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Comparisons between conventional, microwave- and ultrasound-assisted methods for extraction of pectin from grapefruit
Chemical Engineering and Processing 50 (2011) 1237–1243
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Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Comparisons between conventional, microwave- and ultrasound-assisted methods for extraction of pectin from grapefruit Homa Bagherian, Farzin Zokaee Ashtiani ∗ , Amir Fouladitajar, Mahdy Mohtashamy Department of Chemical Engineering, Amirkabir University of Technology, No. 424, Hafez Ave., Tehran, Iran
a r t i c l e
i n f o
Article history: Received 6 February 2011 Received in revised form 6 June 2011 Accepted 7 August 2011 Available online 12 August 2011 Keywords: Pectin Extraction Microwave-assisted Extraction (MAE) Ultrasound-assisted extraction (UAE) Yield
a b s t r a c t Microwave-assisted Extraction (MAE) and Ultrasound-assisted extraction (UAE) techniques have been employed as complementary methods to extract carbohydrates, polysaccharides and other functional compounds from vegetable sources. In this work, the effect of microwave power and heating time on the yield and quality of extracted pectin from grapefruit was investigated. The highest total amount of pectin yield was found to be 27.81% (w/w) for 6 min of extraction at 900 W. It was observed that yield, the galacturonic acid content (GalA), and degree of esterification (DE) increased with an increase in microwave power and heating time. Besides, the molecular weight decreased with an increase in heating time; however, the effects of power on the molecular weight were dramatically more than heating time. In addition, laboratory studies on the extraction of pectin treated with high-intensity ultrasound were carried out. The effects of temperature and time on quality and quantity of extracted pectin were investigated. The highest yield was for sonication time of 25 min (17.92%) in a constant bath temperature of 70 ◦ C. Furthermore, a preliminary ultrasonic heating of grapefruit solution, as a pretreatment for MAE, was found to provide a higher yield. Intermittent sonication gave better results in comparison to the continuous sonication. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Pectin is a family of complex polysaccharides of ␣-d-(1→4) galacturonic acid present in the primary cell wall and middle lamella of the plant tissues. Pectin contains a backbone of (1–4) ␣-d-galacturonic acid residues which are partially esterified with methyl alcohol at the carboxylic acid [1]. All pectins are characterized by a high content of galacturonic acid (GalA) and according to the regulation of FAO and EU ‘pectin’ must contain at least 65% GalA [2]. There are various sources in pectin production. It is possible to produce acceptable pectin from both apple pomace and citrus peels. The pectin content of citrus peel such as orange, grapefruit and lemon is usually as high as 25–30% of the dried peel mass [3]. The grapefruit peel contains several mono and disaccharides; the main ones are glucose, sucrose and fructose, as well as the polysaccharides cellulose, hemicelluloses and pectin [4]. The major use of pectin is as a gelling, stabilizing and thickening agent in food systems such as jams and jellies, confectionery, and
∗ Corresponding author. Tel.: +98 21 6454 3124; fax: +98 21 66405847. E-mail address: [email protected] (F. Zokaee Ashtiani). 0255-2701/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2011.08.002
fruit juice. Pectin is also used in pharmaceutical industry, suggested to reduce heart disease and gallstones. Conventionally, pectin is extracted in a hot dilute mineral acidic solution. The time needed depends on some factors like raw material and the type of pectin desired, and varies from one manufacturer to another, but generally, this process is time consuming [5,6]. This condition leads to pectin degradation, so conventional methods are not appropriate for both quantity and quality of the pectin extraction. Accordingly, using an opportune method is of great importance in order to achieve the best quality and quantity characteristics of extracted pectin. Various methods for extraction of pectin have already been investigated which in most cases results have been satisfactory. These methods include using pulsating hydrodynamic action with turbulent recirculation [7] which leads to increased yield, reduced process time and production costs. Microwave-assisted Extraction (MAE) is another method which has been recently investigated by many researchers finding that the MAE can lead to a considerable increase in the yield and quality of extracted pectin. For instance, extraction of pectin from fruit materials pretreated in an electromagnetic field of super-high frequency [8] led to higher pectin yield and higher values for degree of esterification (DE) and gel strength compared with the no-pretreated samples. In another work, using Scanning electron micrographs Kratchanova et al. [9] reported that
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microwave heating disrupted parenchymal cells. It was also found that specific surface and the water absorption capacity of the orange tissue were reduced; moreover, the endogenous enzymes of the peels became inactive. MAE has also been applied to pectin extraction from dried apple pomace. Response Surface Methodology (RSM) has been used to optimize the effects of processing parameters of extraction on the yield of pectin [1]. Microwave-assisted Extraction of pectin from orange skin has also been investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) [10]. Some similar studies have been done to extract pectin, mostly from orange, with different extraction periods, solvent pHs, and types of solvent systems [11–16]. In one of these studies, pectin was acid extracted from orange albedo by microwave heating under pressure by Fishman et al. [12,13]. As an applicable and new method, the application of ultrasound for assisting extraction (UAE) from plant material is widely published [17]; however, a few experiments have been done for pectin extraction by this method. All of the published studies under ultrasound conditions indicate increased yield or extraction rate as well as reduction in extraction time. The effect of ultrasonic treatment on pectin stability in aqueous solution was studied to establish conditions minimizing degradation [18]. Ultrasonication improved the pectin yield by 28% and reduced the time for extraction. The effect of high-intensity ultrasound on the rheological and optical properties of high-methoxyl pectin dispersions was studied by Seshadri [19]. Ultrasonically pretreated pectin formed weaker gels with increasing sonication power and time. In another work, intensifying the process of pectin deesterification by combining the acid maceration of raw materials with ultrasound treatment was investigated by Panchev et al. [20]. An additional decrease in the degree of esterification of pectin (about 6%) and a significant increase in the yield of pectin (about 18%) were reported. The optimum ultrasound treatment proved to be within 24–30 min and prolonged treatment can result in obtaining pectin with lower gel strengths [20]. To the best of our knowledge, there is no comprehensive study on the effects of microwave and ultrasound on the qualitative and quantitative characteristics of the extracted pectin from grapefruit. This work reports the effects of microwave on the yield and quality of extracted pectin in comparison to the conventional method. In addition, ultrasound and its optimum operating conditions, as a pretreatment for the MAE method or single use, will be discussed. 2. Experimental 2.1. Samples preparation Turkish grapefruit, purchased in a local fruit market, was chosen as the raw material in these experiments. The peels were stripped with a paring knife. The albedos were cut into small pieces then were dried in an oven with a gentle flow of air at 50 ◦ C. The albedos were first ground, then screened by sieve, subsequently the particles smaller than 0.6 mm in diameter were selected. 2.2. Apparatus Microwave-assisted Extraction (MAE) was performed in an experimental microwave oven (Samsung, Model PG-3200, Korea) with the power of 900 W and the frequency was set on 2450 MHz. A 200 W, 24 kHz ultrasonic processor (UP200H with S7, Dr. Hielscher, Teltow, Germany) was also used as the sonic probe in the ultrasound-assisted extraction (UAE). For the temperature measurement, there was a sensor in the microwave oven which could have been used for the temperature measurement. For the ultrasound-assisted extraction (UAE),
