Article pubs.acs.org/JAFC
Determination of Inulin-type Fructooligosaccharides in Edible Plants by High-Performance Liquid Chromatography with Charged Aerosol Detector Jing Li,† Dejun Hu,† Wanrong Zong,† Guangping Lv, Jing Zhao,* and Shaoping Li* State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau, Macao Special Administrative Region, China ABSTRACT: Fructooligosaccharides (FOS), which are regarded as functional ingredients, are commonly classified as dietary fibers in many countries. However, few analytical methods for separation and analysis of individual FOS in plants, crops, and food products have been developed. In this study, a simple, rapid, and sensitive high performance liquid chromatography with charged aerosol detector (HPLC-CAD) method was developed for simultaneous determination of 11 inulin-type FOS with degree of polymerization (DP) 3−13 in different samples. The separation was performed on a Waters XBridge Amide column (4.6 × 250 mm i.d., 3.5 μm) with gradient elution. All calibration curves for investigated analytes showed good linear regression (R2 > 0.9962). Their limits of detection (LOD) and quantification (LOQ) were in the ranges 0.4−0.6 μg/mL and 1.4−2.3 μg/mL, respectively. The recoveries ranged from 94.0% to 114.4%. A liquid chromatography−tandem mass spectrometry (LC-MS/MS) method was applied to qualitative analysis of FOS in different samples. The developed method was successfully applied to analysis of 11 FOS in different samples of plants from Compositae, Campanulaceae, and Rubiaceae families. The developed HPLC-CAD nethod with microwave-assisted extraction can be used for quantitative analysis of FOS and is helpful for quality control of plants containing FOS. KEYWORDS: HPLC-CAD, microwave-assisted extraction, quantitative analysis, inulin-type fructooligosaccharide
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or evaporative light scattering detection (ELSD),21−23 have been developed for the determination of FOS. However, colorization methods can determine only the content of total sugars and the specificity is poor. HPAEC needs specific instruments and columns, which are resistance to alkali. In addition, mass spectrometry (MS) is incompatible with the highly alkaline eluents used in HPAEC. Compared to HPAECPAD, HILIC can provide better results for analysis of mixtures, including oligosaccharides of different degrees of polymerization.24 HPLC-RID method usually suffers from poor resolution because gradient elution is not available for RID. The RID and ELSD also show poor sensitivity of detection, especially for FOS with high degrees of polymerization (DP). Until now only FOS (DP below10) have been determined in plants, so quantitative analysis of FOS is still difficult, owing to poor sensitivity and/or the absence of standards with higher DP. Recently a new type of universal detector, the so-called charged aerosol detector (CAD), has been developed and introduced by Dixon and Peterson.25 Similar to ELSD, CAD provides universal detection for semivolatile or nonvolatile compounds and the response is independent of analyte structural properties with or without a strong chromophore.26 However, generally, CAD is more sensitive than ELSD, about 2−6 times better than that of ELSD.26,27 Recently, it has been used as a powerful tool for determination of oligosaccharides,28 lipids,29
INTRODUCTION Fructooligosaccharides (FOS) are officially recognized as natural food ingredients and classified as dietary fiber in almost all European countries.1 The average daily consumption has been estimated to be between 3 and 11 g in Europe2 and between 1 and 4 g in the United States.3 FOS possess many bioactive characteristics, such as prebiotic effects, suppressing putrefactive pathogens, reducing the risk of colon cancer, cognitive improvement and cerebral protective effects, and decreasing the levels of blood glucose, serum cholesterol, phospholipids, and triglycerides.1,4−9 In addition, FOS was also a promising elicitor in postharvest disease control in various fruits.10 Fructooligosaccharides are found in a number of mono- and dicotyledonous families such as Liliaceae, Amaryllidacea, Gramineae, and Compositae.11 They naturally exist in a large variety of edible and medicinal plants used as functional foods, such as Atractylodes macrocephala Koidz., Platycodon grandiflorum (Jacq.) A.DC., Helianthus tuberosus L., Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson, Morinda officinalis How, and Arctium lappa L.12−17 Actuarially, these medicine and food dual-purpose plants, which are abundant in FOS, have been cultivated and used as vegetable or medicated diet for hundreds of years in China. Therefore, quantitative analysis of FOS is very necessary and important for quality control of FOS in these plants. A series of methods, including colorization (phenol−sulfuric acid, dinitrosalicylic acid) methods,1 high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD),18−20 and hydrophilic interaction chromatography (HILIC) coupled with refractive index detection (RID) © 2014 American Chemical Society
Received: Revised: Accepted: Published: 7707
May 20, 2014 July 17, 2014 July 18, 2014 July 18, 2014 dx.doi.org/10.1021/jf502329n | J. Agric. Food Chem. 2014, 62, 7707−7713
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saponins,26 and pharmaceutical drugs.30 Currently, there are no reports on the application of CAD to the analysis of FOS. Here, a HPLC-CAD and microwave-assisted extraction method was developed for simultaneous determination of 11 FOS with DP 3−13 in 12 different plants in Compositae, Campanulaceae, and Rubiaceae families. The methods were validated and demonstrated for use in analysis of inulin-type FOS and are potentially useful for other plants.
