- Email: [email protected]
Microencapsulation of sweet orange oil terpeneless using the orifice method
Journal of Food Engineering 110 (2012) 390–394
Contents lists available at SciVerse ScienceDirect
Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Microencapsulation of sweet orange oil terpeneless using the orifice method Kehai Liu, Yanqin Xu, Xichang Wang ⇑ College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China
a r t i c l e
i n f o
Article history: Received 14 July 2011 Received in revised form 17 December 2011 Accepted 25 December 2011 Available online 2 January 2012 Keywords: Sweet orange oil Molecular distillation Microcapsules Orifice method Release kinetics
a b s t r a c t This study used molecular distillation to remove terpenes (mainly limonene) from sweet orange oil and prepared microcapsules encapsulating sweet orange oil terpeneless by the orifice method. The morphology and microstructure of the microcapsules under the optimum conditions by orthogonal experiments were observed and the data of release kinetics were plotted according to the three different kinetic models to further investigate the release mechanism for microcapsules at different oven temperatures. The results showed that the limonene content was extremely low at a roller rate of 500–600 rpm, a feed flow rate of 20–30 mL/min, an evaporating temperature of 120 °C and an operating pressure of 0.025 mbar during molecular distillation. Encapsulation efficiency (EE) of microcapsules with good morphology and microstructure reached 87.34% when the CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material were 2.0%, 2.5% and 5:1 respectively. The release profile of sweet orange oil terpeneless from the microcapsules could be well described by Higuchi equation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Sweet orange oil extracted from the fruit or peel by cold grinding, cold pressing, wet distillation or supercritical carbon dioxide fluid extraction is widely used in cosmetics, pharmaceuticals and food products because of its special flavor and fragrance. It is a complex mixture composed of more than 100 natural compounds, including hydrocarbon terpenes and oxygenated compounds, pigments, waxes, resins and flavonoids. Terpenes (mainly limonene) make up about 95% of the oil but do not contribute much to the flavor. They are relatively unstable to heat and light and insoluble in water. Oxygenated compounds, including aldehydes, ketones, esters, alcohols and acids, constitute the flavor fraction that gives the characteristic citrus flavor even though they make up about 5 wt.%. Therefore, it is often necessary to remove terpenes from sweet orange oil to enrich oxygenated compounds (Fang et al., 2009; Beneti et al., 2011). Terpenes contribute little to the aroma of sweet orange oil and are easily oxidized to carvol, carveol, etc. by heat and light. Deterpenation is a process of removing terpenes from the oil to make the product more stable in air and more soluble in water without causing any alteration or contamination (Gironi and Maschietti, 2008). Based on this understanding, molecular distillation (or short path distillation) is developed as an attractive alternative. It is a thermal separation technique of liquid mixer operating in vacuum (<10 pa) for gently thermal treatment of heat sensitive and high-boiling products without affecting thermal decomposition. Unlike ⇑ Corresponding author. Fax: +86 21 61900365. E-mail address: [email protected] (X. Wang). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.12.033
conventional distillation technology, molecular distillation relies on the various mean free paths of different substances (Wang et al., 2009). The short path distillator consists of a cylindrical body with a heating jacket, a rotor and a condenser inside. The material to be distilled is fed continuously onto the heated surface from the top and distributed evenly by means of a wiper system, and then flows downward as a thin film. The molecules of the material evaporate from the surface of the thin film when moving from the heated surface to the condensed surface, and finally condense on the condensed surface. The material distilled and the residue left are collected separately. Molecular distillation is now widely used in fine chemical, petrochemical, pharmaceutical, oil and fat, food and cosmetic industries to purify and condense products, recover solvents, remove dissociative monomers, and improve color and luster of products owing to its advantages of a low distillation temperature, a high vacuum degree, a short heating time, a high separation degree and strong adaptability (Guo et al., 2010a; Wang et al., 2010). In this study, we used molecular distillation to remove terpenes and obtain sweet orange oil with the limonene content approaching zero. Microcapsules are described as a kind of miniature container or wrappage in which bioactive compounds are encapsulated by a biopolymer. They can be used to solidify liquid materials for the convenience of transportation and maintain the stability of bioactive compounds by protecting them against hazards from oxygen, moisture or other stresses (Saénz et al., 2009). Flavor plays an important role in consumer satisfaction and influences the further consumption of foods. It is therefore beneficial to microencapsulate volatile ingredients prior to use in foods to limit aroma degradation or loss during processing and storage (Xiao et al., 2011). In the present
391
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