the material was set in a water bath and the temperature was measured by a thermometer. In the used microwave apparatus, a definite power value was specified and applied within the whole duration of exposure rather than using a pulsating heating cycle with varying time fraction. 2.3. Methods of analysis After the extraction, the wet pectin was dried at 50 ◦ C until its weight remained constant. The yield of pectin was expressed as the weight of dried pectin extracted from dried peels (w/w). Degree of esterification (DE) of extracted pectin was determined using titration with NaOH before saponification and back titration with HCl after saponification [21]. The galacturonic acid content (GalA) was determined by the method of colorimetry with meta-hydroxydiphenyl and a JASCO spectrophotometer (model V-550, Japan) [22]. The value of metoxyl group was calculated using extents of galacturonic acid and degree of esterification. Finally, intrinsic viscosity was obtained by using a capillary tube viscometer (ubbelohde, the diameter of capillary tube was 0.58 mm) [23] then the molecular weight was obtained according to Anger–Berth equation [24]. All the experiments were done in duplicate and results were reproducible with an acceptable average error. 2.4. Procedures 2.4.1. Extraction of pectin from dried albedo using MAE The dry mass (6 g) of dried grapefruit peels was subjected to extraction by adding 300 ml distilled water. The pH was adjusted to 1.5 with 0.1 N HCl as extracting agent. The mixture was placed in the center of a microwave oven, containing a circular, 360◦ rotating carousel with different durations of exposure: 2, 4, 6, 8, 10, 12, 14 min and with different powers: 0.45, 0.63, and 0.9 kW. At the end of extraction, the glass vessel was placed in a cold-water bath, and after cooling, the mixture was filtered by centrifuge at 1500 R.P.M. for 20 min. In the next step, the pH was adjusted to 3.5 with 0.1 N NaOH. Then the filtrate was coagulated using a volume equal to one and a half of 96% ethanol (ER = 1.5) and left for 6 h. The coagulated pectin was separated by centrifuge and washed twice with 96% ethanol. It was dried at 50 ◦ C in a laboratory drier. The ratio of dried peel to water and values of ER and pH kept constant in all experiments. All experiments were done in duplicate and the error percent was calculated and reported for every single step. 2.4.2. Extraction of pectin from dried albedo using UAE In this stage, the effect of ultrasound treatment was studied. Similar to microwave experiments, the dry mass (6 g) of dried grapefruit peels was subjected to extraction by adding 300 ml water and pH was adjusted to 1.5 by 0.1 N HCl. Then the samples were heated in a water bath with constant temperature at three levels of temperature (50, 60, and 70 ◦ C) and were simultaneously sonicated at six periods of 4, 12, 15, 20, 25 and 30 min. 2.4.2.1. UAE as a pretreatment for MAE. To investigate the effects of ultrasound as a pretreatment method on the extracted pectin, some experiments were done like aforementioned method, but without any HCl. First, the grapefruit solution was sonicated for different durations of exposure under continuous or intermittent sonication. After adding HCl, it was heated in the microwave to complete the process in power of 0.45 kW for 8 min. In order to perform intermittent sonication, an apparatus with the adjustable sonication cycle was used. It was set to emit ultrasound waves for a definite time and then stop automatically. In our specific case, ultrasound waves were emitted for 30 s, stop for 30 s, and then the same procedure.
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Fig. 1. The effect of heating time and microwave power on quantity of extracted pectin (yield obtained from conventional method: 19.16 (%w/w)).
The ultrasound-assisted extraction (UAE) was done in a water bath with constant temperature. As soon as the thermometer showed a value different form the desired temperature, it was adjusted by changing the water bath temperature. It should be noted that the ultrasound showed no instant effect on the temperature of the extracted solution, therefore variation of the solution temperature was always less than 3 ◦ C. 2.4.3. Extraction of pectin from dried albedo by conventional method To extract the pectin with conventional method, all of the procedure in Section 2.4.1 was carried out, but instead of microwave heating in extracting stage, a water bath heating was used at constant temperature of 90 ◦ C. The extraction stage was performed in 90 min. 3. Results and discussion 3.1. Pectin extraction using MAE 3.1.1. The effects of MAE on quantitative characteristics (yield) The experimental data showing the effects of the microwave power and duration of microwave heating on the quantity of pectin has been presented in Fig. 1. The average yield values in different microwave field intensities of 0.45, 0.63, and 0.9 kW were 21.23, 22.71, and 26.27%, respectively which showed a remarkable increase in comparison to the conventional method (yield, 19.16%). Besides, the improvements in yield were proportional to the power and duration of microwave heating (Fig. 1). In the conventional method, it took 90 min to get a high yield, whilst this time reduced to 2 min in MAE to extract the same amount of pectin. Theoretically, microwave radiation loosens the cell wall matrix and leads to severing of the parenchymal cells [9], thereby the skin tissues are rapidly and extensively opened up by the microwave. This will lead to increased interaction between extracting agent and source material in extraction process. As a result, permeation of the extracting agent will be increased. It leads to effective increase in the yield of pectin extraction. Based on the reported data by Yoeh et al. [11], the amount of extracted pectin increased with the extraction period, but the increase was gradual. The greatest total amount of pectin yield was found to be 5.27% on a dry basis for 15 min of extraction which was obtained after 5 min. Also, the experimental data obtained by Kratchanova et al. [9] showed a similar trend. There was a rise of only about 1.4% for the yield of pectin, from 14% to 15.4% between 5 min and 10 min of extraction. However, the pectin yield found by Kratchanova et al. [9] was three times larger than that obtained by Yoeh et al. [11]. All of these reports are in accordance with our observations. According to obtained data, the yield of pectin extrac-
Fig. 2. The effect of heating time and microwave power on DE of extracted pectin (DE of pectin obtained from conventional method was 75.61 (%)).
