11 research outputs found
Simple Quantitative Determination of Potent Thiols at Ultratrace Levels in Wine by Derivatization and High-Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC-MS/MS) Analysis
Volatile sulfur compounds contribute
characteristic aromas to foods
and beverages and are widely studied, because of their impact on sensory
properties. Certain thiols are particularly important to the aromas
of roasted coffee, cooked meat, passion fruit, grapefruit, and guava.
These same thiols enhance the aroma profiles of different wine styles,
imparting pleasant aromas reminiscent of citrus and tropical fruits
(due to 3-mercaptohexan-1-ol, 3-mercaptohexyl acetate, 4-mercapto-4-methylpentan-2-one),
roasted coffee (2-furfurylthiol), and struck flint (benzyl mercaptan),
at nanogram-per-liter levels. In contrast to the usual gas chromatography
(GC) approaches, a simple and unique high-performance liquid chromatography–tandem
mass spectrometry (HPLC-MS/MS) method was developed for routine analysis
of five wine thiols, using 4,4′-dithiodipyridine (DTDP) as
a derivatizing agent and polydeuterated internal standards for maximum
accuracy and precision. DTDP reacted rapidly with thiols at wine pH
and provided stable derivatives, which were enriched by solid-phase
extraction (SPE) prior to analysis by HPLC-MS/MS. All steps were optimized
and the method was validated in different wine matrices, with method
performance being comparable to a well-optimized but more cumbersome
gas chromatography–mass spectrometry (GC-MS) method. A range
of commercial wines was analyzed with the new method, revealing the
distribution of the five thiols in white, red, rosé, and sparkling
wine styles
Modulation of volatile thiol and ester aromas by modified wine yeast
The volatile thiols, in particular 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) are potent aroma shown to contribute strongly to the varietal aroma of Sauvignon Blanc wines. The thiols 4MMP and 3MH exist as non-volatile, aroma-inactive cysteine bound conjugates in the grape must and during fermentation the thiol is cleaved from the precursor. However, no cysteine conjugate for 3MHA has been identified. In this work we showed that 3MHA is formed from 3MH by the wine yeast Saccharomyces cerevisiae during fermentation. Furthermore, the alcohol acetyltransferase, Atf1p, the enzyme involved in the formation of the ester ethyl acetate, was shown to be the main enzyme responsible for the formation of 3MHA. Both a laboratory yeast and a commercial wine yeast overexpressing the ATF1 gene produced significantly more 3MHA than the wild-type. Although an atf1Δ laboratory yeast strain showed reduced 3MHA formation, it was not abolished, indicating that other enzymes are also responsible for its formation. Therefore, overexpression of the ATF1 gene in a wine yeast presents the possiblity of modulating both the thiol and ester aromas in wine. © 2006 Elsevier B.V. All rights reserved
Modulation of volatile thiol and ester aromas by modified wine yeast
The volatile thiols, in particular 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) are potent aroma shown to contribute strongly to the varietal aroma of Sauvignon Blanc wines. The thiols 4MMP and 3MH exist as non-volatile, aroma-inactive cysteine bound conjugates in the grape must and during fermentation the thiol is cleaved from the precursor. However, no cysteine conjugate for 3MHA has been identified. In this work we showed that 3MHA is formed from 3MH by the wine yeast Saccharomyces cerevisiae during fermentation. Furthermore, the alcohol acetyltransferase, Atf1p, the enzyme involved in the formation of the ester ethyl acetate, was shown to be the main enzyme responsible for the formation of 3MHA. Both a laboratory yeast and a commercial wine yeast overexpressing the ATF1 gene produced significantly more 3MHA than the wild-type. Although an atf1Δ laboratory yeast strain showed reduced 3MHA formation, it was not abolished, indicating that other enzymes are also responsible for its formation. Therefore, overexpression of the ATF1 gene in a wine yeast presents the possiblity of modulating both the thiol and ester aromas in wine.4 page(s
Assessing the Impact of Smoke Exposure in Grapes: Development and Validation of a HPLC-MS/MS Method for the Quantitative Analysis of Smoke-Derived Phenolic Glycosides in Grapes and Wine
Bushfires occur frequently in the vicinity of grape growing
regions,
resulting in smoke drifting over the vineyards. Wine made from smoked
grapes is often downgraded or unfit for sale due to negative sensory
characters. To manage or avoid the risk of producing smoke-affected