study, we reviewed the methods of flavor microencapsulation (Madene et al., 2006), and used the orifice method to manufacture microcapsules for sweet orange oil terpeneless in order to maintain a good shape and microstructure of the product and well control its release characteristics and heat resistant properties (Dong et al., 2008). Some certain types of goods, such as chewing gum, puffed food or candy as well as baked goods, are prepared under high temperature. The investigation of release profile of oil at different oven temperatures can direct practical applications of the microcapsules. 2. Materials and methods 2.1. Materials Sweet orange oil was obtained from Shanghai Apple Flavor & Fragrance Co., Ltd. (Shanghai, China). Cyclohexane, CaCl2, sodium alginate and glyceryl monostearate of food grade were purchased from China Pharmaceutical (Group) Company of Shanghai Chemical Reagent Corporation (Shanghai, China). 2.2. GC–MS analysis Sweet orange oil and its products were analyzed by GC–MS (5973N, Agilent Technologies, US). GC was conducted on HP-5 MS (30 m 0.25 mm 0.25 lm) capillary column. The oven temperature was controlled at 60 °C for 3 min, with the heating rate from 10 °C/min to 100 °C, from 5 °C/min to 140 °C, and finally from 20 °C/min to 240 °C; the column flow at 1 mL/min with highly purified helium, simple size at 1 lL, and the split ratio at 1:9 (99.999%). Parameters for MS analysis were EI ion source, electron energy 70 eV, temperature of quadrupoles 150 °C, EM voltage 2165 V, temperature of interface 250 °C, solvent delay 3 min, and m/z 40–550 amu (Xiao et al., 2011). 2.3. Separation of sweet orange oil terpeneless by molecular distillation The distillation was performed using a laboratory molecular distillation system (KDL 5, UIC Corporation, Germany) in accordance with different operating conditions. The chemical components of sweet orange oil and its fractions were separated and identified by GC–MS, and then relative percentages of the constitutes were determined by the normalization method and compared with that of the crude oil to establish separation technology of terpenes and oxygenated compounds in sweet orange oil. Major factors influencing of molecular distillation included evaporating temperature, operating pressure and the feed flow rate, of which evaporating temperature and operating pressure were more important (Guo et al., 2010b). In this study, the effects of evaporating temperature and operating pressure on the separation effect were studied at a roller speed of 500–600 rpm and a feed flow rate of 20–30 mL/min during molecular distillation. 2.4. Microencapsulation of sweet orange oil terpeneless by the orifice method Sodium alginate was dissolved in distilled water in thermostatcontrolled waterbath at 50 °C, to which a pre-calculated quantity of sweet orange oil terpeneless and glyceryl monostearate at a concentration of 0.2% (w/v) was added. The solution was stirred thoroughly with a magnetic stirring apparatus (DF-101S, Qiangqiang Equipment Co., China) at the constant temperature of 50–60 °C to ensure complete mixing and thorough emulsification. The gelation medium was prepared by dissolving chitosan at the concentration of 2% (w/v) in 1% acetic acid, and the added with CaCl2. The sodium alginate solution was added dropwise (about 60 drops/min) with a
syringe needle into the gelation medium at a stirring rate of 1000 rpm to form microcapsules spontaneously. After being suspended for 20 min, the microcapsules were filtered, rinsed with distilled water and dried at room temperature (Ren et al., 2010; Wang et al., 2011). 2.5. Optimization of the preparation process for microcapsules by orthogonal experiments The preparation conditions were optimized by orthogonal experiments L9 (34) using encapsulation efficiency (EE) as the target index. The CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material with three levels were chosen in the orthogonal experiments (Table 1). EE, one of the important parameters during the process, was calculated as follows: EE = (TOSO)/TO, EE = encapsulation efficiency, TO = total oil content (mg), SO = surface oil content (mg). Surface oil was measured by adding 15 mL cyclohexane to 2 g microcapsules and shaking with a vortex mixer for 2 min at room temperature. The solvent mixture was then filtered through filter paper and the collected microcapsules on the filter were rinsed six times with 10 mL cyclohexane (Bae and Lee, 2008). The filtrate solution containing the extracted oil was transferred to a clean flask, which was left to evaporate and then was dried at 60 °C until constant weight. The surface oil was calculated based on the difference between the initial clean flask and the flask containing the extracted oil residue (Jafari et al., 2008). Total oil was assumed to be equal to the initial oil, since preliminary tests showed that all the initial oil was retained as expected, since flaxseed oil is not volatile. Variance analysis and directly analyzing on the results of the orthogonal experiments were carried out. The optimum conditions were further verified by duplicate tests. The morphology of moist microcapsules suspended in the water and the microstructure of Table 1 Factors and levels. Levels
1 2 3
Factors CaCl2 concentration (%)
Sodium alginate concentration (%)
A
B
Ratio of wall material to core material C
1.5 2.0 2.5
1.5 2.0 2.5
7:1 6:1 5:1
Table 2 Limonene contents under different process conditions of molecular distillation. No.
Experimental conditions
0 1
50 mbar 60 °C
2
10 mbar 60 °C
3
5 mbar 70 °C
4
5 mbar 90 °C
5
0.1 mbar 90 °C
6
0.025 mbar 120 °C
Limonene content (%) Crude oil Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions
96.123 90.925 96.234 79.825 96.005 20.510 69.285 4.306 27.103 0.326 1.613 0 0.137
392
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
Table 3 Orthogonal experimental design and result. No.
a
Factorsa
EE (%)
A
B
C
e
1 2 3 4 5 6 7 8 9
1 1 1 2 2 2 3 3 3
1 2 3 1 2 3 1 2 3
1 2 3 2 3 1 3 1 2
1 2 3 3 1 2 2 3 1
I
78.74
74.80
79.04
79.98
II
82.01
78.09
78.95
77.81
III R
74.81
82.66
77.56
77.77
7.20
7.86
1.48
2.21
77.01 78.03 81.17 77.98 82.08 85.97 69.42 74.15 80.85
Empty column is denoted by e.
Fig. 2. Release profiles of microcapsules at different oven temperatures.
