B.C. Researchers Test New Polyphenol Analysis
Method in development can quickly indicate authenticity of grapes and wine
Kelowna, B.C.—A team of researchers from the University of British Columbia at Okanagan recently developed and tested a new method for analyzing the polyphenolic content of wine. Completed in the spring of 2013, their work is currently available online prior to publication in the journal Analytical Chemistry.
Named “shotgun polyphenomics” by the researchers, this high-throughput analysis technique has been shown to provide details regarding the polyphenolic content of a wine, which could have multiple applications in the winery as well as in the advancement of wine research. According to Cédric Saucier, co-author of this research along with Adéline Delcambre, polyphenolic characteristics and “authenticity of [both] grape and wine would be the main targets.” Saucier said, “The strategy here is to have a snapshot fingerprint rather than to [identify] individual species.” (Saucier also announced in July the development of an alternative gelatin assay for tannin, see the July 17, 2013 article "British Columbia Winemakers Talk Tannin.")
Current methods for analyzing polyphenolics and the authenticity of wine come with drawbacks. Testing can be time consuming, expensive, and at times limited in distinguishing wine samples from one bottle or tank to the next.
Wine fraud is a potential concern for wineries that buy grapes and bulk wine from others as well as in the wine trade. With rare bottles of new wines reaching thousands of dollars and old vintages selling for tens of thousands, the incentive to create counterfeits is huge. Wineries, private collectors and auction houses alike have been implicated in wine fraud, which suggests a need for a quick and easy way to measure authenticity.
Cedric Saucier and Adéline Delcambre named this process of identifying wine based on a snapshot of polyphenols in a sample “shotgun polyphenomics.” The suffix “omics” refers to the study of processes. The term “shotgun” represents the wide spray of shotgun pellets compared to the single-point impact of a rifle bullet. The researchers intended “shotgun polyphenomics” to indicate a fast, snapshot analysis of total polyphenol content.
Polyphenols in wine vary greatly as a result of several factors, including but not limited to climate and other environmental conditions, soil type, the variety of grape and viticultural practices employed. Polyphenols are responsible for much of the organoleptic character of red wines, in particular the perceptions of flavor, body, color and astringency.
Part of the problem of identifying the components of a wine is that there are hundreds if not thousands of different compounds within the wine, making it extremely difficult to tease out the exact composition of a wine to confirm identification or authenticity. “We know there are probably hundreds of thousands of tannin molecules and it might be impossible to separate them all,” Saucier said. A viable alternative to this complicated situation is to obtain a “snapshot in time” of an entire community of polyphenolics in the sample.
Analysis of red wine
That’s when Saucier and his colleague Delcambre concocted the idea to develop this analysis of wine by ultra-high performance liquid chromatography-electrospray ionization-quadrupole-time-of-flight-mass (UHPLC-ESI-Q-TOF). In simple terms, once the UHPLC conditions are optimized, this method would allow for the very fast characterization of many polyphenolic compounds at once, giving a unique “wine fingerprint” for each wine studied.
Saucier and Delcambre tested this method on 49 different red wines that were all produced within the Okanagan Valley in British Columbia. Specifically, 23 Merlot, 10 Syrah and 11 Pinot Noir wines from the 2007 through 2012 vintages were examined. Nine different families of polyphenols were analyzed using the shotgun method, including proanthocyanidins, organic acid, flavones, flavonones, hydroxygenzoic acid, hydroxycinnamic acid, oxidation products, anthocyanin-O-flavanol, and finally, anthocyanins.
In an attempt to quicken and simplify the method even further, the team also examined the specific ion ratio of two polyphenols (in this experiment, the ratio was malvidin-3-O-glucoside-(epi)catechin and myricetin-3-O-glucoside), which for each wine resulted in a unique value.
The main results from this first test of this approach indicated that shotgun polyphenomics is a novel, rapid, and seemingly reliable method for analyzing the polyphenolic content of red wines that requires little sample preparation. “The results are amazing with more than 100 compounds detected,” Saucier said.
He added they distinguished between the different wine varietals studied. “Another novelty is to use the ion ratio in the spectrum instead of trying to quantify species one by one, which would be very hard and impossible, as sometimes the standards are not available.”
By using the ion ratio, the use of standards would not be required in this analysis, thus reducing the cost and the time needed to run and analyze the results.The team also confirmed that the results are repeatable, as they performed the experiment multiple times over the course of several months. According to Saucier, by using the ion ratio, “this trick gave us phenomenal reproducibility.”
Future research and use
The application and use of shotgun polyphenomics analysis is the first time this sort of fast-paced, high-output fingerprinting method has been tested in wine, according to the researchers. Saucier and Delcambre have developed a rapid method for identifying at least 101 polyphenolic compounds in red wine, and a unique wine polyphenol fingerprint.
In this pilot study, the team was able to successfully distinguish between different wine varietals, giving hope that this sort of technique could be used as a fast and reliable method for determining the authenticity of grapes and wine that would have substantial advantages over the current methods.
From here, scientists could take this knowledge to further advance polyphenolic research in wine, or perhaps develop a portable device with the intent of allowing grape growers and winemakers to take fast samples throughout the growing season, harvest and during the vinification process at a low cost and high reward.
For growers, knowing the polyphenolic composition of their crops using this rapid approach could be extremely helpful while attempting to create a particular style of wine.
A snapshot of the grapes during the growing season could help growers more accurately determine harvest times, as well as help winemakers fine-tune their processes based upon what compounds are present in the juice that they have to work with. Shotgun polyphenomics potentially could help determine the authenticity of grapes and wine if source or origin was in question. Finally it could provide a method for improving sensory analysis both in the laboratory as well as in the cellar.