Abstract:
This paper studies the efects 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
ftting kinetic models on the experimental data. The combined second-order difusional model provided the best goodness
of ft. This model revealed that, at the boundary layer, the efect of washing mechanism of extraction is more important than
extraction due to difusion 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 biorefnery of nutshells.
