Metabolism volatile phenols

Several strains of LAB isolated from wine were tested for their abilities to metabolize ferulic and p-coumaric acids. Cavin et al. (1993) showed that these acids were strongly decarboxylated by growing cultures of Lactobacillus brevis, Lactobacillus plantarum, and Pediococcus when decarboxylation was observed, volatile phenols (4-ethylguaiacol and 4-ethylphenol) were detected, indicating the possibility of reduction of the side chain before or after decarboxylation. Couto et al. (2006) reported L. collinoides as a producer of volatile phenols, although strain specificity concerning this capacity was observed. L. mali, L. sake, L. viridescens, and P. acidi-lactici were also found to be able to produce volatile compounds but they only perform the decarboxylation step. Volatile phenols cause animal taints such as horse sweat, wet animal and urine that are usually attributed to Brettanomyces spoilage. 

Table 11.5 Metabolic activity of microorganisms related with production of volatile phenols in wine industry... 

Heresztyn, T. (1986a). Metabolism of volatile phenolic compounds from hidroxycinnamic acids by Brettanomyces yeast. Arch. Microbiol., 146, 96-98. 

As early as 1964 it was recognized that 4-ethyl phenol and 4-ethyl guaiacol were produced by yeast and bacteria during fermentation by the decarboxylation of the hydroxyciimamic acids p-coumaric and fendic acid (88). Later it was reported that among yeast only Brettanomyces species possess the metabolic ability to enzymatically decarboxylate hydroxycinnamic acids to produce ethyl derivatives (29, 89). Heresztyn was the first to identify 4-ethyl phenol and 4t-ethyl guaiacol as the major volatile phenolic compounds formed by Brettanomyces yeast (84). ... 

Isovaleric acid (3-methyl butanoic acid) was found to be the dominant odorant in the "high Brett" wine as detected by CharmAnalysis. The odor described by the GCO sniffer was rancid the chemical identity of the odorant was confirmed by GC-MS. This acid is produced in wine by yeast as a metabolic byproduct of protein (99). Volatile phenolic compounds, such as 4-ethyl guaiacol, guaiacol, and 4-ethyl phenol, were also among the dominate odor active compounds in this wine however, the individual contribution by each of the three phenolics was half or less than the odor activity of isovaleric acid. 

Chlorocarbons are a particular concern owing to their persistence in the environment and the lack of metabolic cleansing pathways in organisms and high fat solubility. Consequently, these substances bioaccumulate in the food chain, with unclear or deleterious effects on health and environmental quality. Chlorocarbons are considered separate from pesticides (see separate discussion) in this discussion and are chlorinated benzenes or phenols and chlorinated alkanes or alkenes. Volatile compounds in water were purged for determination by IMS with a corona discharge (CD) ion source. Chlorobenzene at 3 to 30 mg/L was determined in 5 min, which was considered suitable for on-site measurements at a restoration site. 

The reaction of diazomethane with carboxylic acids to form methyl esters and with phenols to produce aromatic methyl ethers is easy to perform. In addition to providing a more volatile derivative, this method can be used diagnostically to verify the presence of these compounds as the observed mass will increase by 14 for each reactive OH group. This derivatization is frequently used in drug metabolism smdies, since polar acids and phenols are often produced by the biotransformation of pharmaceutical agents. For more details on chemical derivatization, the reader is referred to the literature (18,34,35). 

Aromatic hydrocarbons are metabolized both in vitro and in vivo to arene oxides, which isomerize to phenols, are enzymatically hydrated to dihydrodiols, and are conjugated with glutathione [12, 13, 196]. The dihydrodiols are further metabolized to catechols by dehydrogenation [12,13,196]. Figure 4 shows a simplified diagram of the correlations applicable to all volatile aromatics [12], while Fig. 5 gives a more detailed diagram of the metabolic pathway of benzene in the human liver [196]. 

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