Identification of Smoke Odorants by Gas Chromatography/Olfactometry and Assessment of Smoke Odorants in Grapes and Wine

There are two primary objectives for this funding cycle. One is to build reliable analytic methods for smoke compounds quantification, and another one is to build a database for smoke assessment. We developed a headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method and a stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS) method to analyze 13 smoke-related compounds. When stable-isotope internal standards are used, the HS-SPME-GC-MS is fast and reliable and can analyze smoke-related compounds in different wines. However, the stable[1]isotope internal standards are not commercially available for all 13 smoke-related compounds. In comparison, the SBSE-GC-MS method is more sensitive and less dependent on the wine matrix.

To respond industry’s smoke exposure concern, we developed a rapid method based on the SPME-GC-MS technique with isotope compounds as the internal standards. We can analyze guaiacol, 4-methylquaiacol, 4-ethylguaiacol, o-cresol, m-cresol, and p-cresol, 4-ethylphenol in 30 min. Our analytical results were verified with a certified commercial lab.

Using this rapid analytical method, we analyzed over 370 smoked exposed red wines and 90 smoke-exposed white wines (including rose wine). A standard was run every ten samples to verify recovery and instrument performance, and a duplicate sample was analyzed every 20 samples. Both free phenols and total phenols (after acid hydrolysis, pH 1, 100C/4h) were analyzed for all the samples. Out of the 370 smoke-exposed red wine, 84 samples had guaiacol concentration in the range of 0-5 μg/L, 159 samples had guaiacol concentration in the range of 5- 10 μg/L. Most of the samples had 4-methylguiacol less than 3 μg/L. In red smoke exposure wine, the average ratio of free guiacol to 4-methylguaiacol was 4.5. But the average ratio of total guaiacol to 4-methylguaiacol was 6.5, higher than the free forms.

A total of 86 control wines were randomly selected from 2013-2016 vintages with about 20 samples from each year. The samples were obtained from industry fermentation without barrel aging. Both free and total volatile phenols were analyzed. Multiple statistical methods were used to analyze the data. Univariate data analysis was used to identify differences between the control and smoke-exposed red wine. The results showed that except for free 4-methylguaiacol and bounded m-cresol, all compounds were significantly higher in smoke-exposed wine. Statistical analysis suggests that the total p-cresol is the best biomarker of smoked wine.