versão impressa ISSN 0104-6632
Braz. J. Chem. Eng. v.17 n.4-7 São Paulo dez. 2000
RECOVERY OF AROMA COMPOUNDS FROM ORANGE ESSENTIAL OIL
E. Haypek 1, L.H.M Silva 1, E.Batista 1, D. S. Marques2,
M.A.A. Meireles 1 and A.J.A.Meirelles 1,*
1 LASEFI, School of Food Engineering, State University of Campinas (UNICAMP),
CP 6121, CEP 13083-970, Campinas - SP, Brazil.
2 CUTRALE , Brazilian Industry of Concentrated Orange Juice, Araraquara, SP, Brazil
(Received: December 3, 1999 ; Accepted: April 6, 2000)
Abstract - The objective of this work was to study the recovery of aroma compounds present in the orange essential oil using experimental data from CUTRALE (a Brazilian Industry of Concentrated Orange Juice). The intention was to reproduce the industrial unit and afterwards to optimize the recovery of aroma compounds from orange essential oil by liquid-liquid extraction. The orange oil deterpenation was simulated using the commercial software PRO/II 4.0 version 1.0. The UNIFAC model was chosen for the calculation of the activity coefficients.
Keywords: UNIFAC, orange oil, simulation, deterpenation.
Orange juice has a delicate and soft flavor which is easily modified by its processing. Concentrated frozen orange juice has been traditionally produced by concentration of the cold-pressed orange juice in multistage vacuum evaporators. During the concentration several naturally occurring aroma compounds are removed. This mixture of low molecular substances such as aldehydes, alcohols, terpenes, and so on are recovered in the essence recovery system. The recovery system consists of a fractionation column and a series of condensers and gas washers, from which two products are obtained: the oil phase (oil-soluble) and aqueous phase (water-soluble). These two mixtures are added back to the frozen concentrated juice at different proportions to impart some of the fresh orange flavor lost during processing.
Aroma or aqueous phase essence is also referred to as natural orange aroma. Typical orange aroma contains 13% ethanol. Some of the most important flavor components of orange aroma include acetaldehyde, ethyl acetate, acetal and ethyl butyrate (Sánchez et al. 1994).
Essential oil or oil phase essence is more susceptible to oxidation when compared to cold pressed orange oil due to absence of antioxidants. Therefore, an extra care in storage and handling should be taken using this product (Johnson and Vora, 1983). The major compound of orange essential oil is d-limonene and the major sesquiterpene is valencene. The orange essential oil presents a predominant proportion of terpenes (>90%). Besides the fact that these hydrocarbons contribute to a lesser extension to the aroma profile of the essential oil compared to the oxygenated compounds, the unsaturated terpenes present another inconvenient. As they are chemically unstable, they are inclined to structural regrouping in contact with air, light, and water. All these modified compounds are undesirable, because they can impart an off flavor when used to aromatize other products. This fact explains the concern with the removing of the terpenes from the orange oil. This process known as deterpenation can be performed in various forms, such as: distillation, liquid-liquid extraction, adsorption and extraction with CO2 (Owusu-Yam et al. 1986; Moyler and Stephens, 1992; Meireles and Nikolov, 1994; Dugo et al., 1995; Simões et al., 1995).
The aim of this work is to simulate the deterpenation of orange essential oil using the concentrated aqueous essence as solvent. The initial concentrations of the essential oil and aqueous essence used in the simulation were obtained by chromatographic analysis of samples taken from Cutrale citrus processing plant (Araraquara, São Paulo, Brazil).
MATERIAL AND METHODS
Gas Chromatographic Analysis
Commercial aqueous orange essence and essential oil were obtained from Cutrale citrus processing plant (Araraquara, São Paulo, Brazil) and analysed by gas chromatography. Gas chromatography data were obtained with a Varian Star 3400 instrument equipped with a FID and a 50-m (0,25 mm i.d.) dimethyl polysiloxane capillary column. Hydrogen was used as carrier gas and the essence samples were 0.5 mL. In the case of the essential oil samples the column temperature was held at 60oC for 13 minutes, then programmed to 160oC at 3oC/min and held there for 10 min, and finally programmed at 3oC/min to 240oC and held there for 2 min. In the case of the aqueous essence samples the column temperature was held at 35oC for 12 min, then programmed at 3oC/min to 240oC and held there for 10 min.