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these samples were deposited at the Institute of Chinese Medical Sciences, University of Macau, Macao SAR, China. Inulin-type FOS with DP between 3 and 13 (all purities determined by HPLC-DAD-ELSD were more than 95%) were separated and purified in our laboratory (Figure 1). The structures were confirmed
MATERIALS AND METHODS
Materials, Reagents, and Chemicals. The analyzed plants belonged to Compositae, Campanulaceae, and Rubiaceae families, and their detailed characteristics are presented in Table 1. Species identification was performed by Dr. C. F. Qiao. Voucher specimens of
Table 1. Characteristics of Analyzed Samples producing area
place of purchase
codes
Atractylodes lancea (Thunb.) DC., family Compositae Jiangsu Shenzhen A1 Hebei Zhuhai A2 unknown Macau A3 Codonopsis pilosula (Franch.) Nannf., family Campanulaceae Gansu Shenzhen B1 Shanxi Zhuhai B2 unknown Macau B3 Atractylodes macrocephala Koidz., family Compositae Anhui Shenzhen C1 Hunan Zhuhai C2 unknown Macau C3 Taraxacum mongolicum Hand.-Mazz., family Compositae Hunan Shenzhen D1 Shanxi Zhuhai D2 Unkonwn Macau D3 Platycodon grandiflorus (Jacq.) A.DC., family Campanulaceae Anhui Shenzhen E1 unknown Zhuhai E2 unknown Macau E3 Aucklandia lappa Decne., family Compositae Guangdong Shenzhen F1 Yunnan Zhuhai F2 unknown Macau F3 Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson, family Compositae Guangdong Zhuhai G1 Guangdong Macau G2 Carthamus tinctorius L., family Compositae Sichuan Shenzhen H1 Sichuan Zhuhai H2 unknown Macau H3 Adenophora tetraphylla (Thunb.) Fisch., family Campanulaceae Anhui Shenzhen I1 unknown Macau I2 Morinda officinalis How., family Rubiaceae unknown Zhuhai J1 unknown Meizhou J2 Deqing Deqing J3 Helianthus tuberosus L., family Compositae Hunan Hunan K1 Arctium lappa L., family Compositae Korea Macau L1 Shandong Shandong L2 Jilin Jilin L3
Figure 1. Structures of inulin-type fructooligosaccharides (FOS). by comparing their methylation, MS, and NMR data with the literature.17,22 Acetonitrile for HPLC was purchased from Merck (Darmstadt, Germany). Purified water for HPLC was prepared on a Millipore Milli-Q Plus system (Millipore, Bedford, MA). All other chemicals and reagents were of analytical grade. Preparation of Standard Solutions. Mixed standard stock solution containing inulin-type FOS (DP3−DP13) was prepared in 60% ethanol. The concentrations of DP3−DP13 were about 20 mg/mL. The standard stock solution was stored in a refrigerator at 4 °C before use. Working standard solutions were prepared from the stock solution by dilution with the appropriate volume of 60% ethanol. Sample Preparation. Extraction experiments were carried out with a Multiwave 3000 reaction system (Anton Paar GmbH, Graz, Austria) equipped with a 64-position extraction rotor. The herbal medicine powder (0.1 g, 40 mesh) and 2 mL of ethanol− water (60:40 v/v) were transferred into 5 mL extraction vessels made of borosilicate glass. After the vessels were closed and capped, the rotor was placed inside the microwave oven. The extractions were performed in temperature-controlled mode. After a heating ramp of 1 min, the microwave program was stated as 400 W for 5 min at the temperature of 80 °C. Immediately after the temperature program had finished, all vessels were cooled down to ambient temperature. All extractions were performed with magnetic stirring. After extraction, an aliquot was taken and centrifuged for 5 min at 5000g. After centrifugation, 1 mL of supernatant was transferred into a 10 mL volumetric flask and made up to the volume with extraction solvent. Then the solution was filtered through a 0.45 μm filter before injection into the HPLC system for analysis. HPLC-CAD Analysis. Chromatographic analyses