Organic acids - Analysis of organic acids and sucrose in roasted coffee

Importance of the Topic

Roasted coffee is characterized by a complex matrix of organic acids and sugars that strongly influence its aroma, flavor balance, acidity perception and overall quality. Reliable profiling of these compounds is essential for quality control, product development and authenticity testing in the coffee industry.

Study Objectives and Overview

The primary goal of this application note is to establish a rapid and comprehensive gas chromatography method for simultaneous separation and quantification of 31 organic acids and sucrose in roasted coffee. The study demonstrates how derivatization of polar acids to their trimethylsilyl (TMS) derivatives and optimized GC conditions enable complete resolution within a 32-minute run time.

Methodology and Instrumentation

This approach relies on GC-capillary analysis with flame ionization detection following silylation derivatization.

Instrumentation details:

• Gas chromatograph equipped with an Agilent CP-Sil 5 CB capillary column (0.25 mm × 25 m, df = 0.12 µm, Part no. CP7710).
• Carrier gas: Helium at 210 kPa (2.1 bar, 30 psi), flow rate 1.0 mL/min.
• Oven temperature program: 100 °C hold 0 min; ramp to 155 °C at 8 °C/min, hold 1 min; ramp to 225 °C at 5 °C/min, hold 0 min; ramp to 300 °C at 15 °C/min, hold 20 min.
• Injector: Split mode (90:1), temperature 310 °C; injection volume 0.2–0.6 µL.
• Detector: Flame ionization detector at 310 °C, sensitivity 2 × 10⁻¹² Afs.

The sample preparation includes derivatization of organic acids and sucrose to their TMS counterparts, enhancing volatility and chromatographic performance.

Main Results and Discussion

The optimized method achieved baseline separation of 31 organic acids—including lactic, oxalic, malic, citric, caffeic and ferulic acids—and sucrose within a single 32-minute analysis. Peak shapes were symmetric and reproducible, demonstrating excellent chromatographic resolution across a wide polarity range. The internal standard n-pentacosane provided reliable retention time alignment and quantitation accuracy.

Advantages and Practical Applications

• Comprehensive profiling of a broad spectrum of acids and sugars in one run.
• High throughput with sub-hour analysis times suitable for routine quality control.
• Robustness and reproducibility enabled by optimized column choice and temperature program.
• Applicability in flavor research, batch-to-batch consistency monitoring and authenticity verification.

Future Trends and Opportunities

Further development may include coupling GC with mass spectrometry for definitive compound identification and quantitation at trace levels. Advances in faster temperature programming and micro-flow columns could reduce analysis time and solvent consumption. Integration of automated sample preparation and data processing workflows will enhance throughput for large-scale screening.

Conclusion

The presented GC-FID method with TMS derivatization offers a fast, reliable and reproducible solution for comprehensive analysis of organic acids and sucrose in roasted coffee. Its high resolution and efficiency make it well suited for routine applications in coffee quality assurance and research.