Table 4 Analysis of variance. Source of variance
Sum of squares of deviation
Degree of freedom
Variance
F
Significance
A B C e
153.56 225.62 1.72 8.55
2 2 2 2
76.78 112.81 0.86 0.23
29.88 43.89
10.27
4
2.57
Error (C + e)
3. Results and discussion
F0.01(2, 4) = 18.00.
dried microcapsules were observed by inverted microscopy (AE-31, Motic Corporation, Germany) (Zheng et al., 2011). 2.6. Release profiles of microcapsules in the oven Six portions of dried microcapsules containing m1 sweet orange oil terpeneless were put in a specific temperature oven (DZF-6030, Shcimo Medical Equipment Co., China), and part of them were taken out at 10, 20, 30, 40, 50 and 60 min to obtain m2 sweet orange oil terpeneless. Cumulative release (CR) of the microencapsulated sweet orange oil terpeneless in the oven was determined according to the following formula (Dong et al., 2011). CR (%) = (1 m1/m2) 100, CR = cumulative release, m1 = the oil content before heating (mL), m2 = the oil content after heating (mL).
3.1. Separation technology of molecular distillation for sweet orange oil terpeneless Limonene contents in different molecular technological conditions are shown in Table 2. The sample used in No. 1 experimental condition (50 mbar, 60 °C) was crude oil, and each sample used in the subsequent experiment was heavy fractions collected in the last experiment one by one. Table 2 shows that the limonene content in heavy fractions (HF) and light fractions (LF) was extremely low when evaporating temperature was at 120 °C and operating pressure was at 0.025 mbar. Sweet orange oil terpeneless were obtained by putting HF and LF together, and reserved for subsequent experiments. 3.2. Optimum conditions for microcapsules In this study, an L9 (34) orthogonal array was employed to determine the effect of three factors on encapsulation efficiency. The L9 (34) orthogonal array along with the experiment results and extreme difference analysis is presented in Table 3, which consisted of nine experiments corresponding to the nine rows and four columns. In this matrix, the chosen three factors were assigned to columns 1–3 and column 4 was arbitrarily designed as an empty column. Analysis of variance (ANOVA) performed by statistical software SPSS 12.0 is shown in Table 4.
Fig. 1. Morphology and microstructure of microcapsules by the optimum process.
393
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394 Table 5 Fitting of release results to different kinetic models. Heating temperature (°C)
Kinetic models Zero-order Mt/M1 = k t + k0
80 140 200
First-order ln(1 Mt/M1) = k t + k0
Higuchi Mt/M1 = k t^(1/2) + k0
k
k0
M1
r
k
k0
M1
r
k
k0
M1
r
0.0132 0.0143 0.0146
0.1486 0.1710 0.2378
20.6 37.8 59.9
0.9300 0.9233 0.8702
0.0301 0.0391 0.0527
0.0800 0.0509 0.1124
20.6 37.8 59.9
0.9842 0.9954 0.9839
0.1125 0.1231 0.1357
0.0028 0.0038 0.0088
20.6 37.8 59.9
0.9984 0.9982 0.9919
Table 3 shows that the influence on EE decreased in order of B > A > C according to the R values. In the ANOVA (Table 4), sum of squares of deviation (SSD) for columns 1–3 were calculated from different level of factor A, B and C, respectively. The SSD for the empty column (column 4) was also calculated. Obviously, it did not result from different level of the chosen three factors, but from SSD of the experiment error. In addition, the SSD from factor C (column 3) was smaller than that from the empty column (column 4), indicating that the factor C had no influence on experimental results. It may be taken that the SSD from factor C was also due to experiment error in statistics. Therefore, the total SSD from experiment error was obtained by pooling the SSD from factor C (column 3) with the SSD from the empty column (column 4) (Montgomery, 1997; Zhang et al., 1995). Accordingly, the error account for four degrees of freedom, the total SSD of 10.27 and the variance of 2.57. In the table F, F0.01(2, 4) = 18.00, the F is far less than F of factor A, B calculated in Table 4, demonstrating that the effect of factor A, B on encapsulation efficiency is highly significant. The level 2, 3 of the major factor A, B should be chosen respectively, while the level 3 of the factor C could be chosen for more oil loading. In other words, optimum conditions were obtained when the CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material were 2.0%, 2.5% and 5:1 respectively. The duplicate tests with EE 87.34% and RSD 2.15% showed that the optimum conditions were reasonable. 3.3. Morphology and microstructure of microcapsules by the optimum process Morphology and microstructure of microcapsules are shown in Fig. 1. As shown in Fig. 1A, the microcapsules exhibited a good spherical shape and an average size, with good hardness and flexibility. Fig. 1B shows that the microcapsules were globular, the surface of which was continuous and smooth. Fig. 1C shows that the microcapsules had a nucleus-shell structure with a compact wall. 3.4. Cumulative release of microcapsules in the oven The average results of the test for in vitro release are shown in Fig. 2 with S.D. bars. The sweet orange oil terpeneless from dried microcapsules under the optimum conditions was slowly released at different oven temperatures. For example, the amount of the sweet orange oil terpeneless released was only 11.24% after heating for 20 min at 80 °C, and increased gradually with temperature rising and time prolonging. It is therefore essential to control the heating temperature and treatment time in the course of processing when microcapsules are applied to food areas such as chewing gum. In order to obtain meaningful information for release models, the release profiles were fitted to three different kinetic models, and the goodness of fit of the release data was assessed. Table 5 is a summary of the correlation coefficients for different release kinetic models for microcapsules of sweet orange oil terpeneless at
