Abstract
Ginger and garlic have long been used in Asian countries to enhance the flavor and to neutralize any unpleasant odors present in fish soup. The purpose of this study was to evaluate the change in the amount of volatile components present in fish soup compared to boiled water solutions of ginger and garlic. The fish soup was prepared by boiling oil-fried grass carp (Ctenopharyngodon idella) with or without ginger and/or garlic. Generally, boiling garlic and ginger in water led to a decrease in the amount of the principal volatile constituents of these spices, together with the formation of some new volatiles such as pentanal, hexanal, and nonanal. The results showed that 16 terpenes present in raw ginger, predominantly camphene, β-phellandrene, β-citral, α-zingiberene, and (E)-neral, were detected in fish soup with added ginger and thus remained in the solution even after boiling. Similarly, 2-propen-1-ol and three sulfur compounds (allyl sulfide, diallyl disulfide, and diallyl trisulfide) present in raw garlic, were present in trace amounts in the boiled garlic solution, but were present in considerably larger amounts in the boiled fish solution with garlic or garlic plus ginger. In conclusion, the effect of adding spices on the volatile profile of grass carp soup can be attributed to the dissolution of flavor volatiles mainly derived from raw spices into the solution, with few additional volatiles being formed during boiling. In addition, boiling previously fried grass carp with spices led to enhanced volatile levels compared to boiled spice solutions.
Keywords: Spice, Ginger, Garlic, Cooking, Volatile profile, Grass carp (Ctenopharyngodon idella) soup
Introduction
Spices, defined as “plant products used for flavoring, seasoning, and imparting aroma in foods” by the International Standards Organization, have been used since antiquity for culinary and medicinal purposes (Dhanya and Sasikumar 2010). The basic effects of spices used in cooking are an enhancement or modification in the flavoring properties, endowing food with pungency, preserving food for longer periods, and modifying color characteristics (Hirasa and Takemasa 1998; Raghavan 2006). In addition, spices have a particularly useful purpose for masking the smell of raw materials when the materials possess an undesirable odor. Fresh fish, especially freshwater fish, have an unpleasant odor, limiting their application in foodstuff (Zakipour Rahimabadi et al. 2011). The masking effect of spices on fish odor has been investigated by a number of studies. Kasahara and Osawa (1998) reported that, according to evaluation through olfactory tests, the combination of Japanese pepper and perilla leaves (1:1) had the strongest effect for suppressing the fish odor of boiled sardines followed by perilla leaves and a formula consisting of a combination of Yuzu and perilla leaves (1:1). Yoshida et al. (1984) found that the amount of volatile carbonyl compounds responsible for the fishy odor released from mackerel meat, could be reduced by treating mackerel muscle tissue with spices including pepper, sage, cloves, thyme, and mustard seeds. Kikuchi et al. (1968) found that the fish odor diminished by the addition of 11 spices (caraway, cassia, clove, ginger, laurel, mace, nutmeg, onion, pepper, sage, and thyme), and that addition of onion, laurel, or sage, was more effective than the other eight spices.
The characteristic gustatory and olfactory profile of each spice depends on the balance of the predominating chemical compounds within the spice, granting it characteristic flavor (Raghavan 2006). Ginger (Zingiber officinale) and garlic (Allium sativum) are two of the most important spices which have been used for thousands of years, both for cooking and medicinal purposes (Raghavan 2006). The volatile components in ginger consist mainly of sesquiterpene hydrocarbons, predominantly zingiberene, curcumene, and farnesene, and a smaller percentage of monoterpenoid hydrocarbons and some oxidized terpene derivatives. The major volatile components in garlic are sulfur containing compounds, mainly diallyl disulfide and diallyl trisulfide (Kim et al. 2011). It has been consistently found that ginger and garlic have a particularly strong ability to reduce fish odor when blended with mackerel meat (Kikuchi et al. 1968; Yoshida et al. 1984). Throughout some Asian countries, and particularly in China, ginger and garlic have traditionally been used extensively to prepare vegetable dishes, soups, meat dishes, roast meat, and many other foods (Shukla and Singh 2007). Typically, fish soups are prepared by boiling in ginger and/or garlic with a previously oil-fried fish, increasing the flavor and improving the odor characteristics of the soup. The addition of spices may change the profile of volatile compounds within the soup. To the best of our knowledge, no investigations have been published on the effect of spices, namely ginger and garlic, on the composition of volatile compounds in fish soup.
Grass carp is the most important species of the ‘four-major-Chinese-carps’, and commercially is one of the most important freshwater fish species both in China and throughout the world (Zhang et al. 2013). The purpose of this study was to investigate the effect of adding ginger and/or garlic to a previously oil-fried piece of grass carp on the volatile components present in the solution, compared to a boiled solution of the fish without any spices added. The results of this study provide a better understanding of how garlic and/or ginger influence the volatile profile of compounds responsible for removing the unpleasant odor of fish, and how the overall compound profile changes in a boiled solution of a pan-fried grass carp. This information can aid the development of fish products and food additives containing ginger and garlic for odor control of fish-based products, and to promote the application of spices in the food industry.
Materials and methods
Materials
Standards of camphene, 3-carene, β-myrcene, 1,8-cineole, p-cymene, citronellal, linalool, α-terpineol, γ-terpinene, citronellol, geraniol, 1-octen-3-ol, octanal, trans-2-heptenal, nonanal, trans-2-octenal, decanal, trans-2-decenal, vanillin, 3-hydroxy-2-butanone, 6-methyl-5-hepten-2-one, 2,5-dimethylpyrazine, 2-pentylfuran, and 5-methyl-2-furfural were purchased from Sigma-Aldrich (Shanghai, China). Standards of limonene, p-cymene, α-farnesene, zingiberone, 2-heptanol, 2-nonanol, trans,trans-2,4-heptadienal, allyl sulfide, diallyl disulfide, octanoic acid, m-cymene, benzyl alcohol, 1-docosanol, 2-nonanone, phenol, and diallyl trisulfide were purchased from Anpel (Anpel Scientific Instrument Co. Ltd., Shanghai, China). Standards of a-farnesene, 1-butanol, 1-pentanol, 2-ethyl-1-hexanol, 1-dodecanol, 1-octadecanol, hexanal, heptanal, benzaldehyde, trans,trans-2,4-decadienal, 2-undecanone, acetophenone, hexadecanoic acid, methyl ester, methyl stearate, p-xylene, m-xylene, o-xylene, 1-methyl-3-(1-methylethyl)-benzene, and 1,2-dichlorobenzene were purchased from Aladdin (Aladdin Reagent Co., Ltd., Shanghai, China). The standard solution containing the n-alkane series (C8–C40) was obtained from AccuStandard (DRH-008S-R2, New Haven, CT, USA). All other chemicals and solvents were of analytical grade; water was purified using a Milli-Q system (Millipore Corp., Billerica, Massachusetts).
Grass carps (Ctenopharyngodon idella), Ginger (Zingiber officinale), garlic (Allium sativum), and soybean oil were purchased from a local market in Nanchang (Rainbow Department Store, China).
Sample preparation
Preparation of ginger or garlic boiled solutions
Before boiling, ginger was cut into slices about 1-mm-thick, and garlic was crushed by applying pressure from the flat side of a knife. Then, 1 L of water was added to a non-stick frying pan, half-covered with a glass lid, and heated by an induction cooker (C21-DC005, Joyoung Co., Ltd, Jinan, China) with the power set at 1400 W. When the water began to boil, a 4.5-g slice of fresh ginger or 8.7 g of the previously crushed garlic was immersed in the boiling water and heated for 25 min with the induction cooker set at the same power. During boiling, the solution was concentrated to about 200 g. After this time, the ginger slice or crushed garlic was removed, and the spiced solution was transferred to a beaker and diluted to 250 g for standard analysis. Since only 2 % of boiled spice solution was used for solid phase microextraction (SPME), 0.09 g of sliced fresh ginger and 0.174 g of crushed garlic was used in a raw control for extraction of volatiles via SPME.
Preparation of grass carp soup
Fresh grass carps, weighing about 1 kg each, were washed with running water several times to remove blood and slime, and then subjected to common household procedures including eviscerating, descaling, and beheading. Next, the fish was rewashed and split along the vertebrae into two equivalent pieces (about 270 ± 10 g each). Each piece was further cut into a 250 g sample and was placed in a frying pan containing 23 g of soybean oil pre-heated for 2 min by the induction cooker at the same power level used for frying fish. The cooker power was set at 1400 W, which raised and maintained the surface temperature of the pan to 180 °C, and each side of the fish piece was fried for 1 min, for a total frying time of 2 min. To prepare the spice added solutions, after adding 1.0 L of water to the pan with the fish present, crushed garlic (8.7 g) and/or ginger slices (4.5 g) were added, and the mixture was held at 97 ± 2 °C for 25 min with the glass lid half-covering the pan. Four kinds of boiled fish samples were prepared: samples with added ginger, added garlic, added ginger plus garlic, and without any spices added. During cooking, the solution was concentrated to about 200 g. The fish and the spices from the solution were filtered with cheesecloth, and the soup was diluted to 250 g for standard analysis.
Extraction of volatiles
Solid-phase microextraction
The solid-phase micro-extraction (SPME) device and fused silica fiber coated with divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS, 1 cm–50/30 μm) were obtained from Supelco (Bellefonte, PA, USA). Prior to use, the SPME fiber was conditioned in the injector of a GC at 270 °C for 30 min according to the manual. Samples (5 g) were placed in a 15 mL sealed head space vial and equilibrated for 30 min at 60 °C. Then, the fiber coating was exposed to the headspace for 30 min at 60 °C (Xiong et al. 2015).
Simultaneous distillation–extraction
Simultaneous distillation–extraction (SDE) extraction was carried out using a Likens-Nickerson apparatus according to the procedure of Rattan et al. (2015). A 100 g sample of the previously prepared 250 g diluted solution formed after boiling the ginger and/or garlic solution in the presence or absence of fish was further diluted with 500 mL of distilled water and placed in a 1 L round bottomed flask at one end of the apparatus while the other end was fitted with a 500 mL round bottomed flask containing 200 mL dichloromethane. The solution was heated at 100 °C while dichloromethane was kept at 58 °C, and the process was allowed to run for 2 h. The SDE extracts were dried over 25 g of anhydrous sodium sulfate and stored at −20 °C overnight. All samples were concentrated to 2 mL with a Vigreux column before being subjected to GC–MS analysis.
