Abstract
The complex formation of zinc with constituents in instant coffee was studied by complexometry, using the modified tetramethyl murexide (TMM) method. The activity of Zn2+ binding was measured in a pH 5.0 hexamine buffer containing 1 m m ZnCl2. Instant coffee to which Zn2+ had been added was separated into three color components by Sephadex G-25 gel permeation chromatography. Among these components, the second was the strongest in Zn2 + binding activity. Instant coffee with Zn2+ was also chromatographed on an anion exchange column of Amberlite IRA-410 (OH−), the zinc adsorbed on the column being eluted with 0.01 m acetic acid. A mixture of zinc chloride and coffee was subjected to paper electrophoresis, and Zn2+ moved toward the anode at pH 8.5 and pH 6.4. Even at pH 3.2, some compounds carrying Zn2+ moved toward the anode. It follows that the ligands in instant coffee to bind Zn2+ are acidic in nature and that their molecular size is less than 5,000.
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