different oven temperatures. Models with higher correlation coefficients were considered as a more appropriate model for the release data. As shown in Table 5, the best linear fitting parameters are all the squareroot of time (Higuchi model) at the heating temperature of 80 °C and 200 °C, while there was no significant difference between the squareroot of time (Higuchi model) and first-order release models at the heating temperature of 140 °C, suggesting that release is controlled by diffusion of oil through the pores. 4. Conclusions Limonene in sweet orange oil can be effectively removed using molecular distillation. It was found that the evaporating temperature and operating pressure are factors significantly affecting the separation effect during distillation. Molecular distillation was shown as a proper method for refining sweet orange oil. Chitosan–sodium alginate microcapsules containing sweet orange oil terpeneless were prepared by the orifice method. Orthogonal experiments exhibited significant deviation for the effect of sodium alginate concentration and CaCl2 concentration on EE. The microcapsules under the optimum conditions had a good spherical shape, an average size, a smooth surface and a nucleus-shell structure. Such microencapsulated sweet orange oil terpeneless can be applied to food products such as chewing gum, puffed food or candy as well as baked goods and limit aroma degradation or loss during processing and storage. The results of oil release at different oven temperatures showed that oil release increased gradually with the temperature rising and treatment time prolonging. Therefore, heating temperature and treatment time should be controlled properly in the course of processing when the microcapsules are applied to certain types of food prepared at high temperature. The data of release kinetics for the microcapsules can be well fitted by the classic Higuchi model. Acknowledgment This study was supported by Leading Academic Discipline Project of Shanghai Municipal Education Commission (J50704). References Bae, E.K., Lee, S.J., 2008. Microencapsulation of avocado oil by spray drying using whey protein and maltodextrin. Journal of Microencapsulation 25 (8), 549–560. Beneti, S.C., Rosset, E., Corazza, M.L., Frizzo, C.D., Luccio, M.D., Oliveira, J.V., 2011. Fractionation of citronella (Cymbopogon winterianus) essential oil and concentrated orange oil phase by batch vacuum distillation. Journal of Food Engineering 102 (4), 348–354. Dong, Z.J., Xi, S.Q., Huab, S., Hayat, K., Zhang, X.M., Xua, S.Y., 2008. Optimisation of cross-linking parameters during production of transglutaminase-hardened spherical multinuclear microcapsules by complex coacervation. Colloids and Surfaces B: Biointerfaces 63 (1), 41–47. Dong, Z.J., Ma, Y., Hayat, K., Jia, C.S., Xia, S., Zhang, X.M., 2011. Morphology and release profile of microcapsules encapsulating peppermint oil by complex coacervation. Journal of Food Engineering 104, 455–460. Fang, T., Goto, M., Sasaki, M., Hirose, T., 2009. Combination of supercritical CO2 and vacuum distillation for the fractionation of bergamot oil. Journal of Agricultural and Food Chemistry 52, 5162–5167.
394
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
Gironi, F., Maschietti, M., 2008. Continuous countercurrent deterpenation of lemon essential oil by means of supercritical carbon dioxide: experimental data and process modeling. Chemical Engineering Science 63, 651–661. Guo, Z.G., Wang, S.R., Gu, Y.L., Xu, G.H., Li, X., Luo, Z.Y., 2010a. Separation characteristics of biomass pyrolysis oil in molecular distillation. Separation and Purification Technology 76, 52–57. Guo, X.J., Wang, S.R., Guo, Z.G., Liu, Q., Luo, Z.Y., Cen, K., 2010b. Pyrolysis characteristics of bio-oil fractions separated by molecular distillation. Applied Energy 87, 2892–2898. Jafari, S.M., Assadpoor, E., He, Y., Bhandari, B., 2008. Encapsulation efficiency of food flavours and oils during spray drying. Drying Technology 26 (7), 816–835. Madene, A., Jacquot, M., Scher, J., Desobry, S., 2006. Flavour encapsulation and controlled release – a review. International Journal of Food Science and Technology 41 (1), 1–21. Montgomery, D.C., 1997. Design and Analysis of Experiments. Wiley Press, New York. Ren, P.W., Ju, X.J., X, R., Chu, L.Y., 2010. Monodisperse alginate microcapsules with oil core generated from a microfluidic device. Journal of Colloid and Interface Science 343 (1), 392–395.
Saénz, C., Tapia, S., Chávez, J., Rober, P., 2009. Microencapsulation by spray drying of bioactive compounds from cactus pear (Opuntia ficus-indica). Food Chemistry 114, 616–622. Wang, S.R., Gu, Y.L., Liu, Q., Yao, Y., Guo, Z.G., Luo, Z.Y., Cen, K.F., 2009. Separation of bio-oil by molecular distillation. Fuel Processing Technology 90, 738–745. Wang, Y., Zhao, M.M., Song, K.k., Wang, L.L., Han, X., Tang, S.Z., Wang, Y., 2010. Separation of diacylglycerols from enzymatically hydrolyzed soybean oil by molecular distillation. Separation and Purification Technology 75 (2), 114–120. Wang, J.Y., Jin, Y., Xie, R., Liu, J.Y., Ju, X.J., Meng, T., Chu, L.Y., 2011. Novel calciumalginate capsules with aqueous core and thermo-responsive membrane. Journal of Colloid and Interface Science 353 (1), 61–68. Xiao, J.X., Yu, H.Y., Yang, J., 2011. Microencapsulation of sweet orange oil by complex coacervation with soybean protein isolate/gum Arabic. Food Chemistry 125 (4), 1267–1272. Zhang, C.H., Zhou, Y.Z., Liu, Y.F., 1995. Mathematical Statistics. Shandong University Press, Jinan. Zheng, L.Q., Ding, Z.S., Zhang, M., Sun, J.C., 2011. Microencapsulation of bayberry polyphenols by ethyl cellulose: preparation and characterization. Journal of Food Engineering 4 (1), 89–95.
