Aroma compounds with olfactometry

A relatively new methodology caEed aroma dEution analysis (ada), which combines aroma dEution and gas chromatography-olfactometry to gain a better understanding of the relative importance of aroma compounds, was recently done for coffee. In a roasted Colombian coffee brew, 41 impact compounds were found with flavor dEution threshold factors (FD) greater than 25, and 26 compounds had FD factors of 100 or above. WhEe the technique permits assessment of the impact of individual compounds, it does not evaluate synergistic effects among compounds (13). 

The complete OAV analysis of a food target is time-consuming and requires an excellent analytical setup. In many cases the well-established combination of GC combined with olfactometry provides an excellent insight with regard to the composition of aroma compounds in a mixture and the role of individual chemicals. 

Concerning the impact of ethanol on aroma perception, Pet ka et al. (2003) showed that ethanol at low concentrations (under 10%) could decrease aroma compound detection threshold. Nevertheless, Grosch (2001) observed that the less ethanol present in a complex wine model mixture, the greater the intensity of the fruity and floral odours. Although this effect could be easily explained by the increased partial pressure of the odorants with reduced ethanol concentration, they showed in GC-0 (gas chromatography-olfactometry) experiments that ethanol strongly increased the odour threshold of wine volatiles. In fact the reduction in odour activity of the wine volatiles when ethanol was added was much larger than the reduction in their partial pressure. 

In this study, the aroma compounds detected by Gas Chromatography Olfactometry (GC-O) and with OAV>l in at least one of the wine samples were considered. The use of OSs allows one to not only identify those series that contribute to the aroma profile of a wine, but also to rank them in terms of their odorant capacity and obtain its aromatic fingerprint. 

The impact of these advances on our understanding of wine flavor has recently been reviewed [2 5], One of the most promising areas of current study is the use of gas chromatography mass spectrometry (GCMS) and gas chromatography olfactometry (GCO) combined with sensory aroma recombination studies to identify a small subset of aroma compounds that can mimic the aroma of varietal wines. These techniques have been successfully used to identify important aroma components of Gewiirtz-traminer, Scheurebe, and Grenache rose wines [6-9]. 

Other volatile compounds present in oak wood can transmit unpleasant aromas to the wine, such as the sawdust aroma of dry wood that is perceptible in some wines aged in new barrels. The substances that cause these aromas have been identified in both American and European oak wood, for instance, ( )-2-nonenal, 3-octen-l-one, ( )-2-octenal, and 1-decanal. Their connection with the sawdust aroma has been established by olfactometry, and they have been identified in wines suffering from this flaw, though toasting the wood (Chatonnet and Dubourdieu 1998). 

Olfactometry techniques can be classified into two categories dilution methods, which are based on successive dilutions of an aroma extract until no odour is perceived at the sniffing port of the GC, and the intensity methods, in which the aroma extract is injected and the assessor records the odour intensity and perception as a function of time. The technical solution is straightforward with a split at the end of a chromatographic column and a heated transfer line to a GC external sniffer port. The eluting compounds are splitted, for example, 1 50 to an FID or MS detector and the sniffing port. The column effluent is combined at the sniffer port with a laminar stream of inert make-up gas, which is heated to a constant temperature and additionally humidified. 

---