S: Sensory & Nutritive Qualities of Food JFS S: Sensory and Nutritive Qualities of Food Optimization and Validation of a Taste Dilution Analysis to Characterize Wine Taste R. LOPEZ, L. MATEO-VIVARACHO, J. CACHO, AND V. FERREIRA ABSTRACT: A procedure for the general taste dilution analysis (TDA) of wine has been optimized and applied to characterize the tastants of 5 different wines. Samples are concentrated first by vacuum distillation at 20 ◦ C to obtain a dearomatized concentrate. Such concentrate is redissolved in water and injected in a semipreparative C18-high performance liquid chromatography (HPLC) column. The effluent is separated in fractions that are collected and concentrated by vacuum distillation. Sequential dilutions of the fractions are further evaluated by a sensory panel to assess the intensity of the basic tastes and in-mouth sensations. Fractions were also submitted to HPLC-mass spectrometry (MS) analysis to screen for known tastants of wines. The Taste Dilution chromatograms showed that taste differences between wines are mainly located in fractions 1, 2, and 6, and are mainly related to bitterness and astringency. Different aspects of the method setup and of its reliability are evaluated and discussed. Keywords: astringency, bitterness, HPLC, sour taste, taste, taste dilution analysis, wine Introduction A lthough a fundamental part of wine flavor quality is related to the taste and mouthfeel sensations elicited during its consump- tion, not much attention has been paid to the isolation, ranking, and characterization of the different chemicals responsible for such in- mouth perceptions (Noble 2002). Sweet taste in wine is primarily elicited by glucose and fructose, and could be enhanced by ethanol and glycerol (Thorngate 1997). Sour taste is induced by organic acids in wine and is influenced by pH, tartaric acid being responsible for more than half of the acidity (Thorngate 1997). Salty taste is as- sociated mostly with inorganic cations and anions (Jackson and Lombard 1993; Guth 1999). Bitter taste in wine could be elicited by structurally diverse phenols and polyphenols, but is often con- fused or masked by astringency sensation. Tannin monomers are the most bitter compounds of their family, but other smaller phe- nols and varied compounds, including ions or amino acids, can produce bitterness (Noble 1998). The most important mouthfeel sensation perceived during wine consumption is astringency, which is believed to be perceived by touch via mechanoreceptors (Noble 2002). Astringency is a puckery or dry-mouth sensation typically ex- perimented with red wines and, from a chemical point of view, it is caused, at least in part, by the precipitation of salivary proteins. This sensation is mainly elicited by flavonoid polyphenols extracted from grape seeds and skins and from wood. Sensory studies of wine taste have been carried out with differ- ent purposes and approaches, among them, time-intensity curves (Noble 1995; Kallithraka and others 1997), descriptive analysis (Francis and others 1992; Gawel and others 2001; Zamora and Guirao 2002), or multidimensional similarity scaling (Kielhorn and Thorngate 1999). The taste thresholds of oak wood polyphenol ex- tracts have also been measured (Pocok and others 1994). Recently, several studies have been conducted on mouthfeel properties of wine and grapes, using a “mouthfeel wheel” with hierarchically MS 20060372 Submitted 7/6/2006, Accepted 5/15/2007. Authors are with Lab- oratory for Flavor Analysis and Enology, Dept. of Analytical Chemistry, Fac- ulty of Sciences, Univ. de Zaragoza. 50009 Zaragoza, Spain. Direct inquiries to author Lopez (E-mail: riclopez@unizar.es). structured terminology to perform descriptive analysis with the help of touch standards (Gawel and others 2000; Vidal and others 2004a, 2004b). As can be seen, most of the research has mainly focused on the sensory properties and relatively little attention has been paid to the chemical nature of wine tastants. Consequently, the number and nature of taste-active compounds in wine are not clearly known and understood. In particular, a complete and systematic study to determine the role played by the different families of tastants has not been yet carried out. This situation contrasts with that of wine aroma analysis, where the development and application of system- atic gas chromatography-olfactometric (GC-O) strategies has made it possible to undertake a series of investigations in which the role of the different compounds in the aroma of wine has been grad- ually deciphered. There is no doubt that a similar strategy, focus- ing on the sensory properties of wine nonvolatile molecules, will eventually lead to a better knowledge of the chemical basis of wine flavor. Many years ago, Tilgner proposed a technique called flavor dilu- tion profile (Tilgner 1962a, 1962b) for characterizing flavor sensa- tions of a product (Tilgner 1965). This idea has been recently refined and combined with modern instrumentation to introduce the so- called taste dilution analysis (TDA) (Frank and others 2001). In this technique a taste extract is fractionated in an HPLC and the taste thresholds of the fractions are determined by serial dilutions. This technique has proved to be a powerful tool to characterize important tastants in foods and beverages (Frank and others 2001; Czepa and Hofmann 2003; Ottinger and Hofmann 2003; Scharbert and others 2004). The application of a TDA to wine is not, however, a straightfor- ward task, since the chemical complexity of wine and the abundance of ethanol in the matrix complicate the experimental setup. On the other hand, and given the extraordinary diversity of wine types, one of the most valuable characteristics of a TDA assay for wine would be to be consistent, robust, and repetitive, so that it would be possi- ble to obtain comparable “tastegrams” from different wines in order to assess the role of the different families of tastants. The main aim of the present work is, therefore, to optimize and validate a method to carry out a consistent TDA assay of wine tastants. C  2007 Institute of Food Technologists Vol. 72, Nr. 6, 2007—JOURNAL OF FOOD SCIENCE S345 doi: 10.1111/j.1750-3841.2007.00424.x Further reproduction without permission is prohibited