Abstract:

Different types of cooking water were used to investigate the effects of pH value and metal ions (Ca2+, Mg2+,
Zn2+, Al3+, and Fe2+) on the pH, color and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity of mung bean
clear soup (MBCS). The results showed that the color of MBCS cooked with tap water turned from green to red and the
DPPH radical scavenging capacity dropped markedly with increasing pH of cooking water, whereas the MBCS cooked with
deionized water changed little. When cooking the soup with solutions of different metal ions, its color and DPPH radical
scavenging capacity were changed differently. Mg2+ at 5 mg/L increased its yellow color whereas 50 mg/L Al3+ increased
its green color and 5 mg/L Fe2+ turned its color to red. In addition, both Zn2+ and Fe2+ at different concentrations decreased
the DPPH radical scavenging capacity of MBCS while Mg2+ at 50 mg/L and 500 mg/L increased its anti-oxidative activity
significantly.

Key words: mung bean clear soup, pH value, metal ions, color, DPPH radical scavenging capacity