Dimethyl Sulfide as a Source of the Seaweed-like Aroma in Cooked

Aug 4, 2014 - Dimethyl sulfide (DMS) is a typical volatile organic sulfur compound with ... n-hexanal, n-hexan-1-ol, and dimethyl sulfide were purchas...
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Dimethyl Sulfide as a Source of the Seaweed-like Aroma in Cooked Soybeans and Correlation with Its Precursor, S‑Methylmethionine (Vitamin U) Akira Morisaki,† Naohiro Yamada,‡ Shiori Yamanaka,† and Kenji Matsui*,† †

Graduate School of Medicine (Agriculture) and Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515, Japan ‡ Nagano Vegetable and Ornamental Crops Experiment Station, Shiojiri, Nagano 399-6461, Japan S Supporting Information *

ABSTRACT: Among the soybean germplasm in Japan, two varieties, Nishiyamahitashi 98-5 (NH) and Shinanokurakake (SKK), have an intense seaweed-like flavor after cooking. Gas−liquid chromatography with mass spectrometry (GC-MS) indicated that a significant amount (11.5 ± 3.46 μg g−1 for NH and 6.66 ± 0.91 μg g−1 for SKK) of dimethyl sulfide (DMS) was formed after heat treatment. DMS is formed from S-methylmethionine (SMM, vitamin U). SMM was detected in all soybean varieties examined here, but its concentration in NH and SKK seeds was >100-fold higher than in the other varieties and ranged from 75 to 290 μg g−1. The SMM content and the ability to form DMS upon heat treatment correlated among them. The plumes and radicles contained SMM exclusively. This is the first report of soybean varieties containing SMM at a level equivalent to or higher than that in vegetables known to contain high levels of SMM, for example, turnip, cabbage, and celery. KEYWORDS: soybean, flavor, dimethyl sulfide, S-methylmethionine

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respectively;5 thus, their use as a functional food is to be expected. Dimethyl sulfide (DMS) is a typical volatile organic sulfur compound with a characteristic seaweed-like and boiled cabbage-like odor. DMS is formed enzymatically in a lyase reaction involving dimethylsulfoniopropionate in a wide variety of seaweed species.6 DMS is considered a key flavor constituent in cooked vegetables, such as tomato, cabbage, and asparagus.7−9 DMS is one of the markers that differentiate black truffle (Tuber melanosporum) and Chinese truffle (Tuber indicum), with stronger aromatic contribution to the former.10 Formation of DMS was also reported in soy milk prepared using heat treatment at 90 °C for 10 min.11 DMS has a disagreeable odor at high concentrations but is beneficial to the aroma of lager types of beer at a concentration between 30 and 100 μg L−112 and some types of red wine at a concentration of 100 μg L−1.13,14 In vegetables and green malts, DMS is formed via thermal degradation of its precursor, S-methylmethionine (SMM).9 The latter was originally called vitamin U because it has an antiulcerogenic activity, and it reduces gastric mucosal damage induced by ethanol in rats.15 It is an active ingredient in an over-the-counter gastrointestinal drug widely used in Japan (Cabagin Kowa, Kowa Co., Ltd.). Furthermore, SMM has been shown to have a choline-sparing activity in poultry.16 It is also reported that SMM inhibits adipocyte differentiation via downregulation of adipogenic factors and up-regulation of AMP-

INTRODUCTION Soybean, Glycine max (L.) Merr., is the most important legume plant and the fifth most important crop in the world in terms of quantity of production after maize, rice, wheat, and potato (FAOSTAT, 2012, http://faostat3.fao.org/faostat-gateway/go/ to/home/E). Soybean seeds contain large amounts of oils (18− 20%) and proteins (40%−45%);1 accordingly, they are widely used as a source of nutritious foods for humans and livestock. Recently, a variety of claims about health benefits of soy products increased the consumption of soybeans. Because of its importance, the soybean is regarded as a model legume crop, and in 2010, a whole-genome sequence of the representative variety Williams 82 was published.2 At the same time, a wide diversity of agronomic and food-related chemical properties such as the level of proteins, lipids, isoflavones, and saponins as well as flavor properties have been reported for different varieties of soybean;1,3,4 therefore, a lot of effort has been devoted to the establishment of germplasm collections worldwide. For example, approximately 11300 soybean-related accession numbers are available in the National Institute of Agrobiological Sciences Genebank, Japan (https://www.gene. affrc.go.jp/index_en.php). Each entry has a distinct color, shape, size, and other agronomic traits.4 During our effort to identify new traits in the Japanese germplasm, we noticed a unique seaweed-like flavor in some of the traditional varieties locally cultivated and consumed in the central part of Japan (around Nagano prefecture). In these regions, soybean seeds with seed coat colors of green and black are widely consumed. The colored soybean seeds with the seaweed-like flavor are consumed after boiling of water-soaked seeds with a modicum of soy sauce and sugar. Colored soybeans such as black and green soybeans have high isoflavone and anthocyanin contents, © 2014 American Chemical Society

