Friday, May 16, 2008

German Research Identifies Wine Phenolics

Braunschweig, Germany -- Winegrapes have long been known to contain healthful properties, and in recent years, these have been the subject of research around the globe. Bioactive wine constituents including anthocyanins and resveratrol also contribute to wine's sensory properties. For the past 25 years, Dr. Peter Winterhalter has been performing wine-related research at the Institute of Food Chemistry at the Technical University of Braunschweig in Germany. When his team started, "There were excellent techniques available for the volatile compounds/flavor compounds (in wine), but what was missing was a gentle methodology by which the aroma progenitors/precursers could be analyzed," he told Wines & Vines via e-mail.

"A major amount of the aroma of wine is present in a nonvolatile form, and during wine production and storage, these compounds are converted to the volatiles, i.e., the aroma active compounds. We therefore needed a gentle and preparative method by which we could handle these labile (unstable) progenitors."

This was the starting point of the team's work with countercurrent chromatography (CCC), the topic of the Honorary Research Lecture that Winterhalter will present at the American Society for Enology & Viticulture's (ASEV) annual meeting in June. Given that much of the program at the Portland, Ore., event will be devoted to sensory analysis of wine and grapes, Winterhalter was an apt choice as presenter.

In a brief abstract of his lecture, "Application of Countercurrent Chromatography in Wine Research and Wine Analysis," Winterhalter described CCC as: "One of the few liquid chromatographic techniques that can be predictably scaled up from analytical to process scale. This technique is ideally suited to the analysis of polar wine constituents."

The principle of CCC "is like a separation funnel that operates under extremely gentle conditions and is also preparative," he added. "In this regard, we could enrich minor or even trace compounds, and we were in many cases able to clarify the structure of important wine aroma precursers." Among those cited were TDN ("petrol note") and wine lactone.

"We also applied this technique to the analysis of phenolic compounds in white wine," Winterhalter continued. "Due to the preparative capabilities of CCC, we were able to work up large amounts of a polar Riesling extract. We ended up with roughly 100 identified structures, approximately 50 of them being identified for the first time in wine."

Since then, the team has scaled-up the technique and now can perform separations on the kilogram scale. The preparative version of CCC, Winterhalter explained, "is mainly used for the study of bioactive wine constituents (such as) anthocyanins or resveratrol derivatives.

"For thorough studies into the mechanism of cancer prevention of these compounds, large amounts of pure specimens are required, and these testing substances have also been isolated by using CCC," he said.

In the first part of his lecture, Winterhalter will explain CCC instrumentation and its application to the analysis of labile aroma precursors, antioxidants and anthocyanins. In the latter part, he'll describe novel centrifugal precipitation chromatography for the fractionation of polymeric wine constituents and describe the scale-up of the technique for separations in the 10-100 gram range, according to ASEV's preview material.

Jane Firstenfeld