HS-GC Analysis of Sake Aroma Compounds Using Hydrogen Carrier Gas

Significance of the topic

The aroma profile of sake is a critical quality attribute that strongly influences consumer perception and product differentiation. Reliable, routine quantification of volatile aroma compounds during production (especially around heat treatments such as pasteurization) supports process control, product consistency, and optimization of sensory properties. Headspace gas chromatography (HS-GC) with efficient sample handling and cost-effective carrier gases enables high-throughput monitoring of volatile compounds in beverage quality control and research.

Aims and study overview

This application study evaluated an HS-GC workflow using a Shimadzu Nexis GC-2030 coupled to an HS-20 NX headspace sampler to quantify nine key sake aroma compounds before and after bottle pasteurization (bin-kan hiire). The study aimed to demonstrate (1) the analytical performance and linearity of HS-GC quantification for target volatiles, (2) the practicality of using hydrogen as a low-cost carrier gas while retaining separation performance, and (3) whether bottle pasteurization alters concentrations of measured aroma compounds.

Methodology

Sample preparation and calibration:

• Matrix: 16% aqueous ethanol; samples and standards prepared in same matrix.
• Volume: 5 mL sample in 20 mL headspace vial; internal standard n-butanol added to 50 ppm (v/v).
• Calibration: three concentration points prepared from a nine-compound mixture; linearity assessed for each compound.

Headspace and GC conditions (summary):

• Headspace sampler: loop injection mode with vial equilibration and pressurization; vial equilibration 45 min at 40 °C; vial pressurization 60 kPa (N2).
• Injection: split 1:10; injection time and needle flush timed for reproducible transfer.
• Carrier gas: hydrogen used as carrier at linear velocity ~60 cm/s; make-up N2.
• Column: SH-PolarWax, 30 m × 0.25 mm ID, 0.50 µm film.
• GC oven program: initial 40 °C (3 min), ramp 5 °C/min to 55 °C, then 15 °C/min to 190 °C (3 min).
• Detector: FID (FID temp 220 °C) with H2, air, and N2 make-up flows as specified.

Safety note: hydrogen’s flammability requires appropriate safeguards; Nexis GC-2030 supports an optional hydrogen sensor to detect leaks and trigger standby/power off modes.

Used instrumentation

• Shimadzu Nexis GC-2030 gas chromatograph (with optional hydrogen leak sensor).
• Shimadzu HS-20 NX headspace sampler (loop injection mode).
• Flame ionization detector (FID).
• SH-PolarWax capillary column (30 m × 0.25 mm ID, 0.50 µm).

Results and discussion

Analytical performance:

• Calibration curves for the nine aroma compounds exhibited excellent linearity (R2 > 0.998 for all compounds; most > 0.999), supporting reliable quantification across the tested range.

Sake before vs. after pasteurization:

• Quantified compounds included acetaldehyde, ethyl acetate, isovaleraldehyde, n-propanol, isobutanol, isoamyl acetate, isoamyl alcohol, ethyl caproate, and ethyl caprylate.
• Most compounds showed negligible concentration changes after bottle pasteurization (bin-kan hiire). Example average concentrations (ppm, v/v): acetaldehyde ~16.6 → 14.4; ethyl acetate ~59.5 → 58.9; isoamyl alcohol ~148.8 → 149.0; ethyl caproate ~5.65 → 5.61.
• Isovaleraldehyde (~0.19 ppm) was detected only in pre-pasteurization samples and not after pasteurization, interpreted as evidence that enzymatic activity producing this aldehyde was deactivated by the heat treatment.
• Chromatograms showed clear, well-resolved peaks under the H2-carrier conditions with FID detection, demonstrating maintained separation performance while using hydrogen.

Interpretation:

• Bin-kan (bottle) pasteurization preserved most aroma compound concentrations, suggesting this gentle heating method reduces aroma loss relative to harsher heat-exchanger pasteurization.
• Absence of isovaleraldehyde post-pasteurization is consistent with enzyme inactivation and supports the method’s effectiveness in halting enzyme-mediated off-flavor formation during storage.

Benefits and practical applications

• HS-GC with HS-20 NX allows direct headspace analysis without derivatization, minimizing sample prep time and complexity—advantageous for routine QA/QC in beverage production.
• Using hydrogen as carrier gas reduces operational cost while preserving chromatographic efficiency across a range of linear velocities.
• The approach supports process control decisions (e.g., verifying pasteurization efficacy and optimizing conditions to preserve aroma).
• Optional hydrogen leak detection enhances safety for routine laboratory deployment of H2 carrier methods.

Future trends and opportunities

• Integration of headspace trapping modes or thermal desorption can increase sensitivity for trace aroma markers and off-flavor compounds.
• Coupling HS-GC with mass spectrometric detection (GC–MS) would strengthen identification confidence and enable non-targeted volatile profiling for R&D and authenticity studies.
• Automated, high-throughput HS-GC workflows combined with chemometrics can support sensory prediction models and rapid QC screening.
• Development of robust safety systems and leak detection is key to wider adoption of hydrogen as a carrier amid helium supply concerns and cost pressures.
• Application expansion to other fermented beverages and flavor matrices, and cross-method standardization, will improve comparability of aroma data across producers.

Conclusion

Combining the HS-20 NX headspace sampler with the Nexis GC-2030 and FID provides a straightforward, sensitive workflow for quantifying primary sake aroma compounds without derivatization. Hydrogen carrier gas offered cost advantages without compromising separation, provided safety monitoring is in place. The studied bottle pasteurization method largely preserved aroma compound concentrations while inactivating enzymes responsible for formation of specific aldehydes, demonstrating the analytical approach’s utility for process verification and product quality control.

Reference

The application is based on an application note reporting HS-GC analysis of sake aroma compounds using Nexis GC-2030 and HS-20 NX (Shimadzu, Apr 2026). Related application notes referenced include HS-GC analysis of beer aroma components, analysis of diacetyl and 2,3-pentanedione in beer, and high-sensitivity fragrance analysis using HS-20 trap mode.