Blind wine testing: Anthocyanin database enables identification in the laboratory

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  • Published: Jul 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics / UV/Vis Spectroscopy
thumbnail image: Blind wine testing: Anthocyanin database enables identification in the laboratory

Seeing red

Anthocyanins are nature’s dyes, creating the characteristic crimson hue of red wines. This family of highly concentrated pigments in grapes underlies the chemistry of wine ageing as new chemical entities emerge from the collisions between the fruits of nature’s (and yeasts’) labours over time.

Anthocyanins are nature’s dyes, creating the characteristic crimson hue of red wines. This family of highly concentrated pigments in grapes underlies the chemistry of wine ageing as new chemical entities emerge from the collisions between the fruits of nature’s (and yeasts’) labours over time. Take pyranoanthocyanins, for example. Responsible for the orange tint of aged red wines, this stable chemical entity is created from anthocyanins reacting with acetaldehyde—a prominent metabolite of ethanol—acetone, and other phenolic compounds contained within the components of wine.

Until now, the systematic exploration of these complex interactions that haphazardly occur within wines has not been possible for numerus reasons. For one, the authors cite a paucity in current anthocyanin standards. Secondly, anthocyanins are invariably modified by an extensive array of chemical tags—glucoside and diglucoside groups, for instance—and adducts, which means that these derivatives are often ‘identified ambiguously.’

One-stop shop

Born out of a demand for establishing highly sensitive and accurate methods for identifying anthocyanins, Li et al. reasoned that a one-step method comprising an HPLC-MS/MS assay and complementary anthocyanin database would surmount these challenges.

Their method is based on the separation of wine components over a short, aqueous-to-organic gradient, followed by multiple reaction monitoring of the separated anthocyanins over three quadrupoles (QqQ). Doing so yields two important identifiers—the retention times and mass information—which are then compared to the curated database for rapid and accurate anthocyanin identification.

The creation of this complementary anthocyanin database—and not just the detection test as previous studies have done—is the forte of this study. First, the order that the anthocyanins, derivatives and adducts would elute in was theorized purely on their polarity. Delphinidin, for example, elutes before cyanidin; non-acetylated glucosides before acetylated glucosides; and acetaldehyde adducts before acetone adducts. Next, with the elution order in hand, the mass information was gathered by zapping the anthocyanins with high-voltage energy and selectively monitoring for the highly specific fragment ions that splinter off. Similarly, the presence of derivatives could be worked out from looking for neutral losses as the uncharged sugar moieties flake off. And adducts were detected purely by accounting for the masses of these adducts.

Plonk test

This one-stop shop was applied to explore the natural anthocyanin content within seven wines. These wines would have yielded different anthocyanin profiles given the range of vintages (2007 to 2013) and climates (six countries). This strategy, the authors write, identified 95 anthocyanins—including their derivatives and adducts—in the laboratory within 29 minutes. Furthermore, their method boasts 82 to 111% recovery of spiked standards and could detect the presence of six common anthocyanins—delphinidin, cyanidin, petunidin, pelargonidin, peonidin, malvidin—at levels of 0.02 to 0.005 mg per litre of wine.

Having achieved what was previously impossible, the researchers are excited by having the tools to probe the chemistry of wine ageing, and even noted the potential for the strategy to be extended for other anthocyanins in the future. But their effort is also altruistic. ‘Although the retention time of each anthocyanin may change due to…different detection devices or mobile phases,’ the collaborators muse, ‘the characteristics of their molecular cleavage modes and elution orders will still remain the same, which will assist other researchers.’

Related Links

Rapid Commun. Mass Spectrom. , 2016, 30: 1619–1626. Li et al. A systematic analysis strategy for accurate detection of anthocyanin pigments in red wines.

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Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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