Received: Revised: Accepted: Published: 8289

April 4, 2014 August 3, 2014 August 4, 2014 August 4, 2014 dx.doi.org/10.1021/jf501614j | J. Agric. Food Chem. 2014, 62, 8289−8294

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activated protein kinase.17 Such beneficial biological activities of SMM should make food products containing it attractive to consumers. Until now, soybeans have not been recognized as food products containing high concentrations of SMM. The traditional soybean varieties that show an intense seaweedlike flavor especially after boiling are believed to contain a relatively high concentration of SMM, which would be degraded to DMS upon heating. We examined the SMM contents of several soybean varieties and compared them with those of other soybean varieties. Because of the unique flavor resulting from DMS and the possible pharmaceutical properties of SMM, identification of varieties that contain a substantial concentration of SMM should open up opportunities for novel uses of soybeans.

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soaked seeds were collected without heat treatment. After chilling of the seeds to 25 °C, we collected the volatiles by using the solid-phase microextraction (SPME) fiber (50/30 μm DVB/Carboxen/PDMS, Supelco, Bellefonte, PA, USA; preconditioned immediately prior to use at 240 °C for 37 min) by exposing the fiber to the headspace for 30 min at 25 °C. The fiber was inserted into the insertion port of a gas chromatography−mass spectrometry (GC-MS) system (QP-5050, Shimadzu, Kyoto, Japan) equipped with a Stabilwax column (30 m × 0.25 mm i.d. × 0.25 μm film thickness, Restek, Bellefonte, PA, USA). The column temperature was programmed as follows: 40 °C for 5 min followed by an increase of 5 °C min−1 to 200 °C. The carrier gas (He) was delivered at 86.1 kPa. The glass insert was an SPME sleeve (Supelco). Splitless injection with a sampling time of 1 min was used. The fiber was held in the injection port for 10 min to remove completely any compounds from the matrix. The temperature of the injector and interface was 240 °C. The mass detector was operated in the electron impact mode with ionization energy of 70 eV. Full-scan acquisition was used in the 40−350 atomic mass unit range of masses. To identify each compound, we used retention time and an MS profile of corresponding standard samples. The corresponding MS profiles in the NIST08 database (Shimadzu) were also used. For quantitation, an aqueous solution (10 mg mL−1) of each compound was prepared in 10 mg mL−1 Tween 20. The solutions were mixed at different ratios, and then water was added to 8 mL in a glass vial. Immediately after mixing of the solutions, the vial was tightly sealed, and the volatiles in the headspace were collected using the SPME fiber at 25 °C for 30 min. A calibration curve for each compound was constructed, and the area was calculated using integration software (GC-MS Solution, Shimadzu; Supporting Information Figure S1). The limit of detection for DMS, nhexanal, n-hexan-1-ol, or 1-octen-3-ol was 30, 10, 20, or 20 ng g−1, respectively. All measurements were performed in triplicate for each sample. The precision of the GC-MS method was determined by injecting a mixture of standards five times: dimethyl sulfide (5 μg), nhexanal (0.1 μg), n-hexan-1-ol (0.1 μg), and 1-octen-3-ol (0.2 μg) suspended in 8 mL of H2O. The relative standard errors (RSEs) for dimethyl sulfide, n-hexanal, n-hexan-1-ol, and 1-octen-3-ol were 3.08, 2.14, 1.03, and 2.46%, respectively. When the volatiles formed after treatment of NH seeds at 80 °C for 30 min were analyzed five times, RSEs for dimethyl sulfide, n-hexanal, n-hexan-1-ol, and 1-octen-3-ol were 5.15, 23.2, 10.2, and 14.4%, respectively. Quantitation of S-Methylmethionine. This procedure was carried out essentially as per the procedure reported by Scherb et al.9 The seeds were powdered using a force mill (Osaka Chemical Co., Ltd., Osaka, Japan). The powder (1 g) was suspended in 20 mL of 0.1 M sodium acetate buffer (pH 4.4). A portion (0.2 mL) of the suspension was mixed with 20 μL of 0.05 mg mL−1 d6-SMM in water as the internal standard and then mixed with 2 mL of MeOH/water (7:3, v/v). The mixture was shaken on a reciprocal shaker at 25 °C for 30 min. Thereafter, the mixture was centrifuged at 1500 rpm (Kubota 8100 centrifuge with RS 3000/6 rotor; Kubota Co., Tokyo, Japan) for 10 min at room temperature, and the resultant supernatant was collected. After removal of MeOH with N2 gas flow, 1 mL of ethyl acetate was added, vigorously mixed, and centrifuged at 1500 rpm (same centrifuge) for 5 min. The lower aqueous phase was collected and cleared using Ekicrodisc 3 (0.45 μm, 3 mm, Wako Pure Chemicals). The cleared solution was mixed with acetonitrile/water (1:1, v/v) to the total volume of 2.5 mL. Liquid chromatography with tandem mass spectrometry (LC-MS/ MS) was performed on an AB Sciex (Framingham, MA, USA) 3200 Q-TRAP LS-MS/MS system equipped with a Prominence UFLC (Shimadzu). Chromatography was carried out on a Discovery HS F5 column (15 cm × 2.1 mm, 3 μm; Supelco) using 20% acetonitrile in water supplemented with 0.1% formic acid at a flow rate of 0.1 mL min−1. The injection volume was 5 μL. The column temperature was set to 40 °C. The compound was detected using electrospray ionization (ESI) in the positive ion mode [ion spray voltage, 5500 V; nitrogen as the curtain gas (set to 35 arbitrary units)] with the multiple reaction monitoring (MRM) mode (Q1/Q3 mass, 164.113/102.000 for SMM and 170.113/102.000 for d6-SMM; declustering potential, 16 V; energy potential, 5 V; collision energy potential, 10 V; collision

