Abstract
Enhancing the extraction rate is one of the key objectives in optimization of extraction of substances from biogenic raw materials. Ultra-fine grinding of plant raw materials (to achieve particle size less than 300 µm) is a very appealing method for increasing the extraction rate using relatively simple equipment. However, this approach often fails to yield the desired result. This study focuses on the kinetics of melanin extraction from two types of raw materials: fungus Ganoderma applanatum and buckwheat husk. Particle size is shown to be just one of the key factors. The degree of order of plant-based feedstock strongly affects the intraparticle diffusion constants and can be a parameter controlling the diffusion rate. It has been shown that there exist optimal degrees of disorder of the crystal structure of plant raw materials, which have a dome-shaped dependence pattern and allow one to increase the diffusion coefficient by several dozen times. The kinetics of melanin extraction was described by some kinetic models that include the first order equation, the Baker and Lonsdale model, the Axelrud equation, and the Ritger–Peppas model.
Highlights
Extraction of plant raw material is one of the basic processes used for obtaining organic matter
A common trend is observed for both groups of study objects: reduction of particle size is accompanied by a decrease in crystallinity index
The kinetics of melanin extraction from Ganoderma applanatum and buckwheat husk is adequately fitted by the extraction equations based on Fickian diffusion with allowance for the particle shape-factor
Summary
Extraction of plant raw material is one of the basic processes used for obtaining organic matter. The extraction yield can be increased by subjecting the liquid phase to treatment with temperature, ultrasound, microwave radiation, oscillating pressure, etc., during extraction [2]. Another approach to increasing extraction yield and rate that is important is to perform preliminary preparation of the solid phase, which often involves mechanical comminution. The general reasoning is as follows: particle size reduction is expected to raise the extraction rate due to increased surface area and fewer pathways of diffusion of the extractable matter inside raw material particles
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