L borneol

n-Hexane (99%), l-borneol (97%), xanthoxylin (97%) and 1,1-diphenyl-2-picrylhydrazyl (DPPH, 95%) were purchased from Sigma-Aldrich (Shanghai, China). β-carotene was purchased from Fluka Chemie (Buchs, Switzerland). Thiobarbituric acid, anhydrous Na₂SO_4, and all of the applied solvents (analysis purity) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). For Linear retention indices (RIs) determination, a hydrocarbon mixture (C₈–C₃₀n-alkanes) purchased from Supelco (Ballefonte, USA) was used to perform in the same condition as real sample determination.
For the measurement of response factors, the chemicals used were: l-borneol, ledol, γ-eudesmol, β-eudesmol, 1-octen-3-ol, linalool, nerolidol, 3-octanol and α-terpineol for alcohols; pentadecanal for aldehydes; camphor, zierone and xanthoxylin for ketones; hexadecanoic acid for acids; β-pinene for monoterpene hydrocarbons; α-muurolene, δ-cadinene caryophyllene and α-caryophyllene for sesquiterpene hydrocarbons; caryophyllene epoxide for oxides; 1,2-dihydro-1,1,6-trimethyl-naphthalene for aromatic hydrocarbons.

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).