Kinetic modeling of phenolic compounds extraction from nutshells: influence of particle size, temperature and solvent ratio

Abstract

This paper studies the effects of particle size, temperature and ethanol–water solvent ratio on the extraction of total phenolic compounds (TPC) from peanut, coconut, and macadamia nutshells. Using an I-optimal design, the maximum TPC extraction obtained from the shells ranged from 63.5 ± 1.6 to 76.2 ± 3.1 mg gallic acid equivalent (GAE) per 100 g dry weight (dw) of nutshell. Next, a response surface model (RSM) was developed to describe the relationship between the process parameters and the extracted TPC concentration, in order to predict the optimal extraction conditions. For all of the examined biomasses, the optimal conditions for extraction were predicted at a particle size of 1 mm, temperature of 75 °C and ethanol/water mixture of 54, 53 and 65% ethanol, for peanut, coconut and macadamia nutshells respectively. Particle size seems to be the most important parameter, while temperature appears to be of lesser importance. Besides, the extraction kinetics were assessed by fitting kinetic models on the experimental data. The combined second-order diffusional model provided the best goodness of fit. This model revealed that, at the boundary layer, the effect of washing mechanism of extraction is more important than extraction due to diffusion kinetics. This study provides an understanding of the mass transfer mechanism involved in the TPC extraction process from nutshells, which yields valuable insights that could facilitate the industrial biorefinery of nutshells. Graphical Abstract