Superheated Water Extraction of Lime Peel: a Comparison with Conventional Methods

Abstract

A comparative study of superheated water extraction (SWE) with several conventional methods was performed on lime (Citrus aurantifolia, Swing) peel. Some superheated water parameters affecting the extraction were studied, such as temperature, dynamic and static time, and flow rate. At 130°C, a static and dynamic time of 5 and 15 min, and a water flow at 1 mL min⁻¹, the main components of aroma compounds were successfully removed and collected in 2 mL hexane. Separation and identification of the components were carried out by using gas chromatography‐flame ionization detection (GC‐FID) and GC‐MS. The extraction technique was compared with steam or water distillation and organic solvent sonication. With the same amount of the extract, the highest oxygenated compound yield was found for SWE, while the less valuable monoterpene yields were maximized when using dichloromethane sonication. The composition of oxygenated components present in the SWE extracts, namely linalool, neral, terpineol, geranial, and geraniol, were 4.94, 19.13, 13.03, 30.00, and 10.48%, respectively. Compared in terms of the equal amount of internal standard, water distillation gave highest efficiency in removal of oxygenated components; however, the method required a long extraction time, making it less attractive. The proposed technique was also modified by adding 10–30% methanol or ethanol into the water. A high percentage of alcohol dramatically increased the extraction efficiency of monoterpene but slightly for the oxygenated components. The modified superheated water extraction, therefore, is considered to be an alternative technique to obtain high extraction efficiencies of low polar organics and possibly at a lower temperature.

Keywords:

• Superheated water
• Subcritical water
• Essential oil
• Lime
• Extraction
• Modification

Acknowledgments

Special thanks are due to the Postgraduate Education and Research Program in Chemistry (PERCH) of Thailand for a scholarship to W. Insuan, and to the Department of Chemistry, Faculty of Science, Kasetsart University, Thailand, for instrumental and facilities support.