Effect of the dried limes (Citrus aurantifolia) on the caffeine kinetic extraction in black tea leaves (kinetic and thermodynamic study)

Abstract

ABSTRACT. The kinetic and thermodynamic parameters were studied for the extraction of caffeine in black tea leaves and tea leaves containing antioxidant dried limes (Citrus aurantifolia). Caffeine is widely used in human consumption and is present in any liquid suitable for drinking except water. However, the health and environmental demerits make it significant to reduce caffeine to much less concentration or decaffeination. Therefore, the effect of the dried antioxidant Citrus aurantifolia on caffeine concentration followed by pseudo-first-order reaction, kinetic parameters (pseudo-first-order rate constant (k), equilibrium absorbance (A∞)), and thermodynamic activation parameters, the activation energy (Ea), change in enthalpy of activation (ΔH#), the change in entropy of activation (ΔS#) and change in activation Gibbs free energy (ΔG#) was calculated at four different temperatures 30, 60, 80, and 100 °C. Using the spectroscopic method the activation energy of the caffeine concentration in free black tea leaves solution (Ea = 13.32 kJmol-1) was higher than the black tea leaves mixed with lime solution (Ea = 9.89 kJmol-1), the higher collision of molecules A-factor (1.96 min-1), and large correlation factor (R2 = 0.95). The thermodynamic activation parameters ΔH#, ΔS#, and ΔG# demonstrate less heat absorption, irreversible, and more spontaneous interaction of lime with caffeine.
 
 KEY WORDS: Caffeine, Tea leaves, Citrus aurantifolia, Thermodynamic parameters, Kinetic
 Bull. Chem. Soc. Ethiop. 2022, 36(3), 697-705. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i3.18