tion significantly increased with an increase in heating time. In the power of 450 W, the extraction yield increased 34.30%, after 8 min. These improvements were 26.25% and 13.46% for the powers of 630 and 900 W, respectively, after 4 min. Furthermore, the yield improvements were more obvious between interval of 2 and 8 min, but less obvious after 8 min at power of 0.45 kW. In the beginning of the process the yield improved with a sharp rate and then by approaching to an equilibrium state, there was a gradual increase in the yield. After a definite duration of exposure for each field power, the pectin degraded which is the main reason for the yield decrease (Fig. 1). In addition, the quantities in Fig. 1 confirm that there is an inverse correlation between the field power and required time to achieve the most yields. In case of weaker field powers, longer heating time is needed. For instance the pectin yield in microwave radiation of 450 W and 14 min (22.11%) was close to the one in power of 630 W and 10 min (22.65%). These results are in accordance with observations reported by Kratchanova et al. [9]. In this section, the results were reproducible with an average error of about 0.6, 0.7, and 0.8% for the power of 0.45, 0.63, and 0.9 kW, respectively. 3.1.2. The effects of MAE on qualitative characteristics The effects of the microwave field power and duration of microwave heating on the degree of esterification (DE) of the extracted pectin are presented in Fig. 2. The values for DE changed from 70.96 to 80.89% which falls in the range of “commercially available food-grade high methoxyl pectin” [25]. It could be seen that DE increased with an increase in microwave power and heating time, the same as Katchanova’s results [8]; however, using MAE method, DE was not significantly more than conventional method. It should be noted that these results were reproducible with an average error of about 2%. The effects of heating time and microwave field power on GalA have been showed in Fig. 3. With changes in operating parameters, GalA values changed from 66.27 to 75.91% which is favorable in food industries. Similar to the others, GalA was improved with an increase in power and time. The increased GalA values can be explained by the improved penetration in the plant tissue of NaOH during the titration analysis of the peels [9]. For the GalA, the experimental data error was about 2.3%. Fig. 4 shows the values of molecular weight versus time and power. It is evident from this graph that the molecular weight decreased with an increase in heating time; moreover, the molecular weight reduction is more substantial with the increase in power. Reduction of molecular weight with increasing heating time and microwave power (temperature) could be explained by this the-
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Fig. 3. The effect of heating time and microwave power on GalA of extracted pectin (GalA of pectin obtained from conventional method was 69.89 (%)).
ory that continued heating of pectin may lead to disaggregation of pectin networks into its component parts (pectin degradation). This phenomenon has been reported elsewhere by Fishman et al. [12]. The presented data in Fig. 4 were also reproducible with almost 3% average error. 3.2. Ultrasound-assisted extraction of pectin 3.2.1. Treatment by ultrasound In this section, the effect of ultrasound on the pectin extraction has been investigated and the obtained experimental data have been presented in Tables 1 and 2. Both UAE and conventional methods have been done to be able to compare the results. As it is shown in Table 1, the values of extracted pectin by UAE method is significantly more than that by conventional method. The lowest yield is for the sonication time of 10 min (13.51%) which is relatively acceptable in comparison to the conventional method yield (19.16%) after 90 min. Besides, with increasing the extraction process in a constant temperature (e.g. 70 ◦ C), the pectin yield increased at first, reached a maximum after 25 min and then decreased within the time. The decrease in the pectin yield by increasing the extraction period may be due to the thermal degradation of the extracted pectin.
It can be concluded that there is always an optimum sonication time to obtain the best yield, as reported by Panchev et al. [18]. They investigated the sonication time from 10 to 60 min and reported 30 min as the optimum time, the observed trend in this study. According to Table 1, galacturonic acid, degree of esterification, and molecular weight were changed from 66.12% to 68.45%, 76.28% to 74.88%, and 84.4 to 56.4 (kDa), respectively. GalA parameter was in an ascending order with the sonication time, whilst DE and the molecular weight decreased with an increase in the sonication time. Although these changes are not significant, but it is worth nothing that these values have been changed and are comparable to the conventional results. Based on the presented data and what was mentioned about the qualitative and quantitative characteristics improvements by UAE, one can say that ultrasound may assist with extraction processes both through cell disruption and by enhancing mass transfer in the boundary layer surrounding the solid matrix [26]. The energy generated from collapsing cavitational bubbles causes the disruption of cell walls and release of cellular materials, so the yield can be improved by the use of ultrasound [27]. On the other hand, the effect of temperature in UAE, in three different levels, on the pectin yield at a constant time (15 min) has been presented in Table 2. It was obtained that the pectin molecular weight decreased with increasing the temperature which is a consequent of pectin degradation. The more the temperature, the more the produced cavitational bubbles. By breaking these bubbles the shear stress increases, resulting in degradation of pectin chain into smaller components. According to the presented data, one can conclude that obtaining an optimum time and temperature is of great importance to achieve high yields. 3.2.2. Pretreatment by ultrasound for MAE In this section, the effect of ultrasound as a pretreatment for the MAE method on the pectin extraction was investigated and the experimental data have been presented in Figs. 5–8. In these conditions, not only a high yield was observed, but also, pectin qualitative characteristics were improved in comparison to the conventional and MAE methods. According to these data and Figs. 5–8, it can be concluded that intermittent sonication resulted in a better yields comparing to continuous sonication. It can be explained by the fact
Fig. 4. The effect of heating time and microwave power on the molecular weight of extracted pectin (pectin viscosity obtained from conventional method was 3.98 (dL/g)).
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Table 1 The effect of sonication time on the pectin yield at constant temperature bath (70 ◦ C). Sonication time (min)
Yield of pectin using UAE (%w/w)
yield of pectin using conventional method (%w/w)
GalA (%)
DE (%)
Molecular weight (kDa)
10 15 20 25 28 30
13.51 14.87 16.68 17.92 16.42 15.71
6.64 7.12 7.59 8.43 9.11 9.51
66.12 67.62 67.51 68.21 68.51 68.45
76.28 75.69 75.45 75.12 75.23 74.88
84.4 76.5 73.8 68.3 63.1 56.4
Table 2 The effect of temperature on the pectin yield at constant time (15 min). Bath temperature (◦ C)
Yield of pectin (%w/w)
GalA (%)
DE (%)
Molecular weight (kDa)
60 70 80
12.72 14.87 13.91
66.12 67.62 68.25
76.12 75.69 75.34
84.4 76.5 57.8
34
84
Intermient Sonicaon
26
81 80
24
79
22 20
30
78
40
20
30
time(min)
that intermittent sonication makes a pulsation in the ultrasound waves leading to decreasing mass boundary layer and reducing the resistances. Consequently, the extraction will be improved as it was showed by the experiments. In addition, the more the sonication time, the better the qualitative and quantitative characteristics. However, since the duration of extraction process is of great importance in a proper method, the range of 30–40 min seems to be an optimum time for the pretreatment process by ultrasound.
GalA(%)
3.3. Comparison of extracted pectin using three extraction methods As illustrated in previous sections, pectin was extracted from grapefruit by different extraction techniques including conventional, MAE, UAE, and using ultrasound as a pretreatment for MAE (UAE + MAE) method (Table 3). UAE + MAE method showed the best effect on the qualitative and quantitative characteristics of extracted pectin. The only problem is that this method is a time con-
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Intermient Sonicaon
74.5 74 73.5 73 72.5 72 71.5
Fig. 7. The effects of sonication time and the kind of sonication, as a pretreatment, on DE of extracted pectin.
Molecular Wieght(Da)
Connuous Sonicaon
40
time(min)
Fig. 5. The effects of sonication time and the kind of sonication, as a pretreatment, on the yield of extracted pectin.
