Kinetic, Thermodynamic, Mass Transfer, and Determination of Controlling Steps in Pectin Extraction from Lemon Peel (Citrus limon L. Osbeck)

Abstract

Lemon peel, a byproduct of citrus processing, contains high levels of pectin valued for its functional roles in food and pharmaceutical products. This study investigates pectin extraction using a mechanistic approach based on the Shrinking Core Model (SCM), which describes the progressive reaction of solid particles. The process follows first-order kinetics, with simultaneous extraction and degradation. Optimal conditions were 95 °C, pH 1.8, and 50 minutes, yielding 36% pectin. Key parameters included extraction rate constant k₁ = 0.0562 min⁻¹, degradation rate constant k₂ = 0.0039 min⁻¹, activation energies Eₐ₁ = 31.7 kJ mol⁻¹, Eₐ₂ = –22.9 kJ mol⁻¹, enthalpy change ΔH° = 76.05 kJ mol⁻¹, entropy change ΔS° = 0.23 J mol⁻¹ K⁻¹, and Gibbs free energy ΔG° < 0. The diffusion coefficient ranged from 0.055 to 0.06 × 10⁻¹⁰ m² s⁻¹ for 0.34 mm particles. The extraction process was controlled by both internal diffusion and chemical reactions. This study presents a novel integration of kinetic, mass transfer, and thermodynamic models, offering a predictive framework for optimizing sustainable and energy-efficient pectin production from lemon waste.