Contents lists available at SciVerse ScienceDirect
Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Microencapsulation of sweet orange oil terpeneless using the orifice method Kehai Liu, Yanqin Xu, Xichang Wang ⇑ College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China
a r t i c l e
i n f o
Article history: Received 14 July 2011 Received in revised form 17 December 2011 Accepted 25 December 2011 Available online 2 January 2012 Keywords: Sweet orange oil Molecular distillation Microcapsules Orifice method Release kinetics
a b s t r a c t This study used molecular distillation to remove terpenes (mainly limonene) from sweet orange oil and prepared microcapsules encapsulating sweet orange oil terpeneless by the orifice method. The morphology and microstructure of the microcapsules under the optimum conditions by orthogonal experiments were observed and the data of release kinetics were plotted according to the three different kinetic models to further investigate the release mechanism for microcapsules at different oven temperatures. The results showed that the limonene content was extremely low at a roller rate of 500–600 rpm, a feed flow rate of 20–30 mL/min, an evaporating temperature of 120 °C and an operating pressure of 0.025 mbar during molecular distillation. Encapsulation efficiency (EE) of microcapsules with good morphology and microstructure reached 87.34% when the CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material were 2.0%, 2.5% and 5:1 respectively. The release profile of sweet orange oil terpeneless from the microcapsules could be well described by Higuchi equation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Sweet orange oil extracted from the fruit or peel by cold grinding, cold pressing, wet distillation or supercritical carbon dioxide fluid extraction is widely used in cosmetics, pharmaceuticals and food products because of its special flavor and fragrance. It is a complex mixture composed of more than 100 natural compounds, including hydrocarbon terpenes and oxygenated compounds, pigments, waxes, resins and flavonoids. Terpenes (mainly limonene) make up about 95% of the oil but do not contribute much to the flavor. They are relatively unstable to heat and light and insoluble in water. Oxygenated compounds, including aldehydes, ketones, esters, alcohols and acids, constitute the flavor fraction that gives the characteristic citrus flavor even though they make up about 5 wt.%. Therefore, it is often necessary to remove terpenes from sweet orange oil to enrich oxygenated compounds (Fang et al., 2009; Beneti et al., 2011). Terpenes contribute little to the aroma of sweet orange oil and are easily oxidized to carvol, carveol, etc. by heat and light. Deterpenation is a process of removing terpenes from the oil to make the product more stable in air and more soluble in water without causing any alteration or contamination (Gironi and Maschietti, 2008). Based on this understanding, molecular distillation (or short path distillation) is developed as an attractive alternative. It is a thermal separation technique of liquid mixer operating in vacuum (<10 pa) for gently thermal treatment of heat sensitive and high-boiling products without affecting thermal decomposition. Unlike ⇑ Corresponding author. Fax: +86 21 61900365. E-mail address: [email protected] (X. Wang). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.12.033
conventional distillation technology, molecular distillation relies on the various mean free paths of different substances (Wang et al., 2009). The short path distillator consists of a cylindrical body with a heating jacket, a rotor and a condenser inside. The material to be distilled is fed continuously onto the heated surface from the top and distributed evenly by means of a wiper system, and then flows downward as a thin film. The molecules of the material evaporate from the surface of the thin film when moving from the heated surface to the condensed surface, and finally condense on the condensed surface. The material distilled and the residue left are collected separately. Molecular distillation is now widely used in fine chemical, petrochemical, pharmaceutical, oil and fat, food and cosmetic industries to purify and condense products, recover solvents, remove dissociative monomers, and improve color and luster of products owing to its advantages of a low distillation temperature, a high vacuum degree, a short heating time, a high separation degree and strong adaptability (Guo et al., 2010a; Wang et al., 2010). In this study, we used molecular distillation to remove terpenes and obtain sweet orange oil with the limonene content approaching zero. Microcapsules are described as a kind of miniature container or wrappage in which bioactive compounds are encapsulated by a biopolymer. They can be used to solidify liquid materials for the convenience of transportation and maintain the stability of bioactive compounds by protecting them against hazards from oxygen, moisture or other stresses (Saénz et al., 2009). Flavor plays an important role in consumer satisfaction and influences the further consumption of foods. It is therefore beneficial to microencapsulate volatile ingredients prior to use in foods to limit aroma degradation or loss during processing and storage (Xiao et al., 2011). In the present
391
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
study, we reviewed the methods of flavor microencapsulation (Madene et al., 2006), and used the orifice method to manufacture microcapsules for sweet orange oil terpeneless in order to maintain a good shape and microstructure of the product and well control its release characteristics and heat resistant properties (Dong et al., 2008). Some certain types of goods, such as chewing gum, puffed food or candy as well as baked goods, are prepared under high temperature. The investigation of release profile of oil at different oven temperatures can direct practical applications of the microcapsules. 2. Materials and methods 2.1. Materials Sweet orange oil was obtained from Shanghai Apple Flavor & Fragrance Co., Ltd. (Shanghai, China). Cyclohexane, CaCl2, sodium alginate and glyceryl monostearate of food grade were purchased from China Pharmaceutical (Group) Company of Shanghai Chemical Reagent Corporation (Shanghai, China). 