were performed on a Dionex (Germering, Germany) Ultimate 3000 UHPLC system equipped with Ultimate 3000 degasser, pump, RS autosampler, and RS column compartment, coupled with a Corona charged aerosol detector (CAD) instrument (ESA, Chelmsford, MA). Data processing was carried out with Chromeleon 6.8 software (Dionex). The N2 pressure of the CAD was adjusted to 35 psi and the response range was set to 100 pA. Separations were carried out on a Waters XBridge Amide column (4.6 × 250 mm id, 3.5 μm). The column temperature was set at 30 °C. The mobile phase was consist of water (A) and acetonitrile 7708
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Table 3. Precision (Intra- and Interday) for Fructooligosaccharides DP3−DP13 peak area (% RSD)
retention time (% RSD)
analyte
intraday (n = 6)
interdaya (n = 6)
intraday (n = 6)
interdaya (n = 6)
DP3 DP4 DP5 DP6 DP7 DP8 DP9 DP10 DP11 DP12 DP13
2.75 2.40 2.10 1.48 1.67 1.58 1.57 1.80 1.72 1.90 2.62
11.10 10.20 9.90 9.56 11.76 11.64 13.05 13.57 13.17 17.33 15.74
1.50 1.30 1.13 1.03 0.95 0.89 0.85 0.81 0.76 0.75 0.72
0.05 0.06 0.05 0.06 0.07 0.06 0.05 0.07 0.06 0.05 0.06
a
Interday precision was determined over a period of 5 days (3 measurements on each day).
Figure 2. Effect of extraction time on extraction efficiency of FOS with different degrees of polymerization (DP).
Table 4. Repeatability, Stability, and Accuracy for Fructooligosaccharides DP3−DP13
Table 2. Linear Regression Data and Limits of Detection and Quantitation for Fructooligosaccharides DP3−DP13 analyte DP3 DP4 DP5 DP6 DP7 DP8 DP9 DP10 DP11 DP12 DP13
R2
linear range (μg/mL)
LOD (μg/mL)
LOQ (μg/mL)
−
0.9993
1.4−53.8
0.4
2.3
−
0.9979
1.6−58.5
0.6
1.9
−
0.9978
1.4−52.5
0.6
1.4
−
0.9983
1.5−36.7
0.4
1.5
−
0.9968
1.5−38.3
0.5
1.5
−
0.9962
1.5−38.0
0.4
1.6
−
0.9967
1.5−37.5
0.4
1.6
−
0.9981
1.4−34.7
0.4
1.4
−
0.9971
1.4−106.5
0.4
1.4
−
0.9978
1.3−96.0
0.6
1.6
−
0.9981
1.5−221.0
0.5
1.5
regression eq y = 1.3400x 2.3594 y = 1.3437x 2.2999 y = 1.3309x 2.2231 y = 1.3285x 2.1593 y = 1.3112x 2.232 y = 1.2913x 2.1935 y = 1.3084x 2.2270 y = 1.3165x 2.2200 y = 1.2250x 2.1673 y = 1.2024x 2.2063 y = 1.1955x 2.2064
repeatability
stability
accuracy
analyte
content (mg/g)
RSD (%)
RSD (%)
recovery (%)
RSD (%)
DP3 DP4 DP5 DP6 DP7 DP8 DP9 DP10 DP11 DP12 DP13
19.28 29.74 31.72 30.14 35.25 32.51 28.52 23.45 25.62 24.37 19.39
2.44 2.18 2.11 2.07 2.03 2.25 2.28 2.44 3.09 2.93 2.94
2.21 2.36 3.53 3.49 3.36 3.48 3.71 3.54 4.46 4.97 4.88
99.0 100.4 95.9 97.5 94.0 94.1 95.6 98.7 113.3 114.4 99.5
3.92 4.43 5.26 4.44 5.18 5.07 5.00 5.17 5.36 5.40 7.25
chromatographic conditions were determined at a signal-to-noise ratio (S/N) of 3 and 10, respectively. Precision, Repeatability, Accuracy, and Stability. Precision of the HPLC-CAD method was determined by evaluating the repeatability of intraday and interday measurements. Intraday precision was determined by repeating the analysis of the mixed standards solution for six replicates within 1 day, while interday precision was determined in duplicates on three successive days. Repeatability of the developed method was confirmed with preparation and analysis of six parallel samples. Stability was tested and analyzed at 0, 1, 2, 4, 8, 12, and 24 h. In order to check the accuracy of the developed method, recovery experiments were carried out as follows: accurate amounts of the standards were spiked into the samples (0.05 g) in the form of solution. The spiked samples were extracted, processed, and quantified in accordance with methods mentioned above. Average recoveries were determined by the equation recovery (percent) = 100 × (observed amount − original amount)/spiked amount, and relative standard deviation (RSD, percent) = 100 × standard deviation (SD)/mean. Liquid Chromatography−Tandem Mass Spectrometric Analyses. LC-MS/MS analyses were carried out on an Agilent 1100 Series LC/MSD Trap system (Agilent Technologies, Palo Alto, CA), equipped with vacuum degasser, quaternary pump, autosampler, column compartment, diode-array detector (DAD), and ion-trap mass spectrometer with electrospray ionization (ESI) interface, connected to Agilent LC/MSD Trap software. ESI-MS conditions were as follows: drying gas N2 at 7 L/min, temperature 325 °C, pressure of nebulizer 25 psi, source voltage 3.5 kV. ESI-MS/MS