75
Intermient Sonicaon
82
28
20
Connuous Sonicaon
83
30
DE(%)
yield(%w/w)
32
connuous sonicaon
connuous sonicaon
Intermient Sonicaon
115000 110000 105000 100000 95000 90000 85000 80000
20
30
40
time(min) Fig. 6. The effects of sonication time and the kind of sonication, as a pretreatment, on GalA of extracted pectin.
20
30
40
time(min) Fig. 8. The effects of sonication time and the kind of sonication, as a pretreatment, on the extracted pectin.
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Table 3 The effects of different extraction methods on the qualitative and quantitative characteristics of extracted pectin. Extraction technique
References
Properties
Conditions
Yield
DE
GalA
Intrinsic viscosity
[3]
21.1%
68.2%
74%
–
[11]
18%
–
–
This paper
19.16%
75.6%
69.9%
3.98 dL/g
[25]
11.3%
93.0%
98.0%
7.7 dL/g
[9]
18%
74.8%
66.5%
3.1 dL/g
[11] [28]
15.4% 6.2%
– 66%
– 88%
– 14 dL/g
This paper
27.81%
79.35%
74.86%
2.61 dL/g
[18]
13.3%
66.4%
58.5%
250 ◦ TB
This paper
17.92%
75.12%
68.21%
3.23 dL/g
This paper
31.88%
82.61%
74.25%
4.8 dL/g
Conventional
MAE
UAE
UAE + MAE
a
–
T = 85 ◦ C; t = 90 min; pH = 2.5; AWRa = 1 g/25 ml AWR = 1 g/16 ml; t = 3 h, T = 100 ◦ C, pH = 1.5 T = 90 ◦ C; t = 90 min; pH = 1.5; AWR = 1 g/30 ml t = 3 min; AWR = 1 g/25 ml, pw = 0.63 KW AWR = 1 g/16 ml; pw = 0.9 kW; t = 10 min AWR = 1 g/16 ml; t = 10 min; T = 120 ◦ C AWR = 1 g/25 ml; t = 2.5 min, P = 50 lbs/in2 ; pw = 0.9 kW; time = 6 min; AWR = = 1 g/30 ml Intermittent sonication; T = 80 ◦ C; time = 45 min; AWR = 1 g/20 ml Intermittent sonication; AWR = 1 g/30 ml; T = 70 ◦ C; t = 25 min AWR = 1 g/30 ml; intermittent sonication; the time of sonication = 30 min; the time of microwave heating = 10 min; PW = 0.45 kW
AWR: Albedo/Water Ratio.
Fig. 9. Comparison of pectin yield and various characteristics using different extraction methods.
suming one, whilst the shortest process time was for UAE method taking a relatively short time and giving acceptable results. On the other hand, the single MAE method gave better results than UAE with the optimum operating conditions like time and power. The whole results are presented in Fig. 9 for more comparison. Total energy consumption associated with each technique was roughly estimated for the different extraction techniques. These estimations were for the maximum yield obtained by the microwave and ultrasound methods. The consumed energy was equal to the power field multiply by the exposure time. The energy consumption associated with MAE (0.9 kW and 6 min) and UAE (200 W and 25 min) are 324 and 300 kJ, respectively, which are roughly the same.
4. Conclusions The effects of microwave field power and heating time were investigated using microwave extraction. These parameters improved the qualitative and quantitative characteristics of extracted pectin. These improvements included the considerable increase in the yield of pectin as well as degree of esterification, Galactronic Acid, and viscosity. Besides, the 2 min microwave heating period was enough to extract the same amount of pectin as obtained from the 90 min conventional extraction period. On the other hand, the extraction procedure with application of ultrasound in water bath were used to examine the effects of sonication on the extracted pectin. Sonication time and bath temperature are impor-
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tant factors influencing the extraction of pectin. It was concluded that there is an optimum sonication time and (bath) temperature to obtain the best yield. In comparison to the ultrasound assisted extraction, the conventional method gave a slightly higher yield; however, the rate of ultrasonic extraction was over 3 times faster than conventional extraction. In addition, ultrasound was used as a pretreatment for the microwave heating giving better results than microwave assisted extraction.
References [1] S. Wang, F. Chen, J. Wu, Z. Wang, X. Liao, X. Hu, Optimization of pectin extraction assisted by microwave from apple pomace using response surface methodology, Journal of Food Engineering 78 (2007) 693–700. [2] W.G.T. Willatsa, J.P. Knox, J.D. Mikkelsen, Pectin: new insights into an old polymer are starting to gel, Journal of Trends in Food Science & Technology 17 (3) (2006) 97–104. [3] N. Arslan, H. Togru 1, Filtration of pectin extract from grapefruit peel and viscosity of pectin solutions, Journal of Food Engineering. 27 (1996) 191– 201. [4] M.R. Wilkins, W.W. Widmer, K. Grohmann, R.G. Cameron, Hydrolysis of grapefruit peel waste with cellulase and pectinase enzymes, Journal of Bioresource Technology 98 (8) (2007) 1596–1601. [5] C.D. May, Industerial pectins: sources, production and application, Journal of Carbohydrate Polymers 12 (1990) 79–99. [6] R. Sanati Faravash, F. Zokaee Ashtiani, The influence of acid volume, ethanolto-extract ratio and acid-washing time on the yield of pectic substances extraction from peach pomace, Journal of Food Hydrocolloids 22 (2008) 196– 202. [7] C. Kratchanov, K. Marew, N. Kirtchev, A. Bratanoff, Improving pectin technology: extraction using pulsating hydrodynamic action, Journal of Food Technology 21 (1986) 751–761. [8] M. Kratchanova, I. Panchev, E. Pavlova, L. Shtereva, Extraction of pectin from fruit materials pretreated in an electromagnetic field of super-high frequency, Journal of Carbohydrate Polymers 25 (1994) 141–144. [9] M. Kratchanova, I. Panchev, E. Pavlova, The effect of microwave heating of fresh orange peels on the fruit tissue and quality of extracted pectin, Journal of Carbohydrate Polymers 56 (2004) 181–185. [10] L. Zhongdong, W. Guohua, G. Yunchang, J.F. Kennedy, Image study of pectin extraction from orange skin assisted by microwave, Journal of Carbohydrate Polymers 64 (2006) 548–552.