Analysis of volatiles
Volatile extracts were analyzed with an Agilent 7890A gas chromatograph with 5975C mass selective detector (GC-MSD; Agilent Technologies Inc., Palo Alto, CA, USA), equipped with a DB-wax column (30 m × 0.25 mm ID × 0.25 μm film thickness), according to the method reported by Aminifar et al. with some modifications (Aminifar et al. 2014). The GC oven temperature was initially held at 40 °C for 3 min, and increased at a rate of 5 °C/min to 240 °C where it was held for an additional 15 min. For SPME, the injector, heated at 250 °C, was held in the splitless mode for the first 2 min of the analysis and then in split mode (20:1) for the remainder of the analysis. The extract obtained via SDE (1 μL) was injected under the same conditions of as the sample extracted via SPME with a solvent delay time of 3.8 min. Helium was used as the carrier gas with a constant flow rate of 1.0 ml/min. The MS was operated in electron ionization mode (70 eV) and data was acquired in full scan mode from 35 to 400 Da. The temperature of the source and the detector were 150 and 230 °C, respectively, while the MS transfer line was kept at 280 °C. n-Alkanes (C8–C40) were examined under identical conditions to determine the linear retention index (LRI) according to the method of Van den Dool and Kratz (1963).
Identification of the components was performed by matching their mass spectra with the NIST 08 mass spectral database and comparing their LRIs with that of authentic standards. When authentic standards were not available, tentative identifications were carried out by matching mass spectra with those in the NIST 08 library and/or comparing LRIs with those reported in literature.
Statistical analysis
All experiments were performed in triplicate. Significant differences analysis among data was performed by paired-samples T test, or one-way Analysis of variance (ANOVA) by the Duncan’s multiple range test. p < 0.05 was considered statistically significant. Statistical analysis was performed by using SPSS19.0 software (SPSS, IBM Corp, Armonk, NY, USA).
Results and discussion
Effect of boiling on the content of volatiles from ginger
Spices contain both volatile and nonvolatile components. The flavor for most spices is the result of components present in the volatile oil, but some flavors are a result of the release of volatile compounds generated during heating of nonvolatile components (Hirasa and Takemasa 1998). In order to avoid a change in the composition of volatile components during extraction, SPME was used for extraction of volatiles from raw ginger, and SDE and SPME were employed for extraction of volatiles from boiled ginger soup. Volatile compounds detected from raw ginger and boiled ginger soup are shown in Table 1. There were 57 volatile compounds (containing 43 terpenes, 4 aldehydes, 4 ketones, 3 alcohols, and 3 other volatile compounds) directly detected by headspace SPME–GC–MS from the raw ginger. Among these, terpenes were the major components and accounted for 97.1 % of total volatiles (shown as area). The ten most abundant terpenes were camphene, followed by 1,8-cineole, β-phellandrene, β-sesquiphellandrene, α-zingiberene, β-myrcene, α-phellanderene, β-bisabolene, (E)-neral, and terpinolene. However, other researchers have obtained slightly different results using different extraction methods. For example, Variyar et al. (1997) used the SDE technique to elucidate the composition of the most abundant volatile compounds present in essential oils obtained from fresh ginger, and found that the major components were the sesquiterpenes zingiberene, zingiberol, α-curcumene, β-sesquiphellandrene, and β-bisabolene, accounting for 70 % of the total chromatographic area. While Bartley and Jacobs (2000) reported that the main compounds extracted from fresh ginger oil extracts with supercritical carbon dioxide were geranial, zingiberene, zingerone, α-farnesene, 6-shogaol, β-sesquiphellandrene, geraniol, geranyl acetate, and β-bisabolene, which accounted for more than 60 % of the chromatographic area. These results highlight the differences in ginger composition that can be obtained from different extraction procedures. Therefore, it is important to use the same extraction technique throughout the study in order to obtain consistent results.
Table 1.
Volatile compounds identified from raw ginger and boiled ginger soup using SPME (as peak area, 1 × 106) and SDE (as total amount, µg) (n = 3)
| Name | LRIA | IdentificationB | Raw ginger | Boiled ginger soup | |
|---|---|---|---|---|---|
| SPMEC | SDED | SPMEC | |||
| Terpenes | |||||
| α-Tricyclene | 995 | MS + LRI | 3.68 ± 0.68a | nd | 0.00 ± 0.00b |
| α-Pinene | 1015 | MS + LRI | 14.24 ± 2.80a | nd | 0.00 ± 0.00b |
| Camphene | 1058 | MS + LRI + Std | 392.88 ± 85.98a | 0.18 ± 0.05 | 0.16 ± 0.03b |
| Sabinene | 1111 | MS + LRI | 1.41 ± 0.30a | nd | 0.00 ± 0.00b |
| 3-Carene | 1140 | MS + LRI + Std | 0.34 ± 0.17a | nd | 0.00 ± 0.00b |
| α-Phellanderene | 1159 | MS + LRI | 183.36 ± 20.04a | nd | 0.00 ± 0.00b |
| β-Myrcene | 1160 | MS + LRI + Std | 191.77 ± 27.75a | nd | 0.00 ± 0.00b |
| α-Terpinene | 1171 | MS + LRI | 5.25 ± 0.56a | nd | 0.00 ± 0.00b |
| Limonene | 1194 | MS + LRI + Std | 80.67 ± 33.56a | nd | 0.00 ± 0.00b |
| β-Phellandrene | 1204 | MS + LRI | 239.45 ± 47.77a | nd | 0.02 ± 0.00b |
| 1,8-Cineole | 1208 | MS + LRI + Std | 360.50 ± 137.00a | nd | 2.89 ± 0.30b |
| trans-Ocimene | 1230 | MS + LRI | 2.03 ± 0.28a | nd | 0.00 ± 0.00b |
| γ-Terpinene | 1238 | MS + LRI + Std | 17.63 ± 2.10a | nd | 0.00 ± 0.00b |
| Ocimene | 1245 | MS + LRI | 2.36 ± 0.52a | nd | 0.00 ± 0.00b |
| Terpinolene | 1275 | MS + LRI | 133.23 ± 6.35a | nd | 0.00 ± 0.00b |
| Allo-Ocimene | 1365 | MS + LRI | 0.43 ± 0.08a | nd | 0.00 ± 0.00b |
| a-Cubebene | 1452 | MS + LRI | 1.47 ± 0.17a | nd | 0.00 ± 0.00b |
| Citronellal | 1472 | MS + LRI + Std | 3.44 ± 0.64a | nd | 0.11 ± 0.01b |
| a-Copaene | 1485 | MS + LRI | 12.77 ± 2.05a | nd | 0.00 ± 0.00b |
| Camphor | 1507 | MS + LRI | 14.00 ± 1.90a | nd | 0.00 ± 0.00b |
| Linalool | 1546 | MS + LRI + Std | 23.17 ± 7.38a | nd | 0.11 ± 0.02b |
| α-Bergamotene | 1551 | MS + LRI | 6.74 ± 1.36a | nd | 0.00 ± 0.00b |
| Bornyl Acetate | 1573 | MS + LRI | 9.65 ± 2.00a | nd | 0.00 ± 0.00b |
| β-Elemene | 1583 | MS + LRI | 10.71 ± 1.79a | nd | 0.00 ± 0.00b |
| L-4-terpineneol | 1599 | MS | 9.23 ± 0.10a | nd | 0.00 ± 0.00b |
| Alloaromadendrene | 1636 | MS + LRI | 1.21 ± 1.11a | nd | 0.00 ± 0.00b |
| (E)-(β)-Farnesene | 1653 | MS + LRI | 4.48 ± 0.89a | nd | 0.00 ± 0.00b |
| Isoborneol | 1662 | MS + LRI | 2.17 ± 0.19a | nd | 0.00 ± 0.00b |
| β-Citral | 1678 | MS + LRI | 73.43 ± 9.86a | nd | 1.05 ± 0.05b |
| α-Terpineol | 1696 | MS + LRI + Std | 21.97 ± 5.71a | nd | 0.07 ± 0.01b |
| Borneol | 1698 | MS + LRI | 44.20 ± 10.10a | nd | 0.27 ± 0.04b |
| α-Zingiberene | 1730 | MS + LRI | 188.46 ± 40.27a | 0.30 ± 0.15 | 0.00 ± 0.00b |
| β-Bisabolene | 1733 | MS + LRI | 149.03 ± 29.62a | nd | 0.00 ± 0.00b |
| (E)-Neral | 1733 | MS + LRI | 127.65 ± 24.30a | 0.13 ± 0.04 | 1.09 ± 0.18b |
| α-Farnesene | 1749 | MS + LRI + Std | 85.92 ± 19.38a | nd | 0.00 ± 0.00b |
| δ-Cadinene | 1757 | MS + LRI | 6.44 ± 0.10a | nd | 0.00 ± 0.00b |
| α-Curcumene | 1762 | MS + LRI | 8.31 ± 0.77a | 0.11 ± 0.06 | 0.01 ± 0.01b |
| Citronellol | 1762 | MS + LRI + Std | 7.36 ± 1.20a | nd | 0.00 ± 0.00b |
| β-Sesquiphellandrene | 1773 | MS + LRI | 260.20 ± 46.81a | nd | 0.00 ± 0.00b |
| Nerol | 1799 | MS + LRI + Std | 22.91 ± 1.37a | nd | 0.00 ± 0.00b |
| Geraniol | 1848 | MS + LRI + Std | 47.62 ± 10.80a | nd | 0.00 ± 0.00b |
| Nerolidol | 2037 | MS + LRI | 4.14 ± 1.05a | nd | 0.00 ± 0.00b |
| Cedrol | 2107 | MS + LRI | 0.00 ± 0.00a | 0.13 ± 0.01 | 0.76 ± 0.21b |
| Zingerone | 2777 | MS + LRI + Std | nd | 0.11 ± 0.03 | nd |
