The fate of carotenoids in sediments: An overview

Despite carotenoids being abundant natural products, there are only scattered literature reports of carotenoid derivatives (mainly in the form of their 'perhydro' derivatives) in ancient sediments and petroleum. This was thought to be due to the sensitivity of carotenoids toward oxygen and their preservation potential in sediments was judged to be low. Detailed studies in the past years have indicated, however, that the fossil 'perhydro' derivatives of carotenoids represent only the tip of the iceberg and that a number of reactions occurring with the polyene chain (i.e. expulsion of toluene and xylene, cyclisation and aromatisation, reaction with reduced inorganic sulfur species, hydrogenation, C-C bond cleavage) determine the fate of carotenoids in ancient sediments and lead to complex mixtures of carotenoid derivatives. In addition, aromatisation of cyclohexenyl moieties (as present in e.g. beta-carotene) occurs. An overview of these reactions is given.