Process simulation can be performed by using commercial software like Pro/II, Aspen, Hysim. In comparison to software developed for simulating specific unit operations (Meirelles et al., 1992; Batista and Meirelles, 1997; Batista et al., 1998), commercial software have many advantages: for instance, they make possible to simulate simultaneously several unit operations and also have a comprehensive data bank for calculating and estimating physicochemical properties. In this work the software Pro/II 4.0, version 1.0 (SIMSCI - Simulation Science Inc., 1994) was used for simulating distillation and liquid-liquid extraction columns involved in the recovery of aroma compounds from the orange essential oil. The first step was the simulation of the industrial distillation column used by Cutrale for recovering the compounds from the aqueous stream produced during the evaporation process. This stream produced as byproduct during the concentration of orange juice is a dilute aqueous solution containing alcohols, aldehydes, esters, acetals, and terpene and sesquiterpene hydrocarbons. Its concentration in distillation recovery units produces two top products that can be mechanically separated: the limonene-rich fraction, named essential oil, and the aqueous essence that is predominantly composed by water and ethanol. The industrial unit used by Cutrale has following characteristics: 7.2 m high, diameter = 35.5 cm and 30 stages. The aqueous solution from the evaporation process is fed as a vapour stream into the 16 th stage of the column, counted from the top, and at a pressure of 4.41 x 104 Pa. The column pressure is 3.14 x 104 Pa. The mass flow rates and their temperatures are given in Table 1 (Cutrale, 1996). Such constructive and operational conditions were used in the simulation.
The feed concentration was obtained by mass balance for each compound. From the 29 compounds detected in essential oil or/and aqueous essence, the 15 components with higher concentration were considered in the simulation.
The essential oil and aqueous essence streams calculated by the commercial software were then used as feed streams for simulating the unit for recovery of aroma compounds from the essential oil fraction, according to the flowsheet shown in Figure 1. In this figure the first column is the industrial distillation column for obtaining the aqueous essence and the essential oil fraction, the second one is a distillation column for concentrating the aqueous essence, the third and fourth columns are extraction units for recovering the aroma compounds from essential oil. The concentrated aqueous essence was used as solvent for liquid-liquid extraction.
The reflux rate and the number of stages for the second column were varied in order to obtain a minimum loss of aroma compounds in the bottom stream and in order to achieve the desired ethanol concentration in the distillate. Concerning the extraction units, the number of stages, the ratio of essential oil to solvent (concentrated aqueous essence) streams and the ethanol concentration in the solvent were varied. Table 2 gives the range of operational and constructive variables studied in the present work.
The UNIFAC (UNIquac Functional-group Activity Coefficient) method was used in this work for predicting the phase equilibrium. Based on the group contribution concept, the UNIFAC method (Fredenslund et al., 1975) makes it possible to calculate the phase equilibrium of complex mixtures containing a great variety of organic compounds, like the orange essential oil and aqueous essence used in the present work. The software PRO II/4.0 has a comprehensive and up-to-date data bank for the UNIFAC model.
Information concerning the stream enthalpies is also necessary, particularly for simulation of the distillation columns. Data for liquid enthalpy and latent heat of vaporization as a function of temperature are available in the software's library for many compounds. In our case such data are available for acetaldehyde, water, decanal, dodecanal, ethanol, limonene, methanol, nonanal, octanal and pinene, which represent 99.89 mass % of the feed stream used in the simulations. The liquid and vapor enthalpies are calculated from the pure component data considering an ideal behavior for both phases.