| Total | 2775.87 ± 434.77a | 0.97 ± 0.27 | 6.53 ± 0.69b | ||
| Aldehydes | |||||
| Pentanal | 959 | MS + LRI | nd | 0.09 ± 0.03 | nd |
| Hexanal | 1070 | MS + LRI + Std | 0.00 ± 0.00a | 4.00 ± 0.30 | 1.26 ± 0.06b |
| Heptanal | 1179 | MS + LRI + Std | 0.00 ± 0.00a | 0.07 ± 0.04 | 0.00 ± 0.00b |
| Octanal | 1283 | MS + LRI + Std | 1.39 ± 0.10a | 0.40 ± 0.05 | 0.53 ± 0.06b |
| Nonanal | 1387 | MS + LRI + Std | 0.00 ± 0.00a | 1.46 ± 0.44 | 0.72 ± 0.06b |
| trans-2-Octenal | 1423 | MS + LRI + Std | 0.72 ± 0.23a | nd | 0.00 ± 0.00b |
| Decanal | 1513 | MS + LRI + Std | 0.00 ± 0.00a | nd | 0.65 ± 0.06b |
| trans-2-Decenal | 1637 | MS + LRI + Std | 2.05 ± 0.07a | nd | 0.00 ± 0.00b |
| trans-2-Dodecenal | 1857 | MS + LRI | 0.18 ± 0.09a | nd | 0.00 ± 0.00b |
| Total | 4.34 ± 0.46a | 6.03 ± 0.66 | 3.15 ± 0.25b | ||
| Ketones | |||||
| 2-Heptanone | 1178 | MS + LRI | 2.23 ± 0.48a | 0.30 ± 0.11 | 1.24 ± 0.16a |
| 6-Methyl-5-hepten-2-one | 1333 | MS + LRI + Std | 26.17 ± 9.03a | nd | 0.75 ± 0.11b |
| 2-Nonanone | 1384 | MS + LRI + Std | 7.62 ± 1.74a | nd | 0.14 ± 0.01b |
| 2-Undecanone | 1594 | MS + LRI + Std | 3.94 ± 1.07a | nd | 0.00 ± 0.00b |
| Total | 39.95 ± 12.27a | 0.30 ± 0.11 | 2.13 ± 0.25b | ||
| Alcohols | |||||
| 2-Heptanol | 1322 | MS + LRI + Std | 11.31 ± 1.85a | nd | 0.00 ± 0.00b |
| 2-Ethyl-1-hexanol | 1485 | MS + LRI + Std | 0.00 ± 0.00a | 0.06 ± 0.00 | 0.45 ± 0.14b |
| 2-Nonanol | 1522 | MS + LRI + Std | 0.00 ± 0.00a | nd | 0.12 ± 0.02b |
| 1-Octanol | 1558 | MS + LRI | 2.50 ± 0.41a | 0.34 ± 0.12 | 0.05 ± 0.01b |
| 1-Dodecanol | 1958 | MS + LRI + Std | 0.00 ± 0.00a | 0.13 ± 0.01 | 0.23 ± 0.02b |
| 1-Octadecanol | 2583 | MS + LRI + Std | 0.07 ± 0.02a | 0.31 ± 0.04 | 14.87 ± 4.15b |
| Total | 13.88 ± 2.12a | 0.83 ± 0.09 | 15.72 ± 4.31a | ||
| Alkanes | |||||
| Decane | 983 | MS + LRI + Std | nd | 0.58 ± 0.07 | nd |
| Undecane | 1097 | MS + LRI + Std | nd | 0.59 ± 0.09 | nd |
| Dodecane | 1198 | MS + LRI + Std | nd | 2.46 ± 0.68 | nd |
| Tridecane | 1298 | MS + LRI + Std | nd | 2.98 ± 0.14 | nd |
| Tetradecane | 1398 | MS + LRI + Std | nd | 0.89 ± 0.09 | nd |
| Pentadecane | 1497 | MS + LRI + Std | nd | 2.37 ± 0.06 | nd |
| Hexadecane | 1598 | MS + LRI + Std | nd | 4.64 ± 1.29 | nd |
| Heptadecane | 1696 | MS + LRI + Std | nd | 4.78 ± 1.86 | nd |
| Octadecane | 1795 | MS + LRI + Std | nd | 1.97 ± 0.54 | nd |
| Nonadecane | 1896 | MS + LRI + Std | nd | 1.46 ± 0.47 | nd |
| Eicosane | 1996 | MS + LRI + Std | nd | 1.41 ± 0.09 | nd |
| Heneicosane | 2095 | MS + LRI + Std | nd | 0.74 ± 0.04 | nd |
| Tricosane | 2294 | MS + LRI + Std | nd | 0.52 ± 0.06 | nd |
| Tetracosane | 2394 | MS + LRI + Std | nd | 0.88 ± 0.25 | nd |
| Pentacosane | 2495 | MS + LRI + Std | nd | 1.15 ± 0.01 | nd |
| Total | nd | 27.44 ± 5.36 | nd | ||
| Aromatic compounds | |||||
| Toluene | 1018 | MS + LRI | nd | 0.12 ± 0.00 | nd |
| Ethylbenzene | 1118 | MS + LRI | nd | 0.31 ± 0.08 | nd |
| p-Xylene | 1126 | MS + LRI + Std | nd | 0.10 ± 0.05 | nd |
| 1,3-Dimethylbenzene | 1132 | MS + LRI + Std | nd | 0.17 ± 0.02 | nd |
| o-Xylene | 1175 | MS + LRI + Std | 0.00 ± 0.00a | 0.12 ± 0.08 | 0.01 ± 0.01a |
| Styrene | 1249 | MS + LRI | nd | 0.22 ± 0.03 | nd |
| 1-Methyl-3-(1-methylethyl)-benzen | 1261 | MS + LRI + Std | 24.04 ± 3.64a | nd | 0.00 ± 0.00b |
| Benzaldehyde | 1510 | MS + LRI + Std | 0.00 ± 0.00a | 0.10 ± 0.02 | 0.09 ± 0.01b |
| Acetophenone | 1636 | MS + LRI + Std | nd | 0.08 ± 0.04 | nd |
| Benzyl alcohol | 1863 | MS + LRI + Std | nd | 3.49 ± 1.19 | nd |
| Butylated hydroxytoluene | 1899 | MS + LRI | 0.00 ± 0.00a | 0.16 ± 0.06 | 0.02 ± 0.00b |
| Phenol | 2003 | MS + LRI + Std | 0.00 ± 0.00a | nd | 0.07 ± 0.01b |
| 2,4-Di-tert-butylphenol | 2312 | MS + LRI | 0.00 ± 0.00a | nd | 1.34 ± 0.31b |
| Vanillin | 2565 | MS + LRI + Std | 0.00 ± 0.00a | nd | 0.05 ± 0.01b |
| Total | 24.04 ± 3.64a | 4.86 ± 1.56 | 1.58 ± 0.31b | ||
| Acids | |||||
| Acetic acid | 1464 | MS + LRI | nd | 0.06 ± 0.02 | nd |
| Hexadecanoic acid | 2942 | MS + LRI | 0.10 ± 0.02a | 2.73 ± 0.48 | 0.03 ± 0.01b |
| Total | 0.10 ± 0.02a | 2.78 ± 0.46 | 0.03 ± 0.01b | ||
| Esters | |||||
| Butyl ethanoate | 1062 | MS + LRI | nd | 0.10 ± 0.00 | nd |
| Hexadecanoic acid, methyl ester | 2206 | MS + LRI + Std | nd | 0.22 ± 0.03 | nd |
| Octadecanoic acid, methyl ester | 2413 | MS + LRI | nd | 0.11 ± 0.01 | nd |
| Diisobutyl phthalate | 2526 | MS + LRI | nd | 0.86 ± 0.02 | nd |
| Total | nd | 1.29 ± 0.03 | nd | ||
| Furans | |||||
| 2-Pentylfuran | 1227 | MS + LRI + Std | 0.00 ± 0.00a | 0.25 ± 0.05 | 0.14 ± 0.04b |
| Furfural | 1453 | MS + LRI | nd | 1.96 ± 0.46 | nd |
| 5-Methyl-2-furfural | 1561 | MS + LRI + Std | nd | 0.05 ± 0.03 | nd |
| Total | 0.00 ± 0.00a | 2.25 ± 0.54 | 0.14 ± 0.04b | ||
| Others | |||||
| Pyridine | 1182 | MS + LRI | 1.12 ± 0.36a | nd | 0.00 ± 0.00b |
| Total | 1.12 ± 0.36a | nd | 0.00 ± 0.00b | ||
| Total | 2859.3 ± 452.95a | 46.76 ± 7.55 | 29.28 ± 3.43b | ||
Analyzed by pared-samples T test, different letters within a row are significantly different at p < 0.05
nd not detected
ALinear retention indices calculated in relation to the retention time of a series of alkanes (C8–C40) determined by using a DB-Wax column
BMS + LRI + Std, mass spectrum and LRI agree with those of authentic compound; MS + LRI, mass spectrum identified using the NIST Mass Spectral Database and LRI agrees with the NIST Chemistry WebBook (Linstrom and Mallard 2001)
CPeak area of the deconvoluted compound extracted by SPME with fiber of DVB/CAR/PDMS, 1 × 106
DTotal amount of volatile compounds extracted by SDE from soup was calculated by using 1,2-dichlorobenzene as internal reference, in μg
The volatile profile of a boiled ginger solution was significantly different from that of the raw sample. With the combination of SDE–GC–MS and SPME–GC–MS, 54 compounds were identified from the boiled ginger solution, of these, 46 compounds went undetected in the raw ginger (two terpenes, five aldehydes, three alcohols, fifteen alkanes, fourteen aromatic compounds, one acid, three esters, and three furans) (Table 1). Aldehydes included pentanal, hexanal, heptanal, nonanal, and decanal. The hexanal and decanal detected in this study have been demonstrated to be derived from thermal degradation of non-volatile gingerol compounds during steam distillation (Chu-Chin and Chi-Tand 1987), and were thus likely formed from gingerol during the boiling process. Since aldehydes, alcohols, and furans in food were generated from multiple routes including oxidation of lipids, the Maillard reaction, and thermal decomposition of carbohydrates, further research into these reaction pathways would help to elucidate the origin of these compounds in samples of boiling ginger (Van Lancker et al. 2010; Yaylayan 2006).
The sensitivity of each SPME fiber is different depending on the molecular mass, volatility, and polarity of the analytes being extracted. Early studies showed that DVB-CAR-PDMS fibers were especially effective for polar terpene and sulfur based compounds (Hamm et al. 2003; Wardencki et al. 2004). Since SPME–GC–MS failed to detect the nonpolar or weakly polar compounds detected by SDE–GC–MS in the boiled ginger solution (mostly alkanes and aromatics: fifteen alkanes, fourteen aromatic compounds, and three esters), we could not judge whether the newly detected compounds in the boiled ginger solution were formed as a result of boiling or went undetected as a result of using the DVB-CAR-PDMS fiber in the SPME extraction method. Fortunately, the three groups of volatiles, which are odorless or possess weak odors and have relatively high threshold values, are less important to the overall flavor of ginger solution or fish soup, which will be further illustrated from the results described in this study.
