The tracking of people by trained dogs is based on the recognition of which of the following compounds in the sweat from feet?

Trained dogs track humans by detecting specific volatile organic compounds (VOCs) present in sweat. While fresh sweat is largely odorless, skin-resident microorganisms, such as staphylococci, metabolize odorless secretions into malodorous substances [t1]. A primary component of this 'sweaty' scent is isovaleric acid, which is a type of carboxylic acid [t1]. These carboxylic acids, along with other fatty acids and lipids secreted by eccrine and sebaceous glands, form a unique chemical signature or 'latent print residue' [t2]. Dogs possess an extraordinary olfactory sense, with 125-300 million olfactory cells, allowing them to detect these molecules in concentrations as low as one part per quadrillion [t3]. Although sweat contains salts (sodium chloride) and trace amounts of other metabolites, it is the volatile nature of carboxylic acids that enables canine tracking over distances [t1][t2].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC8033842/
2. [2] https://ptacts.uspto.gov/ptacts/public-informations/petitions/1471295/download-documents?artifactId=OWIysqgE8VJ9Nst3ShfcTW_-1XEFkqQPdt9-aagMKBaYMLpE4NMx9eQ