Analysis of Sensory-Active Volatile Phenols in Smoke-Exposed Grapes by Gas Chromatography

Importance of Topic

The presence of volatile phenolic compounds in grapes exposed to wildfire smoke poses a significant risk to wine quality and consumer perception. These compounds can impart undesirable sensory attributes such as ashy or medicinal notes. Accurate detection and quantification serve as critical quality control measures for viticulture and winemaking operations.

Objectives and Study Overview

This study aimed to develop and validate a gas chromatographic method for the separation and quantitation of key smoke-related volatile phenols in grape extracts. The focus was on structural isomers including cresols, guaiacol derivatives, eugenol and syringol, which require high chromatographic resolution for precise analysis.

Used Methodology and Instrumentation

The analytical workflow combined selective extraction of volatile phenols with gas chromatography-triple quadrupole mass spectrometry. Key instrumental parameters included:

• Column: Zebron ZB-WAX, polyethylene glycol stationary phase (30 m x 0.32 mm x 0.50 μm)
• Injection: Splitless mode at 220 °C, 5 μL sample, 1 min
• Carrier gas: Helium at 1.5 mL/min constant flow
• Oven program: 10 °C/min to 170 °C (9.5 min), 2.5 °C/min to 180 °C (4 min), 75 °C/min to 250 °C (1 min hold)
• Detector: Triple quadrupole MS with electron ionization
• Transfer line and ion source temperatures set at 230 °C and 250 °C, respectively

Main Results and Discussion

The polyethylene glycol (WAX) column resolved all critical compound pairs, including the challenging o-, m- and p-cresol isomers within a 14 min gradient. In contrast, a 5 % phenyl phase failed to separate m/p-cresol even with extended run times. High resolution of these isomers ensures accurate quantitation and reliable risk assessment of smoke taint in grape samples.

Benefits and Practical Applications

Implementation of this method delivers:

• Precise measurement of smoke-derived phenols in grape and wine matrices
• Enhanced screening capability for vineyard smoke exposure events
• Support for predictive modelling of sensory impact in winemaking

Future Trends and Potential Applications

Further developments may include:

• Automation and high-throughput workflows for large-scale vineyard testing
• Real-time monitoring of phenolic volatiles during fermentation
• Expansion to additional smoke markers and related matrices

Conclusion

The optimized GC-MS/MS approach using a Zebron ZB-WAX column provides a robust and efficient means to resolve and quantify key volatile phenols in smoke-exposed grapes. This method enhances quality control in the wine industry and offers a foundation for improved management of smoke taint risks.