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Influence of vacuum distillation parameters on the chemical composition of a five-fold sweet orange oil (Citrus sinensis Osbeck)

Journal of Essential Oil Research: JEOR, Nov/Dec 2003 by Lopes, Daise, Raga, Augusto C, Stuart, Giane R, de Oliveira, Jose V

Abstract

The chemical composition of a five-told sweet orange oil, Pera variety, prepared by vacuum distillation process has been investigated. The experimental conditions applied were: temperature of 80°C, from 10-30 mbar and with a reflux ratio in the range of 0.25-0.75. Forty-four components were identified by GC/MS, representing greater than 99% of total volatiles.

Key Word Index

Citrus sinensis, Rutaceae, five-fold sweet orange oil, essential oil composition, vacuum distillation.

Introduction

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Cold pressed citrus oils are mixtures of volatile components such as terpene hydrocarbons, oxygenated compounds and nonvolatile compounds such as pigments and waxes. Despite the high content, the terpene hydrocarbons do not contribute much to the flavor and fragrance of the oil. Since they are unstable to heat and light, and decrease the solubility of the whole oil in alcohol, they must be removed to stabilize the final product. The oxygenated fraction, on the other hand, provides much of the characteristic flavor strength of citrus oils and consists mainly of alcohols, aldehydes, ketones and esters (1).

Terpene hydrocarbons are conventionally removed by vacuum distillation, solvent extraction and adsorption chromatography, which involve steps applying higher temperatures resulting in thermal degradation of essential oils (2,3). To minimize the thermal degradation, other technologies have been investigated e.g. the distillation using a thin film evaporator (4), a Chromatographie technique using "poroplast" (Teflon, P.T.F.E., polytetrafluorethylene) packed columns (5), membrane process (6,7) and the use of CO, as an extracting solvent in desorption and in countercurrent modes (8-10). Though new fractionation techniques have been reported in the literature, the deterpenation of citrus oils is still being conducted in several industries by means of vacuum distillation (11).

Indeed, it has been difficult to indicate general and definite limits for the physico-chemical properties of folded oils due to the fact that these properties depend upon the degree of concentration, operation conditions, technology applied and also upon the relative proportions of oxygenated constituents originally present (12). Economic factors, flavor concentration and oil stability generally determine the extent of folding by the trade (1).

One of the most widely used concentrated citrus oils is a five-fold concentrate, which is concentrated to 1/5 of its original weight. The utilization of vacuum distillation to produce deterpenated citrus oils has been known for a long time, however, only a little information about quantitative composition of orange oil concentrates produced by this process is available in the open literature, as reported by Lawrence (13,14).

Vora et al. (15) have concentrated Valencia and Midseason orange oil by vacuum distillation upon 10 and 25 fold at 57°-62°C and 10 mm Hg. The compositions of both fractions were compared with the original cold pressed oil. Concentrates were analyzed by gas chromatography and the compounds were identified by mass spectrometry. Their results showed that different compositions thus influencing the color and flavor characteristics of the oil may be, as expected, obtained from different raw materials.

Lifshitz et al. (16) have concentrated orange oil by vacuum distillation upon 10-fold at 45°-50°C and 3-5 mm Hg. Analytical examination of various steps in the process of concentration showed that the specific gravity, refractive index, optical rotation, aldehyde and ester values changed linearly with the concentration.

Pino et al. (17) have verified that the content of total aldehydes and alcohols (measured by GC) increased linearly with the concentration of cold pressed Valencia orange oil from six to 10-fold. The concentration was achieved at 58°-64°C and 10 mm Hg.

The main objective of this work was to present the results of our recent findings concerning five-fold orange oils obtained by vacuum distillation process. The qualitative and quantitative composition of these concentrates were defined in order to evaluate the influence of the studied variables on the characteristics of these products (18).

Experimental

Vacuum, distillation procedures: Sweet orange oil (Citrus sinensis Osbeck) was kindly supplied by Citrosuco S.A, Matao, SP, Brazil. The oil was obtained by FMC in-line juice extractors during orange juice extraction. A crude oil emulsion was obtained from the juice extractor being afterwards centrifuged in order to separate the oil from the water and winterized to remove paraffin waxes.

Five-fold orange oils were prepared in an automatic vacuum distillation column (1.30 m height, 15 mm i.d.) packed with Raschig rings (Karl Kolb Scientific Supplier-Vakuumat-X). The equipment was operated in a batch mode in the temperature of 80°C, from 10-30 mbar and with a reflux ratio (RR) in the range of 0.25-0.75, as presented in Table I.

Orange oil sample (200 mL) was fed into the column bottom. The temperature and pressure were adjusted to the desired values and the operation started after 1 h of total reflux to allow the stabilization of the whole equipment. Then, a preestablished reflux ratio was set and samples were collected from the top (distillate) and bottom (concentrate). Taking into account commercial aspects, an experimental planning was carried out to obtain a five-fold orange oil (based on the mass of the original crude oil). Duplicate runs were accomplished leading to a maximum average deviation of 0.33 fold. Experimental results were evaluated by gas chromatography. Concentration factor (CF) has been defined as the relative percent of oxygenates in the concentrated oil and in the raw oil.

Influence of vacuum distillation parameters on the chemical composition of a five-fold sweet orange oil (Citrus sinensis Osbeck)

Journal of Essential Oil Research: JEOR, Nov/Dec 2003 by Lopes, Daise, Raga, Augusto C, Stuart, Giane R, de Oliveira, Jose V

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