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[11] S. Yeoh, J. Shi, T.A.G. Langrish, Comparisons between different techniques for water-based extraction of pectin from orange peels, Journal of Desalination 218 (2008) 229–237. [12] M.L. Fishman, H.K. Chau, P. Hoagland, K. Ayyad, Characterization of pectin, flash-extracted from orange albedo by microwave heating, under pressure, Journal of Carbohydrate Research 323 (2000) 126–138. [13] M.L. Fishman, H.K. Chau, Extraction of pectin by microwave heating under pressure. United States Patent, 6(143) (2000) 337. [14] Z. Kohg, Z.D. Lin, S.T. LinChen, Study on the extraction of pectin from apple pomace with MW, Journal of Zhengzhou Grain College 21 (2000) 11–15. [15] M. Kratchanova, E. Pavlova, I. Panchev, Chr. Kratchanov, Influence of microwave pretreatment of fresh orange peels on pectin extraction, Journal of Progress in Biotechnology 14 (1996) 941–944. [16] M. Manabe, I. Naohara, T. Sato, J. Okada, The extraction of pectin by microwave heating, Nippon Shokuhin Kogyo Gakkaishi 35 (1988) 497–501. [17] C. Leonellia, T.J. Masonb, Microwave and ultrasonic processing: now a realistic option for industry, Journal of Chemical Engineering and Processing 49 (2010) 885–900. [18] I. Panchev, N. Kirchev, C. Kratchanov, Improving pectin technology. 11. Extraction using ultrasonic treatment, Journal of Food Science and Technology 23 (1988) 337–341. [19] R. Seshadri, J. Weiss, J.G. Hulbert, Ultrasonic processing influences rheological and optical properties of highmethoxyl pectin dispersions, Journal of Food Hydrocolloids 17 (2003) 191–197. [20] I. Panchev, N. Kirchev, C. Kratchanov, On the production of low esterified pectins by acid maceration of pectic raw materials with ultrasound treatment, Journal of Food Hydrocolloids 8 (1994) 9–17. [21] T.H. Schultz, Determination of the degree of esterification of pectin, Journal of Carbohydrate Chemistry 5 (1965) 189–191. [22] A. Ibarz, A. Pagan, F. Tribaldo, J. Pagan, Improvement in the measurement of spectrophotometric data in the m-hydroxydiphenyl pectin determination methods, Journal of Food Control 17 (2006) 890–893. [23] J. Pagan, A. Ibraz, M. Llorca, A. Pagan, G.V. Barbosa Canovas, Extraction and characterization of pectin from stored peach pomace, Journal of Food Research International 34 (2001) 605–612. [24] M.S. Alistair, O.P. Glyn, A.W. Peter, Food Polysaccharide and their Applications, 2nd ed., CRC Press, New York, 2006. [25] C. Brain, B. Johnston, Spreadable honey, US patents, 4,532,143 (1985). [26] R.K. Bhaskaracharya, S. Kentish, M. Ashokkumar, Selected applications of ultrasonics in food processing, Journal of Food Engineering Review 1 (2009) 31–49. [27] A. Patist, D. Bates, Ultrasonic innovations in the food industry: from the laboratory to commercial production, Journal of Innovative Food Science and Emerging Technologies 9 (2008) 147–154. [28] M.L. Fishman, H.K. Chau, P. Hoagland, T.H. Arland, Microwave-assisted extraction of lime pectin, Journal of Food Hydrocolloids 20 (2006) 1170–1177.
Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Comparisons between conventional, microwave- and ultrasound-assisted methods for extraction of pectin from grapefruit Homa Bagherian, Farzin Zokaee Ashtiani ∗ , Amir Fouladitajar, Mahdy Mohtashamy Department of Chemical Engineering, Amirkabir University of Technology, No. 424, Hafez Ave., Tehran, Iran
a r t i c l e
i n f o
Article history: Received 6 February 2011 Received in revised form 6 June 2011 Accepted 7 August 2011 Available online 12 August 2011 Keywords: Pectin Extraction Microwave-assisted Extraction (MAE) Ultrasound-assisted extraction (UAE) Yield
a b s t r a c t Microwave-assisted Extraction (MAE) and Ultrasound-assisted extraction (UAE) techniques have been employed as complementary methods to extract carbohydrates, polysaccharides and other functional compounds from vegetable sources. In this work, the effect of microwave power and heating time on the yield and quality of extracted pectin from grapefruit was investigated. The highest total amount of pectin yield was found to be 27.81% (w/w) for 6 min of extraction at 900 W. It was observed that yield, the galacturonic acid content (GalA), and degree of esterification (DE) increased with an increase in microwave power and heating time. Besides, the molecular weight decreased with an increase in heating time; however, the effects of power on the molecular weight were dramatically more than heating time. In addition, laboratory studies on the extraction of pectin treated with high-intensity ultrasound were carried out. The effects of temperature and time on quality and quantity of extracted pectin were investigated. The highest yield was for sonication time of 25 min (17.92%) in a constant bath temperature of 70 ◦ C. Furthermore, a preliminary ultrasonic heating of grapefruit solution, as a pretreatment for MAE, was found to provide a higher yield. Intermittent sonication gave better results in comparison to the continuous sonication. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Pectin is a family of complex polysaccharides of ␣-d-(1→4) galacturonic acid present in the primary cell wall and middle lamella of the plant tissues. Pectin contains a backbone of (1–4) ␣-d-galacturonic acid residues which are partially esterified with methyl alcohol at the carboxylic acid [1]. All pectins are characterized by a high content of galacturonic acid (GalA) and according to the regulation of FAO and EU ‘pectin’ must contain at least 65% GalA [2]. There are various sources in pectin production. It is possible to produce acceptable pectin from both apple pomace and citrus peels. The pectin content of citrus peel such as orange, grapefruit and lemon is usually as high as 25–30% of the dried peel mass [3]. The grapefruit peel contains several mono and disaccharides; the main ones are glucose, sucrose and fructose, as well as the polysaccharides cellulose, hemicelluloses and pectin [4]. The major use of pectin is as a gelling, stabilizing and thickening agent in food systems such as jams and jellies, confectionery, and
∗ Corresponding author. Tel.: +98 21 6454 3124; fax: +98 21 66405847. E-mail address: [email protected] (F. Zokaee Ashtiani). 0255-2701/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2011.08.002
fruit juice. Pectin is also used in pharmaceutical industry, suggested to reduce heart disease and gallstones. Conventionally, pectin is extracted in a hot dilute mineral acidic solution. The time needed depends on some factors like raw material and the type of pectin desired, and varies from one manufacturer to another, but generally, this process is time consuming [5,6]. This condition leads to pectin degradation, so conventional methods are not appropriate for both quantity and quality of the pectin extraction. Accordingly, using an opportune method is of great importance in order to achieve the best quality and quantity characteristics of extracted pectin. Various methods for extraction of pectin have already been investigated which in most cases results have been satisfactory. These methods include using pulsating hydrodynamic action with turbulent recirculation [7] which leads to increased yield, reduced process time and production costs. Microwave-assisted Extraction (MAE) is another method which has been recently investigated by many researchers finding that the MAE can lead to a considerable increase in the yield and quality of extracted pectin. For instance, extraction of pectin from fruit materials pretreated in an electromagnetic field of super-high frequency [8] led to higher pectin yield and higher values for degree of esterification (DE) and gel strength compared with the no-pretreated samples. In another work, using Scanning electron micrographs Kratchanova et al. [9] reported that
