Volatile Compounds Among Chinese, European And American Oaks

Original brandy would be aged in oak barrels for a period of time to complete the matureprocess, and physical, chemical, and biochemical reactions will take place during the aging ofbrandy and promote organoleptic properties and stabilize color at the same time. With therising demanding of oak wood for aging brandy, more and more attention has been paid totake advantage of Chinese oak. Oak chips were researched in this paper, applying advancedanalysis measures to identify volatile compounds in oak, and analying the influence that oakspecies、toasting degree and seasoning time have on volatile compounds, and compare thedifference among Chinese, French and American oaks, and the evolution of volatilecompounds in oak in the aging process of brandy. The main contents are as follows:(1) Volatile compounds in alcoholic extracts of oak chips were extracted、separated andconcentrated by liquid-liquid extraction (LLE). Qualitative analysis of volatile compounds inoaks was carried out through searching mass spectral library, and comparing retention indexes(RI) with those of the standards, and retention indexes from the literature (RIL). A total of83volatile compounds were isolated and detected in oak chips, including2terpenoid alcohols,2aldehydes,7fatty acids,2esters,4lactones,7aromatic compounds,6ketones,14furaniccompounds,35phenolic compounds, and4others.(2) Volatile compounds in alcoholic extracts of oak chips were analyzed by liquid-liquidextraction (LLE) coupled with gas chromatography-mass spectrometry (GC-MS),investigating the influence that oak species、seasoning time and toasting degree have onvolatile compounds. Oak species have important effect on the components in oak wood; Theuntoasted Quercus Cyclobalanopsis have the most kinds and highest concentration of volatilecompounds; however, the highest concentration of volatile compounds in Quecus mongolicaoak after toasting. As can be seen from the quantitative results, it is best time to seasoning24months, and the levels of volatile compounds reach the highest which degrade from themacromolecules through enzymatic reaction and chemical reaction. However, some ofcompounds appear degradation, and the concentration begin to reduce. From a quantitativepoint of view, the levels of furfural、5-methylfurfural、guaiacol、syringol、vanillin andsyringaldehyde significantly increase after toasting, and toasting is favor of the formation ofthe majority of volatile compounds. As can be seen from the results at the same time,excessive toasting will destroy and degrade them, and the concentrations reduce in oak atheavy toasted degree. The important compounds, whiskey lactones, the concentrations ofthem will reduce after toasting.(3) Volatile compounds in alcoholic extracts of oak chips were analyzed by liquid-liquidextraction (LLE) coupled with gas chromatography-mass spectrometry (GC-MS), comparethe difference of volatile compounds among Chinese, French and American oaks. As can beseen that the high concentrations of furfural、vanillin、syringol and whiskey lactones in oakchips have great impact on the whole flavor of oak. The concentrations of syringaldehyde,vanillin, guaiacol, syringol in Chinese oaks were significantly higher than those of French andAmerican oaks; besides, French oaks were characterized by high levels of furanic compounds at medium toasted degree. In addition, the situation of ratios ofcis/trans-β-methyl-γ-octalactone of Chinese oak was more similar to that of American oakthan that of French oak.(4) Volatile compounds in oak chips were analyzed by liquid-liquid microextraction(LLME) coupled with gas chromatography-mass spectrometry (GC-MS), investigating theevolution of13volatile compounds in the aging process of brandy. Compared with other oakchips, phenolic compounds in brandy macerated with Chinese oak had remarkable advantage,and reach the highest concentrations when aging10days. The brandy macerated with Frenchoak chip was characteristic by high levels of furanic compounds and whiskey lactones.However, the rate of extracting from American oak was less than that of other oak chip, andreach the highest concentrations when aging20days.