Which of the following is a thiol involved in the smell of asparagus, coffee, and onion?

• A. Indole
• B. Methyl benzoate
• C. Eucalyptol
• D. Methanethil

Answer: (D)

Thiols are sulfur-containing compounds that have an -SH group, and they’re notorious for their strong, volatile odors. Methanethiol, or methyl mercaptan, is one of the simplest and most pungent thiols. It’s well known for contributing sharp, onion- or asparagus-like notes when sulfur-containing precursors in foods are released and volatilize during chopping or heating. Among the options, the one that fits is methanethiol because it is a thiol. The others are different types of compounds: indole is an aromatic nitrogen-containing compound, methyl benzoate is an ester with a fruity scent, and eucalyptol is a monoterpene ether with a eucalyptus aroma; none of these are thiols.