Analysis of Grape Volatiles by Solid Phase Microextraction and Comprehensive Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometry (GCxGC-TOFMS)

Importance of the Topic

The volatile composition of grapes critically influences wine aroma, varietal character, and perceived quality. Understanding and accurately profiling these compounds aids in quality control, terroir assessment, and flavor optimization in the wine and food industries.

Study Objectives and Overview

This study investigated the varietal volatile profiles of mature Fernão Pires (white) and Baga (red) grapes from Portugal’s Bairrada appellation using headspace solid phase microextraction (SPME) coupled with comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (GC×GC-TOFMS). The aim was to achieve detailed separation and identification of free and glycosidically bound volatiles, with emphasis on monoterpenoids and sesquiterpenoids.

Methodology and Instrumentation

• Sample Preparation: 50 g frozen grapes ground with 8 g NaCl in a 125 ml SPME vial; conditioned at 40 °C for 1 h, followed by 1 h headspace extraction using a 65 μm Carbowax/DVB fiber.
• GC×GC Parameters:
  • Primary column: Equity-5 (60 m × 0.25 mm × 1 μm)
  • Secondary column: Supelcowax (2.5 m × 0.1 mm × 0.1 μm)
  • Oven programs: primary (40 °C→260 °C), secondary (45 °C→265 °C)
• MS Detection: LECO Pegasus 4D TOFMS with EI at 70 eV, acquisition 33–350 u at 125 spectra/s.
• Data Processing: ChromaTOF software, automated peak finding (S/N ≥500), classification filters, removal of column bleed, library match factor ≥850.

Main Results and Discussion

The approach detected 1562 peaks, with 301 compounds confidently identified across diverse chemical classes (alkanes, alcohols, aldehydes, ketones, esters, acids, lactones, phenols, terpenes, sesquiterpenes). GC×GC revealed quantitative and limited qualitative differences between white and red grapes, notably higher monoterpene and sesquiterpene levels in Fernão Pires. Critical coelutions on the primary column (e.g., nerol oxide vs. 2-nonenal) were resolved in the second dimension, yielding clean mass spectra and reliable identifications.

Benefits and Practical Implications

• Enhanced separation boosts confidence in compound annotation in complex matrices.
• Comprehensive profiling supports varietal fingerprinting and authenticity verification.
• The solvent-free, headspace SPME approach streamlines sample preparation for routine QA/QC.
• Data richness facilitates aroma‐flavor research and breeding programs.

Future Trends and Possibilities

• Integration with quantitative calibration for absolute concentration data.
• Development of faster modulation and data processing algorithms to reduce analysis time.
• Miniaturized or portable GC×GC-TOFMS systems for field and on-site testing.
• Extension to other food matrices and real-time monitoring during fermentation.

Conclusion

Headspace SPME GC×GC-TOFMS proved highly effective for in‐depth volatile analysis of grape varieties, resolving critical coelutions and enabling identification of over 300 compounds. This methodology offers powerful capabilities for aroma profiling, quality control, and varietal differentiation in enology and broader food analytics.

Reference

• Wilson, B., et al. Relationship between terpenoids and varietal character in grapes. Journal of Agricultural and Food Chemistry, 1986.
• Rocha, S. M., et al. Role of aromatic alcohols in grape must. Food Chemistry, 2000.