Detection of Copper Ions in Liquid Foods and
Beverages Based on an Enzymatic Method
JING-IONG YANG1*, DONG-BOR YEH2, JEN-MIN KUO1*, BONNIE SUN PAN3,
GUO-CHI LEE4, YA-HUI LIU1 AND Ying-Jang LAI5
1. Department of Seafood Science, National Kaohsiung Marine University, Kaohsiung, Taiwan, R.O.C.
2. Department of Biotechnology, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan, R.O.C.
3. Department of Food Science, National Taiwan Ocean University, Keelung, Taiwan, R.O.C.
4. Department of Science and Technology, Council of Agriculture, Taipei City, Taiwan, R.O.C.
5. Department of Food Science, National Quemoy University, Kinmen, Taiwan, R.O.C.
(Received: April 8, 2011; Accepted: September 6, 2011)
ABSTRACT
An economic, simple and sensitive enzymatic method for the determination of copper in aqueous samples was proposed in this study. By removal of copper, superoxide dismutase (SOD) becomes apoenzyme SOD (apo-SOD) that has no SOD activity. The amount of copper added can be estimated by the recovery of SOD activity from reconstituted apo-SOD. The concentration of copper in an aqueous sample can thus be determined. A linear relationship (R2 = 0.998) between the concentrations of copper, ranging from 20 to 80 ppb, and the recovered SOD activities was observed. The detection limit for copper in the proposed assay was 20 ppb. Moreover, interfering effects of some common metals on the recovery of SOD activity was evaluated. It showed that the concentrations of these metals less than 45 μg/mL exhibited no interference in the assay. In addition, data obtained from this assay were very close to those estimated by inductively-coupled plasma atomic emission spectrometry (ICP-AES). This enzymatic method can be adapted as a routine assay for the determination of copper in aqueous samples such as beverages, drinking water and liquid foods. The assay can be applied for large number of samples (about 96 samples per hour) on an ELISA microplate reader.
Key words: enzymatic method, superoxide dismutase, apoenzyme, copper ion, ELSIA microplate reader