In general, the peak area of volatiles extracted from ginger solution and detected by SPME–GC–MS were far lower than those from fresh ginger, and 30 terpenes, three aldehydes, one alcohol, and two other compounds went undetected in the boiled ginger solution (Table 1). Although it was difficult to accurately compare the volatile content in solid and liquid samples by SPME–GC–MS, the decrease of the peak area and disappearance of a large number of volatiles as a result of boiling ginger in water suggested that the volatiles were susceptible to evaporation or to decomposition and/or side reactions at elevated temperatures. These results were generally in good agreement with earlier studies which reported that high temperature conditions could lead to the loss of compounds with flavor properties due to evaporation, oxidative reactions, or even through the activity of endogenous enzymes (Raghavan 2006; Schweiggert et al. 2007).
Effect of boiling on volatiles content garlic
As in the study with ginger samples, SPME was used for extraction of volatiles from raw garlic, and SDE and SPME were employed for extraction of volatiles from boiled garlic solution. There were 18 volatile compounds detected from crushed garlic directly by headspace SPME–GC–MS, and 48 volatile compounds identified from boiled garlic solution by a combination of SPME–GC–MS and SDE–GC–MS (Table 2). The headspace volatile components in crushed ginger consisted mainly of sulfur compounds, predominantly diallyl disulphide (37.9 %), allyl methyl disulfide (35.3 %), and methyl propenyl disulfide (10.0 %), with lesser amounts of other sulfides. Alcohols were also present in smaller amounts (with 2-propenol being the most abundant), together with lesser quantities of aldehydes, esters and aromatics.
Table 2.
Volatile compounds identified from raw garlic and boiled garlic soup using SPME (as peak area, 1 × 106) and SDE (as total amount, μg) (n = 3)
| Name | LRIA | IdentificationB | Raw garlic | Boiled garlic soup | |
|---|---|---|---|---|---|
| SPMEC | SDED | SPMEC | |||
| Aldehydes | |||||
| Pentanal | 959 | MS + LRI | nd | 0.11 ± 0.01 | nd |
| Hexanal | 1077 | MS + LRI + Std | 0.00 ± 0.00a | 2.21 ± 0.05 | 0.12 ± 0.02b |
| Octanal | 1286 | MS + LRI + Std | 0.00 ± 0.00a | nd | 0.07 ± 0.02b |
| Nonanal | 1387 | MS + LRI + Std | 0.00 ± 0.00a | 0.85 ± 0.10 | 0.66 ± 0.08b |
| Decanal | 1499 | MS + LRI + Std | 0.12 ± 0.03a | nd | 0.74 ± 0.09b |
| Total | 0.12 ± 0.03a | 3.16 ± 0.15 | 1.58 ± 0.17b | ||
| Alcohols | |||||
| 2-Propen-1-ol | 1112 | MS + LRI | 1.21 ± 0.17a | 3.08 ± 0.30 | 0.2 ± 0.06b |
| Butyl alcohol | 1141 | MS + LRI + Std | 0.00 ± 0.00a | 0.03 ± 0.01 | 0.08 ± 0.04b |
| 2-Ethyl-1-hexanol | 1485 | MS + LRI + Std | 0.00 ± 0.00a | 0.19 ± 0.07 | 0.03 ± 0.02b |
| 1-Octanol | 1559 | MS + LRI | 0.14 ± 0.02a | nd | 0.10 ± 0.13a |
| 1-Dodecanol | 1958 | MS + LRI + Std | 0.00 ± 0.00a | 0.12 ± 0.07 | 0.22 ± 0.03b |
| 1-Octadecanol | 2584 | MS + LRI + Std | 0.44 ± 0.13a | 2.06 ± 0.11 | 0.15 ± 0.08b |
| Total | 1.80 ± 0.10a | 5.48 ± 0.20 | 0.79 ± 0.20b | ||
| Alkanes | |||||
| Decane | 983 | MS + LRI + Std | nd | 0.32 ± 0.04 | nd |
| Undecane | 1097 | MS + LRI + Std | nd | 0.52 ± 0.03 | nd |
| Dodecane | 1198 | MS + LRI + Std | nd | 2.03 ± 0.16 | nd |
| Tridecane | 1321 | MS + LRI + Std | 0.35 ± 0.24a | 3.07 ± 0.08 | 0.00 ± 0.00b |
| Tetradecane | 1398 | MS + LRI + Std | nd | 0.83 ± 0.05 | nd |
| Pentadecane | 1497 | MS + LRI + Std | nd | 2.70 ± 0.58 | nd |
| Hexadecane | 1597 | MS + LRI + Std | nd | 3.12 ± 0.24 | nd |
| Heptadecane | 1696 | MS + LRI + Std | nd | 1.90 ± 1.41 | nd |
| Octadecane | 1795 | MS + LRI + Std | nd | 1.69 ± 0.13 | nd |
| Nonadecane | 1896 | MS + LRI + Std | nd | 1.11 ± 0.46 | nd |
| Eicosane | 1996 | MS + LRI + Std | nd | 1.12 ± 0.01 | nd |
| Heneicosane | 2095 | MS + LRI + Std | nd | 0.73 ± 0.05 | nd |
| Docosane | 2194 | MS + LRI + Std | nd | 0.31 ± 0.01 | nd |
| Tricosane | 2294 | MS + LRI + Std | nd | 0.99 ± 0.04 | nd |
| Tetracosane | 2394 | MS + LRI + Std | nd | 0.48 ± 0.12 | nd |
| Total | 0.35 ± 0.24a | 20.95 ± 1.15 | 0.00 ± 0.00b | ||
| Aromatic compounds | |||||
| Toluene | 1018 | MS + LRI | nd | 0.14 ± 0.05 | nd |
| Ethylbenzene | 1118 | MS + LRI | nd | 0.30 ± 0.04 | nd |
| p-Xylene | 1126 | MS + LRI + Std | nd | 0.14 ± 0.01 | nd |
| 1,3-Dimethylbenzene | 1132 | MS + LRI + Std | nd | 0.29 ± 0.02 | nd |
| o-Xylene | 1175 | MS + LRI + Std | nd | 0.10 ± 0.03 | nd |
| Benzaldehyde | 1510 | MS + LRI + Std | 0.00 ± 0.00a | 0.07 ± 0.02 | 0.01 ± 0.00b |
| Acetophenone | 1642 | MS + LRI + Std | 0.05 ± 0.01a | nd | 0.00 ± 0.00b |
| Benzyl alcohol | 1863 | MS + LRI + Std | nd | 2.32 ± 0.19 | nd |
| Butylated hydroxytoluene | 1899 | MS + LRI | nd | 0.15 ± 0.08 | nd |
| Phenol | 1990 | MS + LRI + Std | 0.00 ± 0.00a | 0.03 ± 0.01 | 0.14 ± 0.03b |
| 2,4-Di-tert-butylphenol | 2296 | MS + LRI | 0.00 ± 0.00a | 2.25 ± 0.29 | 1.25 ± 0.29b |
| Total | 0.05 ± 0.01a | 5.80 ± 0.60 | 1.39 ± 0.31b | ||
| Sulfur compounds | |||||
| Methyl disulfide | 1058 | MS + LRI | 17.5 ± 6.02a | 0.00 ± 0.01 | 0.00 ± 0.00b |
| Allyl sulfide | 1137 | MS + LRI + Std | 4.69 ± 1.87a | 0.04 ± 0.00 | 0.40 ± 0.03a |
| Methyl propyl disulfide | 1221 | MS + LRI | 1.58 ± 0.53a | nd | 0.38 ± 0.33a |
| 3,4-dimethylthiophene | 1244 | MS + LRI | 2.37 ± 0.58a | nd | 0.00 ± 0.00b |
| Allyl methyl disulfide | 1277 | MS + LRI | 342.92 ± 19.78a | 0.22 ± 0.06 | 0.55 ± 0.03b |
| Methyl propenyl disulfide | 1281 | MS + LRI | 97.14 ± 12.88a | nd | 0.00 ± 0.00b |
| Dimethyltrisulfide | 1365 | MS + LRI | 1.57 ± 0.27a | nd | 0.00 ± 0.00b |
| Diallyl disulfide | 1469 | MS + LRI + Std | 368.62 ± 25.09a | 0.87 ± 0.22 | 7.11 ± 1.68b |
| Methyl allyl trisulfide | 1579 | MS + LRI | 75.86 ± 18.90a | nd | 0.00 ± 0.00b |
| Methyl (methylthiomethyl) persulfide | 1648 | MS + LRI | 0.45 ± 0.01a | nd | 0.00 ± 0.00b |
| Diallyl trisulfide | 1776 | MS + LRI + Std | 56.25 ± 11.70a | 1.17 ± 0.11 | 0.00 ± 0.00b |
| Total | 968.95 ± 3.56a | 2.30 ± 0.05 | 8.44 ± 1.36b | ||
| Acids | |||||
| Acetic acid | 1470 | MS + LRI | nd | 0.06 ± 0.01 | nd |
| Hexadecanoic acid | 2942 | MS + LRI | nd | 1.31 ± 0.02 | nd |
| Total | nd | 1.37 ± 0.03 | nd | ||
| Esters | |||||
| Butyl ethanoate | 1061 | MS + LRI | nd | 0.07 ± 0.00 | nd |
| Methyl hexadecanoate | 2215 | MS + LRI + Std | 0.32 ± 0.11a | 0.14 ± 0.06 | 0.00 ± 0.00b |
| Total | 0.32 ± 0.11a | 0.22 ± 0.06 | 0.00 ± 0.00b | ||
| Furans | |||||
| 2-Pentylfuran | 1227 | MS + LRI + Std | nd | 0.25 ± 0.05 | nd |
| Furfural | 1453 | MS + LRI | nd | 2.83 ± 0.67 | nd |
| Total | nd | 3.08 ± 0.62 | nd | ||
| Total | 971.59 ± 3.73a | 42.36 ± 1.14 | 12.21 ± 1.12b | ||
Analyzed by pared-samples T test, different letters within a row are significantly different at p < 0.05
nd not detected
ALinear retention indices calculated in relation to the retention time of a series of alkanes (C8–C40) determined by using a DB-Wax column
BMS + LRI + Std, mass spectrum and LRI agree with those of authentic compound; MS + LRI, mass spectrum identified using the NIST Mass Spectral Database and LRI agrees with the NIST Chemistry WebBook (Linstrom and Mallard 2001)
CPeak area of the deconvoluted compound extracted by SPME with fiber of DVB/CAR/PDMS, 1 × 106
DTotal amount of volatile compounds extracted by SDE from soup was calculated by using 1,2-dichlorobenzene as internal reference, in μg
Due to the pungent odor of garlic, various cooking treatments have been used to enhance its olfactory and gustatory characteristics or nutritional and medicinal properties. As seen from Table 2, the profiles of the volatile components in garlic changed after boiling in water. After the boiling process, levels of most volatiles, especially sulfides clearly decreased, however the heating process also resulted in the detection of more components. The decrease in the concentration of sulfides at elevated temperatures has also been reported by Kim et al. (2011), who found that the content of most sulfur compounds such as diallyl disulfide decreased when garlic received autoclaving and roasting treatment, and roasting at 200 °C for 60 min caused the formation of a large amount of pyrazines in garlic. In this study, the boiled garlic sample contained a total of 36 new compounds, consisting of four aldehydes, three alcohols, fourteen alkanes, ten aromatic compounds, two acids, one ester, and two furans. It has been reported that some components in garlic are unstable beyond 100 °C, and boiling may have caused degradation of non-volatiles such as thiosulfinates to volatiles. Therefore, heating may have decreased the amount of volatiles through evaporation or chemical degradation of volatiles, but may also resulted in the formation of new volatile compounds. This result is not unexpected since Chyau and Mau (1999) also reported that levels of most volatiles in garlic decreased as the heating time continued during microwave heating. Interestingly, previously undetected nonanal and 2-octenal were found in microwave-heated garlic; the former was also found in the boiled garlic sample but not in the raw sample.
