Comparative kinetic analysis of isothermal extraction of caffeine from guarana seed under conventional and microwave heating

The kinetics of the isothermal extraction of caffeine from the guarana seed powder with water under conventional (CH) and microwave heating (MWH) were investigated. By applying the isoconversional method, it was established that the kinetics of the caffeine extraction under CH and also under MWH is an elementary kinetic process. The model fitting method was used to determine the kinetics model of caffeine extraction. It was found that the kinetics of the caffeine extraction for both heating modes can be described by the Jander's equation. The rate of the extraction of caffeine under MWH is similar to 2 times higher than under CH. The values of kinetics parameters (Ea and lnA) of the extraction process under MWH are lower than for CH. The established influence of MWH on the kinetics of caffeine extraction is explained with a specific activation mechanism of water molecules and with an increase in the energy of the ground vibration level of resonant oscillator of N-3-CH3 band of caffeine molecule (v=317 cm(-1)) which is caused by the absorption of microwave energy. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.