RESULTS AND DISCUSSION
Gas Chromatographic Analysis
The results of the chromatographic analysis are given in Table 3: 29 compounds were identified, 21 in the orange essential oil and 19 in the aqueous essence. Some components, like ethylbutyrate, octanal, decanal and neral, are of special importance for the orange flavor (Ahmed et al., 1978). Concerning such compounds, some quantitative differences were observed between our data and other results reported in the literature: the concentrations of decanal and octanal were higher in our samples, while the concentrations of neral and ethylbutyrate were lower than the levels reported by Moshonas and Shaw (1990). These differences were quantitative. The same compounds were detected in samples from Florida and from Brazil by Moshonas and Shaw (1990). As can be seen in the work of Moshonas and Shaw (1990), such quantitative differences should be expected between samples of different sources. Furthermore, some qualitative differences can also be reported. In our samples, 1-butanol, 1-penten-3-ol, 1-propanol and carvone were not detected, while in Moshonas and Shaws samples a-sinensal, b-sinensal, b-cariofilene and Nootkatone were not identified.
The simulation results for the first column, used in the recovery of the aroma compounds from the aqueous stream produced during orange juice evaporation, are shown in Table 4. Water plus fifteen (15) compounds detected by the chromatographic analysis were considered in the simulation. As can be seen in Table 4, for the majority of the substances the experimental and calculated concentrations are close to each other. This indicates that the process simulation and the phase equilibrium prediction reproduced well the behavior observed in the industrial equipment (Cutrale). The major exceptions are decanal, limonene, myrcene and nonanal in the aqueous essence and ethanol in the essential oil. This probably reflects the fact that the UNIFAC model does not give good results for compounds present in very low concentrations, as is the case for such components. Despite this fact, the results indicate that the use of the commercial software can produce satisfactory results, at least concerning to the qualitative influence of the operational and constructive variables studied in the present work.
To evaluate the proposed system for the recovery of aroma compounds from the essential oil, the following two variables were calculated using the simulation results: i) the ratio of the mass concentration of aroma compounds to the mass concentration of terpene compounds in the extract stream, named aromas/terpenes ratio, and ii) the recovery of the aroma compounds. This last variable takes into account how much of the aroma compounds fed to the extraction columns was recovered in the extract stream. The aroma compounds include acetaldehyde, decanal, dodecanal, geranial, linalool, neral, nonanal and octanal; the terpene compounds are limonene, myrcene, pinene, sabinene and valencene.
Figure 2 and 3 show the influence of the solvent concentration on the aromas/terpenes ratio and on the aroma recovery for the extraction columns 3 and 4, respectively. As can be seen in those figures the aromas/terpenes ratio decreases as the ethanol concentration in solvent increases, indicating that the solvent selectivity decreases and higher quantities of terpenes are extracted together with the aroma compounds. But the recovery of the aroma compounds increases as the ethanol concentration in solvent increases, reducing the loss of aromas in the refined stream.
The effect of the solvent/essential oil ratio is represented in Figures 4 and 5 for the extraction columns 3 and 4, respectively. The recovery of aromas exhibits a significant increase as function of the solvent/essential oil ratio, suggesting the use of high values for this operational variable. At least in the column 3 (the first extraction column), the aromas/terpenes ratio does not change much as a function of the solvent/essential oil ratio. In the case of this column a high value for the solvent/essential oil ratio is the best choice. For the extraction column 4 the aromas/terpenes ratio is more sensitive to the solvent/essential oil ratio, so that either a higher recovery or a higher aromas/terpenes ratio should be chosen.
Table 5 shows a typical result for the extraction column. As can be seen, most aroma compounds are transferred from the essential oil stream to the extract, but unfortunately the terpene concentration in the extract are not very low.
The results show that in most cases the process simulation and the phase equilibrium prediction reproduce well the experimental concentration data obtained in the Cutrale industrial processing plant. Major exceptions are those compounds present in very low concentrations, such as decanal and nonanal in the aqueous essence. For these compounds the deviations are expressive, probably due to the fact that the UNIFAC model does not predict well the phase equilibrium for compounds with very low concentration. Concerning the recovery of the aroma compounds from the essential oil stream, the simulation results also indicate that liquid-liquid extraction makes it possible to recover part of these compounds. But unfortunately high levels of recovery can be obtained only when the terpene concentration in the extract is not very low.
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*To whom correspondence should be addressed