As mentioned above, due to the low sensitivity of the DVB-CAR-PDMS fiber used in the SPME method for non-polar or weakly-polar compounds, we could not establish whether the newly detected non-polar or weakly-polar compounds in the boiled garlic solution were formed as a result of boiling or whether they went undetected as a result of using the SPME extraction method with the DVB-CAR-PDMS fiber.
Effect of ginger and/or garlic on volatiles of grass carp soup
The four basic uses of spices in cooking are to enhance flavor, endow food with pungency, impart color, and mask unpleasant odors (Hirasa and Takemasa 1998). The “masking” function can be achieved three ways: chemical (compounds with unpleasant odors are changed to nonvolatile compounds or to odorless substances by undergoing chemical changes), physical (unpleasant smelling compounds are adsorbed by porous activated carbon or zeolites), and sensation (a strong spice flavor covers an unpleasant smell or two compounds having different odors combined emit an odor that is no longer undesirable or even become odorless when mixed) (Hirasa and Takemasa 1998). Raw fish is generally characterized by a sweet, mild, green, plant-like, metallic, and weak fish odor (Morita et al. 2003). However, the grass carp soup we obtained after boiling in water without any added spices is characterized by a strong fish odor but a weak sweet, mild, green, plant-like odor, and cooked meat smell. Ginger and garlic are commonly used for neutralizing any unpleasant fish odor and for enhancing the flavor and aroma of fish soup cooked throughout Asia, and especially in China. Volatiles identified from fish soup prepared by boiling pan-fried grass carp with and without added ginger and/or garlic are shown in Table 3. Through a combination of SPME–GC–MS and SDE–GC–MS, a total of 46 volatile compounds (eleven aldehydes, two ketones, seven alcohols, five alkanes, fourteen aromatic compounds, two acids, two esters, one furan and two other compounds), were detected in grass carp soup without added spices. Among these compounds, aldehydes, ketones, and alcohols account for 61.9 % of the total identified volatiles from SDE extracts, and were mainly derived from enzymatic and non-enzymatic oxidation of polyunsaturated fatty acids in fish (Kawai and Sakaguchi 1996). Aldehydes, which were the second most abundant group of compounds from the mixture of volatiles, generally possess the lowest threshold values compared with other kinds of volatiles (Table 3), and may be the most significant group of volatiles in the grass carp soup cooked without any spices. The presence of the aldehydes trans,trans-2,4-decadienal; 2,4-decadienal; trans,trans-2,4-heptadienal; hexanal; and heptanal, which are reported to be some of the most prominent compounds responsible for the presence of a fish odor (Suffet et al. 1999), might be the main factor contributing to the fish odor of the grass carp soup. Other compounds which have an important role in the flavor and aroma of the fish soup cooked without any spices are 2-pentylfuran, some aromatic compounds (ethylbenzene, styrene, acetophenone, vanillin, eugenol), and 2,5-dimethylpyrazine.
Table 3.
Mean of volatile compounds isolated from fish soup prepared by boiling pan-fried grass carp with and without ginger and/or garlic using SPME (as peak area, 1 × 106) and SDE (as total amount, μg) (n = 3)
| Name | LRIA | IdentificationB | Threshold value (mg/kg)C | Odor descriptionD | Control | Ginger added | ||
|---|---|---|---|---|---|---|---|---|
| SDEE | SPMEF | SDEE | SPMEF | |||||
| Terpenes | ||||||||
| α-Pinene | 1008 | MS + LRI | 6.0(a) | Pine, turpentine | nd | 0.00 ± 0.00e | nd | 2.01 ± 0.36f |
| Camphene | 1048 | MS + LRI + Std | 1900.0(a) | Camphor | 0.00 ± 0.00a | 0.00 ± 0.00e | 1.85 ± 0.02b | 4.68 ± 0.45f |
| β-Myrcene | 1157 | MS + LRI + Std | 13.0(a) | Balsamic, must, spice | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.11 ± 0.01f |
| Limonene | 1189 | MS + LRI + Std | 10.0(a) | Lemon, orange | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.86 ± 0.04b | 1.65 ± 0.28f |
| β-Phellandrene | 1198 | MS + LRI | – | Mint, terpentine | 0.00 ± 0.00a | 0.00 ± 0.00e | 6.19 ± 0.12b | 7.16 ± 1.01f |
| 1,8-Cineole | 1203 | MS + LRI + Std | 12.0(a) | Mint, sweet | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.80 ± 0.05b | 0.76 ± 0.09f |
| Citronellal | 1471 | MS + LRI + Std | 25.0(a) | Fat | nd | 0.00 ± 0.00e | nd | 0.15 ± 0.04f |
| Linalool | 1545 | MS + LRI + Std | 6.0(a) | Flower, lavender | nd | 0.00 ± 0.00e | nd | 0.17 ± 0.04f |
| β-Citral | 1676 | MS + LRI | 32.0(a) | Lemon | 0.00 ± 0.00a | 0.00 ± 0.00e | 4.44 ± 0.05b | 4.95 ± 0.54f |
| α-Terpineol | 1694 | MS + LRI + Std | 330.0(a) | Oil, anise, mint | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.28 ± 0.05b | 0.00 ± 0.00e |
| α-Zingiberene | 1711 | MS + LRI | – | Spice, fresh, sharp | 0.00 ± 0.00a | 0.00 ± 0.00e | 3.76 ± 0.18b | 0.00 ± 0.00e |
| (E)-Neral | 1727 | MS + LRI | 32.0(a) | Lemon, mint | 0.00 ± 0.00a | 0.00 ± 0.00e | 7.22 ± 0.19b | 7.21 ± 1.00f |
| α-Farnesene | 1739 | MS + LRI + Std | medium(b) | Wood, sweet | 0.00 ± 0.00a | nd | 0.47 ± 0.07b | nd |
| α-Curcumene | 1762 | MS + LRI | – | Herb | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.54 ± 0.05b | 0.09 ± 0.03f |
| Citronellol | 1763 | MS + LRI + Std | 40.0(a) | Rose | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.19 ± 0.01b | 0.00 ± 0.00e |
| Geraniol | 1847 | MS + LRI + Std | 40.0(a) | Rose, geranium | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.34 ± 0.08b | 0.00 ± 0.00e |
| Total | 0.00 ± 0.00a | 0.00 ± 0.00e | 26.95 ± 0.16b | 28.94 ± 1.86f | ||||
| Aldehydes | ||||||||
| Pentanal | 973 | MS + LRI | 12(a) | Almond, malt, pungent | nd | 0.17 ± 0.03e | nd | 0.08 ± 0.01f |
| Hexanal | 1073 | MS + LRI + Std | 4.50(a) | Grass, tallow, fat, fishy | 2.23 ± 0.51a | 2.24 ± 0.61e | 2.33 ± 0.05a | 1.44 ± 0.20f |
| Heptanal | 1180 | MS + LRI + Std | 3.0(a) | Fat, citrus, rancid, fishy | 0.00 ± 0.00a | nd | 0.35 ± 0.01b | nd |
| Octanal | 1283 | MS + LRI + Std | 0.7(a) | Fat, soap, lemon, green | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e |
| trans-2-Heptenal | 1318 | MS + LRI + Std | 13.0(a) | Soap, fat, almond | 1.19 ± 0.38a | 0.35 ± 0.06e | 1.33 ± 0.12a | 0.17 ± 0.01f |
| Nonanal | 1387 | MS + LRI + Std | 1.0(a) | Fat, citrus, green | 0.90 ± 0.46a | 0.00 ± 0.00e | 2.08 ± 0.01b | 0.84 ± .15f |
| trans-2-Octenal | 1423 | MS + LRI + Std | 3.0(a) | Green leaf, walnut | 0.43 ± 0.03a | 0.25 ± 0.05e | 0.78 ± 0.02b | 0.00 ± 0.00f |
| trans, trans-2, 4-Heptadienal | 1487 | MS + LRI + Std | 49.0(a) | Nut, fat, fishy | 1.70 ± 0.19a | nd | 1.97 ± 0.11a | nd |
| Decanal | 1491 | MS + LRI + Std | 0.1(a) | Soap, orange, tallow | nd | 0.00 ± 0.00e | nd | 0.00 ± 0.00e |
| trans-2-Nonenal | 1528 | MS + LRI + Std | 0.08(a) | Cucumber, fat, green | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.37 ± 0.06b | 0.00 ± 0.00e |
| trans-2-Decenal | 1637 | MS + LRI + Std | 0.3(a) | Orange | 1.53 ± 0.24ab | 0.25 ± 0.10e | 2.10 ± 0.06a | 0.00 ± 0.00f |
| trans-2-Undecenal | 1746 | MS + LRI | 4200(a) | Soap, fat, green | 0.59 ± 0.31a | nd | 1.31 ± 0.03b | nd |
| 2,4-Decadienal | 1759 | MS + LRI | 0.07(c) | Seaweed, fishy | 5.26 ± 2.69a | 0.38 ± 0.03e | 11.88 ± 0.15b | 0.15 ± 0.03f |
