Time Dependence of Caffeine in Coffee using Optical Method
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Date
2006-06
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Addis Ababa University
Abstract
In this project optical properties of pure caffeine, i.e., time dependency of caffeine in coffee
powder and solution kept under different conditions and temperatures were inyestigated. FOI'
the pure caffeine molar decadic absorption coefficient and transitional dipole moment were
computed and found to be (1095 ± 37) m2 mol-I and (I \.3 ± 0.2).\0-30 C m. Respectively in
all the systems and temperatures caffeine in coffee was investigated , a decrease in caffeine
concentration as a function of time was observed. For the solution both in closed and open
storage conditions the pseudo zero order kinetics was observed. The rate constant of
decomposition k" = 2.41667xI0-5 mol m-3 hr-I for closed system and kJ = 5.50417xI0-5
mol m-3hr-1 for open system were determined. The linear regression coefficient values were
above R = 0.99 in both cases. The half-life time of caffeine were 1177 hI' and 517 hI' for closed
and open systems, respectively. In the contrary, for open powder system the kinetics obeyed the
expected first order rate expression. For open powder coffee the monoexponential fits resulted
in rate constant of decay at room temperature (23°C) and in ambient atmosphere is computed
to be k" = 2.4xI0-4 111.-1 and half-life time of caffeine is 289 hI', which implies again chemical
reaction during half-life was fastest for powder form storage than other conditions. Reaction
rate was faster, as expected, for storage at 23°C than 8°C
Key words: Caffeine, Coffee, Spectrophotometer, Pseudo Zero-Order, Monoexponential fit
Description
Keywords
Caffeine, Coffee, Spectrophotometer, Pseudo Zero-Order, Monoexponential fit