(B) with gradient elution: 75%−45% B at 0−30 min, 45%−75% B at 30−32 min, and then equilibrated with 75% B for 10 min. The flow rate was 1.0 mL/min and injection volume was 5 μL. Calibration Curves and Limits of Detection and Quantification. Standard stock solutions containing reference compounds were prepared and diluted to appropriate concentrations for construction of calibration curves. Six concentrations of 11 analyte solutions were injected in triplicate, and then the calibration curves were constructed and their linear ranges determined. Since CAD response was nonlinear and it can be represented by y = axb, where y refers to peak area, while x is the analyte amount, a is the constant term, and b is the exponential response factor.31 Therefore, calibration of CAD was constructed by a double logarithmic plot as in previous reports.26,29,31 Stock solutions were diluted to a series of appropriate concentration with 60% ethanol, and aliquots of the diluted solutions were injected into HPLC for determining the limit of detection (LOD) and limit of quantification (LOQ). The LOD and LOQ under the present 7709
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Figure 3. (a) LC−MS/MS spectra and (b−d) Domon and Costello nomenclature for the fragmentation of separated FOS (DP3−DP10).
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conditions included isolation width 4 and fragment amplification 1.5. Scan ranges of both MS and MS/MS were 200−2200 m/z. The liquid chromatographic conditions for LC-MS/MS were the same as described for HPLC-CAD analysis.
RESULTS AND DISCUSSION
Optimization of Sample Preparation. In order to obtain quantitative extraction, the extraction method, extraction solvents,
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respectively (Table 2). For intraday precision, RSDs of the peak area was 1.48−2.75% and RSD of the retention time was 0.72− 1.50%; for interday precision, the corresponding RSDs were 9.56−17.33% and 0.05−0.07% (Table 3). Recoveries ranged from 94.0% to 114.4%, and the analytes were very stable in 60% ethanol solution during the tested period (Table 4). The high recoveries (113.3% and 114.4%) of DP11 and DP12 might be attributed to the variation of their purities, and more attention should be paid in future. LC-MS/MS Analysis. Molecular mass information on the standards and the extracted samples were determined in negative ion mode. In the negative ion mode, the [M − H]− of FOS (DP3−DP13) were detected at m/z 503, 665, 827, 989, 1151, 1313, 1475, 1637, 1799, 1961, and 2123. ESI-MS/MS of their [M − H]− ions was performed to obtain the individual fragment patterns. Their MS/MS spectra are shown in Figure 3. The fragment ions of FOS include glycosidic cleavages between two sugar residues and cross-ring cleavages of two bonds within the sugar ring. In our MS/MS spectra, the fragment ions of FOS mainly result from glycosidic cleavages between two sugar residues, which were as the same as those reported in previous literature.17 That little fragments with low abundance of the cross-ring cleavages of two bonds within the sugar ring were found might be derived from the low collision energy or few sodium ions in mobile phase.17,32 FOS (DP11−DP13) with high molecular weights