Aromas from wine grapes are very important for determining the quality of a wine. These aromas arise from volatile compounds (and their precursors) during the ripening stage of the grapes. The increase of glycosylation (sugar compounds) can vary among varieties as well as during ripening. As a wine grape ripens, a tradeoff is made, as glycosylated precursors increase, and aromatic compounds accumulate.
Measuring wine contents to determine ripening and the right timing of harvest has been difficult. Brix (measuring total sugar content), pH and titratable acidity are used to estimate ripening, but none of these show grape aroma or aroma potential. Aromas are often not very strong at first, and an aroma can result from different compounds. Increasing the accuracy of these estimates can both contribute to a better wine and help optimize growing conditions and predict ripening in areas where seasons are short.
To find a more precise way to estimate grape quality and the optimal ripening stage of wine grapes, researchers from Oregon State University analyzed pinot noir grapes from a vineyard in Oregon. The grapes were collected during the first five to six weeks of ripening.
The researchers studied the grape extracts using a gas chromatography technique known as aroma extract dilution analysis (AEDA), which involved dilution of aroma extracts and gas chromatography (GC) analysis until no odorant could be detected. A GC/MS analysis was conducted using a GERSTEL ODP 2 sniffing port for research study panelists to smell compounds as they were released. Quantities of volatile compounds were measured using SPME-GC-MS by first extracting and injecting compounds using a GERSTEL autosampler. However, since low concentrations and low affinity to SPME fibers made measurements of extract difficult, a GERSTEL Twister SBSE method with an ethylene glycol-silicone coated stir bar was used to quantitate benzene-derived compounds. Analysis was conducted on a gas chromatograph and mass selective detector, using a GERSTEL MPS-2 TDU system.
The studies discovered 49 major odor-producing chemicals. The most odor-active compounds were 1-hexanal, phenylethyl alcohol, beta-damascenone, guaiacol, and vanillin. The researchers noted that most of the odorants discovered were minor compounds and present in low concentrations, underscoring the need for sensitive extraction and separation using technology like GERSTEL SBSE for understanding aroma production in wine.
The Oregon study was published in the Journal of Agricultural and Food Chemistry.
After reading the details of this experiment, we invite you to reach out to us for an in-depth conversation about how we can help increase the sensitivity of extraction and detection of aroma-producing compounds, or other chemical analyses, in your laboratory.