| trans, trans-2, 4-Decadienal | 1804 | MS + LRI + Std | 0.07(c) | Fried, fat, fishy | 29.40 ± 2.09a | 1.99 ± 0.20 g | 46.53 ± 1.65b | 1.18 ± 0.11e |
| Hexadecanal | 2129 | MS + LRI | – | Cardboard | 0.24 ± 0.11a | nd | 1.14 ± 0.26b | nd |
| Total | 43.46 ± 1.15a | 5.62 ± 1.01e | 72.17 ± 1.74b | 3.87 ± 0.28f | ||||
| Ketones | ||||||||
| 2,3-Pentanedione | 1047 | MS + LRI | 20(a) | Pungent, sweet, butter, creamy, caramel, nutty, cheese | 0.10 ± 0.06a | nd | 0.00 ± 0.00b | nd |
| 3-Penten-2-one | 1121 | MS + LRI | 1.5(a) | Fishy, pungent | nd | 0.00 ± 0.00e | nd | 0.24 ± 0.09f |
| 3-Hydroxy-2-butanone | 1280 | MS + LRI + Std | 55.0(a) | Sweet, buttery, creamy, dairy, milky, fatty | 0.40 ± 0.03a | nd | 0.75 ± 0.03b | nd |
| 6-Methyl-5-hepten-2-one | 1332 | MS + LRI + Std | 50.0(a) | Citrus, green, musty, lemongrass, apple | nd | 0.00 ± 0.00e | nd | 0.39 ± 0.04f |
| Total | 0.50 ± 0.09a | 0.00 ± 0.00e | 0.75 ± 0.03b | 0.63 ± 0.05f | ||||
| Alcohols | ||||||||
| 2-Propen-1-ol | 1112 | MS + LRI | – | Pungent, mustard | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e |
| 1-Pentanol | 1251 | MS + LRI + Std | 4000.0(a) | Fusel, oil, sweet, balsam | nd | 0.53 ± 0.07e | nd | 0.10 ± 0.02f |
| 1-Octen-3-ol | 1448 | MS + LRI + Std | 1.0(a) | Mushroom | nd | 0.43 ± 0.04e | nd | 0.00 ± 0.00f |
| 1-Heptanol | 1455 | MS + LRI | 330(a) | Herb | nd | 0.05 ± 0.00e | nd | 0.00 ± 0.00f |
| 2-Ethyl-1-hexanol | 1489 | MS + LRI + Std | 1000.0(a) | Rose, green | 0.55 ± 0.32a | 0.34 ± 0.04e | 1.77 ± 0.18b | 0.30 ± 0.04e |
| 1-Octanol | 1558 | MS + LRI | 110.0(a) | Chemical, metal, burnt | 0.00 ± 0.00a | 0.20 ± 0.05e | 0.45 ± 0.06b | 0.00 ± 0.00f |
| 1-Dodecanol | 1966 | MS + LRI + Std | 100.0(a) | Earthy, soapy, waxy, fatty, honey, coconut | 2.43 ± 1.08ab | nd | 3.50 ± 1.46a | nd |
| 1-Octadecanol | 2586 | MS + LRI + Std | – | Bland | 79.53 ± 7.70a | 0.16 ± 0.02e | 79.12 ± 4.08a | 0.65 ± 0.13f |
| Total | 82.51 ± 9.09a | 1.72 ± 0.04e | 84.83 ± 5.66a | 1.05 ± 0.10f | ||||
| Alkanes | ||||||||
| Decane | 984 | MS + LRI + Std | – | Alkane | 0.93 ± 0.34a | nd | 2.14 ± 0.12b | nd |
| Undecane | 1186 | MS + LRI + Std | – | Alkane | 7.25 ± 2.03a | nd | 3.67 ± 0.32b | nd |
| Dodecane | 1201 | MS + LRI + Std | – | Alkane | 0.00 ± 0.00a | nd | 1.24 ± 0.20b | nd |
| Tridecane | 1303 | MS + LRI + Std | – | Alkane | 0.00 ± 0.00a | nd | 5.27 ± 0.06b | nd |
| Tetradecane | 1403 | MS + LRI + Std | – | Alkane | 0.00 ± 0.00a | nd | 1.07 ± 0.04b | nd |
| Pentadecane | 1504 | MS + LRI + Std | – | Alkane | 8.82 ± 1.15a | nd | 8.36 ± 1.03ab | nd |
| Hexadecane | 1604 | MS + LRI + Std | – | Alkane | 0.57 ± 0.26a | nd | 1.64 ± 0.01ab | nd |
| Heptadecane | 1696 | MS + LRI + Std | – | Alkane | 4.20 ± 1.23a | nd | 4.14 ± 0.10a | nd |
| Total | 21.78 ± 2.71a | nd | 27.54 ± 1.66b | nd | ||||
| Aromatic compounds | ||||||||
| Toluene | 1018 | MS + LRI | – | Paint | 0.00 ± 0.00a | nd | 0.84 ± 0.03b | nd |
| Ethylbenzene | 1118 | MS + LRI | – | – | 0.66 ± 0.16a | nd | 1.19 ± 0.17a | nd |
| p-Xylene | 1125 | MS + LRI + Std | – | – | 0.79 ± 0.06a | nd | 0.91 ± 0.11a | nd |
| 1,3-Dimethylbenzene | 1131 | MS + LRI + Std | – | Plastic | 1.44 ± 0.21ab | nd | 1.87 ± 0.15a | nd |
| o-Xylene | 1174 | MS + LRI + Std | – | Geranium | 0.90 ± 0.26a | nd | 2.05 ± 0.04b | nd |
| Propylbenzene | 1199 | MS + LRI | – | – | 0.51 ± 0.18a | nd | 2.00 ± 0.16c | nd |
| 1-Methyl-4-ethylbenzene | 1213 | MS + LRI | – | – | 0.93 ± 0.02ac | nd | 2.80 ± 1.19a | nd |
| 1-Ethyl-3-methylbenzene | 1216 | MS + LRI | – | – | 1.79 ± 0.17a | nd | 5.03 ± 0.52b | nd |
| 1,3,5-Trimethylbenzene | 1234 | MS + LRI | – | – | 0.71 ± 0.02a | nd | 1.38 ± 0.10b | nd |
| Styrene | 1247 | MS + LRI | 44(a) | Balsamic, gasoline | 0.07 ± 0.01a | nd | 0.38 ± 0.18b | nd |
| 11-Ethyl-2-methylbenzene | 1251 | MS + LRI | – | – | 0.76 ± 0.15a | nd | 1.23 ± 0.06a | nd |
| p-Cymene | 1261 | MS + LRI + Std | 150.0(a) | Solvent, gasoline, citrus | nd | 0.00 ± 0.00e | nd | 0.28 ± 0.06f |
| 1,2,4-Trimethylbenzene | 1270 | MS + LRI | – | Plastic | 0.00 ± 0.00a | nd | 1.07 ± 0.70b | nd |
| α-Formylethylbenzene | 1293 | MS + LRI | 5,760,000(a) | Fresh, sharp, green, hyacinth, leaf lilac | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| 1,2,3-Trimethylbenzene | 1325 | MS + LRI | – | – | 0.00 ± 0.00a | nd | 0.21 ± 0.11b | nd |
| Benzaldehyde | 1512 | MS + LRI + Std | 350.0(a) | Almond, burnt sugar | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.13 ± 0.02f |
| Acetophenone | 1642 | MS + LRI + Std | 65.0(a) | Must, flower, almond | 1.27 ± 0.71a | nd | 2.39 ± 0.15ab | nd |
| Butylated hydroxytoluene | 1903 | MS + LRI | 1000(a) | Mild phenolic, camphor | nd | 1.53 ± 0.64e | nd | 0.00 ± 0.00f |
| Decylbenzene | 1936 | MS + LRI | – | – | 0.00 ± 0.00a | nd | 0.54 ± 0.14b | nd |
| Vanillin | 2560 | MS + LRI + Std | 58.0(a) | Vanilla | 0.00 ± 0.00a | nd | 0.20 ± 0.07b | nd |
| 3,4-Dimethylbenzaldehyde | 1800 | MS + LRI | – | – | 0.10 ± 0.05a | nd | 0.38 ± 0.09b | nd |
| Phenol | 1998 | MS + LRI + Std | 5500.0(a) | Phenol | 4.76 ± 1.79a | 3.48 ± 0.49e | 13.33 ± 4.84b | 5.79 ± 0.91f |
| Eugenol | 2160 | MS + LRI | 6(a) | Clove, honey | 0.00 ± 0.00a | nd | 2.31 ± 0.03b | nd |
| 2,4-Di-tert-butylphenol | 2305 | MS + LRI | – | – | nd | 0.00 ± 0.00e | nd | 0.29 ± 0.02f |
| Total | 14.68 ± 2.41a | 5.01 ± 1.13ef | 40.13 ± 5.40b | 6.48 ± 0.99e | ||||
| Acids | ||||||||
| Hexanoic acid | 1863 | MS + LRI | 3000(a) | Sour, fatty, sweat, cheese | nd | 0.19 ± 0.02e | nd | 0.16 ± 0.02e |
| Octanoic Acid | 2080 | MS + LRI + Std | 3000.0(a) | Sweat, cheese | nd | 0.00 ± 0.00e | nd | 0.00 ± 0.00e |
| Hexadecanoic acid | 2928 | MS + LRI | 10,000(a) | Slightly waxy, fatty | 5.10 ± 0.07a | 0.00 ± 0.00e | 5.05 ± 0.49a | 0.28 ± 0.06e |
| Total | 5.10 ± 0.07a | 0.19 ± 0.02e | 5.05 ± 0.49a | 0.44 ± 0.07e | ||||
| Esters | ||||||||
| Ethyl citrate | 2473 | MS | – | Odorless to mild fruity wine | 34.31 ± 12.77a | nd | 58.95 ± 3.53b | nd |
| Phthalic acid, diisobutyl ester | 2539 | MS + LRI | – | – | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| Dibutyl phthalate | 2695 | MS + LRI | – | Faint odor | 1.42 ± 0.36a | nd | 0.00 ± 0.00b | nd |
| Total | 35.73 ± 13.13a | nd | 58.95 ± 3.53b | nd | ||||
| Sulfur compounds | ||||||||
| Allyl sulfide | 1138 | MS + LRI + Std | 32.5(a) | Sulfurous, onion, garlic | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e |
| Diallyl disulfide | 1469 | MS + LRI + Std | 30.0(a) | Onion, garlic, metallic | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e |
| Diallyl trisulfide | 1775 | MS + LRI + Std | high(b) | Garlic, green, onion, metallic | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| Total | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e | ||||
| Furan | ||||||||
| 2-Pentylfuran | 1224 | MS + LRI + Std | 6.0(a) | Green bean, butter | 0.46 ± 0.16a | 0.08 ± 0.01e | 1.07 ± 0.23b | 0.00 ± 0.00f |
| Furfural | 1456 | MS + LRI | 3000(a) | Bread, almond, sweet | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.00 ± 0.00e |
| 5-Hydroxymethyl furfural | 2499 | MS + LRI + Std | high(b) | Fatty, buttery, musty, waxy, caramellic | nd | 0.00 ± 0.00e | nd | 0.17 ± 0.02f |
| Total | 0.46 ± 0.16a | 0.08 ± 0.01e | 1.07 ± 0.23b | 0.17 ± 0.02f | ||||
| Others | ||||||||
| 2,5-Dimethylpyrazine | 1320 | MS + LRI + Std | 800.0(a) | Cocoa, roasted nuts, roast beef, woody, grass, medical | nd | 0.04 ± 0.01e | nd | 0.00 ± 0.00f |
