Measurement of Volatile Aldehydes in Grapes, Wines, and Musts

AVF Proj. ID: 9734 / /Cat.: ,
Primary Investigator(s): Susan E. Ebelerby

Volatile, saturated aldehydes (C1-C9) in wine or aqueous ethanol solutions were derivatized with cysteamine to form the corresponding thiazolidine derivative. Following extraction into chloroform and gas chromatographic analysis, a limit of quantitation of 1 mg/mL was achieved using a nitrogen phosphorous detector. Spiked recoveries in wine were 112% with an overall coefficient of variation of 16%. The derivatization procedure was used to determine aldehyde levels in several wines: acetaldehyde was observed in the highest concentrations in these wines, however, other aldehydes were also often present. During the current year the focus has been on decreasing the variability of the analytical method.

Novel Optimization Methods for Wine Processing

AVF Proj. ID: 9738 / /Cat.: ,
Primary Investigator(s): David Blockby

We are developing an optimization method for wine processing based on historical winery data and artificial neural networks (ANNs). This method will allow winemakers to fully use the information collected in their wineries over the years in order to produce a final product which has the qualities that they desire, even as grape characteristics vary from year to year. To date, we have established that ANNs can be used successfully to correlate wine processing inputs with chemical and sensory properties of the finished wine. In particular, we have been able to predict primary and malolactic fermentation kinetics based solely on grape characteristics and intended processing. This result will likely have application to prediction of sluggish and stuck fermentations. In addition, we have been able to predict how the color of Cabernet Sauvignon wines that we have made are a function of the processing completed. Increasing fermentation temperature and enzyme addition were found to increase color intensity, while increasing skin contact time (extended maceration) was found to decrease color intensity. We are currently conducting more experiments to clarify these relationships, and thereby maximize color extraction. Using chemical and sensory data from Sauvignon Blanc wines made in our winery, a sample optimization has demonstrated that the method developed predicts different optimal processing conditions for different “target” wines given grapes at a fixed maturity level. We are now in the process of extending this optimization method to actual winery data.

Other Ethyl Carbamate Precursors in Grape Juice and Wine

AVF Proj. ID: 9741 / /Cat.: ,
Primary Investigator(s): Carlos Mullerby

The study shows the results of duplicate experiments where the production of ethyl carbamate upon accelerated storage respectively on a white, and a red wine control were compared with the same wine to which urea, the glucose ureide, and the glucose monoureide were individually added at 2 ppm. The results for both types of wine show that, as expected, the glucose diureide does release some of its urea increasing the ethyl carbamate content upon accelerated storage. Thus, this compound could be a source of post-bottling ethyl carbamate in wines. It was surprising however, that the monoureide did not similarly release urea, indicating that, contrary to what was expected, the monoureide is not a precursor of ethyl carbamate in wine. Apparently in the latter compound, urea is tenaciously held by glucose even in the acidic conditions of the wine. Our results also indicate that under prolonged urease contact, no additional ethyl carbamate was produced from the diureide. We believe this was due to the diureide reaching an equilibrium between it and the glucose plus urea, thereby allowing the urease to destroy the freed urea. As urea is destroyed, the equilibrium eventually shifts, resulting in the complete destruction of the diureide. At this time, it is not known whether the diureide is susceptible to destruction by the urease directly. From the results obtained herewith, it is obvious that the sugar ureides are not a serious source of post-bottling ethyl carbamate in wines when these wines are properly treated with urease. Thus, work on these compounds as potential sources of ethyl carbamate in wines is hereby discontinued.

Studies on the Interaction of Flavor Compounds with Nonvolatile Components of Wine

AVF Proj. ID: 9744 / /Cat.: ,
Primary Investigator(s): Susan Ebeler, Linda Bissonby

Objectives: We proposed to investigate the effects that polyphenols, important nonvolatile constituents of wine, have on the volatility and aroma intensity of selected aroma compounds through: a) use of model odorant compounds to provide a systematic exploration of the effect odorant structure has on interactions with polyphenols; b) application of sensitive gas chromatographic headspace procedures to measure changes in volatility of odorants in the presence of polyphenols; c) correlation of instrumental results with measurements of sensory intensity to understand the effect interactions may have on flavor perception, and utilization of NMR technology to provide an understanding of the mechanisms of polyphenol and odorant interactions. Summary: During previous years of this proposal we focused on developing sensitive gas chromatographic headspace procedures for quantifying odorant/polyphenol interactions in model solutions. We also developed and evaluated sensory procedures for measuring these interactions. Using a time-intensity procedure and model solutions, we showed that retronasal aroma perception is significantly affected by the chemical/physical nature of the aroma compound, by the nature of the matrix, and by individual judge factors such as salivary flow rate. This work was recently published (Mialon and Ebeler, 1997). During the past year we have largely focused on optimizing NMR techniques to study flavor odorant interactions. We have observed that the structure of both the polyphenol and the odorant are critical for determining the strength of the interaction.