are difficult to ionize for LC-MS/MS analysis, so the characteristic MS/MS spectra of FOS (DP11− DP13) could not be shown. However, in the MS spectrum of FOS (DP11−DP13), the characteristic ions at m/z 161, 179, 323, 341, 485, 503, 647, 665, 809, 827, 971, 989, 1133, 1151, 1313, 1475, 1457, 1638, and 1800 were obtained. In summary, all the results suggested that FOS should consist of the corresponding number of hexoses. Quantitative Determination of FOS in Plants. The established HPLC-CAD method was applied for analysis of inulin-type FOS (DP3−DP13) in different samples of Compositae, Campanulaceae, and Rubiaceae families. HPLC-CAD chromatograms of the mixed standards and different samples are shown in Figure 4. Besides the investigated 11 oligosaccharides, many oligosaccharides with DP of more than 13 were also found in these samples. Unfortunately, we could not quantitatively determine these oligosaccharides because of the absence of related reference compounds, which should be performed in the future. The contents of the 11 investigated FOS in different samples are summarized in Table 5 and Figure 5. The results showed that the three samples with highest contents of FOS were Morinda officinalis, Helianthus tuberosus and Arctium lappa, and both H. tuberosus and A. lappa belong to the Compositae family. The data also indicated there was no FOS detected in Taraxacum mongolicum and Carthamus tinctorius, which are also of the Compositae family. That is because FOS are usually the chemical compounds for storing energy in organs such as bulbs, tubers, and tuberous roots. The flowers contain little FOS. In summary, there are many reports on the existence of FOS in plants of Liliaceae, Compositae, Campanulaceae, and Rubiaceae families, but few reports on their contents in these samples. This is the first report for quantitative analysis of inulin-type FOS (DP3−DP13) in different samples of plants in Compositae, Campanulaceae, and Rubiaceae families, which is helpful to improve their qualities. The developed HPLC-CAD method, which is accurate and specific, can also be used for determination of inulin-type FOS in other plants.
Figure 4. HPLC-CAD chromatograms of (A) mixed standards and (B−D) samples of (B) Atractylodes macrocephala, (C) Platycodon grandiflorum, and (D) Morinda officinalis.
extraction solvent volume, extraction time, and temperature were optimized. Solvent choices, solvent volumes, and temperature used in this study were fixed according to our previous study.23 We investigated the effect of extraction time, which directly influence the extraction yields of FOS. In order to get the optimal reaction time, we performed the extraction by microwave extraction in a range from 2 to 20 min at 80 °C, using a sample (Morinda officinalis, sample J3) of approximately 0.1 g. Results (Figure 2) showed that the optimal extraction time of FOS was 5 min, whereas longer extraction time did not significantly increase extraction yields and FOS degradation was observed at 20 min. We therefore selected 5 min as the optimal extraction time. Optimization of HPLC Conditions. Analysis of FOS is a challenge due to their high polarity and complexity and lack of specific UV absorptivity. Therefore, the HPLC-CAD method was selected for analysis of FOS. Several different commercial columns were tested, and finally the Waters XBridge Amide column (4.6 × 250 mm id, 3.5 μm) was selected for separation of 11 investigated inulin-type FOS because of its high resolution and good signal-to-noise performance. The analytes in both mixed standard solution and sample solutions can be well separated by gradient elution with water and acetonitrile. Method Validation. Linearity, regression, and linear ranges of the 11 analytes were determined by the developed HPLC method. The data indicated the calibration curves of the 11 analytes had good linearity (R2 > 0.9962), and their LODs and LOQs were in the ranges 0.4−0.6 μg/mL and 1.4−2.3 μg/mL, 7711