MATERIALS AND METHODS

Plant Materials. Seeds of a leading Japanese cultivar, Fukuyutaka (FK), widely used for tofu in Japan,18 were harvested at Saga City (E 130° 18′, N 33° 14′; annual mean temperature, 17 °C), Saga, Japan, in 2011 (provided by Dr. Toyoaki Anai, Saga University, Japan). The other varieties, Shinanomidori (SM), Shinanokuro (SK), Nakasennari (NS), Gankui (GK), Shinanokurakake (SKK), and Nishiyamahitashi 98-5 (NH; Figure 1), are traditional varieties in the Nagano prefecture

Figure 1. Seven varieties of soybean used in this study. (central Japan) and were harvested in 2011 in an experimental field at the Nagano Vegetable and Ornamental Crops Experimental Station, Shiojiri City (E 137° 57′, N 36° 06′; annual mean temperature, 11 °C), Nagano, Japan. SKK and NH have a green color with a black patch and are known to produce a seaweed-like flavor. The seaweedlike flavor is enhanced after boiling. The seaweed-like flavor is hardly detected in the other varieties used here even after boiling. SM is a green soybean without a black patch, and SK and GK are black soybeans. NS is a yellow soybean and is used as a control similar to FK but grown in the same field with the other colored soybeans. The seeds were kept at 4 °C under dry conditions until use. Chemicals. L-Methionine-S-methyl-d6 sulfonium chloride (d6SMM) was purchased from Toronto Research Chemicals Inc. (Toronto, Ontario, Canada) via the distributor Funakoshi Co., Ltd. (Tokyo, Japan). DL-SMM sulfonium chloride was purchased from Tokyo Chemical Industry Co. (Tokyo, Japan). 1-Octen-3-ol was from Alfa Aesar (Lancashire, UK), and isobutanol, n-hexanal, n-hexan-1-ol, and dimethyl sulfide were purchased from Wako Pure Chemicals (Osaka, Japan). Analysis of Volatiles. We collected volatiles at 25 °C to avoid any further changes that might happen at higher temperatures. The volatiles from intact soaked seeds, with and without heat treatment, were collected to analyze the way the colored seeds were consumed in the region where they were popular. The seeds (1 g, corresponding to 2−5 seeds depending on the seed size) were soaked in 8 mL of distilled water for 8 h at 4 °C in a glass vial (22 mL, PerkinElmer, Waltham, MA, USA). The vial was kept open during the soaking period. Thereafter, the vial was sealed tightly with a butyl rubber stopper and a crimp top seal (National Scientific, Rockwood, TN, USA). Heat treatment of soybean seeds was carried out at 80 °C for 30 min, keeping the vial sealed. This temperature was chosen because it is often used to prepare various types of soy milk.19,20 Volatiles from the 8290