2.2. GC–MS analysis Sweet orange oil and its products were analyzed by GC–MS (5973N, Agilent Technologies, US). GC was conducted on HP-5 MS (30 m 0.25 mm 0.25 lm) capillary column. The oven temperature was controlled at 60 °C for 3 min, with the heating rate from 10 °C/min to 100 °C, from 5 °C/min to 140 °C, and finally from 20 °C/min to 240 °C; the column flow at 1 mL/min with highly purified helium, simple size at 1 lL, and the split ratio at 1:9 (99.999%). Parameters for MS analysis were EI ion source, electron energy 70 eV, temperature of quadrupoles 150 °C, EM voltage 2165 V, temperature of interface 250 °C, solvent delay 3 min, and m/z 40–550 amu (Xiao et al., 2011). 2.3. Separation of sweet orange oil terpeneless by molecular distillation The distillation was performed using a laboratory molecular distillation system (KDL 5, UIC Corporation, Germany) in accordance with different operating conditions. The chemical components of sweet orange oil and its fractions were separated and identified by GC–MS, and then relative percentages of the constitutes were determined by the normalization method and compared with that of the crude oil to establish separation technology of terpenes and oxygenated compounds in sweet orange oil. Major factors influencing of molecular distillation included evaporating temperature, operating pressure and the feed flow rate, of which evaporating temperature and operating pressure were more important (Guo et al., 2010b). In this study, the effects of evaporating temperature and operating pressure on the separation effect were studied at a roller speed of 500–600 rpm and a feed flow rate of 20–30 mL/min during molecular distillation. 2.4. Microencapsulation of sweet orange oil terpeneless by the orifice method Sodium alginate was dissolved in distilled water in thermostatcontrolled waterbath at 50 °C, to which a pre-calculated quantity of sweet orange oil terpeneless and glyceryl monostearate at a concentration of 0.2% (w/v) was added. The solution was stirred thoroughly with a magnetic stirring apparatus (DF-101S, Qiangqiang Equipment Co., China) at the constant temperature of 50–60 °C to ensure complete mixing and thorough emulsification. The gelation medium was prepared by dissolving chitosan at the concentration of 2% (w/v) in 1% acetic acid, and the added with CaCl2. The sodium alginate solution was added dropwise (about 60 drops/min) with a
syringe needle into the gelation medium at a stirring rate of 1000 rpm to form microcapsules spontaneously. After being suspended for 20 min, the microcapsules were filtered, rinsed with distilled water and dried at room temperature (Ren et al., 2010; Wang et al., 2011). 2.5. Optimization of the preparation process for microcapsules by orthogonal experiments The preparation conditions were optimized by orthogonal experiments L9 (34) using encapsulation efficiency (EE) as the target index. The CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material with three levels were chosen in the orthogonal experiments (Table 1). EE, one of the important parameters during the process, was calculated as follows: EE = (TOSO)/TO, EE = encapsulation efficiency, TO = total oil content (mg), SO = surface oil content (mg). Surface oil was measured by adding 15 mL cyclohexane to 2 g microcapsules and shaking with a vortex mixer for 2 min at room temperature. The solvent mixture was then filtered through filter paper and the collected microcapsules on the filter were rinsed six times with 10 mL cyclohexane (Bae and Lee, 2008). The filtrate solution containing the extracted oil was transferred to a clean flask, which was left to evaporate and then was dried at 60 °C until constant weight. The surface oil was calculated based on the difference between the initial clean flask and the flask containing the extracted oil residue (Jafari et al., 2008). Total oil was assumed to be equal to the initial oil, since preliminary tests showed that all the initial oil was retained as expected, since flaxseed oil is not volatile. Variance analysis and directly analyzing on the results of the orthogonal experiments were carried out. The optimum conditions were further verified by duplicate tests. The morphology of moist microcapsules suspended in the water and the microstructure of Table 1 Factors and levels. Levels
1 2 3
Factors CaCl2 concentration (%)
Sodium alginate concentration (%)
A
B
Ratio of wall material to core material C
1.5 2.0 2.5
1.5 2.0 2.5
7:1 6:1 5:1
Table 2 Limonene contents under different process conditions of molecular distillation. No.
Experimental conditions
0 1
50 mbar 60 °C
2
10 mbar 60 °C
3
5 mbar 70 °C
4
5 mbar 90 °C
5
0.1 mbar 90 °C
6
0.025 mbar 120 °C
Limonene content (%) Crude oil Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions Heavy fractions Light fractions
96.123 90.925 96.234 79.825 96.005 20.510 69.285 4.306 27.103 0.326 1.613 0 0.137
392
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
Table 3 Orthogonal experimental design and result. No.
a
Factorsa
EE (%)
A
B
C
e
1 2 3 4 5 6 7 8 9
1 1 1 2 2 2 3 3 3
1 2 3 1 2 3 1 2 3
1 2 3 2 3 1 3 1 2
1 2 3 3 1 2 2 3 1
I
78.74
74.80
79.04
79.98
II
82.01
78.09
78.95
77.81
III R
74.81
82.66
77.56
77.77
7.20
7.86
1.48
2.21
77.01 78.03 81.17 77.98 82.08 85.97 69.42 74.15 80.85
Empty column is denoted by e.
Fig. 2. Release profiles of microcapsules at different oven temperatures.
Table 4 Analysis of variance. Source of variance
Sum of squares of deviation
Degree of freedom
Variance
F
Significance
A B C e
153.56 225.62 1.72 8.55
2 2 2 2
76.78 112.81 0.86 0.23
29.88 43.89
10.27
4
2.57
Error (C + e)
3. Results and discussion
F0.01(2, 4) = 18.00.
dried microcapsules were observed by inverted microscopy (AE-31, Motic Corporation, Germany) (Zheng et al., 2011). 2.6. Release profiles of microcapsules in the oven Six portions of dried microcapsules containing m1 sweet orange oil terpeneless were put in a specific temperature oven (DZF-6030, Shcimo Medical Equipment Co., China), and part of them were taken out at 10, 20, 30, 40, 50 and 60 min to obtain m2 sweet orange oil terpeneless. Cumulative release (CR) of the microencapsulated sweet orange oil terpeneless in the oven was determined according to the following formula (Dong et al., 2011). CR (%) = (1 m1/m2) 100, CR = cumulative release, m1 = the oil content before heating (mL), m2 = the oil content after heating (mL).
