Optimizing CO2-expanded Hexane for Enhanced Yield and Antioxidant Activity of Essential Oils from Citrus reticulata

Abstract

Wide range applications of citrus essential oil (EO) and environmental issues resulting from citrus processing industries render in the evolution of extraction techniques. The efficacy of the CO₂-expanded hexane (CXH) extraction technique on mandarin orange EO, D-limonene, and total phenolic compounds (TPC) was evaluated and compared with conventional methods; hexane extraction and hydro-distillation. Moreover, the correlation of EO components with antioxidant activity was studied. It was revealed that CXH had better EO and D-limonene yields than conventional methods. The CXH optimal extraction conditions of 25 °C, 6.5 MPa, and 0.70 CO₂ mole fraction offered 0.155 g-EO/g-dry peel and 51% D-limonene in EO. Less total phenolic compounds and phospholipids were extracted using CXH compared to hexane extraction. However, a similar inhibition capability (12–54%) of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical was obtained regardless of the extraction technique. In addition, DPPH scavenging activity depended on the TPC composition. The results suggest the potential application of CXH for citrus waste valorization.