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energy, 13 V). A calibration curve for SMM was constructed, and the area was calculated using integration software (Analyst, ABSciex; Supporting Information Figure S2). On the basis of the calibration curve, a response factor of 0.863 was calculated. The precision of the LC-MS/MS method was determined by injecting a 1 μg mL−1 solution of d6-SMM four times. The RSE was found to be 0.84%. When SMM in NH seed powder was analyzed four times, the RSE for SMM was 2.22%. The recovery was validated by spiking the heat-treated NH seeds with a known amount of d6-SMM. The results showed that 52.7% of the theoretical amount of d6-SMM was recovered. Statistical Analysis. All of the experiments were conducted at least in triplicate. The differences were evaluated using one-way analysis of variance (ANOVA) with Tukey’s test in Excel Toukei (Social Survey Research Information Co., Ltd., Tokyo, Japan).

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RESULTS AND DISCUSSION We collected six varieties of soybeans that are grown in the local area in the central part of Japan and one variety that is Figure 3. Effect of heat treatment on the concentration of dimethyl sulfide (DMS) in the headspace of Sinanokurakake (SKK) and Nishiyamahitashi (NH) soybean seeds. The seeds were soaked in 8 mL of water, and immediately, or after heating at 80 °C for 30 min, the concentration of DMS was determined. Means ± standard error (error bars) are shown (n = 3). Different letters indicate significant differences (analysis of variance, Tukey’s test, p < 0.05).

Figure 2. Concentration of volatile compounds formed in heat-treated soybean seeds. The concentrations of n-hexanal, n-hexan-1-ol, and 1octen-3-ol (left panel) and dimethyl sulfide (DMS; right panel) detected in the headspace of heat-treated soybean seeds were determined using solid phase microextraction with gas−liquid chromatography and mass spectrometry. Means ± standard error (error bars) are shown (n = 3). Different letters indicate significant differences, and n.s. means that there is no significant difference (analysis of variance, Tukey’s test, p < 0.05).

Figure 4. Detection of S-methylmethionine (SMM) in the multiple reaction monitoring (MRM) mode of liquid chromatography with tandem mass spectrometry (LC-MS/MS). We performed LC-MS/MS analyses of the extracts from Nishiyamahitashi (NH) and Fukuyutaka (FY) by following the signal of 164.113 (Q1)/102.000 (Q3) as well as the analysis of a standard sample of L-methionine-S-methyl-d6 sulfonium chloride (d6-SMM) by following the signal of 170.113 (Q1)/102.000 (Q3) (top, middle, and bottom chromatograms, respectively). The structures of SMM and d6-SMM are shown.

widely grown throughout Japan (Figure 1). Fukuyutaka (FK) is a strain widely grown in Japan as an ingredient of tofu and was used as a control in this study. Nakasennari (NS) is also a soybean variety that is widely grown (for tofu production) in the central part of Japan. Shinanokurakake (SKK) and Nishiyamahitashi 98-5 (NH) are the traditional varieties in the Nagano prefecture (central Japan). These soybean seeds are usually eaten after boiling with a modicum of soy sauce and sugar, and they are known to produce a seaweed-like flavor, especially after boiling. Their seed coat color is green with a black patch that resembles a saddle on horseback; therefore, they are sometimes called “saddle-bearing” soybeans (Kurakakemame in Japanese). Shinanomidori (SM) is also a traditional variety in Nagano prefecture and is consumed after boiling, but it does not smell like seaweed. It has a green seed coat without the black “saddle”. Shinanokuro (SK) and Gankui (GK) are black soybeans. SM, SK, and GK were used as controls to evaluate the effect of the seed coat color on the

