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Characterization of Free and Bound Monoterpene Alcohols during Riesling Fermentation.
Andrew J Caffrey1,2, Larry A Lerno1,2, Jerry Zweigenbaum3
1Department of Viticulture and Enology, University of California, Davis, Davis, California 95616, United States.
Journal of Agricultural and Food Chemistry
|July 2, 2021
Summary
This study identifies monoterpenyl glycosides in Riesling grapes and tracks their changes during wine fermentation. Yeast strains and grape maturity influence glycoside hydrolysis and volatile compound release.
Area of Science:
- Oenology
- Analytical Chemistry
- Plant Biochemistry
Background:
- Monoterpenyl glycosides are precursors to volatile aroma compounds in wine.
- Isomeric forms and difficulty in identifying intact glycosides hinder understanding of their role in wine aroma.
- Relating free monoterpenol concentrations to glycosides during wine fermentation and storage is challenging.
Purpose of the Study:
- To isolate and identify specific monoterpenyl glycosides (linalool, nerol, geraniol) from Vitis vinifera cv. Riesling grapes.
- To monitor changes in these identified glycosides and their free volatile forms during alcoholic fermentation.
- To investigate the influence of different yeast strains and vintage variations on glycoside hydrolysis.
Main Methods:
- Fractionation of grape extracts followed by acid or enzyme hydrolysis.
- Analysis of free volatile monoterpenols using solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS).
- Analysis of intact monoterpenyl glycosides using ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS).
Main Results:
- Linalool, nerol, and geraniol monoterpenyl glycosides were successfully isolated and identified from Riesling grapes.
- Glycoside hydrolysis during fermentation correlated with the concentrations of their corresponding free aglycones (volatiles).
- Variations in glycoside hydrolysis were observed between different yeast strains and across two consecutive years, potentially linked to grape maturity and nutrient availability.
Conclusions:
- The study provides insights into the fate of monoterpenyl glycosides during wine fermentation.
- Yeast strain selection and grape growing conditions significantly impact the release of volatile aroma compounds from glycosidic precursors.
- Further research is needed to fully elucidate the complex pathways influencing monoterpenol release in wine.
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