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microwave heating disrupted parenchymal cells. It was also found that specific surface and the water absorption capacity of the orange tissue were reduced; moreover, the endogenous enzymes of the peels became inactive. MAE has also been applied to pectin extraction from dried apple pomace. Response Surface Methodology (RSM) has been used to optimize the effects of processing parameters of extraction on the yield of pectin [1]. Microwave-assisted Extraction of pectin from orange skin has also been investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) [10]. Some similar studies have been done to extract pectin, mostly from orange, with different extraction periods, solvent pHs, and types of solvent systems [11–16]. In one of these studies, pectin was acid extracted from orange albedo by microwave heating under pressure by Fishman et al. [12,13]. As an applicable and new method, the application of ultrasound for assisting extraction (UAE) from plant material is widely published [17]; however, a few experiments have been done for pectin extraction by this method. All of the published studies under ultrasound conditions indicate increased yield or extraction rate as well as reduction in extraction time. The effect of ultrasonic treatment on pectin stability in aqueous solution was studied to establish conditions minimizing degradation [18]. Ultrasonication improved the pectin yield by 28% and reduced the time for extraction. The effect of high-intensity ultrasound on the rheological and optical properties of high-methoxyl pectin dispersions was studied by Seshadri [19]. Ultrasonically pretreated pectin formed weaker gels with increasing sonication power and time. In another work, intensifying the process of pectin deesterification by combining the acid maceration of raw materials with ultrasound treatment was investigated by Panchev et al. [20]. An additional decrease in the degree of esterification of pectin (about 6%) and a significant increase in the yield of pectin (about 18%) were reported. The optimum ultrasound treatment proved to be within 24–30 min and prolonged treatment can result in obtaining pectin with lower gel strengths [20]. To the best of our knowledge, there is no comprehensive study on the effects of microwave and ultrasound on the qualitative and quantitative characteristics of the extracted pectin from grapefruit. This work reports the effects of microwave on the yield and quality of extracted pectin in comparison to the conventional method. In addition, ultrasound and its optimum operating conditions, as a pretreatment for the MAE method or single use, will be discussed. 2. Experimental 2.1. Samples preparation Turkish grapefruit, purchased in a local fruit market, was chosen as the raw material in these experiments. The peels were stripped with a paring knife. The albedos were cut into small pieces then were dried in an oven with a gentle flow of air at 50 ◦ C. The albedos were first ground, then screened by sieve, subsequently the particles smaller than 0.6 mm in diameter were selected. 2.2. Apparatus Microwave-assisted Extraction (MAE) was performed in an experimental microwave oven (Samsung, Model PG-3200, Korea) with the power of 900 W and the frequency was set on 2450 MHz. A 200 W, 24 kHz ultrasonic processor (UP200H with S7, Dr. Hielscher, Teltow, Germany) was also used as the sonic probe in the ultrasound-assisted extraction (UAE). For the temperature measurement, there was a sensor in the microwave oven which could have been used for the temperature measurement. For the ultrasound-assisted extraction (UAE),
the material was set in a water bath and the temperature was measured by a thermometer. In the used microwave apparatus, a definite power value was specified and applied within the whole duration of exposure rather than using a pulsating heating cycle with varying time fraction. 2.3. Methods of analysis After the extraction, the wet pectin was dried at 50 ◦ C until its weight remained constant. The yield of pectin was expressed as the weight of dried pectin extracted from dried peels (w/w). Degree of esterification (DE) of extracted pectin was determined using titration with NaOH before saponification and back titration with HCl after saponification [21]. The galacturonic acid content (GalA) was determined by the method of colorimetry with meta-hydroxydiphenyl and a JASCO spectrophotometer (model V-550, Japan) [22]. The value of metoxyl group was calculated using extents of galacturonic acid and degree of esterification. Finally, intrinsic viscosity was obtained by using a capillary tube viscometer (ubbelohde, the diameter of capillary tube was 0.58 mm) [23] then the molecular weight was obtained according to Anger–Berth equation [24]. All the experiments were done in duplicate and results were reproducible with an acceptable average error. 2.4. Procedures 2.4.1. Extraction of pectin from dried albedo using MAE The dry mass (6 g) of dried grapefruit peels was subjected to extraction by adding 300 ml distilled water. The pH was adjusted to 1.5 with 0.1 N HCl as extracting agent. The mixture was placed in the center of a microwave oven, containing a circular, 360◦ rotating carousel with different durations of exposure: 2, 4, 6, 8, 10, 12, 14 min and with different powers: 0.45, 0.63, and 0.9 kW. At the end of extraction, the glass vessel was placed in a cold-water bath, and after cooling, the mixture was filtered by centrifuge at 1500 R.P.M. for 20 min. In the next step, the pH was adjusted to 3.5 with 0.1 N NaOH. Then the filtrate was coagulated using a volume equal to one and a half of 96% ethanol (ER = 1.5) and left for 6 h. The coagulated pectin was separated by centrifuge and washed twice with 96% ethanol. It was dried at 50 ◦ C in a laboratory drier. The ratio of dried peel to water and values of ER and pH kept constant in all experiments. All experiments were done in duplicate and the error percent was calculated and reported for every single step. 2.4.2. Extraction of pectin from dried albedo using UAE In this stage, the effect of ultrasound treatment was studied. Similar to microwave experiments, the dry mass (6 g) of dried grapefruit peels was subjected to extraction by adding 300 ml water and pH was adjusted to 1.5 by 0.1 N HCl. Then the samples were heated in a water bath with constant temperature at three levels of temperature (50, 60, and 70 ◦ C) and were simultaneously sonicated at six periods of 4, 12, 15, 20, 25 and 30 min. 2.4.2.1. UAE as a pretreatment for MAE. To investigate the effects of ultrasound as a pretreatment method on the extracted pectin, some experiments were done like aforementioned method, but without any HCl. First, the grapefruit solution was sonicated for different durations of exposure under continuous or intermittent sonication. After adding HCl, it was heated in the microwave to complete the process in power of 0.45 kW for 8 min. In order to perform intermittent sonication, an apparatus with the adjustable sonication cycle was used. It was set to emit ultrasound waves for a definite time and then stop automatically. In our specific case, ultrasound waves were emitted for 30 s, stop for 30 s, and then the same procedure.
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Fig. 1. The effect of heating time and microwave power on quantity of extracted pectin (yield obtained from conventional method: 19.16 (%w/w)).