wine, a diagnostic assay was developed for assessing the extent of
smoke exposure in grapes and the resulting wines. The method relies
on the quantitation of the glycosidic grape metabolites that are formed
from major volatile phenols present in smoke. Using HPLC-MS/MS with
APCI, a quantitation method for phenolic glycosides as smoke marker
compounds was developed and validated. The method was confirmed to
be of sufficient sensitivity and reliability to use as a diagnostic
assay. On the basis of phenolic glycoside concentrations, grapes or
wine can be assessed as smoke exposed or not, and the relative intensity
of smoke exposure can be determined
Identification and quantitation of 3-S-cysteinyiglycinehexan-1-ol (cysgly-3-MH) in sauvignon blanc grape juice by HPLC-MS/MS
Precursors to varietal wine thiols are a key area of grape and wine research. Several such precursors, in the form of odorless conjugates, have been closely studied in recent years. A new conjugate has now been identified as 3-S-cysteinylglycinehexan-1-ol (Cysgly-3-MH), being the dipeptide intermediate between cysteine and glutathione precursors of tropical thiol 3-mercaptohexan-1-ol (3-MH). Authentic Cysgly-3-MH was produced via enzymatic transformation of the glutathione conjugate and used to verify the presence of both diastereomers of Cysgly-3-MH in Sauvignon blanc juice extracts. Cysgly-3-MH was added into our HPLC-MS/MS precursor method, and the validated method was used to quantify this new analyte in a selection of Sauvignon blanc juice extracts. Cysgly-3-MH was found in the highest concentrations (10-28.5 μg/L combined diastereomer total) in extracts from berries that had been machine-harvested and transported for 800 km in 12 h. This dipeptide conjugate was much less abundant than the glutathione and cysteine conjugates in the samples studied. On the basis of the results, the new cysteinylglycine conjugate of 3-MH seemingly has a short existence as an intermediate precursor, which may explain why it has not been identified as a natural juice component until now.Dimitra L. Capone, Kevin H. Pardon, Antonio G. Cordente and David W. Jeffer
Determination of the Importance of In-Mouth Release of Volatile Phenol Glycoconjugates to the Flavor of Smoke-Tainted Wines
The
volatile phenols guaiacol, 4-methylguaiacol, syringol, 4-methylsyringol, <i>o</i>-, <i>m</i>-, and <i>p-</i>cresol,
as well as their glycoconjugates, have previously been shown to be
present in elevated concentrations in smoke-tainted wine. Sensory
descriptive analysis experiments, with addition of free volatile phenols
in combination with their glycosidically bound forms, were used to
mimic smoke taint in red wines. The addition of volatile phenols together
with glycoconjugates gave the strongest off-flavor. The hydrolysis
of glycosidically bound flavor compounds in-mouth was further investigated
by in vitro and in vivo experiments. The results indicate that enzymes
present in human saliva are able to release the volatile aglycones
from their glycoconjugates even under low pH and elevated ethanol
conditions, confirming that in-mouth breakdown of monosaccharide and
disaccharide glycosides is an important mechanism for smoke flavor
from smoke affected wines, and that this mechanism may play an important
general role in the flavor and aftertaste of wine
Contribution of Several Volatile Phenols and Their Glycoconjugates to Smoke-Related Sensory Properties of Red Wine
Guaiacol and 4-methylguaiacol are well-known as contributors
to
the flavor of wines made from smoke-affected grapes, but there are
other volatile phenols commonly found in smoke from forest fires that
are also potentially important. The relationships between the concentration
of a range of volatile phenols and their glycoconjugates with the
sensory characteristics of wines and model wines were investigated.
Modeling of the attribute ratings from a sensory descriptive analysis
of smoke-affected wines with their chemical composition indicated
the concentrations of guaiacol, <i>o</i>-cresol, <i>m</i>-cresol, and <i>p</i>-cresol were related to
smoky attributes. The best-estimate odor thresholds of these compounds
were determined in red wine, together with the flavor threshold of
guaiacol. Guaiacol β-d-glucoside and <i>m</i>-cresol β-d-glucoside in model wine were found to
give rise to a <i>smoky/ashy</i> flavor in-mouth, and the
respective free volatiles were released. The study indicated that
a combination of volatile phenols and their glycosides produces an
undesirable smoke flavor in affected wines. The observation of flavor
generation from nonvolatile glycoconjugates in-mouth has potentially
important implications