Spectrophotometric investigation of Major bioactive compounds of coffee Beans
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Date
2011-10
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Addis Ababa University
Abstract
In this research the methods of measuring major bioactive compounds in coffee beans,
their optical transition properties, self-association, hetero-association and thermodynamic
properties were investigated by experimental and computational methods. The implemented
methods for determination the contents of biocactive compounds in coffee beans
are the extraction of caffeine from water solution or liquid-liquid extraction and fitting
Gaussian function to the spectrum of the compound by non-linear curve fitting based on
the Lavenberg-Marquardt algorithm to eliminate the possible interferences. The contents
of caffeine and chlorogenic acids determined by these methods for green coffee beans
are in the ranges of 0.90-1.27 %, 6.05-6.25 % respectively. The optical transition properties
of caffeine, caffeic and 5-caffeoylquinic acids were determined in different solvents by
integrating the absorption coefficients in the wave number regions. The calculated values
of transition dipole moment of caffeine, caffeic and 5-caffeoylquinic acids in water in
their wave number regions are 10.40×10−30, 19×10−30, 20×10−30Cm respectively. The corresponding
oscillator strength are 0.19, 0.49 and 0.56. The concentration dependent selfassociation
of caffeic, 5-caffeoylquinic acids and their hetero-association were analyzed
by dimer model and Benesi-Hildebrand approaches. The thermodynamic parameters, enthalpy,
Gibbs free energy and entropy of dimerzation reactions were calculated from Van’t
Hoff equation. The calculated molar enthalpy change for caffeic and 5-caffeoylquinic acids
of self-association are -63.20, -12.89 kJmol−1 respectively.In addition, the time dependent
Schrodinger equations were solved by semi-classical approach to relate the theoretical expressions
with the experimentally measurable quantities
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Keywords
compounds of coffee Beans