Identification of the major drivers of 'phenolic' taste in ... - GWRDC

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AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines A.2.4 Preparative Scale Up To obtain sufficient quantities of caftaric acid and grape reaction product for formal sensory assessment, the system was scaled up in an attempt to fractionate the phenolics from 2.25 L of wine using a 500 mL coil. However, it was found that this scale up resulted in a substantial loss of resolution between caftaric acid and grape reaction product due to overloading (data not shown), and although the problem could be resolved, it meant loading smaller amounts of sample in combination with excessively long and impractical run times. To overcome this limitation, a preliminary separation stage was applied, and is described below. A.2.5 Compound Extraction and Purification Both solvent systems provided good resolution of the compounds tested. While the ETANWAT (2:2:3) system was shown to be equally as effective in separating the phenolic test compounds as the HEMBWAT (3:7:3:0:7) system, the latter was chosen for further testing as its solvent components could be found in food grade form. 102
AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines A.3 Development of a Separation and Identification Strategy for Phenolic Compounds in White Wine by HPLC-DAD and HPLC-QTOF A.3.1 Introduction In order to identify and quantify the diverse ‘phenolic’ compounds found in white wine, an HPLC technique suitable for migration to mass spectrometry was developed. With the express intention of not discriminating against possible species present that might elicit taste sensations characterized by the broad term ‘phenolic’, a SPE sample clean-up step was not considered appropriate. These decisions meant the chosen method had to be highly selective and discriminatory. Sample preparation was thus based only on removal of alcohol by rotary evaporation and centrifugation replaced filtration to avoid adsorption onto filtration fibres. Method development followed a path of column selection – based on separating the maximum number of separate peaks – and then mobile phase optimization. A.3.2 Material and Methods Chemicals All chromatographic solvents were HPLC grade and chemicals were analytical grade unless otherwise stated. Water was obtained from a Milli-Q Academic (Millipore, France) purification system using a “Quantum” cartridge. methanol, acetonitrile (LiChrosolv, Merck, Germany), formic acid (98% v/v Emsure, Merck, Germany) and trifluoroacetic acid (100% v/v Thermo, IL) were purchased from Rowe Scientific (Lonsdale, SA, Australia). Polyphenolic standards were purchased from Sigma- Aldrich or Extrasynthèse (France). Wine Samples Experimental wine was made at the Hickinbotham-Roseworthy Wine Science Laboratory using established protocols. For the purposes of method development, a 2009 Riesling and a 2009 Chardonnay wine, made from the hard pressings juice fractions, was used throughout. Preparation of Wine Samples White wine samples were prepared by first removing alcohol by rotary evaporation (Heildorf, Germany) with a water bath temperature
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