3.1. Separation technology of molecular distillation for sweet orange oil terpeneless Limonene contents in different molecular technological conditions are shown in Table 2. The sample used in No. 1 experimental condition (50 mbar, 60 °C) was crude oil, and each sample used in the subsequent experiment was heavy fractions collected in the last experiment one by one. Table 2 shows that the limonene content in heavy fractions (HF) and light fractions (LF) was extremely low when evaporating temperature was at 120 °C and operating pressure was at 0.025 mbar. Sweet orange oil terpeneless were obtained by putting HF and LF together, and reserved for subsequent experiments. 3.2. Optimum conditions for microcapsules In this study, an L9 (34) orthogonal array was employed to determine the effect of three factors on encapsulation efficiency. The L9 (34) orthogonal array along with the experiment results and extreme difference analysis is presented in Table 3, which consisted of nine experiments corresponding to the nine rows and four columns. In this matrix, the chosen three factors were assigned to columns 1–3 and column 4 was arbitrarily designed as an empty column. Analysis of variance (ANOVA) performed by statistical software SPSS 12.0 is shown in Table 4.
Fig. 1. Morphology and microstructure of microcapsules by the optimum process.
393
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394 Table 5 Fitting of release results to different kinetic models. Heating temperature (°C)
Kinetic models Zero-order Mt/M1 = k t + k0
80 140 200
First-order ln(1 Mt/M1) = k t + k0
Higuchi Mt/M1 = k t^(1/2) + k0
k
k0
M1
r
k
k0
M1
r
k
k0
M1
r
0.0132 0.0143 0.0146
0.1486 0.1710 0.2378
20.6 37.8 59.9
0.9300 0.9233 0.8702
0.0301 0.0391 0.0527
0.0800 0.0509 0.1124
20.6 37.8 59.9
0.9842 0.9954 0.9839
0.1125 0.1231 0.1357
0.0028 0.0038 0.0088
20.6 37.8 59.9
0.9984 0.9982 0.9919
Table 3 shows that the influence on EE decreased in order of B > A > C according to the R values. In the ANOVA (Table 4), sum of squares of deviation (SSD) for columns 1–3 were calculated from different level of factor A, B and C, respectively. The SSD for the empty column (column 4) was also calculated. Obviously, it did not result from different level of the chosen three factors, but from SSD of the experiment error. In addition, the SSD from factor C (column 3) was smaller than that from the empty column (column 4), indicating that the factor C had no influence on experimental results. It may be taken that the SSD from factor C was also due to experiment error in statistics. Therefore, the total SSD from experiment error was obtained by pooling the SSD from factor C (column 3) with the SSD from the empty column (column 4) (Montgomery, 1997; Zhang et al., 1995). Accordingly, the error account for four degrees of freedom, the total SSD of 10.27 and the variance of 2.57. In the table F, F0.01(2, 4) = 18.00, the F is far less than F of factor A, B calculated in Table 4, demonstrating that the effect of factor A, B on encapsulation efficiency is highly significant. The level 2, 3 of the major factor A, B should be chosen respectively, while the level 3 of the factor C could be chosen for more oil loading. In other words, optimum conditions were obtained when the CaCl2 concentration, sodium alginate concentration and ratio of wall material to core material were 2.0%, 2.5% and 5:1 respectively. The duplicate tests with EE 87.34% and RSD 2.15% showed that the optimum conditions were reasonable. 3.3. Morphology and microstructure of microcapsules by the optimum process Morphology and microstructure of microcapsules are shown in Fig. 1. As shown in Fig. 1A, the microcapsules exhibited a good spherical shape and an average size, with good hardness and flexibility. Fig. 1B shows that the microcapsules were globular, the surface of which was continuous and smooth. Fig. 1C shows that the microcapsules had a nucleus-shell structure with a compact wall. 3.4. Cumulative release of microcapsules in the oven The average results of the test for in vitro release are shown in Fig. 2 with S.D. bars. The sweet orange oil terpeneless from dried microcapsules under the optimum conditions was slowly released at different oven temperatures. For example, the amount of the sweet orange oil terpeneless released was only 11.24% after heating for 20 min at 80 °C, and increased gradually with temperature rising and time prolonging. It is therefore essential to control the heating temperature and treatment time in the course of processing when microcapsules are applied to food areas such as chewing gum. In order to obtain meaningful information for release models, the release profiles were fitted to three different kinetic models, and the goodness of fit of the release data was assessed. Table 5 is a summary of the correlation coefficients for different release kinetic models for microcapsules of sweet orange oil terpeneless at