flavor. To identify the compound responsible for the seaweedlike flavor after boiling, we examined volatiles formed before and after heat treatment in whole seeds. After overnight soaking and heat treatment of the intact seeds, n-hexanal, n-hexan-1-ol, and 1-octen-3-ol were detected in all seven varieties (Figure 2; Supporting Information Figure S3). These were the typical volatile compounds most abundant in homogenized soybean seeds.21,22 Even though the content of n-hexanal, n-hexan-1-ol, and 1-octen-3-ol somehow varied depending on the variety analyzed, the differences in their concentrations in the seven soybean varieties were insignificant (Figure 2). The concentrations of n-hexanal detected in heattreated soybean seeds in this study (ranging from 0.01 to 0.13 8291

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Figure 5. Concentration of SMM in whole seeds of each variety of soybean (A) and that in seed coats, cotyledons, and plumules with radicles in Nishiyamahitashi (NH) soybean seeds (B). Means ± standard error (error bars) are shown (n = 3). Different letters indicate significant differences (analysis of variance, Tukey’s test, p < 0.05).

(celery).9 It was apparent that the ability to form DMS in soybean seeds was independent of the ability to form volatile oxylipins examined here. The concentrations of n-hexanal, n-hexan-1-ol, 1-octen-3-ol, and DMS were low in SKK and NH seeds soaked for 8 h; however, these concentrations significantly increased after we heated the soaked seeds at 80 °C for 30 min (Figure 3). It was assumed that DMS was formed from an endogenous substrate. DMS is formed in large amounts by algae and bacteria, especially in marine environments through the action of a lyase enzyme on dimethylsulfoniopropionate.6 On the contrary, it is known that DMS is formed as a result of thermal degradation of SMM in angiosperms including vegetables and green malt.9 SMM has been found in various vegetables such as cabbage, tomato, celery, and spinach.9 Soybean has the ability to form SMM from methionine,24 and SMM at 1.65 mg g−1 was detected after acid hydrolysis (at 105 °C for 24 h in HCl) of dehulled-soybean meal.16 We used a stable isotope dilution assay involving LC-MS/MS to measure the concentration of SMM, essentially as per the procedure developed by Scherb et al.9 With the modified assay system, SMM was eluted at a retention time of 8.1 min and was detected with the limit of detection of 0.1 μg g−1 with a signal/noise ratio >3 (Figure 4). We quantified the concentration of SMM in soaked soybean seeds (Figure 5). The soybean varieties showing a low ability to form DMS, that is, FY, SM, SK, NS, and GK, contained SMM in the range between 0.5 and 3.0 μg g−1 without any significant differences among these varieties. In contrast, the concentrations in SKK and NH were 75 and 290 μg g−1: 30−600-fold higher than those in the other soybeans. The level found in SKK and NH was comparable to or even higher than that found in vegetables reported to contain a high concentration of SMM such as celery (176.0 μg g−1), turnip cabbage (124.0 μg g−1), leek (94.0 μg g−1), beetroot (89.0 μg g−1), and cabbage (81.0 μg g−1).9 Nonetheless, the concentration in SKK and NH was still much lower than that found in acid-hydrolyzed soybean meal (1.65 mg g−1).16 Because we estimated the concentration of SMM in its free form without acid hydrolysis, a large proportion of SMM might exist as its bound form as a component of a protein, as in the LaeA protein in Aspergillus nidulans.25 Most plant seeds have the biosynthetic pathway that produces SMM in seeds;26 however, no studies have been reported to examine its distribution in seeds. When the seed of the NH soybean was dissected into the seed coat, cotyledon,

Figure 6. Effects of heating temperature and duration on the concentration of S-methylmethionine (SMM) remaining in the soaked soybean seeds (Nishiyamahitashi, NH). The seeds were soaked in 8 mL of water at 4 °C and were then heated at 80 or 100 °C for 30 or 60 min. After the seeds had chilled to room temperature, we quantified SMM using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Means ± standard error (error bars) are shown (n = 3). Statistical analysis by using analysis of variance and Tukey’s test indicated no statistically significant differences among the treatments.

