Phenolic acids aroma precursors

Therefore, volatile phenols play a minor role in the aroma of most wines, and when their influence is significant in certain wines, they have mostly a negative effect, which can definitely depreciate their aroma in limit cases (phenolic off-flavors). Thus, the corresponding precursors in grape, phenolic acids, as well as the above-mentioned unsaturated lipids, are hardly taken into account to capture an essential characteristic of the varietal aroma, but to avoid their transformation into off-flavors. 

Smith (1963a) and Feldman et al. (1969) underlined the importance of non-volatile compounds to the flavor of coffee. The comparison between the composition of green and of roasted coffee showed an important decrease in the content of proteins, chlorogenic acid and sucrose on roasting. Fractionation and analysis of the aroma precursors in green coffee have also been studied by Russwurm (1970) who considers that the non-volatile constituents of green coffee that may be involved in flavor formation are carbohydrates, proteins, peptides and free amino acids, polyamines and tryptamines, lipids, phenolic acids, trigonelline and various non-volatile acids. 

Some phenolic acids like caffeic acid, p-coumaric acid and ferulic acid can act as precursors of volatile phenols, which could contribute positively to wine aroma, when they are present at low concentrations associated descriptors are smoky, dove-like and leather (Table 1). Yeasts can conduct the decarboxylation of phenolic adds to volatile phenols, as well as esterase activities present in enzymatic preparations used in winemaking. During wine storage and ageing, volatile phenols may be further transformed. 

Seeds of Theobroma cacao are worldwide in use for production of cocoa butter and confectionary products. The production of raw cocoa from fresh seeds is based on a complex fermentation process, which leads to the aroma precursors. This process enhances the amount of peptides and free amino acids in the seeds, but it also reduces the amount of phenolic compounds, especially the proantho-cyanidins. These antioxidative compounds are mostly composed of catechin and epicatechin monomers and oligomers up to decamers. The fermentation has to take into account that both factors, production of aroma precursors as well as... 

Rohan TA, Connell M (1964) The precursors of chocolate aroma a study of the flavanoids and phenolic acids. J Food Sci 29 460-463... 

The main substrates for wine bacteria known to date are simple molecules sugars and organic acids. Although their transformation is not currently verified, other more complex wine components, such as phenolic compounds, aromatic compounds or aroma precursors, present in small quantities, are without doubt partially metabolized. The repercussion of these minor transformations on organoleptic characters can be (depending on the molecules concerned) at least as important as the principal reactions. 

More than 700 constituents have been identified in aroma extracts of roasted coffee. Heterocyclic aroma components represent the greatest amount of the steam volatile aroma complex (80 - 85 %) which amounts to 700 -900 ppm in medium roasted Arabica coffees. The concentration of individual components varies depending on coffee varieties and roasting conditions. Typical components are formed by thermal degradation of free and bound amino acid and chlorogenic acid precursors. Compared to other roasted foodstuffs, sulfur containing constituents and phenols are formed in high amounts and contribute to desirable coffee flavor or off-flavor. 

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