The ultrasound-assisted extraction (UAE) was done in a water bath with constant temperature. As soon as the thermometer showed a value different form the desired temperature, it was adjusted by changing the water bath temperature. It should be noted that the ultrasound showed no instant effect on the temperature of the extracted solution, therefore variation of the solution temperature was always less than 3 ◦ C. 2.4.3. Extraction of pectin from dried albedo by conventional method To extract the pectin with conventional method, all of the procedure in Section 2.4.1 was carried out, but instead of microwave heating in extracting stage, a water bath heating was used at constant temperature of 90 ◦ C. The extraction stage was performed in 90 min. 3. Results and discussion 3.1. Pectin extraction using MAE 3.1.1. The effects of MAE on quantitative characteristics (yield) The experimental data showing the effects of the microwave power and duration of microwave heating on the quantity of pectin has been presented in Fig. 1. The average yield values in different microwave field intensities of 0.45, 0.63, and 0.9 kW were 21.23, 22.71, and 26.27%, respectively which showed a remarkable increase in comparison to the conventional method (yield, 19.16%). Besides, the improvements in yield were proportional to the power and duration of microwave heating (Fig. 1). In the conventional method, it took 90 min to get a high yield, whilst this time reduced to 2 min in MAE to extract the same amount of pectin. Theoretically, microwave radiation loosens the cell wall matrix and leads to severing of the parenchymal cells [9], thereby the skin tissues are rapidly and extensively opened up by the microwave. This will lead to increased interaction between extracting agent and source material in extraction process. As a result, permeation of the extracting agent will be increased. It leads to effective increase in the yield of pectin extraction. Based on the reported data by Yoeh et al. [11], the amount of extracted pectin increased with the extraction period, but the increase was gradual. The greatest total amount of pectin yield was found to be 5.27% on a dry basis for 15 min of extraction which was obtained after 5 min. Also, the experimental data obtained by Kratchanova et al. [9] showed a similar trend. There was a rise of only about 1.4% for the yield of pectin, from 14% to 15.4% between 5 min and 10 min of extraction. However, the pectin yield found by Kratchanova et al. [9] was three times larger than that obtained by Yoeh et al. [11]. All of these reports are in accordance with our observations. According to obtained data, the yield of pectin extrac-
Fig. 2. The effect of heating time and microwave power on DE of extracted pectin (DE of pectin obtained from conventional method was 75.61 (%)).
tion significantly increased with an increase in heating time. In the power of 450 W, the extraction yield increased 34.30%, after 8 min. These improvements were 26.25% and 13.46% for the powers of 630 and 900 W, respectively, after 4 min. Furthermore, the yield improvements were more obvious between interval of 2 and 8 min, but less obvious after 8 min at power of 0.45 kW. In the beginning of the process the yield improved with a sharp rate and then by approaching to an equilibrium state, there was a gradual increase in the yield. After a definite duration of exposure for each field power, the pectin degraded which is the main reason for the yield decrease (Fig. 1). In addition, the quantities in Fig. 1 confirm that there is an inverse correlation between the field power and required time to achieve the most yields. In case of weaker field powers, longer heating time is needed. For instance the pectin yield in microwave radiation of 450 W and 14 min (22.11%) was close to the one in power of 630 W and 10 min (22.65%). These results are in accordance with observations reported by Kratchanova et al. [9]. In this section, the results were reproducible with an average error of about 0.6, 0.7, and 0.8% for the power of 0.45, 0.63, and 0.9 kW, respectively. 3.1.2. The effects of MAE on qualitative characteristics The effects of the microwave field power and duration of microwave heating on the degree of esterification (DE) of the extracted pectin are presented in Fig. 2. The values for DE changed from 70.96 to 80.89% which falls in the range of “commercially available food-grade high methoxyl pectin” [25]. It could be seen that DE increased with an increase in microwave power and heating time, the same as Katchanova’s results [8]; however, using MAE method, DE was not significantly more than conventional method. It should be noted that these results were reproducible with an average error of about 2%. The effects of heating time and microwave field power on GalA have been showed in Fig. 3. With changes in operating parameters, GalA values changed from 66.27 to 75.91% which is favorable in food industries. Similar to the others, GalA was improved with an increase in power and time. The increased GalA values can be explained by the improved penetration in the plant tissue of NaOH during the titration analysis of the peels [9]. For the GalA, the experimental data error was about 2.3%. Fig. 4 shows the values of molecular weight versus time and power. It is evident from this graph that the molecular weight decreased with an increase in heating time; moreover, the molecular weight reduction is more substantial with the increase in power. Reduction of molecular weight with increasing heating time and microwave power (temperature) could be explained by this the-
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Fig. 3. The effect of heating time and microwave power on GalA of extracted pectin (GalA of pectin obtained from conventional method was 69.89 (%)).
ory that continued heating of pectin may lead to disaggregation of pectin networks into its component parts (pectin degradation). This phenomenon has been reported elsewhere by Fishman et al. [12]. The presented data in Fig. 4 were also reproducible with almost 3% average error. 3.2. Ultrasound-assisted extraction of pectin 3.2.1. Treatment by ultrasound In this section, the effect of ultrasound on the pectin extraction has been investigated and the obtained experimental data have been presented in Tables 1 and 2. Both UAE and conventional methods have been done to be able to compare the results. As it is shown in Table 1, the values of extracted pectin by UAE method is significantly more than that by conventional method. The lowest yield is for the sonication time of 10 min (13.51%) which is relatively acceptable in comparison to the conventional method yield (19.16%) after 90 min. Besides, with increasing the extraction process in a constant temperature (e.g. 70 ◦ C), the pectin yield increased at first, reached a maximum after 25 min and then decreased within the time. The decrease in the pectin yield by increasing the extraction period may be due to the thermal degradation of the extracted pectin.
It can be concluded that there is always an optimum sonication time to obtain the best yield, as reported by Panchev et al. [18]. They investigated the sonication time from 10 to 60 min and reported 30 min as the optimum time, the observed trend in this study. According to Table 1, galacturonic acid, degree of esterification, and molecular weight were changed from 66.12% to 68.45%, 76.28% to 74.88%, and 84.4 to 56.4 (kDa), respectively. GalA parameter was in an ascending order with the sonication time, whilst DE and the molecular weight decreased with an increase in the sonication time. Although these changes are not significant, but it is worth nothing that these values have been changed and are comparable to the conventional results. Based on the presented data and what was mentioned about the qualitative and quantitative characteristics improvements by UAE, one can say that ultrasound may assist with extraction processes both through cell disruption and by enhancing mass transfer in the boundary layer surrounding the solid matrix [26]. The energy generated from collapsing cavitational bubbles causes the disruption of cell walls and release of cellular materials, so the yield can be improved by the use of ultrasound [27]. On the other hand, the effect of temperature in UAE, in three different levels, on the pectin yield at a constant time (15 min) has been presented in Table 2. It was obtained that the pectin molecular weight decreased with increasing the temperature which is a consequent of pectin degradation. The more the temperature, the more the produced cavitational bubbles. By breaking these bubbles the shear stress increases, resulting in degradation of pectin chain into smaller components. According to the presented data, one can conclude that obtaining an optimum time and temperature is of great importance to achieve high yields. 3.2.2. Pretreatment by ultrasound for MAE In this section, the effect of ultrasound as a pretreatment for the MAE method on the pectin extraction was investigated and the experimental data have been presented in Figs. 5–8. In these conditions, not only a high yield was observed, but also, pectin qualitative characteristics were improved in comparison to the conventional and MAE methods. According to these data and Figs. 5–8, it can be concluded that intermittent sonication resulted in a better yields comparing to continuous sonication. It can be explained by the fact
Fig. 4. The effect of heating time and microwave power on the molecular weight of extracted pectin (pectin viscosity obtained from conventional method was 3.98 (dL/g)).
