Evaluation of PDMS-Based Extraction Techniques and GC-TOFMS for the Analysis of Off-Flavor Chemicals in Beer

Importance of the Topic

Understanding and quantifying off-flavor compounds in beer is essential for product consistency and sensory quality in brewing. Trace aldehydes, sulfur volatiles, and Maillard reaction products can degrade taste during storage or light exposure, impacting consumer perception and shelf life.

Objectives and Study Overview

This study aimed to develop and compare four PDMS-based extraction techniques—stir bar sorptive extraction (SBSE), headspace sorptive extraction (HSSE), purge-and-trap (P&T), and dynamic headspace closed-loop stripping (DHSCLS)—coupled with gas chromatography–time-of-flight mass spectrometry (GC-TOFMS) to measure a suite of 14 odor-active chemicals in beer at low parts-per-billion levels.

Instrumentation

The analyses employed an Agilent 6890 GC with a CIS 4 inlet and Gerstel MPS 2 robotic sampler with thermal desorption unit. Separation used a 30 m HP-5MS column (0.32 mm ID, 0.25 μm film), helium carrier gas at 1.5 mL/min, and a LECO Pegasus TOFMS acquiring 40–300 amu at 10 spectra/s with advanced peak deconvolution algorithms.

Methodology

• SBSE – 10 mL beer stirred with a PDMS-coated stir bar (Twister) at 900 rpm for 2 h, followed by rinsing and thermal desorption.
• HSSE – Twister suspended in headspace for 2 h with stirring.
• P&T – 20 mL beer purged with N₂ (30 mL/min) for 20 min through a PDMS foam trap.
• DHSCLS – 10 mL beer in a gas-washing bottle recirculated with air through a PDMS foam trap for 5 min.

Main Results and Discussion

SBSE demonstrated the highest accuracy (average R² 0.984) and sensitivity, detecting all 14 targeted compounds with <10 % precision, outperforming HSSE, P&T, and DHSCLS. Heat aging (12 weeks at 30 °C) elevated Maillard-derived furfural, furfuryl ethyl ether, and ß-damascenone, while light exposure (8 h sunlight) generated dimethyl disulfide, dimethyl trisulfide, and increased benzeneacetaldehyde. Advanced TOFMS deconvolution enabled resolution of coeluting peaks such as ß-damascenone, furfuryl ethyl ether, and (Z)-2-nonenal, ensuring accurate quantitation of key off-flavor markers.

Benefits and Practical Applications

The solventless PDMS-based approaches streamline sample preparation, reduce chemical use, and provide robust detection of trace off-flavor volatiles. SBSE–GC–TOFMS is particularly valuable for quality control, shelf-life assessment, and flavor profiling in brewery laboratories.

Future Trends and Potential Uses

• Integration with selective detectors (e.g., PFPD) to enhance sulfur compound analysis.
• Coupling instrumental data with sensory panels for aroma impact studies.
• Extending methods to other beverages and food matrices.
• Automation and miniaturization for high-throughput screening.

Conclusion

The comparison of four PDMS extraction techniques confirmed SBSE–GC–TOFMS as a superior, solventless method for comprehensive off-flavor analysis in beer. Critical to this approach is the TOFMS deconvolution capability, which allows precise quantitation of overlapping volatile compounds, supporting effective quality management in brewing.

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