Diffusion Coefficients Of Caffeine Research Articles

High intensity ultrasound assisted decaffeination process of coffee beans in aqueous medium.

The purpose of this study was to determine the influence of ultrasound intensity, pulse and temperature on extraction of caffeine, from Arabica coffee beans using water as solvent, and ultrasound frequency of 24kHz. A central composite design was used, using ultrasound intensity (31.5-105Wcm-2), pulse (0.30-1) and extraction temperature of the extraction (30-60°C) as independent factor. The caffeine recovery and caffeine diffusion coefficient were response variables. The ultrasound intensity and extraction temperature significantly influenced the caffeine recovery rate and the diffusion coefficient of caffeine. Activation energy of 48.95kJmol-1 for the caffeine diffusion coefficient in ultrasound assisted extraction was observed. The best results were obtained at 68.25-105Wcm-2 ultrasound intensity and 60°C temperature, corresponding to caffeine recovery of 58.4-69.4% and diffusion coefficient of 8.92-10.57 × 10-11m2s-1. The pulse effect was not significant in the range of the studied variables.

Kinetics of tea infusion: the effect of the manufacturing process on the rate of extraction of caffeine

The temperature effect on the rate of infusion of caffeine from South African black tea has been determined over a temperature range with the help of high performance liquid chromatography (HPLC). The activation energy was found to be 40.3 kJ mol −1 which is similar to the reports for other teas. The leaf size used was 1.40–2.00 mm. The rate constant at 80°C was determined to be 0.99 min −1 using a steady state model ( Spiro and Jago, 1982). This value is slightly larger than the expected value for tea with similar particle size. Using the rate constants, diffusion coefficients of caffeine over a temperature range have been calculated. These have been compared with the corresponding values of caffeine in water at similar temperatures giving hindrance factors of 86 to 54 over the temperature range. These results indicate that the diffusion of caffeine through the leaf matrix is a greatly hindered process. A detailed comparison of kinetic and equilibrium data reported in the literature has been carried out between different teas manufactured through different processes. It is clear that the manufacturing method has a direct influence on the infusion of caffeine from the tea leaf.

Kinetics and equilibria of tea infusion: Part 9. The rates and temperature coefficients of caffeine extraction from green Chun Mee and black Assam Bukial teas

The rates of infusion of caffeine from green Chun Mee tea and from black orthodox Assam Bukial tea, using leaf of size 1.70–2.00 mm, were measured over a range of temperatures. The activation energies were found to be 62 and 40 kJ mol −1, respectively. The diffusion coefficients of caffeine within the tea leaves, calculated from the first-order rate constants at 80°C, were respectively 96 and 132 times smaller than the diffusion coefficient of caffeine in water at 80°C. These results show that diffusion of caffeine through the leaf is a greatly hindered process.

Diffusion phenomena during the decaffeination of coffee beans*

SummaryThe diffusion of caffeine in green coffee beans was investigated at atmospheric pressure using dichlormethane as a solvent.The diffusion coefficient of caffeine was determined as a function of temperature and water content of the beans. the mathematical treatment was based on Fick's second law of diffusion applied to a spherical model.The apparent diffusion coefficients are in the range of 0.2‐1.1. 10−6 cm2 sec−1.

The diffusion coefficient of caffeine through agar gels containing a hyaluronic acid-protein complex. A model system for the study of the permeability of connective tissues.

A hyaluronic acid-protein complex was embedded into agar gel. This gel complex resembles in some respects the physiological situation in connective tissue, but still permits precise physicochemical measurements to be made. The diffusion coefficient of caffeine into and from such gels has been measured as a function of both agar and hyaluronate concentration. The value for the diffusion coefficient of caffeine was also measured by using a Gouy type diffusiometer. From both types of measurement the value for D (Fick) for caffeine when extrapolated to zero caffeine and agar concentrations agreed at (6.79+/-0.01)x10(-6)cm(2).s(-1) at 25 degrees C. Although agar concentration had only a small effect on caffeine diffusion, hyaluronic acid caused a large decrease in caffeine diffusion co-efficient. The presence of the hyaluronic acid-protein complex within the gel tended to oppose gel syneresis, a concentration of 1.7mg/ml abolishing the effect and higher concentrations reversing it. The possible physiological implications of these results are discussed.