DETERMINATION OF THE FATTY ACIDS IN BEER BY SPME

Significance of the Topic

The presence of free medium-chain fatty acids (C6–C12) in beer and wort can adversely affect yeast vitality, foam stability, and sensory profile. Reliable quantification of these compounds is therefore critical for quality control and consistent beer production.

Objectives and Overview

This study aimed to develop a rapid, selective, and solvent-free method for determining free fatty acids (C6–C12) in beer and wort. Key extraction parameters—salt addition, sampling time, and ethanol concentration—were optimized. The method was validated in terms of calibration, recovery, and repeatability.

Methodology and Instrumentation Used

• Sample: 4 mL beer or model solution (5 % v/v ethanol) spiked with heptanoic and undecanoic acids (1.3 mg/L each) as internal standards.
• Salting: Addition of ammonium sulfate (optimal 4 g per 4 mL sample).
• Extraction: Headspace SPME with a 65 µm Carbowax–Divinylbenzene fiber for 30 min at ambient temperature.
• GC–FID Conditions: Carlo Erba 5300 Mega Series with fused-silica capillary SPB-1000 (30 m × 0.32 mm, 0.25 µm film), injector and detector at 250 °C; column program 120 °C (2 min) → 150 °C at 10 °C/min → 200 °C at 30 °C/min (15 min); helium carrier at 100 kPa.

Main Results and Discussion

• Salting-out effect saturated at 2 g ammonium sulfate for C10–C12 and at 4 g for C6–C9.
• Equilibrium reached within 30 min; longer sampling did not change analyte/internal standard response ratios significantly (CV 2.5–6.9 %).
• Increasing ethanol content reduced absolute responses, but response ratios remained stable (CV 2.1–7.5 %).
• Calibration over 0.0015–8 mg/L followed a quadratic model (r² > 0.9956). Linear fits gave r² 0.9931–0.9989.
• Recoveries in spiked beer (2 mg/L) ranged from 95 % to 110 %; repeatability CVs were 2.3–8.1 %.

Benefits and Practical Applications of the Method

The proposed HS-SPME–GC-FID procedure is rapid, low-cost, solvent-free, and highly sensitive. It requires only small sample volumes and minimal preparation, making it well suited for routine quality control in brewery laboratories.

Future Trends and Opportunities

• Extension of HS-SPME to broader volatile and semi-volatile beer components.
• Coupling with mass spectrometry for improved selectivity and structural elucidation.
• Automation and on-line SPME integration for real-time fermentation monitoring.
• Adaptation of the method to other fermented beverages and complex matrices.

Conclusion

A headspace SPME–GC-FID method was successfully optimized and validated for medium-chain free fatty acids in beer and wort. The approach delivers accurate, reproducible results with minimal waste and is recommended for routine brewery QC.

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