Skatole, p-Cresol

The amino acids tryptophan and tyrosine are degraded by microorganisms to skatole and p-cresol respectively (cf. Formula 5.40). 

The odor thresholds of skatole have been determined in sunflower oil (15.6pg/kg) and on starch (0.23 pg/kg). This compound plays a role in the aroma of Emmental cheese (cf. 10.3.5) and causes an aroma defect in white pepper (cf. 22.1.1.2.1). It can probably also be formed nonenzymatically from tryptophan by the 

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Pepper, white Faecal smell Skatole, p-cresol [83]... 

Of the twenty amino acids found in proteins, three may be classified as aromatic in character and account for virtually all of the protein absorption of ultraviolet light above 250 nm and for all of the observed luminescence. The molecular structures of the aromatic amino acids are shown in Fig. 1. The parent aromatic molecules of tryptophan, tyrosine and phenylalanine are, respectively, indole, phenol and benzene. The parents with methyl substituents in place of the amino acid side chains have the common names skatole, p-cresol and toluene, respectively. 

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