George K. Skouroumounis

Microwave-assistance provides very rapid and efficient extraction of grape seed polyphenols

A microwave assisted extraction (MAE) method has been developed for the extraction of polyphenols from grape seeds of Vitis vinifera cultivars Cabernet Sauvignon, Shiraz, Sauvignon Blanc and Chardonnay. An initial five-factor (ethanol concentration in the extraction solvent, liquid:solid ratio, time, power and temperature), five-level orthogonal experimental array was designed and three factors (ethanol concentration in the extraction solvent, liquid:solid ratio and time) plus their best levels were chosen to optimise the extraction using a central composite rotatable design (CCRD) experiment. This revealed, after the use of response surface methodology, that the optimal extraction conditions were ethanol concentration (47.2%), liquid:solid ratio (45.3:1) and time (4.6min). Total polyphenols were determined by application of the Folin-Ciocalteau method. Sequential application of the optimal conditions to one sample revealed that approximately 92% of the total polyphenols were extracted in the first instance. In comparison with other extraction methods, MAE provided comparable or better extraction, but was very much quicker. One key finding was that varying the applied power to the extraction was essentially irrelevant; inspection of the applied power profile during extraction revealed that the power was strictly modulated to maintain a constant temperature in the reaction cell.

Precursors of damascenone in fruit juices

Abstract The acid catalysed reactions of 6,7-megastigmadiene-3,5,9-triol and the β-D-glucosides of 5-megastigmen-7-yne-3,9-diol and 3-hydroxyl-β-damascone have been studied in relation to the formation of damascenone. The results show that hydrolysis of the allene triol could account for damascenone formation in the juices of grapes and other fruits.

Identification of a precursor to naturally occurring β-damascenone ☆

Abstract 9-Hydroxymegastigma-3,5-dien-7-yne 8a was synthesised and shown to be identical to an intermediate found in the acid-catalysed conversion of 3,5,9-trihydroxymegastigma-6,7-diene 4 to β-damascenone 1 , 3-hydroxydamascone 5 and megastigma-5-en-7-yne-3,9-diol 6 . When subjected to acid hydrolysis, 8a produced β-damascenone 1 , in high yield. Importantly, the hydrolysate was completely free of 3-hydroxydamascone 5 .

Formation of Damascenone under both commercial and model fermentation conditions.

The fermentations, at a commercial winery, of six different grape musts encompassing the varieties Riesling, Chardonnay, Sauvignon blanc, Shiraz, Grenache, and Pinot noir were monitored for damascenone concentration. In every case, the concentration of damascenone increased during fermentation from low or undetectable levels to concentrations of several parts per billion. Further increases in damascenone concentration were observed during barrel aging of three of these wines. Two ketones, megastigma-4,6,7-triene-3,9-dione (4) and 3-hydroxymegastigma-4,6,7-trien-9-one (5), were synthesized and subjected to fermentation conditions using two yeasts, AWRI 796, and AWRI 1537. In the case of the former compound, 4, synthesis confirmed the original, tentative assignment of the structure and confirmed 4 as a natural product, isolated from honey. Both compounds, under the action of both yeasts, produced appreciable amounts of damascenone (1), with ketone 5 and AWRI 796 yeast yielding the highest concentration of 1.

Sensing Free Sulfur Dioxide in Wine

Sulfur dioxide (SO2) is important in the winemaking process as it aids in preventing microbial growth and the oxidation of wine. These processes and others consume the SO2 over time, resulting in wines with little SO2 protection. Furthermore, SO2 and sulfiting agents are known to be allergens to many individuals and for that reason their levels need to be monitored and regulated in final wine products. Many of the current techniques for monitoring SO2 in wine require the SO2 to be separated from the wine prior to analysis. This investigation demonstrates a technique capable of measuring free sulfite concentrations in low volume liquid samples in white wine. This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte. We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

Distributed Wireless Monitoring System for Ullage and Temperature in Wine Barrels.

This paper presents a multipurpose and low cost sensor for the simultaneous monitoring of temperature and ullage of wine in barrels in two of the most important stages of winemaking, that being fermentation and maturation. The distributed sensor subsystem is imbedded within the bung of the barrel and runs on battery for a period of at least 12 months and costs around

Precursors to oak lactone: synthesis of gallate ester derivatives of 3-methyl-4-hydroxyoctanoic acid

27 AUD for all parts. In addition, software was designed which allows for the remote transmission and easy visual interpretation of the data for the winemaker. Early warning signals can be sent when the temperature or ullage deviates from a winemakers expectations so remedial action can be taken, such as when topping is required or the movement of the barrels to a cooler cellar location. Such knowledge of a wine’s properties or storage conditions allows for a more precise control of the final wine quality.

Stable isotope dilution analysis of wine fermentation products by HS-SPME-GC-MS.

Abstract (3R,4R- and 3S,4S)-3-Methyl-4-(3′-O-methylgalloyloxy)octanoic acid ( 2b ), the corresponding methyl ester ( 2c ) and the straight galloyl derivative, (3R,4R- and 3S,4S)-3-methyl-4-galloyloxyoctanoic acid ( 2a ) were synthesised from cis-oak lactone ( 1 ). Analysis by TLC and mass spectrometry established that the original assignment of structure ( 2c ) to a methylated natural oak component was in error.