Determination of Malic Acid and Lactic Acid in Wine by CE-MS/MS

Importance of the Topic

Organic acids such as malic and lactic acids play a critical role in the sensory profile and microbial stability of wine. Monitoring their concentrations enables winemakers to assess the progress of malolactic fermentation and ensure product quality.

Objectives and Study Overview

This study aimed to develop a rapid, sensitive, and selective capillary electrophoresis tandem mass spectrometry (CE-MS/MS) method for simultaneous quantification of malic and lactic acids in wine, without sample derivatization, using minimal sample preparation.

Methodology and Instrumentation

Wine samples were diluted (1:50) in deionized water, filtered through 0.2 µm PVDF/PP membranes, and directly injected hydrodynamically (100 mbar, 10 s) into a fused silica capillary (50 µm i.d., 60 cm length). Separation employed a background electrolyte of 25 mM propionic acid and 50 mM ammonium hydroxide (pH 9.3) at 25 kV and 25 °C. MS detection used negative electrospray ionization in multiple reaction monitoring mode with trichloroacetic acid as an internal standard.

Instrumentation

• Capillary electrophoresis: Agilent 7100 CE system
• Mass spectrometry: Agilent 6430 Triple Quadrupole MS, ESI negative mode
• MRM transitions: lactate m/z 89 → 43 (40 V), malate m/z 133 → 115 (76 V), TCA IS m/z 160.9 → 116.9 (10 V)
• Sheath liquid: 1:1 water/methanol diluted background electrolyte, flow 5 µL/min

Key Results and Discussion

Calibration curves for both acids were linear over 0.01–2 mM with R² of 0.999 (lactic) and 0.998 (malic). Limits of detection were below 0.8 µM, and limits of quantitation under 2.6 µM. Analysis time per sample was approximately 10 minutes. In commercial wines, malic acid ranged from 0.4 to 27.8 mM and lactic acid from 3.6 to 31.1 mM, reflecting the extent of malolactic fermentation (higher lactic acid coupled with low malic acid in fully fermented red wines).

Benefits and Practical Applications of the Method

• No derivatization or extensive sample cleanup required
• High sensitivity and selectivity with minimal reagent consumption
• Rapid turnaround suitable for quality control in wineries and laboratories
• Direct monitoring of fermentation progress and product consistency

Future Trends and Potential Applications

Advances may include coupling CE-MS/MS with high-resolution instruments for detailed profiling of minor organic acids, automation for online fermentation monitoring, and adaptation to other complex food matrices such as fruit juices and dairy products.

Conclusion

The developed CE-MS/MS method offers a fast, precise, and robust approach to quantify malic and lactic acids in wine. Its high sensitivity, minimal sample preparation, and suitability for routine analysis make it an effective tool for quality control and fermentation monitoring in the wine industry.

References

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3. Mato I, Suarez-Luque S, Huidobro JF. A review of the analytical methods to determine organic acids in grape juices and wines. Food Res Int. 2005;38:1175–1188.
4. Klampfl CW, Buchberger W, Haddad PR. Determination of organic acids in food samples by capillary zone electrophoresis. J Chromatogr A. 2000;881:357–364.