Mass Transfer During Vanilla Pods Solid Liquid Extraction: Effect of Extraction Method

Abstract

In this paper, experimental kinetics of vanilla pods’ solid–liquid extraction were obtained by three different methods: with agitation, without agitation, and microwave-assisted (MAE) without agitation. The extraction kinetics of aroma compounds (vanillin, p-hydroxybenzaldehyde, and p-hydroxybenzoic acid) was measured in vanilla pods (refined) and extracts by high-performance liquid chromatography. Additionally, the equilibrium distribution of aroma compounds between phases and the retained solution by refined pods were experimentally evaluated. A mechanistic model of two simultaneous algebraic equations was fitted to experimental data in order to estimate the aroma compound diffusivities inside the pods and mass transfer coefficients in the extract. The diffusivities in vanilla pods at 50 °C were 4.31 × 10−11, 2.93 × 10−11, and 3.50 × 10−11 m2 s−1 for vanillin, p-hydroxybenzaldehyde, and p-hydroxybenzoic acid, respectively. External mass transfer coefficients were in the order of 1.0 × 10−4 m s−1 for forced convection extraction and MAE and 3.33 × 10−7 m s−1 for natural convection extraction.