μg g−1) were 7−500-fold lower than those in soy milk (ranging from 1 to 5.4 μg g−1).11,19−21 The difference might be attributable to the differences in processing procedures such as the method of heating and whether the seeds were homogenized. n-Hexan-1-ol was generally undetectable in soy milk prepared through homogenization of seeds with hot water (80 °C),11,22 whereas a substantial level of n-hexan-1-ol was found here (ranging from 0.025 to 0.063 μg g−1). Again, this effect might be explained by differences in the processing procedures, for example, rapid homogenization of seeds with hot water in the study by Lozano et al.11 and a gradual temperature increase to 80 °C with intact seeds in the present study. The level of 1-octen-3-ol detected in the heat-treated soybean seeds used in this study was comparable to that reported for soy milk regardless of the differences in processing procedures. This is probably because the formation of 1-octen3-ol is independent of disruption of soybean tissues.21,23 A low but substantial concentration of DMS was detected in FY, SM, SK, NS, and GK, whereas this concentration in SKK and NH was quite high and reached 6−11 μg g−1 of seeds. The concentrations are roughly equivalent to the levels found in cooked vegetables: from 1.1 μg g−1 (tomato) to 25 μg g−1 8292

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and plumules with radicles, the cotyledons accounted for ∼87% of the total SMM found in the whole seeds, followed by the plumules and radicles, which comprised ∼12% of the total SMM (Figure 6B). On the basis of the weight of each part, the plumules and radicles accounted for only 1.8% of the total weight of soaked soybean seeds, whereas the cotyledons accounted for 89%. Thus, the plumules and radicles contain the highest concentration of SMM (1071 ± 179 μg g−1) followed by the cotyledons (159 ± 36.0 μg g−1). The concentration of SMM tended to decrease depending on the heating temperature and heating time, even though there was no statistically significant difference among the treatments (Figure 6). At low pH (pH 2−5), DMS is formed as a result of a nucleophilic substitution of the dimethyl sulfonium group by water, whereas at higher pH values (pH >7), an intramolecular nucleophilic substitution caused by the carboxyl group of SMM takes place.27 Because the pH of the homogenate prepared from soybean seeds after soaking or after heat treatment was 5.7−6.0, both mechanisms might be possible. Under the experimental conditions used here, where soybean seeds (NH) are heated without disruption, ∼90% of SMM found in intact seeds was retained even after heat treatment at 100 °C for 60 min. This yield was expected because the concentration of DMS (10−12 μg g−1, see Figure 2) after heating of the NH seeds accounted for only 3−4% of the initial concentration of SMM found in intact seeds before heat treatment (Figure 5). The thermal stability of SMM is dependent on the pH value of the solution and on the matrix; therefore, its degradation in tomato or orange juice is higher than that in an aqueous buffer at the same pH.9 This seems to be the first study on soybean varieties that contain SMM at a level (75−290 μg g−1) equivalent to or even higher than that in vegetables that are known to contain high concentrations of SMM such as cabbage and celery (80−180 μg g−1).9 It was reported that the biosynthetic pathway that produces SMM (SMM cycle) is widespread among angiosperms28 and is active during seed development in alfalfa (Medicago truncatula)29 and flax (Linum usitatissimum).30 In fact, all of the soybean seeds examined here, except for the two that showed extraordinarily high SMM content, exhibited a low but substantial concentration of SMM. These findings suggest that a mutation in the metabolic pathway results in the high SMM concentration in the seeds of NH and SKK. The SMM cycle partly accounts for the methionine level, which is an important nutritional parameter of soybeans.31 Therefore, deciphering the cause of the high SMM content of the two varieties at the molecular level would be worthwhile. Currently, we are trying to locate genetic loci responsible for the accumulation of SMM.

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Funding

This work was supported in part by the Japan Society for the Promotion of Science (JSPS; KAKENHI, Grants 23580151 and 26660095) and by Yamaguchi University (Yobimizu Project; grant to M.K.). Notes

The authors declare no competing financial interest.

