*3.1. Materials*

Thirty-six different soybean samples (17 from Korea, 13 from China, and 6 from North America) cultivated in 2016 (Figures S1–S3, Table 4) were used. Soybeans from Korea were provided by the National Agricultural Products Quality Management Service, whereas those from China were obtained from Chinese markets (Figures S4 and S5, Table S4). Soybeans from North America were gifts from a soybean processing company in Korea (Figure S6, Table S4). All samples were stored at −70 ◦C in a deep freezer before they were analyzed. Solid-phase microextraction (SPME) fibers and holders were purchased from Supelco (Bellefonte, PA, USA), whereas vials and screw caps (Ultraclean 18 mm) were purchased from Agilent Technologies (Santa Clara, CA, USA). l-Borneol was purchased from Sigma-Aldrich (St. Louis, MO, USA). Authentic standard compounds for positive identification of volatile compounds were purchased as follows: 3-methylphenol and hexan-1-ol were purchased from Supelco (Bellefonte, PA, USA), 1,3-benzothiazole, acetaldehyde, α-terpinene were obtained from Fluka (St. Gallen, Switzerland), and acetonitrile was bought from J.T. Baker (Phillipsburg, NJ, USA), while all of the other authentic standards were purchased from Sigma-Aldrich (St. Louis, MO, USA).




**Table 4.** *Cont.*

<sup>1</sup> GGIC—Gyeonggi province Anseong, GGAS—Gyeonggi province Icheon, GWCC—Gangwon province Chuncheon, GWYW—Gangwon province Yeongwol, CBES—Chungcheongbuk province Eumseong, CNCA— Chungcheongnam province Cheonan, CNGJ—Chungcheongnam province Gongju, JBGJ—Jeollabuk province Gimje, JBIS—Jeollabuk province Imsil, JNNJ—Jeollanam province Naju, JNYG—Jeollanam province Yeonggwang, KBCD—Kyeongsangbuk province Cheongdo, KBES—Kyeongsangbuk province Uiseong, KBYC—Kyeongsangbuk province Yeongcheon, KNCN—Kyeongsangnam province Changnyeong, KNMY—Kyeongsangnam province Miryang, KNGC—Kyeongsangnam province Geochang, INUL—Neimenggu province Ulanhot, HEHA—Heilongjiang province Harbin, JIME—Jilin province Meihekou, LIDA—Liaoning province Dandong, HESH—Hebei province Shijiazhuang, SHJI—Shandong province Jining, ANHU—Anhui province Huaibei, HUHU—Hubei province Huangshi, ZHPI—Zhejiang province Pinghu, JIJI—Jiangxi province Jiujiang, FULO—Fujian province Longyan, GUSH—Guangdong province Shaoguan, GUBA—Guangxi province Hechi, IL—Illinois province, IN—Indiana province, MN—Minnesota province, MI—Michigan province, QB—Quebec province, ON—Ontario province.

#### *3.2. Extraction of Volatile Metabolites Using SPME*

l-Borneol was prepared at 200 mg/L with *tert*-butanol. Then, distilled water was added at a final concentration of 1 mg/L before soybean (5 g) was placed in a 20 mL screw vial with a screw cap. SPME was used to obtain volatile metabolites of soybeans. The sample was maintained at 40 ◦C for 30 min to reach the equilibrium state. SPME fiber coated with carboxen/polydimethylsiloxane/ divinylbenzene (CAR/PDMS/DVB) was used to adsorb volatile compounds at 40 ◦C for 20 min, and desorption was executed at 200 ◦C in a GC injector for 5 min while cryo-trapping at −80 ◦C. For every other ten runs in GC-MS analysis, we included quality control (QC) soybean samples to confirm the relative peak areas and retention times of several main volatile compounds.

#### *3.3. GC-MS Analysis*

The GC-MS analysis was performed using a 7890A series gas chromatograph (Agilent Technologies, Santa Clara, CA, USA) and a 5975C mass detector (Agilent Technologies, Santa Clara, CA, USA) equipped with a DB-Wax column (30 m length × 0.25 mm i.d. × 0.25 μm film thickness, J&W Scientific, Folsom, CA, USA). GC oven temperature was programmed as follows; initial temperature was maintained 40 ◦C for 10 min, raised to 42 ◦C at a rate of 2 ◦C/min and held for 3 min, and increased to 100 ◦C at a rate of 4 ◦C/min and kept for 5 min, and raised 180 ◦C at a rate of 4 ◦C/min, and the ramped to 200 ◦C at a rate of 10 ◦C/min. The flow rate of helium, carrier gas, was constant at 0.8 mL/min, whereas mass spectra were obtained with a mass scan rage of 35–350 atomic mass unites (a.m.u.) at a rate of 4.5 scans/sec, and the electron impact (EI) mode was 70 eV. All sample preparations and analyses were independently performed in triplicate. In the preliminary study, we confirmed the repeatability and precision of our method on the results of the main volatile compounds in soybean in more than six replicates.

#### *3.4. Identification and Quantification of Volatile Metabolites*

The identification of each volatile compound was positively confirmed by comparison of retention time and mass spectral data with those of authentic standard compounds. When standard compounds were not available, each volatile compound was identified on the basis of its mass spectral data using the NIST.08 and Wiley.9 mass spectral libraries and the retention index (RI) values in the previous literature. The RI value of volatile compounds was calculated with *n*-alkane from C6 to C30 as an external standard. The quantification of the volatile components was calculated to obtain relative peak areas by comparing their peak areas with that of the internal standard compound on the total ion chromatogram of GC-MS. Five microliters of l-borneol (1 mg/L in *tert*-butanol/distilled water solvents mixture (1:200, *v*/*v*)) was used as an internal standard.