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Table 1 The effect of sonication time on the pectin yield at constant temperature bath (70 ◦ C). Sonication time (min)
Yield of pectin using UAE (%w/w)
yield of pectin using conventional method (%w/w)
GalA (%)
DE (%)
Molecular weight (kDa)
10 15 20 25 28 30
13.51 14.87 16.68 17.92 16.42 15.71
6.64 7.12 7.59 8.43 9.11 9.51
66.12 67.62 67.51 68.21 68.51 68.45
76.28 75.69 75.45 75.12 75.23 74.88
84.4 76.5 73.8 68.3 63.1 56.4
Table 2 The effect of temperature on the pectin yield at constant time (15 min). Bath temperature (◦ C)
Yield of pectin (%w/w)
GalA (%)
DE (%)
Molecular weight (kDa)
60 70 80
12.72 14.87 13.91
66.12 67.62 68.25
76.12 75.69 75.34
84.4 76.5 57.8
34
84
Intermient Sonicaon
26
81 80
24
79
22 20
30
78
40
20
30
time(min)
that intermittent sonication makes a pulsation in the ultrasound waves leading to decreasing mass boundary layer and reducing the resistances. Consequently, the extraction will be improved as it was showed by the experiments. In addition, the more the sonication time, the better the qualitative and quantitative characteristics. However, since the duration of extraction process is of great importance in a proper method, the range of 30–40 min seems to be an optimum time for the pretreatment process by ultrasound.
GalA(%)
3.3. Comparison of extracted pectin using three extraction methods As illustrated in previous sections, pectin was extracted from grapefruit by different extraction techniques including conventional, MAE, UAE, and using ultrasound as a pretreatment for MAE (UAE + MAE) method (Table 3). UAE + MAE method showed the best effect on the qualitative and quantitative characteristics of extracted pectin. The only problem is that this method is a time con-
120000
Intermient Sonicaon
74.5 74 73.5 73 72.5 72 71.5
Fig. 7. The effects of sonication time and the kind of sonication, as a pretreatment, on DE of extracted pectin.
Molecular Wieght(Da)
Connuous Sonicaon
40
time(min)
Fig. 5. The effects of sonication time and the kind of sonication, as a pretreatment, on the yield of extracted pectin.
75
Intermient Sonicaon
82
28
20
Connuous Sonicaon
83
30
DE(%)
yield(%w/w)
32
connuous sonicaon
connuous sonicaon
Intermient Sonicaon
115000 110000 105000 100000 95000 90000 85000 80000
20
30
40
time(min) Fig. 6. The effects of sonication time and the kind of sonication, as a pretreatment, on GalA of extracted pectin.
20
30
40
time(min) Fig. 8. The effects of sonication time and the kind of sonication, as a pretreatment, on the extracted pectin.
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Table 3 The effects of different extraction methods on the qualitative and quantitative characteristics of extracted pectin. Extraction technique
References
Properties
Conditions
Yield
DE
GalA
Intrinsic viscosity
[3]
21.1%
68.2%
74%
–
[11]
18%
–
–
This paper
19.16%
75.6%
69.9%
3.98 dL/g
[25]
11.3%
93.0%
98.0%
7.7 dL/g
[9]
18%
74.8%
66.5%
3.1 dL/g
[11] [28]
15.4% 6.2%
– 66%
– 88%
– 14 dL/g
This paper
27.81%
79.35%
74.86%
2.61 dL/g
[18]
13.3%
66.4%
58.5%
250 ◦ TB
This paper
17.92%
75.12%
68.21%
3.23 dL/g
This paper
31.88%
82.61%
74.25%
4.8 dL/g
Conventional
MAE
UAE
UAE + MAE
a
–
T = 85 ◦ C; t = 90 min; pH = 2.5; AWRa = 1 g/25 ml AWR = 1 g/16 ml; t = 3 h, T = 100 ◦ C, pH = 1.5 T = 90 ◦ C; t = 90 min; pH = 1.5; AWR = 1 g/30 ml t = 3 min; AWR = 1 g/25 ml, pw = 0.63 KW AWR = 1 g/16 ml; pw = 0.9 kW; t = 10 min AWR = 1 g/16 ml; t = 10 min; T = 120 ◦ C AWR = 1 g/25 ml; t = 2.5 min, P = 50 lbs/in2 ; pw = 0.9 kW; time = 6 min; AWR = = 1 g/30 ml Intermittent sonication; T = 80 ◦ C; time = 45 min; AWR = 1 g/20 ml Intermittent sonication; AWR = 1 g/30 ml; T = 70 ◦ C; t = 25 min AWR = 1 g/30 ml; intermittent sonication; the time of sonication = 30 min; the time of microwave heating = 10 min; PW = 0.45 kW
AWR: Albedo/Water Ratio.
Fig. 9. Comparison of pectin yield and various characteristics using different extraction methods.
suming one, whilst the shortest process time was for UAE method taking a relatively short time and giving acceptable results. On the other hand, the single MAE method gave better results than UAE with the optimum operating conditions like time and power. The whole results are presented in Fig. 9 for more comparison. Total energy consumption associated with each technique was roughly estimated for the different extraction techniques. These estimations were for the maximum yield obtained by the microwave and ultrasound methods. The consumed energy was equal to the power field multiply by the exposure time. The energy consumption associated with MAE (0.9 kW and 6 min) and UAE (200 W and 25 min) are 324 and 300 kJ, respectively, which are roughly the same.
4. Conclusions The effects of microwave field power and heating time were investigated using microwave extraction. These parameters improved the qualitative and quantitative characteristics of extracted pectin. These improvements included the considerable increase in the yield of pectin as well as degree of esterification, Galactronic Acid, and viscosity. Besides, the 2 min microwave heating period was enough to extract the same amount of pectin as obtained from the 90 min conventional extraction period. On the other hand, the extraction procedure with application of ultrasound in water bath were used to examine the effects of sonication on the extracted pectin. Sonication time and bath temperature are impor-
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tant factors influencing the extraction of pectin. It was concluded that there is an optimum sonication time and (bath) temperature to obtain the best yield. In comparison to the ultrasound assisted extraction, the conventional method gave a slightly higher yield; however, the rate of ultrasonic extraction was over 3 times faster than conventional extraction. In addition, ultrasound was used as a pretreatment for the microwave heating giving better results than microwave assisted extraction.
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