Validation of a high-throughput method for the quantification of volatile carbonyl compounds in wine and its use in accelerated ageing experiments

AIM: the aim of this study was the optimization and validation of a robust and comprehensive method for the determination of volatile carbonyl compounds (VCCs) in wines. The protocol was then applied to determine the evolution of VCCs in wines after accelerated ageing. VCCs are widely present in foods and beverages; their formation is due to chemical reactions and biological processes where oxygen plays a key role [1]. However, many of these are side transformations that highly affect the final aroma. The total package oxygen is usually negligible in bottled wines. However, that amount combined with temperature and light, can modify the oxidative status with a consequent loss in varietal aroma and an increase in off flavors and defects [2]. At the same time, several carbonyls are related to pleasant scents so the winemaking of many oxidized wines like Madeira, Port, Vin Santo is tailored to emphasize their productions. We expect that a high-throughput method for the measure of the concentration of carbonyls could be added as a new quality control tool for the evaluation of a complete fermentation, correct winemaking style, and proper bottling and storage.

METHODS: Various white wines (cv. Gewürztraminer) and red wines (cv. Teroldego) were submitted to accelerated-ageing process. All bottles were opened under inert atmosphere inside a sealed hood and submitted to the accelerated-ageing procedure, according to Oliveira et. al. [3]. The extraction procedure was based on the protocol purposed by Moreira et. al. [4], upgraded with a fully automated sample preparation performed by a CTC-PAL3 autosampler. The sample was transferred from the 2 mL vial (kept at 5°C) to a 20 mL vial and then spiked with internal standard (IS) and derivatizing agent (PFBHA) solutions. After a 7 minutes derivatization at 45°C, the SPME extraction is performed at 40°C for 20 minutes. Finally, the fiber desorption takes place at 250°C for 4 min. GC-MS analysis was carried out using a TSQ Quantum XLS Ultra Triple Quadrupole GC-MS/MS using MRM acquisition. Calibration curves were acquired in matrix using a commercial white wine treated with activated carbon to remove odor active compounds. Acetone d6, 4-methyl-4-penten-2-one d10, Octanal d16 and 4-fluorobenzaldehyde were used as IS. As many as 56 VCCs were the analytes under investigation.

RESULTS: all compounds showed a good linearity spanning from approximately 0.1 to 50 µg/L (R2>0.99). Intra-day and 5 days repeatability showed an RSD<30% at 5 and 50 µg/L. IS recoveries have RSD comprised between 4.86% and 17.58%. Complete results are expected shortly.

CONCLUSIONS: A fully robotized method for the determination of VCCs is presented; thanks to its high automation ratio an improved robustness and high- throughput was achieved. Good performance and repeatability, suitable for the use in the quality control, were demonstrated. Examples will be presented and discussed.