different oven temperatures. Models with higher correlation coefficients were considered as a more appropriate model for the release data. As shown in Table 5, the best linear fitting parameters are all the squareroot of time (Higuchi model) at the heating temperature of 80 °C and 200 °C, while there was no significant difference between the squareroot of time (Higuchi model) and first-order release models at the heating temperature of 140 °C, suggesting that release is controlled by diffusion of oil through the pores. 4. Conclusions Limonene in sweet orange oil can be effectively removed using molecular distillation. It was found that the evaporating temperature and operating pressure are factors significantly affecting the separation effect during distillation. Molecular distillation was shown as a proper method for refining sweet orange oil. Chitosan–sodium alginate microcapsules containing sweet orange oil terpeneless were prepared by the orifice method. Orthogonal experiments exhibited significant deviation for the effect of sodium alginate concentration and CaCl2 concentration on EE. The microcapsules under the optimum conditions had a good spherical shape, an average size, a smooth surface and a nucleus-shell structure. Such microencapsulated sweet orange oil terpeneless can be applied to food products such as chewing gum, puffed food or candy as well as baked goods and limit aroma degradation or loss during processing and storage. The results of oil release at different oven temperatures showed that oil release increased gradually with the temperature rising and treatment time prolonging. Therefore, heating temperature and treatment time should be controlled properly in the course of processing when the microcapsules are applied to certain types of food prepared at high temperature. The data of release kinetics for the microcapsules can be well fitted by the classic Higuchi model. Acknowledgment This study was supported by Leading Academic Discipline Project of Shanghai Municipal Education Commission (J50704). References Bae, E.K., Lee, S.J., 2008. Microencapsulation of avocado oil by spray drying using whey protein and maltodextrin. Journal of Microencapsulation 25 (8), 549–560. Beneti, S.C., Rosset, E., Corazza, M.L., Frizzo, C.D., Luccio, M.D., Oliveira, J.V., 2011. Fractionation of citronella (Cymbopogon winterianus) essential oil and concentrated orange oil phase by batch vacuum distillation. Journal of Food Engineering 102 (4), 348–354. Dong, Z.J., Xi, S.Q., Huab, S., Hayat, K., Zhang, X.M., Xua, S.Y., 2008. Optimisation of cross-linking parameters during production of transglutaminase-hardened spherical multinuclear microcapsules by complex coacervation. Colloids and Surfaces B: Biointerfaces 63 (1), 41–47. Dong, Z.J., Ma, Y., Hayat, K., Jia, C.S., Xia, S., Zhang, X.M., 2011. Morphology and release profile of microcapsules encapsulating peppermint oil by complex coacervation. Journal of Food Engineering 104, 455–460. Fang, T., Goto, M., Sasaki, M., Hirose, T., 2009. Combination of supercritical CO2 and vacuum distillation for the fractionation of bergamot oil. Journal of Agricultural and Food Chemistry 52, 5162–5167.
394
K. Liu et al. / Journal of Food Engineering 110 (2012) 390–394
Gironi, F., Maschietti, M., 2008. Continuous countercurrent deterpenation of lemon essential oil by means of supercritical carbon dioxide: experimental data and process modeling. Chemical Engineering Science 63, 651–661. Guo, Z.G., Wang, S.R., Gu, Y.L., Xu, G.H., Li, X., Luo, Z.Y., 2010a. Separation characteristics of biomass pyrolysis oil in molecular distillation. Separation and Purification Technology 76, 52–57. Guo, X.J., Wang, S.R., Guo, Z.G., Liu, Q., Luo, Z.Y., Cen, K., 2010b. Pyrolysis characteristics of bio-oil fractions separated by molecular distillation. Applied Energy 87, 2892–2898. Jafari, S.M., Assadpoor, E., He, Y., Bhandari, B., 2008. Encapsulation efficiency of food flavours and oils during spray drying. Drying Technology 26 (7), 816–835. Madene, A., Jacquot, M., Scher, J., Desobry, S., 2006. Flavour encapsulation and controlled release – a review. International Journal of Food Science and Technology 41 (1), 1–21. Montgomery, D.C., 1997. Design and Analysis of Experiments. Wiley Press, New York. Ren, P.W., Ju, X.J., X, R., Chu, L.Y., 2010. Monodisperse alginate microcapsules with oil core generated from a microfluidic device. Journal of Colloid and Interface Science 343 (1), 392–395.
Saénz, C., Tapia, S., Chávez, J., Rober, P., 2009. Microencapsulation by spray drying of bioactive compounds from cactus pear (Opuntia ficus-indica). Food Chemistry 114, 616–622. Wang, S.R., Gu, Y.L., Liu, Q., Yao, Y., Guo, Z.G., Luo, Z.Y., Cen, K.F., 2009. Separation of bio-oil by molecular distillation. Fuel Processing Technology 90, 738–745. Wang, Y., Zhao, M.M., Song, K.k., Wang, L.L., Han, X., Tang, S.Z., Wang, Y., 2010. Separation of diacylglycerols from enzymatically hydrolyzed soybean oil by molecular distillation. Separation and Purification Technology 75 (2), 114–120. Wang, J.Y., Jin, Y., Xie, R., Liu, J.Y., Ju, X.J., Meng, T., Chu, L.Y., 2011. Novel calciumalginate capsules with aqueous core and thermo-responsive membrane. Journal of Colloid and Interface Science 353 (1), 61–68. Xiao, J.X., Yu, H.Y., Yang, J., 2011. Microencapsulation of sweet orange oil by complex coacervation with soybean protein isolate/gum Arabic. Food Chemistry 125 (4), 1267–1272. Zhang, C.H., Zhou, Y.Z., Liu, Y.F., 1995. Mathematical Statistics. Shandong University Press, Jinan. Zheng, L.Q., Ding, Z.S., Zhang, M., Sun, J.C., 2011. Microencapsulation of bayberry polyphenols by ethyl cellulose: preparation and characterization. Journal of Food Engineering 4 (1), 89–95.