| Carbitol | 1621 | MS + LRI + Std | – | – | nd | 0.32 ± 0.06e | nd | 0.00 ± 0.00f |
| Total | nd | 0.36 ± 0.05e | nd | 0.00 ± 0.00f | ||||
| Total | 204.22 ± 28.50a | 12.99 ± 2.13e | 317.45 ± 7.24b | 41.59 ± 0.59f | ||||
| Name | Garlic added | Ginger and garlic added | ||
|---|---|---|---|---|
| SDEE | SPMEF | SDEE | SPMEF | |
| Terpenes | ||||
| α-Pinene | nd | 0.00 ± 0.00e | nd | 1.77 ± 0.22f |
| Camphene | 0.00 ± 0.00a | 0.00 ± 0.00e | 1.97 ± 0.25b | 5.94 ± 0.38g |
| β-Myrcene | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.34 ± 0.03b | 0.52 ± 0.05g |
| Limonene | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.37 ± 0.28b | 1.69 ± 0.21f |
| β-Phellandrene | 0.00 ± 0.00a | 0.00 ± 0.00e | 1.95 ± 0.38c | 6.40 ± 0.31f |
| 1,8-Cineole | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.25 ± 0.13c | 0.86 ± 0.14f |
| Citronellal | nd | 0.00 ± 0.00e | nd | 0.35 ± 0.05g |
| Linalool | nd | 0.00 ± 0.00e | nd | 0.46 ± 0.07g |
| β-Citral | 0.00 ± 0.00a | 0.00 ± 0.00e | 1.63 ± 0.08c | 6.19 ± 0.46g |
| α-Terpineol | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 1.04 ± 0.31f |
| α-Zingiberene | 0.00 ± 0.00a | 0.00 ± 0.00e | 3.07 ± 0.28c | 1.11 ± 0.12f |
| (E)-Neral | 0.00 ± 0.00a | 0.00 ± 0.00e | 2.82 ± 0.12c | 9.2 ± 1.12g |
| α-Farnesene | 0.00 ± 0.00a | nd | 0.28 ± 0.09c | nd |
| α-Curcumene | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.50 ± 0.11b | 0.15 ± 0.04g |
| Citronellol | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.29 ± 0.03f |
| Geraniol | 0.00 ± 0.00a | 0.00 ± 0.00e | 0.28 ± 0.02b | 0.53 ± 0.09f |
| Total | 0.00 ± 0.00a | 0.00 ± 0.00e | 13.45 ± 1.17c | 36.5 ± 1.76g |
| Aldehydes | ||||
| Pentanal | nd | 0.00 ± 0.00 g | nd | 0.00 ± 0.00g |
| Hexanal | 1.03 ± 0.42b | 2.44 ± 0.30 g | 1.98 ± 0.46a | 0.88 ± 0.27f |
| Heptanal | 0.11 ± 0.03c | nd | 0.00 ± 0.00a | nd |
| Octanal | 0.10 ± 0.04b | 0.00 ± 0.00e | 0.15 ± 0.04b | 0.13 ± 0.01f |
| trans-2-Heptenal | 0.92 ± 0.32ab | 0.00 ± 0.00 g | 0.59 ± 0.03b | 0.13 ± 0.02f |
| Nonanal | 1.41 ± 0.06c | 1.69 ± 0.50 g | 0.98 ± 0.06ac | 3.13 ± 0.35h |
| trans-2-Octenal | 0.48 ± 0.03a | 0.24 ± 0.04e | 0.34 ± 0.06c | 0.51 ± 0.09g |
| trans, trans-2, 4-Heptadienal | 0.87 ± 0.22b | nd | 0.65 ± 0.10b | nd |
| Decanal | nd | 0.00 ± 0.00e | nd | 0.09 ± 0.00f |
| trans-2-Nonenal | 0.34 ± 0.19b | 0.00 ± 0.00e | 0.00 ± 0.00a | 0.43 ± 0.06f |
| trans-2-Decenal | 1.45 ± 0.75ab | 0.00 ± 0.00f | 1.11 ± 0.07b | 0.00 ± 0.00f |
| trans-2-Undecenal | 0.47 ± 0.15a | nd | 0.73 ± 0.05a | nd |
| 2,4-Decadienal | 4.25 ± 1.36a | 0.29 ± 0.03 g | 3.81 ± 0.12a | 0.37 ± 0.04e |
| trans, trans-2, 4-Decadienal | 17.71 ± 5.26c | 1.51 ± 0.21ef | 16.34 ± 1.23c | 1.83 ± 0.20 fg |
| Hexadecanal | 0.63 ± 0.28a | nd | 0.58 ± 0.21a | nd |
| Total | 29.77 ± 8.84c | 6.16 ± 0.51e | 27.24 ± 1.32c | 7.49 ± 0.59g |
| Ketones | ||||
| 2,3-Pentanedione | 0.00 ± 0.00b | nd | 0.00 ± 0.00b | nd |
| 3-Penten-2-one | nd | 0.00 ± 0.00e | nd | 0.00 ± 0.00e |
| 3-Hydroxy-2-butanone | 0.00 ± 0.00c | nd | 0.51 ± 0.03d | nd |
| 6-Methyl-5-hepten-2-one | nd | 0.00 ± 0.00e | nd | 0.32 ± 0.09f |
| Total | 0.00 ± 0.00c | 0.00 ± 0.00e | 0.51 ± 0.03a | 0.32 ± 0.09g |
| Alcohols | ||||
| 2-Propen-1-ol | 7.01 ± 3.17b | 0.94 ± 0.35f | 6.38 ± 2.07b | 0.31 ± 0.04e |
| 1-Pentanol | nd | 0.23 ± 0.03 g | nd | 0.13 ± 0.03f |
| 1-Octen-3-ol | nd | 0.49 ± 0.08e | nd | 0.39 ± 0.10e |
| 1-Heptanol | nd | 0.00 ± 0.00f | nd | 0.00 ± 0.00f |
| 2-Ethyl-1-hexanol | 1.09 ± 0.33c | 0.45 ± 0.03e | 0.49 ± 0.02a | 1.06 ± 0.19f |
| 1-Octanol | 0.00 ± 0.00a | 0.10 ± 0.02 g | 0.15 ± 0.05c | 0.11 ± 0.01g |
| 1-Dodecanol | 1.10 ± 0.39b | nd | 1.58 ± 0.13b | nd |
| 1-Octadecanol | 31.35 ± 5.99b | 0.00 ± 0.00 g | 52.54 ± 3.64c | 0.31 ± 0.09h |
| Total | 40.54 ± 9.85b | 2.21 ± 0.39 g | 61.14 ± 1.48c | 2.32 ± 0.12g |
| Alkanes | ||||
| Decane | 1.50 ± 0.47a | nd | 1.32 ± 0.05a | nd |
| Undecane | 1.71 ± 0.02b | nd | 3.44 ± 0.67b | nd |
| Dodecane | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| Tridecane | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| Tetradecane | 0.60 ± 0.03c | nd | 0.55 ± 0.07c | nd |
| Pentadecane | 6.26 ± 2.92ab | nd | 5.28 ± 0.44b | nd |
| Hexadecane | 2.28 ± 1.16b | nd | 0.94 ± 0.09a | nd |
| Heptadecane | 2.56 ± 0.62b | nd | 3.85 ± 0.35ab | nd |
| Total | 14.89 ± 5.04c | nd | 15.38 ± 0.38c | nd |
| Aromatic compounds | ||||
| Toluene | 0.00 ± 0.00a | nd | 0.25 ± 0.05c | nd |
| Ethylbenzene | 1.07 ± 0.51a | nd | 0.81 ± 0.23a | nd |
| p-Xylene | 0.74 ± 0.31a | nd | 0.71 ± 0.14a | nd |
| 1,3-Dimethylbenzene | 1.08 ± 0.30b | nd | 1.51 ± 0.24ab | nd |
| o-Xylene | 0.68 ± 0.23a | nd | 0.76 ± 0.43a | nd |
| Propylbenzene | 0.59 ± 0.20ab | nd | 0.90 ± 0.23b | nd |
| 1-Methyl-4-ethylbenzene | 0.00 ± 0.00b | nd | 1.38 ± 0.63c | nd |
| 1-Ethyl-3-methylbenzene | 2.45 ± 0.80a | nd | 2.45 ± 0.63a | nd |
| 1,3,5-Trimethylbenzene | 0.93 ± 0.20ab | nd | 1.14 ± 0.60ab | nd |
| Styrene | 0.00 ± 0.00a | nd | 0.17 ± 0.13a | nd |
| 11-Ethyl-2-methylbenzene | 0.00 ± 0.00b | nd | 1.03 ± 0.54a | nd |
| p-Cymene | nd | 0.00 ± 0.00e | nd | 0.20 ± 0.02g |
| 1,2,4-Trimethylbenzene | 0.00 ± 0.00a | nd | 0.00 ± 0.00a | nd |
| α-Formylethylbenzene | 0.05 ± 0.01b | nd | 0.00 ± 0.00a | nd |
| 1,2,3-Trimethylbenzene | 0.00 ± 0.00a | nd | 0.19 ± 0.07b | nd |
| Benzaldehyde | 0.17 ± 0.06b | 0.10 ± 0.02f | 0.08 ± 0.05c | 0.26 ± 0.10g |
| Acetophenone | 4.32 ± 2.24b | nd | 3.31 ± 0.25ab | nd |
| Butylated hydroxytoluene | nd | 0.00 ± 0.00f | nd | 0.00 ± 0.00f |
| Decylbenzene | 0.34 ± 0.05c | nd | 0.00 ± 0.00a | nd |
| Vanillin | 0.08 ± 0.01c | nd | 0.09 ± 0.03c | nd |
| 3,4-Dimethylbenzaldehyde | 0.18 ± 0.03a | nd | 0.15 ± 0.04a | nd |
| Phenol | 8.64 ± 2.82ab | 4.25 ± 0.90e | 2.88 ± 0.21a | 3.35 ± 0.77e |
| Eugenol | 1.38 ± 0.30c | nd | 3.47 ± 0.21d | nd |
| 2,4-Di-tert-butylphenol | nd | 0.10 ± 0.04 g | nd | 0.00 ± 0.00e |
| Total | 22.7 ± 7.90a | 4.46 ± 0.89f | 21.29 ± 3.45a | 3.81 ± 0.85f |
| Acids | ||||
| Hexanoic acid | nd | 0.00 ± 0.00f | nd | 0.19 ± 0.03e |
| Octanoic Acid | nd | 0.08 ± 0.01f | nd | 0.00 ± 0.00e |
| Hexadecanoic acid | 1.78 ± 0.31b | 1.54 ± 0.40f | 4.86 ± 1.77a | 0.00 ± 0.00e |
| Total | 1.78 ± 0.31b | 1.62 ± 0.41f | 4.86 ± 1.77a | 0.19 ± 0.03e |
| Esters | ||||
| Ethyl citrate | 41.81 ± 12.30ab | nd | 44.67 ± 2.52ab | nd |
| Phthalic acid, diisobutyl ester | 0.77 ± 0.22b | nd | 0.00 ± 0.00a | nd |
| Dibutyl phthalate | 1.58 ± 0.46a | nd | 1.67 ± 0.14a | nd |
| Total | 44.15 ± 12.97ab | nd | 46.34 ± 2.66ab | nd |
| Sulfur compounds | ||||
| Allyl sulfide | 0.16 ± 0.06b | 1.46 ± 0.15f | 0.24 ± 0.01c | 0.24 ± 0.02g |
| Diallyl disulfide | 4.59 ± 0.40b | 20.77 ± 1.50f | 1.90 ± 0.12c | 24.92 ± 2.71g |
| Diallyl trisulfide | 0.21 ± 0.03b | nd | 0.27 ± 0.04c | nd |
| Total | 4.96 ± 0.39b | 22.23 ± 1.65f | 2.41 ± 0.17c | 25.16 ± 2.73f |
| Furan | ||||
| 2-Pentylfuran | 0.00 ± 0.00c | 0.00 ± 0.00f | 0.71 ± 0.36a | 0.14 ± 0.02g |
| Furfural | 4.96 ± 0.39b | 0.00 ± 0.00e | 2.41 ± 0.17c | 0.07 ± 0.01f |
| 5-Hydroxymethyl furfural | nd | 0.00 ± 0.00e | nd | 0.00 ± 0.00e |
| Total | 0.00 ± 0.00c | 0.00 ± 0.00 g | 0.71 ± 0.36a | 0.21 ± 0.03h |
| Others | ||||
| 2,5-Dimethylpyrazine | nd | 0.00 ± 0.00f | nd | 0.00 ± 0.00f |
| Carbitol | nd | 0.00 ± 0.00f | nd | 0.00 ± 0.00f |
| Total | nd | 0.00 ± 0.00f | nd | 0.00 ± 0.00f |
