Spectrophotometric Investigation of Major Bioactive Compounds of Coffee Beans

Abebe, Belay Gemta (2011) Spectrophotometric Investigation of Major Bioactive Compounds of Coffee Beans. PhD thesis, Addis Ababa University.

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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.

Item Type:	Thesis (PhD)
Subjects:	Q Science > Q Science (General) Q Science > QC Physics Q Science > QK Botany
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	22 Jun 2018 09:07
Last Modified:	22 Jun 2018 09:07
URI:	http://thesisbank.jhia.ac.ke/id/eprint/4236

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