* To whom correspondence should be addressed. Department of Bio- science and Biotechnology, University of Strathclyde, 204 George Street, Glasgow G1 1XW, Scotland (U.K.) Fax: #44 141 553 4124; E-mail: j.r.piggott@strath.ac.uk Lebensm.-Wiss. u.-Technol., 34, 76 } 80 (2001) E!ect of Potassium Bitartrate, ( # )-Catechin and Wood Extracts on the Volatility of Ethyl Hexanaote and Octanal in Ethanol/Water Solutions Hector Escalona, Meryem Homman-Ludiye, John R. Piggott* and Alistair Paterson University of Strathclyde, Glasgow (U.K.) (Received June 19, 2000; accepted November 23, 2000) The volatility of wine aroma compounds can be awected by other components in solution. The aim of this work was to determine whether potassium bitartrate, ( # )-catechin, and wood extracts inyuenced the activity coezcients of representative wine aroma volatiles in ethanol-water solutions. ( # )-Catechin caused a small reduction in the activity coezcient of ethyl hexanoate in aqueous ethanol at 10 }20 mL /100 mL, while octanal was awected by ( # )-catechin and potassium bitartrate, suggesting that these components reacted with the aldehyde. Interactions between volatiles and macromolecules seemed to be the main source of yavour matrix interactions in wines, though specixc interactions due to chemical properties of some volatiles also determine their impact on wine yavour.  2001 Academic Press Keywords: activity coe$cient; aldehydes; #avour; model wine; phenolics; tartaric acid Introduction The #avour of wine, and other alcoholic drinks, is in#uenced not only by the volatile composition but also by the way these compounds are released from the solu- tion when smelling and drinking. The e!ects of "ning treatments (Voilley et al., 1990, 1991), yeast cell walls and products released from yeast during fermentation (Lubbers et al., 1994a, b) have been studied, showing reductions of the volatility of wine aroma compounds. Interactions of polysaccharides and glycopeptides with aroma volatiles have been reported (Langourieux & Crouzet, 1994, 1997), which were con"rmed recently (Dufour & Bayanove, 1999a). Furthermore, the e!ect was studied of both (#)-catechin and a wine polyphenol fraction on the activity coe$cients of some aroma com- pounds in model solutions (Dufour & Bayanove, 1999b). Limonene was salted out by the tannin fraction and weakly retained by catechin, while isoamyl acetate, ethyl hexanoate and benzaldehyde were just retained by cat- echin. These interactions were studied at molecular level using H NMR suggesting a hydrophobic driving force related to the binding of aroma compounds. The e!ect of ethanol strength has been previously studied in ethyl esters, higher alcohols and aldehydes (Conner et al., 1998; Escalona et al., 1999) dissolved in aqueous solutions. Increasing levels of ethanol showed a reduc- tion of the activity coe$cients of all these compounds due mainly to an increase of their solubility. However, there was a more important reduction in the volatility of ethyl esters and aldehydes when they were dissolved in aqueous ethanol at 17}20 mL/100 mL. Moreover, the addition of wood extracts in spirit model solutions has been reported to increase this e!ect on ethyl decanoate at lower ethanol strengths (Conner et al., 1999). The e!ect above mentioned is presumed to be related to changes in the structure of the solution where ethanol molecules aggregate at molar fractions above 0.05} 0.06 (about 15}17 mL ethanol/100 mL solution) (D'Angelo et al., 1994) creating hydrophobic areas able to retain other low water-soluble components. As other components in the system can a!ect the struc- ture of the hydroalcoholic solution, this study was directed to evaluate the e!ect of potassium bitartrate, ( # )-catechin and wood extracts on the volatility (esti- mated by calculation of activity coe$cients) of aroma compounds at several ethanol strengths. Materials and Methods Experimental samples Ethanol (HPLC grade, Rathburn Ltd, Walkerburn, U.K.) and distilled water, "ltered using a Millipore-Q system, were used to prepare solutions at di!erent ethanolic strengths. 0023-6438/01/030076 #05 $35.00/0 doi:10.1006/ fstl.2000.0737  2001 Academic Press All articles available online at http://www.idealibrary.com on 76