Sensory impacts of the obturator used for the Chasselas: study over the time

The composition of wine is largely determined by the composition of pre-fermentation juice, which is influenced by extraction of grape components. Different grape harvesting and processing conditions could affect the extraction of grape components into juice. Among these grape components, pathogenesis-related (PR) proteins are of great concern for white wine maker as they are the main cause of haze formation in finished white wine. If not removed before bottling, these PR proteins may progress into haze through the formation of complex with phenolics under certain conditions. Thaumatin-like proteins (TLPs) and chitinases are the main constituents of PR proteins found in protein haze.

Light-struck taste is a defect prevalent in white wines bottled in clear glass light-exposed for a considerable amount of time leading to a loss of color and appearance of sulfur-like odors. The reaction involves riboflavin (RF), a highly photosensitive compound that undergoes to intermolecular photoreduction by the uptake of two electron equivalents from an external donor, the methionine. The reaction includes different steps forming methional which is extremely unstable and decomposes to methane thiol and acrolein. The reaction of two molecules of methane thiol yields dimethyl disulfide. Methane thiol is highly volatile, has a low perception threshold (2 to 10 µg/L in wine) and confers aroma-like rotten eggs or cabbage.

During red wine ageing or conservation, color and taste change and astringency tends to reduce. These changes result from reactions of flavan-3-ols and/or anthocyanins among which condensation reactions with acetaldehyde are particularly important. The full characterization of these reactions has not been fully achieved because of difficulties in extracting and separating the newly formed compounds directly from wine. Model solutions mimicking food products constitute a simplified medium for their exploration, allowing the detection of the newly formed compounds, their isolation, and their structure elucidation.

Grape phenolic compounds are very important constituents of red wine because, in addition to their antioxidant properties, they contribute to color, astringency and bitterness, oxidation reactions, interactions with proteins and ageing behavior of wines. The aim of our study was to assess the structural characteristics of grape and wine proanthocyanidins of Agiorgitiko variety and to evaluate the influence of the vintage year. Twelve vineyard locations were designated in the Nemea wine region. For three consecutive years (2012-2014), the grapes were harvested at technological maturity and the method of phloroglucinolysis was employed to determine the mean degree of polymerization (mDP) and subunit composition of the samples.

Polyphenols are present in a wide variety of plants and foods such as tea, cacao and grape1. An important sub-class of these compounds is the flavanols present in grapes and wines as monomers (e.g (+)-catechin or (-)-epicatechin), or polymers also called condensed tannins or proanthocyanidins. They have important antioxidant properties2 but their biosynthesis remains partly unknown. Some recent studies have focused on the role of glycosylated intermediates that are involved in the transport of the monomers and may serve as precursors in the polymerization mechanism3, 4. The global objective of this work is to identify flavanol glycosides in grapes or wines, describe their structure and determine their abundance during grape development and in wine.