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Table 5. Contents of the 11 Analytes in Tested Samples analyte content(mg/g)
a
sample
DP3
DP4
DP5
DP6
DP7
DP8
DP9
DP10
DP11
DP12
DP13
total
A1 A2 A3 B1 B2 B3 C1 C2 C3 D1a D2a D3a E1 E2 E3 F1 F2 F3 G1 G2 H1a H2a H3a I1 I2 J1 J2 J3 K1 L1 L2 L3
6.01 4.68 2.69 1.49 3.59 0.65 4.29 4.52 7.15
4.05 2.86 2.14 0.8 1.62 0.42 4.08 4.36 5.65
3.27 1.96 1.66 0.75 1.25 0.39 4.39 4.78 5.4
4.22 3.24 1.7 1.34 3.01 0.4 4.42 4.91 5.22
5.08 3.85 2.09 1.48 3.15 0.48 5.61 6.28 6.68
5.44 2.96 2.22 1.48 2.81 0.51 5.77 6.57 6.7
5.59 3.08 2.5 1.59 2.49 0.64 6.03 6.89 6.92
5.59 3.02 2.75 1.64 1.99 0.76 6.06 6.69 6.7
6.63 3.48 3.63 2.13 2.19 1.05 7.32 7.79 7.83
7.56 3.88 4.33 2.46 2.2 1.34 8.41 8.76 8.72
7.46 3.3 4.64 2.35 1.91 1.38 8.24 8.3 8.41
60.89 36.32 30.36 17.52 26.21 8.01 64.62 69.84 75.38
4.02 4.8 8.49 4.5 4.28 2.92 29.43 23.8
4.71 4.67 6.58 2.97 2.59 2.25 27.17 24.54
4.93 4.28 6.56 1.96 1.85 1.65 19.8 18.91
5.67 4.52 7.14 2.23 1.78 2.13 14.17 13.92
7.47 5.55 9.42 2.28 1.89 2.5 13.04 15.25
8.01 5.61 10.07 2.33 1.83 2.46 11.09 14.32
8.78 5.48 10.74 2.74 2.05 2.74 9.36 13
8.97 5.93 10.75 2.85 2.36 3.2 7.1 10.35
11.19 7.47 13.52 3.47 3.14 4.21 6.06 9.61
12.93 9.22 15.65 4.22 4.28 5.17 4.75 7.89
12.65 9.38 15.6 4.32 4.51 5.49 3.17 5.57
89.34 66.91 114.52 33.86 30.55 34.72 145.13 157.17
4.28 5.17 22.28 11.92 19.58 36.42 24.05 22.8 16.52
4.69 4.98 28.97 18.02 29.24 28.58 22.08 18.59 13.33
4.22 5.65 30.34 20.53 31.61 23.82 15 16.06 12.87
4.47 5.97 29.16 20.08 29.89 19.6 15.7 14.86 11.71
4.81 8.11 32.11 23.93 35.06 19.85 18.54 17.21 13.97
4.21 9.01 27.47 22.5 32.44 18.57 17.68 14.57 13.72
4.13 10.11 22.93 20.3 28.46 16.16 15.81 13.52 13.11
4.11 10.62 18.36 17.39 23.61 15.13 13.54 11.72 11.87
5.22 13.92 19.35 19.6 25.56 15.54 14.76 12.06 13.93
6.59 16.7 18.62 19.88 24.47 14.54 14.74 12.82 15.44
7.31 17.08 15.52 17.11 19.54 11.81 13.22 11.37 14.78
54.04 107.31 265.11 211.24 299.44 220.02 185.13 165.59 151.26
Not detected.
* Phone +853-8397-4692; fax +853-2884-1358; e-mail spli@ umac.mo. Author Contributions †
J.L., D.H., and W.Z. contributed equally to this work
Funding
This research was supported by grants from the Science and Technology Development Fund of Macao (FDCT059/2011/A3), and the University of Macau (MYRG140 and MYRG085). Notes
The authors declare no competing financial interest.
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ABBREVIATIONS HPLC, high-performance liquid chromatography; CAD, charged aerosol detector; FOS, fructooligosaccharides; DP, degree of polymerization; ELSD, evaporative light scattering detector; HPAEC, high-performance anion-exchange chromatography; PAD, pulsed amperometric detection; RID, refractive index detector; MS, mass spectrometry; LOD, limit of detection; LOQ, limit of quantification; S/N, signal-to-noise ratio
Figure 5. Average contents of FOS with different degree of polymerization (DP) in different edible plants. A−L mean the average of three related samples in Table 1.
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AUTHOR INFORMATION
Corresponding Authors
REFERENCES
(1) Milani, E.; Koocheki, A.; Golimovahhed, Q. A. Extraction of inulin from Burdock root (Arctium lappa) using high intensity ultrasound. Int. J. Food Sci. Technol. 2011, 46, 1699−1704.
* Phone +853-8397-4692; fax +853-2884-1358; e-mail
[email protected]. 7712
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Journal of Agricultural and Food Chemistry
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dx.doi.org/10.1021/jf502329n | J. Agric. Food Chem. 2014, 62, 7707−7713
