Esculin

Esculin is a natural glucoside of esculetin, a 6,7-dihydroxycoumarin. It occurs in a variety of plants, most notably in the seeds of the horse chestnut (Aesculus hippocastanum) and in the bark of some buckthorn species. In plants, esculin can serve as a storage form of phenolic compounds and is related to other glycosides that release active aglycones upon hydrolysis.

Chemistry and properties: Esulin is the β-D-glucoside of esculetin, i.e., esculetin-2-O-β-D-glucopyranoside. It can be hydrolyzed by acidic conditions or by specific glycosidases to yield esculetin and glucose. The aglycone esculetin is a phenolic compound with a characteristic blue-green fluorescence under some conditions and various biological activities associated with coumarins.

Applications: The most common use of esculin is in microbiology as a substrate for bile esculin tests. In bile esculin agar, bacteria capable of hydrolyzing esculin in the presence of bile release esculetin, which reacts with ferric ions in the medium to form a dark brown to black complex, indicating a positive result. This test supports identification of enterococci and some group D streptococci. Esulin is also encountered in analytical and pharmacognostic studies of plant glycosides and their hydrolysis.

Safety: As a natural plant product, esculin should be handled with standard laboratory safety precautions. It is not intended for ingestion and may be irritating in some exposures.