous ions are the most effective pro-oxidants (Zha et al., 2009). As shown in Figure 4, all ten lotus extracts showed a significant metal chelating activity. At concentration of 5 mg/ml, the metal chelating activity of all ten lotus extracts is in a descending order of rhizome knot > rhizome > embryo > flower > seed epicarp > seed > petiole > leaf > stamen > receptacle. Compared with the BHT control, all ten lotus extracts even exhibited significantly (p < 0.05) higher metal chelating activity. It is interesting to note that for those lotus extracts having remarkable metal chelating ability (such as rhizome knot, rhizome and embryo extracts), their total phenolic, flavonoids and proanthocyanidins contents were relatively low (Table 1), while their DPPH, ABTS and hydroxyl radical scavenging activities, reducing power as well as total antioxidant activity were also insignificant (Table 2 and Figures 1 to 3). These findings might suggest that instead of those phenolic compounds which are responsible for scavenging the free radicals and reducing power of the lotus extracts, strong metal chelators especially for the ferrous ions would likely be present in the ten lotus extracts.