The Extraction of Condensed Tannins in Red Wine Production

AVF Proj. ID: 9745 / /Cat.: ,
Primary Investigator(s): Andrew L. Waterhouseby

A commercial scale maceration trial was set up with two wineries, Wente Brothers and Sebastiani Vineyards. Cabernet Sauvignon grapes were harvested from four vineyards, two lots going to each of the wineries. In each case, five wines were made in 20 ton fermentations. The fruit was distributed between all fermentors. The treatments were a control, delayed fermentation, extended maceration, an oak tannin treatment, color extracting enzymes and rotary fermentors. The phenolic composition of the wines was tested using the Folin Ciocalteau, spectral tests, and both reverse and normal phase HPLC procedures. In general, the differences between vineyards were greater than those of the treatments. One of the most notable features was that many of the treatments did not cause consistent changes. The delayed fermentation increased phenol levels slightly, the extended maceration had very little effect on total phenol except for one vineyard which increased significantly, while the rotary and color extraction procedures had little effect. Only the oak tannin treatment significantly decreased the total phenols. Treatments did have trends for specific components. The extended maceration did increase catechin and epicatechin while it decreased unbleached anthocyanins as well as monomelic anthocyanins in most but not all wines. Catechin and epicatechin levels were very low in the wines with short maceration time, those in the oak tannin and color enzyme treatments, although the short but intensive rotary treatment had mixed results. The ratio of small to large tannin was not affected by any of the treatments. In conclusion, none of the treatments significantly altered any of the wines total phenol content consistently except to decrease when short contact times were used, and some individual compounds did respond to treatments.

Adaptation of a Simple Assay to Measure Tannins in Grapes and Wines

AVF Proj. ID: 9603 / /Cat.: ,
Primary Investigator(s): Douglas O. Adamsby

We have accomplished the objectives proposed for the 1996 season. We extracted seed tannin from Cabernet Sauvignon seeds and obtained enough to construct standard curves for several years. We will provide an aliquot this standard tannin preparation to those who wish to conduct similar assays. By assaying fractions from a seed tannin extract separated by HPLC, we determined that the microtiter assay detects the large polymeric tannins present in seed extracts. Simulated fining experiments showed that casein, gelatin and ovalbumin removed the tannin material detected by the assay. We determined that of the total amount of tannin detected by the plate-binding assay, 22%came from the skins and 78%came from the seeds. We have used the principal of the microtiter plate assay to develop a solution assay for tannin. This novel analysis is based on the observation that alkaline phosphatase activity, unlike many other enzymes, is not inhibited by tannin binding. The solution assay is less sensitive but shows less variation than the titer plate assay. The solution assay can be carried out using only a spectrophotometer and eliminates the need for a microtiter plate reader. Thus, the solution assay should prove useful in more winery laboratories than the plate assay.

Alternatives to Bentonite

AVF Proj. ID: 9607 / /Cat.: ,
Primary Investigator(s): Linda Bissonby

In this grant year, we have nearly completed the analysis of genetically engineered wine strains of Saccharomyces over-expressing Protease A. The over-expression of Protease A does not lead to release of protease into the medium as is found in laboratory strains under laboratory conditions. We are in the process of determining if the vacuolar level of protease A activity is higher or not in these strains. MALDI and SELDI-TOF analyses are allowing characterization of wine proteins, and, more importantly, direct analysis of wine hazes, sediments and precipitates. The analysis of hazes has revealed a significant amount of low molecular weight material is present. This has not been previously observed, most likely because other techniques do not allow detection of low molecular weight substances. Protein profiles are similar for wines made form the same varietal, but there are marked seasonal differences in the level of protein present. Wines behave very differently upon aging on yeast lees. In the case sparkling wines from one winery, grape protein was completely degraded within 9 months, while in another winery protein persisted for years during aging. The proteins do not appear to be dramatically different among these wines, suggesting that other factors, such as the yeast used, are critical in proteolysis during aging.

