Supercritical Carbon Dioxide Extraction of the Volatiles from the Peel of Japanese Citrus Fruits

Journal of Essential Oil Research: JEOR, Jan/Feb 2007 by Roy, Bhupesh C, Hoshino, Munehiro, Ueno, Hiro, Sasaki, Mitsuru, Goto, Motonobu

Abstract

Citrus volatiles were extracted from the peel of yuzu and kabosu (Citrus junos Sieb. ex Tanaka and Citrus sphaerocarpa Hort. ex Tanaka) which are typical citrus fruits in Japan, with supercritical carbon dioxide in a semi-continuous flow extractor. The peel of citrus fruits containing oil, water, and solid cellulose materials was used as a feed material in this work. Extraction was carried out at 313-333 K and 10-30 MPa with supercritical CO2 in order to optimize the extraction conditions and to compare the compositions of extracted oils from these fruits. The volatiles were also extracted using hexane (as the solvent) at atmospheric conditions to compare the efficiency of supercritical CO2 extraction. Among the studied conditions, the highest extraction efficiency was observed for both yuzu and kabosu peel at a pressure of 10 MPa and temperature of 333 K that was about 91% and 85%, respectively. The compositions of extracts differed qualitatively and quantitatively from each other in such a way that the monoterpene (C^sub 10^H^sub 16^) content obtained was 89.9% in yuzu and 92.5% in kabosu; limonene was the major compound from both fruits. Oxygenated compounds in these oils represented 7.7%, and 4.6% in yuzu and kabosu peel, respectively.

Key Word Index

Citrus junos, Citrus sphaerocarpa, Rutaceae, supercritical CO2 extraction, limonene, myrcene, extraction efficiency.

Introduction

The peels of citrus fruits contain citrus oils, water and solid cellulose materials. Citrus oils are widely used in the food, beverage, pharmaceutical, perfume and cosmetic industries. It is usually extracted from citrus fruits by cold-pressing or steam distillation. The cold pressing process is not suitable for Japanese citrus fruits because of a very low content of oil. Citrus oils from Colombian lemon and orange have been isolated by steam distillation and/or cold pressing and the compositions also have been compared at different stages of maturity of the fruits by Tirado et al. (1). The conventional production methods of oils such as steam distillation or solvent extraction can lead to the degradation of heat sensitive compounds and partial hydrolysis of water sensitive compounds. Supercritical fluid extraction is an effective alternative process to these conventional methods.

Supercritical fluid extraction has received increasing attention in a variety of fields due to the following factors: (i) supercritical fluids provide satisfactorily solubility and improved mass transfer rates; (ii) operation can be manipulated by changing the pressure or temperature. Carbon dioxide is mostly used as supercritical fluid for the extraction of citrus volatiles from natural materials because of its low critical temperature that prevents the thermal degradation of volatile components of the citrus peel, its residue limits approach zero, and its odorless and colorless properties. It is also non-toxic and is generally accepted as a harmless ingredient of foods and beverages, and easily available. The physical properties of carbon dioxide that make it widely used in extraction processes are low surface tension and viscosity, and high diffusivity. The diffusivity of supercritical fluid is one to two orders of magnitude than those of other liquids, which permits rapid mass transfer, resulting in a larger extraction rate than that obtained by conventional methods.

The extraction of flavoring materials from fruit juice and from many other natural products with supercritical carbon dioxide has been carried out by a number of workers as Shutlz et al. (2), Caragay et al. (3) and Moyler et al. (4). Meyer-Warnod (5) reported that this method showed a great potential in replacing conventional methods such as liquid solvent extraction and steam distillation. The volatiles from peppermint leaves, and the cuticular waxes have been extracted from peppermint plants using supercritical carbon dioxide by Goto et al. (6), and Roy et al. (7), respectively.

The characteristics of citrus oil have been reported by Kondo et al. (8). The citrus oil generally contains over 90% monoterpenes, about 5% oxygenated compounds, and less than 1% non volatiles such as wax and pigments. Limonene is a principal (about 70%) compound of monoterpenes but does not contribute much to the flavor or fragrance of the oil, but can be used as a good solvent for polystyrol in chemical recycling process, reported by Kondo et al. (9). Furthermore, the non-volatiles such as wax and pigments are highly viscous and show phototoxic activity that produces the turbidity in the oil. The characteristic flavor of citrus oil is provided by the oxygenated terpenes that mainly consist of alcohols, aldehydes, and esters such as linalool, citral (neral and geranial), and linalyl acetate. Considering these properties of terpenes, a new technique for the fractionation of citrus oil was developed by Sato et al. (10), and oxygenated terpenes have been separated from essential oils with the combination of supercritical carbon dioxide and vacuum distillation by Fang et al. (11).