| Total | 158.79 ± 44.51b | 36.69 ± 2.17f | 193.34 ± 11.83b | 76.00 ± 4.71g |
Analyzed by ANOVA, different letters within a row are significantly different at p < 0.05; a–d are for SDE; e–h are for SPME
–Not obtained
nd not detected
ALinear retention indices calculated in relation to the retention time of a series of alkanes (C8–C40) determined by using a DB-Wax column
BMS + LRI + Std, mass spectrum and LRI agree with those of authentic compound; MS + LRI, mass spectrum identified using the NIST Mass Spectral Database and LRI agrees with the NIST Chemistry WebBook (Linstrom and Mallard 2001). MS, mass spectrum agrees with spectrum in the NIST Mass Spectral Database
CThreshold value in water: (a) Lowest threshold obtained from Leffingwell and Associates database (2012); (b) Obtained from Perflavory website (Luebke 2016); (c) obtained from literature of Chevance and Farmer (1999)
DObtained from literature of Suffet et al. (1999) and electronic references (Acree and Arn 2015; Luebke 2016)
ETotal amount of volatile compounds extracted by SDE from soup was calculated by using 1,2-dichlorbenzene as the internal reference, in μg
FPeak area of the deconvoluted compound extracted by SPME with fiber of DVB/CAR/PDMS, 1 × 106
When spices were added, the volatile profile of the grass carp soup changed considerably. When ginger, garlic, or ginger plus garlic were added, there were 72, 51, and 71 compounds identified, respectively. Compared with the soup without ginger, the ginger and ginger plus garlic soups contained a large amount of terpenoids (including reduced and oxidized terpenes), which were shown to originate from ginger and to be stable under boiling conditions as demonstrated by their presence in fresh ginger and in the solution of boiled ginger (Table 1). Terpenes are described as typically having a floral, rose-like, coriander, camphoraceous, green, and herbaceous odor (Meilgaard 1975; Simpson 1979). The addition of ginger modified the flavor of the grass carp soup, giving it a floral smell which is attributed to the presence of terpenes. Similarly, 2-propen-1-ol and various sulfur compounds (allyl sulfide, diallyl disulfide, diallyl trisulfide) which are present in raw garlic and in the boiled garlic solution (Table 2), were also identified in the fish soup with added garlic and ginger plus garlic, it thus seems plausible to assume that these compounds originate directly from the garlic. Sulfur compounds play an important role in the flavor and odor of food due to their relatively low threshold values and their intense odor (Schutte and Teranishi 1974), e.g. the threshold value of allyl sulfide and diallyl disulfide in water is 32.5 and 30 μg/kg, respectively. The sulfur compounds detected in garlic conferred upon the fish soup a slight garlic and onion odor which masked the fish odor (Yoshida et al. 1984). The 2-Propen-1-ol detected in garlic-added soup has been reported to be formed in considerable quantities in heated garlic and alliin (Lee et al. 2006), and thus may also have been derived from thermal degradation of alliin in garlic when boiling.
With the exception of terpenes, 2-propen-1-ol, and sulfur compounds, generally, there was no obvious difference in the presence of other volatiles between the soups prepared by boiling pan-fried grass carp with and without spices. For example, in the soups without any added spices, with ginger, with garlic, and with garlic plus ginger, a total of 11, 13, 13, and 13 aldehydes were detected, respectively. The four samples had ten aldehydes in common: hexanal; trans-2-heptenal; nonanal; trans-2-octenal; trans,trans-2,4-heptadienal; trans-2-decenal; trans-2-undecenal; 2,4-decadienal; trans,trans-2,4-decadienal; and hexadecanal. However, the content of these compounds was not consistent throughout the four samples. Meanwhile, some volatiles such as pentanal, hexanal, nonanal, and dodecanol, were only detected in fish soup (including with and without spices) and boiled spiced solutions (Tables 1, 2), which suggested that these volatiles may be formed as a result of boiling spices and the pan-fried fish.
In addition, the levels of volatiles derived from ginger or garlic in the fish soups with added spices were generally higher than those in the boiled spiced solutions. One possible reason was that the volatiles were soluble in the soybean oil used for frying the grass carp and were protected by the soybean oil from evaporation or reacting with other substances during boiling, and this hypothesis was in agreement with the research results of Kim et al. (1995).
Overall, alcohol and the carbonyl compounds, alkane and furan in fish soups could be mainly formed during frying or boiling of fish and derived from the oxidation of lipids (Zakipour Rahimabadi et al. 2011; Zhang et al. 2013). With the addition of ginger and garlic, the content of volatiles responsible for the presence of a fish odor (such as trans,trans-2,4-decadienal; 2,4-decadienal; trans,trans-2,4-heptadienal; hexanal; and heptanal) was not significantly decreased, and in fact some volatiles increased in amount. Therefore, the masking function by ginger and garlic of the fish odor was not through physical absorption or chemical conversion of the compounds responsible for the undesirable odors, but through the release of strongly flavored compounds such as terpenes and sulfur compounds which covered the unpleasant fish smell or mixed with the fish-odor compounds thereby creating an odorless mixture, a process called “sensational deodorizing” according to the classification of Hirasa and Takemasa (1998).
Conclusion
The most abundant volatile compounds in ginger were found to be terpenes, while raw garlic consisted mostly of sulfides (diallyl disulfide, allyl methyl disulfide, and methyl propenyl disulfide). Boiling spices in water decreased the amount of the principal volatile constituents and result in the formation of new volatiles, whereas boiling spices together with grass carp previously fried in soybean oil increased content of the residual volatile compounds. Terpenes detected in the fish soup with added ginger were derived from fresh ginger and, in contrast to the boiled ginger solution where their content was negligible which were retained in the fish soup despite the boiling. Similarly, 2-propen-1-ol and sulfides detected in the fish soup with added garlic were derived from crushed garlic and also remained in the solution even after boiling. In conclusion, the addition of spices into a fish soup resulted in the dissolution of the main flavor volatiles from ginger and garlic into the solution, and that in contrast to the boiled ginger and garlic solution, the volatiles were retained to a greater extent in the solution even after boiling without prior frying of fish. In addition, few additional volatiles were formed during the boiling process. The masking function of ginger and garlic on fish odor was the result of “sensational deodorizing”.
Acknowledgments
This work was supported by the Earmarked Fund for Jiangxi Agriculture Research System (JXARS-04) and the Collaborative Innovation Center for Major Ecological Security Issues of Jiangxi Province and Monitoring Implementation (No. JXS-EW-00).
Compliance with ethical standards
Conflict of interest
None.
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