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40 WINES&VINES April 2017 BARRELS PRACTICAL WINERY & VINEYARD Sensory threshold and occurrence of wine The purified compounds were characterized by a strong, sweet taste. They were tasted in white wine, and the sensory thresh- olds were measured using Inter- n a t i o n a l O r g a n i z a t i o n f o r Standardization (ISO) proce- dure. The threshold found was 590 µg/L for QTT I, which made this compound a very promi- nent marker of sweet taste aris- ing from élevage. This sensory threshold is the lowest among compounds that could be ob- served in wine. The analysis of wines aged in oak barrels dem- onstrated that the amount of QTT in wines varies widely and can reach 1,000 µg/L for the sum of QTT. This fact proves the implication of this compound in sweet perception at least for one part of cited wines. Other triperpenosides Further research identified a group of similar compounds com- ing from the same family, differing by galloyl and glycoside groups as well as their isomers. 22 Sensory properties of these compounds were not completely elucidated, but they are more likely characterized by the sweet taste. Their concomitant occur- rence in oak lets us think about cumulative impact on the wine sweetness and the possibility of modulating of taste balance. The group of other triterpe- noids carrying carboxylic acid function on carbon 24 of the non-sugar part of molecules and more particularly glucosyl de- rivative of bartogenic acid (Glu- BA) attracted our attention. This compound (see "Chemical Struc- tures of Quercotriterpenosides Isomers and Glucosyl Derivative of Bartogenic Acid"), first identi- fied by G. Arramon et al., 9 exhib- its a bitter taste and had very specific distribution in oak ex- tracts in comparison with occur- rence of the QTT family. Impact of botanical species on QTTs and Glu-BA There are two major European oak species used in cooperage (Quercus robur and Quercus pe- traea). Previous research sug- gested that the difference between species arises from geographic origin. But in some cases this dif- ference is not constant regarding known chemical markers. Fill your bottle selection with... Fill your bottle selection with... a a c w i n e . c o m a a c w i n e . c o m All American Containers Local Inventor y | S uperior S election | E xper t Advice Windsor, CA • San Leandro, CA • Kalama, WA CHEMICAL STRUCTURES OF QUERCOTRITERPENO- SIDES ISOMERS AND GLUCOSYL DERIVATIVE OF BARTOGENIC ACID QTT I and II refer to quercotriterpenosides isomers, while Glu-BA refers to glucosyl derivative of bartogenic acid. HO HO HO HO HOOC OH OH OH O O O H Glu-BA HO HO R 1 HO OH OH OH O O O H R 1 R 2 R 3 QTT I OH CH 3 CH 2 OGall QTT II OGall CH 2 OH CH 3 QTT III OGall CH 3 CH 2 OH Gall = galloyl R 2 R 3 O OH OH HO