Characterization of Flavor Properties, Chemistry, and Occurrence of

AVF Proj. ID: 9609 / /Cat.: ,
Primary Investigator(s): Susan Ebelerby

Short chain, volatile aldehydes contribute important sensory properties to wines and can affect aging and color stability. We optimized a derivatization procedure for the quantitative analysis of volatile, saturated aldehydes (CI – C9) in wine. Aldehydes were derivatized with cysteamine to form the corresponding thiazolidine derivative. The derivatives were then extracted into chloroform and analyzed by gas chromatography. Using a nitrogen phosphorous detector, the limit of quantitation was 1 mg/mL with average spiked recoveries in wine of 113% (Coefficient of Variation = 16%). The method was able to show differences in aldehyde levels in wines as a function of grape variety and processing conditions. Although acetaldehyde was observed in the highest concentrations, other aldehydes were also often present.

Chemical Changes of Some Important Sulfur-Containing Compounds

AVF Proj. ID: 9611 / /Cat.: ,
Primary Investigator(s): Douglas Adamsby

We added glutathione (300 mg/L) to a Chardonnay juice prior to yeast inoculation. .After primary fermentation the wine was subjected to malolactic fermentation. The resulting wines were compared to corresponding control wines which were made in parallel without glutathione addition. Results indicate that added glutathione does not seem to contribute to sulfur defects that occur in wines. Indeed, if anything, glutathione seems to provide some protection against oxidation in the resulting wines. We added glutathione (300 mg/L) to a Cabernet Sauvignon must just after crushing. The must was fermented to dryness and subjected to malolactic fermentation. The resulting wine was compared to the corresponding control wine which was made in parallel without glutathione addition. Testing shows some interesting differences, but once again no sulfur defects were found in the wine to which glutathione had been added. Unexpectedly, the differences noted in testing are related to color and tannin. We determined the amount of tannin in the Cabernet Sauvignon wines using a plate binding assay we developed in conjunction with another project. We found that the amount of tannin in the wine to which glutathione was added was significantly higher than the control wine. There also appears to be more anthocyanin in the wine to which glutathione was added. The results related to anthocyanin and tannin were completely unanticipated, but the experiments are consistent with the white fermentations in showing that glutathione added to a must prior to yeast inoculation does not give rise to sulfur defects in the resulting wine. We have compared several parameters related to color in the Cabernet Sauvignon wines made with and without added glutathione. Total red color was higher in the glutathione treated wine at pH 3.6 even though the percent color due to anthocyanins was lower than in the control. The percent of the color due to polymer was higher in control wines than in the glutathione-treated wine, and total phenols and tannin were higher in glutathione-treated wine. The largest difference was observed in the amount of color due to copigment complex. Color due to copigmentation as only 2%for the control wine but was found to be 23%in the glutathione treated wine, a difference of more than 10 fold.

Compositional Factors Affecting Sulfide Formation During Wine

AVF Proj. ID: 9613 / /Cat.: ,
Primary Investigator(s): Kevin Sea, Christian Butzke, Roger Boultonby

Sixteen samples of grapes from commercial vineyards were fermented during the 1996 harvest studies. These included 1 each of Chardonnay, Cabernet Franc, Sangiovese and Syrah, 4 Merlot and 8 Cabernet Sauvignon samples. Musts were supplemented with diammonium phosphate and a vitamin mixture to avoid deficiencies in these being a cause of sulfide formation. The levels of hydrogen sulfide produced during fermentation were measured by GC using direct headspace sampling and flame photometric detection. The values obtained ranged from 0 to 155.8 ug (mean of 23.6, sd of 25.9). Yeast strain comparisons on 3 musts gave the following sulfide formation results (in ug): Fermevin (mean of 26.1, sd of 27.2), Lavin D254 (mean of 30.2, sd of 37.3), PDM (32.8,sd of 42.3) and Montrachet (mean of 35.6, sd of 44.1) and are not significantly different from each other when tested on multiple juices. The juices were analyzed for individual amino acids, glutathione and sulfate concentrations and these were correlated with the formation of hydrogen sulfide using principal component analysis (PC A). The levels of sulfate, glutathione and free amino nitrogen (FAN) were all positively correlated with higher sulfide production. Studies with one of the juices show the effects of addition of glutathione and separately, sulfate on the increased levels of hydrogen sulfide production.