CONFERENCE 10 MARCH 2006
LATEST TECHNICS TO IMPROVE THE MONITORING OF GRAPEBERRY
RIPENING
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II - Evaluation of ripeness – Analytic tools |
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ABSTRACT Varietal aroma of most wines from non aromatic grapes is partly dependent on the qualitative and quantitative composition of glycosidic precursors in grapes. The most used method (reference method) to determine those precursors is a multi-step process, based on the quantitation of aglycons extracted after enzymatic hydrolis of grape glycosidic extracts. This method is time-consuming and requires specific apparatus such as GC-MS, and thus is not convenient for a large scale use in wineries or enological labs. The only rapid method to assess these glycoconjugates (Red-Free Glycosyl-Glucose method) allows only their total quantitative determination, without distinction between the different chemical families of glycosidic precursors,which limits its interest. We developed a new method using FT-IR spectroscopy and chemometric techniques allowing to determine rapidly but more finely these glycosidic precursors. Vitis vinifera cv. Melon B. grapes grown in different areas of Muscadet vineyard (Western France) and harvested at different maturity stages were used to demonstrate the potentiality of this analysis method. Predictive PLS regressions were established using samples representative of glycoside variability These statisticall correlations were performed between the quantitative data obtained using the reference method and the IR-TF spectra (2000-1000 cm-1) of glycosidic extracts from the same samples. These models allowed to quantitatively determine the total levels of C13-norisoprenoidic and monoterpenic glycoconjugates, the most relevant aroma glycoconjugates for Muscadet wines. The same method was then succesfully applied on Riesling, Gewurztraminer and Chardonnay, with similar performance results and new developpements are now studied on red varieties such as Grenache noir and Syrah. |
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