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ABBREVIATIONS USED DMS, dimethyl sulfide; SMM, S-methylmethionine; SPME, solid phase microextraction; GC, gas−liquid chromatography; LC, liquid chromatography; MS, mass spectrometry; ESI, electrospray ionization; MRM, multiple reaction monitoring

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(1) Hwang, E. Y.; Song, Q.; Jia, G.; Specht, J. E.; Hyten, D. L.; Costa, J.; Cregan, P. B. A genome-wide association study of seed protein and oil content in soybean. BMC Genomics 2014, 15, 1 DOI: 10.1186/ 1471-2164-15-1. (2) Schmutz, J.; Cannon, S. B.; Schlueter, J.; Ma, J.; Mitros, T.; Nelson, W.; et al. Genome sequence of the palaeopolyploid soybean. Nature 2010, 463, 178−183. (3) Kim, J. K.; Kim, E. H.; Park, I.; Yu, B. R.; Lim, J. D.; Lee, Y. S.; Lee, J. H.; Kim, S. H.; Chung, I. M. Isoflavones profiling of soybean [Glycine max (L.) Merrill] germplasms and their correlations with metabolic pathways. Food Chem. 2014, 153, 258−264. (4) Kaga, A.; Shimizu, T.; Watanabe, S.; Tsubokura, Y.; Katayose, Y.; Harada, K.; Vaughan, D. A.; Tomooka, N. Evaluation of soybean germplasm conserved in NIAS genebank and development of mini core collections. Breed. Sci. 2012, 61, 566−592. (5) Cho, K. M.; Ha, T. J.; Lee, Y. B.; Seo, W. D.; Kim, J. Y.; Ryu, H. W.; Jeong, S. H.; Kang, Y. M.; Lee, J. H. Soluble phenolics and antioxidant properties of soybean (Glycine max L.) cultivars with varying seed coat colours. J. Funct. Foods 2013, 5, 1065−1076. (6) Bentley, R.; Chasteen, T. G. Environmental VOSCs-formation and degradation of dimethyl sulfide, methanethiol and related materials. Chemosphere 2004, 55, 291−317. (7) Miers, J. C. Formation of volatile sulfur compounds in processed tomato products. J. Agric. Food Chem. 1966, 14, 419−423. (8) Ney, K. J.; Freytag, W. Dimethyl sulfide as an essential component of asparagus flavor. Volatile components of boiled asparagus. Z. Lebensm. Unters. Forsch. 1972, 149, 154−155. (9) Scherb, J.; Kreissl, J.; Haupt, S.; Schieberle, P. Quantitation of Smethylmethionine in raw vegetables and green malt by a stable isotope dilution assay using LC-MS/MS: comparison with dimethyl sulfide formation after heat treatment. J. Agric. Food Chem. 2009, 57, 9091− 9096. (10) Culleré, L.; Ferreira, V.; Venturini, M. E.; Marco, P.; Blanco, D. Potential aromatic compounds as markers to differentiate between Tuber melanosporum and Tuber indicum truffles. Food Chem. 2013, 141, 105−110. (11) Lozano, P. R.; Drake, M.; Benitez, D.; Cadwallader, K. R. Instrumental and sensory characterization of heat-induced odorants in aseptically packaged soy milk. J. Agric. Food Chem. 2007, 55, 3018− 3026. (12) Anness, B. J.; Bamforth, C. W. Dimethyl sulphide − a review. J. Inst. Brew. 1982, 88, 244−252. (13) Segurel, M. A.; Razungles, A. J.; Riou, C.; Salles, M.; Baumes, R. L. Contribution of dimethyl sulfide to the aroma of Syrah and Grenache Noir wines and estimation of its potential in grapes of these varieties. J. Agric. Food Chem. 2004, 52, 7084−7093. (14) DeMora, S. J.; Knowles, S. J.; Eschenbruch, R.; Torrey, W. J. Dimethyl sulphide in some Australian red wines. Vitis 1987, 26, 79− 84. (15) Watanabe, T.; Ohara, S.; Miyazawa, S.; Saigenji, K.; Hotta, K. Augmentative effects of L-cysteine and methylmethionine sulfonium

ASSOCIATED CONTENT

S Supporting Information *

Calibration curves for DMS, n-hexanal, n-hexan-1-ol, 1-octen-3ol, and SMM and typical total ion chromatograms of volatiles. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*(K.M.) Phone: +81-83-933-5850. Fax: +81-83-933-5820. Email: [email protected]. 8293

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Journal of Agricultural and Food Chemistry

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dx.doi.org/10.1021/jf501614j | J. Agric. Food Chem. 2014, 62, 8289−8294