Peter Winterhalter

Relevance of chromatographic efficiency in varietal authenticity verification of red wines based on their anthocyanin profiles: Interference of pyranoanthocyanins formed during wine ageing.

The determination of the grape variety of aged red wines based on the ratio of acetylated and coumaroylated anthocyanins (R(ac/coum)) can be influenced by the formation of pyranoanthocyanins. Coelution of the pyranoanthocyanin pinotin A and the 3-coumaroylglucoside of malvidin can affect the obtained data for the R(ac/coum) values, which in turn could lead to a false classification of wine variety and rejection of the wines by the food authorities. Investigations using different reversed phase high performance liquid chromatography columns demonstrate the importance of a good chromatographic resolution of these analytes.

Quantitative Determination of Isoflavones in Soy Based Nutritional Supplements by High-Performance Liquid Chromatography

Abstract:An increasing number of nutritional supplements contain phytoestrogens, in particular isoflavones, which potentially alleviate climacteric complaints. Intention of the present study was the qualitative and quantitative determination of isoflavones in soy based nutritional supplements in order to compare the actual content with the labeling of these products. For the analysis high-performance liquid chromatography (HPLC) with photo diode array (PDA) detection was used. The amount of isoflavones was determined via external calibration functions. Our analyses revealed certain variations in the isoflavone content of soy based nutritional supplements, with regard to the individual and the total amount. Furthermore, the total amount of isoflavones per serving unit in some products was higher than declared on the labeling, although only the major isoflavones were taken into account. This study shows that there is the necessity to clearly specify the isoflavone composition on the labeling and - due to safety aspects - to standardize and control the isoflavone content.Zusammenfassung:Nahrungsergänzungsmittel mit Zusatz von Soja werden vermehrt als “Alternative” zur klassischen Hormonersatztherapie für Frauen im Klimakterium angeboten. Diese Präparate enthalten Isoflavone, welche zu den Phytoestrogenen zählen und eine estrogene Wirkung aufweisen. Die in Sojabohnen enthaltenen Isoflavone sollen unter anderem klimakterische Beschwerden wie z.B. Hitzewallungen oder Tachykardie lindern. In der vorliegenden Studie wird eine Methode beschrieben, mit der aus Nahrungsergänzungsmitteln mit Zusatz von Soja-Extrakten der Gehalt an Isoflavonen bestimmt werden kann. Dazu wurde eine HPLC-Methode mitDioden-Array-Detektion entwickelt, mit welcher die Quantifizierung der in Soja vorliegenden Isoflavone über externe Kalibrierfunktionen erfolgen kann. Damit war es möglich, die vom Hersteller gemachten Angaben bezüglich der Isoflavongehalte zu überprüfen. Unsere Untersuchungen wiesen deutliche Unterschiede sowohl im Gesamtgehalt an Isoflavonen als auch in der individuellen Zusammensetzung der einzelnen Produkte auf. In einigen Fällen war der Isoflavongehalt in einigen Produkten pro Verzehrseinheit deutlich höher als vom Hersteller angegeben. Unsere Untersuchungen belegen die Notwendigkeit im Sinne des Verbraucherschutzes, die Isoflavongehalte in Nahrungsergänzungsmitteln klar zu spezifizieren und zu deklarieren.

(+)-Dihydrorobinetin: a Marker of Vinegar Aging in Acacia (Robinia pseudoacacia) Wood

The use of acacia wood for the aging of vinegars is increasing because the efficient air transfer through the pores permits a good acetification rate. In this study, vinegars aged in acacia (Robinia pseudoacacia) wood barrels were analyzed and found to contain a characteristic compound, which increased during the aging process. This so far unknown compound was isolated by semipreparative LC and structurally identified by NMR spectroscopy. (1)H and (13)C NMR chemical shifts and optical rotation revealed its structure to be (+)-dihydrorobinetin, a dihydroflavonol identified for the first time in vinegars as a marker of aging in this kind of wood. This study also reports for the first time the complete assignment of (13)C NMR data for this compound. Moreover, it revealed a longer contact time with acacia wood results in higher concentrations of (+)-dihydrorobinetin found in vinegars. Another finding was that the vinegars aged with nontoasted acacia chips showed significantly higher concentrations of (+)-dihydrorobinetin than found in vinegars aged with toasted acacia chips (384.8 and 23.5 mg/L, respectively). The in vitro antioxidant activity (DPPH(*) and ORAC assays) of (+)-dihydrorobinetin was also determined. (+)-Dihydrorobinetin is reported here for the first time as a chemical marker of vinegars aged in acacia wood and can be used for authenticity purposes.

New Approach for the Synthesis and Isolation of Dimeric Procyanidins

A semisynthetic approach for the strategic formation of various procyanidins has been developed. Procyanidin-rich grape seed extracts were reacted with flavan-3-ols under acid catalysis. The reaction enables the formation of dimeric procyanidins and the elimination of higher oligomeric and polymeric procyanidins through degradation. An easy and fast method for the isolation of large amounts of procyanidins after semisynthetic formation by high-speed countercurrent chromatography is presented. Dimeric procyanidins (B1, B2, B3, B4, B5, and B7) were obtained and isolated. Furthermore, galloylated dimeric procyanidins [(-)-epicatechin-3- O-gallate-4beta-->8-(+)-catechin, (-)-epicatechin-3- O-gallate-4beta-->8-(-)-epicatechin, (-)-epicatechin-3- O-gallate-4beta-->6-(-)-epicatechin, and (-)-epicatechin-4beta-->8-(-)-epicatechin-3- O-gallate], as well as trimeric procyanidins [C1, (-)-epicatechin-4beta-->6-(-)-epicatechin-4beta-->8-(-)-epicatechin, and (-)-epicatechin-4beta-->6-(-)-epicatechin-4beta-->6-(+)-catechin] were obtained and isolated as side products. This approach also afforded gambiriins A1 and A2, which were all isolated and unambiguously identified, and the novel 3-(2,4,6-trihydroxyphenyl)-1-(3,4-dihydroxyphenyl)-propan-2-ol-1beta-->8-(-)-epicatechin (gambiriin A4).