Fermentation compounds

Since glucose and other fermentable compounds are products of photosynthesis, this system probably represents an approximation to the reality of the natural environment. 

The majority of volatiles in wines are, however, fermentation compounds, starting with the so-called higher alcohols and going on to important flavouring compounds such acetates as of higher alcohols and the ethyl ester of C4-C10 fatty acids for the fruity scents. The free fatty acids, when in abundance, contribute to the goaty flavour (Meilgaard, 1975). 

Applications of the Kaltron method and GC-MS in wine aroma analysis were reported by Rapp et al. (1996). The study of the data repeatability in the analysis performed using both Kaltron (Rapp et al., 1994) and polystyrene XAD-2 resin (Gunata et al., 1985 Versini et al., 1988 Voirin et al., 1992) extraction, has already been performed in the cited papers. Besides this, a test with eight repetitions of the whole analytical process using XAD-2 resin has been performed both on a non-floral (Pinot blanc) and a floral (Morio-Muskat) varietal wine for the quantification of 25 varietal and fermentation compounds (Carlin, 1998) for each wine sample the mean CV % values ranged from about 7.0 to 7.5 with a standard deviation from about 3 to 4.7 %, respectively, depending on the different level of some compounds, mostly monoter-penes, in each wine type. 

Bowing to consumer demand for these products, the flavor industry is beginning to enlist the help of biotechnology to produce natural flavor and aroma compounds via fermentative routes. At this time, the production of these fermentation compounds is a largely untapped area of bioconversion research in which bioesterification has great potential as esters play a key role in flavors. 

As another example of successful metabolic engineering of a fermentation compound that is not common to nature, the adipoyl-7-ADCA process of DSM anti-in-... 

The preparation of avermectins has been carried out by fermentation, microsomal oxidation of early fermentation compounds and by semi-synthetic methods [57,113]. Approaches to synthesize some avermectins such as abamectin [114] and ivermectin [115-117] have also been published. Recently the total synthesis of aver-mectin [118], avermectin A g [119] and the aglycones of avermectin A g and B g [120,121] have been reported. 

In some cases, the substrate must be chemically or biochemically hydrolyzed to low-molecular-weight fermentable compounds prior to fermentation. Two steps are then needed to carry out the overall transformation, namely hydrolysis and fermentation. Sometimes, raw substrate hydrolysis is conveniently performed via an enzymatic route, as in the case of ethanol production from cellulose or starch, This two-step transformation can be coupled into a single step in which raw materials are continuously converted to valuable product. 

Fermentative compounds are alcohols, fatty acids, esters, carbonyl compounds, sulphur compounds and some volatile phenols (Bayonove et al., 1998) they contribute to the vinous character of wine and are, quantitatively, the majority of volatile compounds. These compoxmds are produced mainly during alcoholic fermentation and the minor part, but not less important, if it occurs, during malolactic fermentation. Therefore, all wines present a similar pattern of fermentative compounds. 

Although compounds from the grapes themselves are responsible for the varietal character of wines, the compounds formed during alcohol fermentation via yeast metabolism may have a positive or negative influence on wine sensory properties (Ferreira et al., 1995). Table 2 shows concentrations of volatile compounds formed paincipjally during the alcoholic fermentation of Rojal red wines over four vintages expressed as mg/1 as mean of two replicates. The major fermentation compounds such alcohols, ethyl esters, acetates and fatty adds were detected at similar total levels in both wines, some minor differences were observed. 

Boidron et al. (1969) compared the volatile fermentation compounds involved in Champagne aromas with those found in other sparkling wines. Champagnes characteristically have lower concentrations of methanol, higher alcohols, propanol,... 

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