Chemical Studies on the Quality of Coffee

Part II. New method for determination of chlorogenic acids in roast coffee

Abstract

A new method for determination of unchanged chlorogenic acids in roast coffee was established based on the specific green coloration of caffeic acid esters in ammonia alkalinity.
A. Two ml of 1M NH₄Cl-NH₄OH buffer solution (pH 9.1) was added to 10ml of the extract. After shaking for 7 hours at 30°, the optical density at 620nm was measured.
B. The optical density at 620nm on the mixture of 2ml of 0.5M Na₂HPO₄-Na₂CO₃ buffer solution (pH 9.1) and 10ml of the extract was measured by the same procedure.
The difference of absorption between A and B was in linear with concentration of chlorogenic acid to 70mg/100ml. But the absorption with isochlorogenic acid was twice as much as chlorogenic acid, resulting that the content of chlorogenic acids in roast coffee was equal to 0.72 times the content calculated as chlorogenic acid.
Percentages of unchanged chlorogenic acids in the various roast coffee determined by this method were as follows; Medium roast, av. 3.66, French roast, 2.75, Italian roast, 0.16.