Optimization and Characterization of Orange Peel Oil Via Microwave-Assisted Aqueous Extraction

Aims: This study aimed to develop a green, sustainable, and efficient method for extracting high-quality oil from orange peel using Microwave-Assisted Aqueous Extraction (MWAE) by targeting the disruption of orange peel cell walls. Study Design: An experimental design combining one-factor-at-a-time (OFAT) optimization and Response Surface Methodology (RSM) using a Central Composite Design-Face Centered (CCD-FCC) approach was followed. Place and Duration of Study: Department of Chemical Engineering, Institute of Chemical Technology, Mumbai, India, from 2012 to 2017. Methodology: Orange peels were subjected to microwave (MW) pretreatment under varying conditions of power (240–600 W), time (0–5 minutes), and particle size (0.01–5 mm). Aqueous extraction was subsequently performed at optimized temperatures (60–100°C) and agitation speeds (500–1500 rpm). The extracted oil was characterized for antioxidant activity, physical properties, and chemical composition. Process engineering aspects such as diffusion coefficients, activation energy, eddy drop size, extraction kinetics, and energy efficiency were analyzed. Scanning Electron Microscopy (SEM) was used to study peel morphology pre- and post-treatment. Results: Optimized conditions (400 W MW pretreatment for 4 minutes, peel particle size of 0.16 mm, aqueous extraction at 70°C and 500 rpm) yielded 0.84% w/w orange peel oil in significantly reduced time and energy compared to conventional methods. SEM images confirmed cell wall rupture after MWAE. The extracted oil exhibited good antioxidant activity, typical bright orange color (CIELAB values: L*=60.1, a*=+33.0, b*=+64.2), and a composition rich in terpenes and flavonoids. The MWAE method required 5.78 times less energy compared to traditional steam distillation and resulted in lower CO₂ emissions. Conclusion: MWAE is a promising, sustainable, and efficient alternative to conventional orange peel oil extraction methods, offering reduced extraction time, moderate energy requirements, solvent-free operation, and preservation of oil quality.