The simplest aldehyde in use is acetaldehyde 1, which is ubiquitous in fruit formulations; a dilute solution of acetaldehyde has a pleasant apple taste (F-1). As the chain extends, a fatty character develops, which is exhibited by the C12 lauric aldehyde 2 and the synthetic material methylnonylacetaldehyde 3 (aldehyde MNA) (F-1); this fatty, “animalic” character has been used to effect in perfumery, most famously in the aldehyde cocktail of “Chanel No. 5.”
An interesting aldehyde is 12-methyltridecanal 4 (F-2). This compound, which is FEMA GRAS, is found in beef fat and appears to originate from microorganisms in the rumen of cattle. It is absorbed by the gut as plasmanogens, and released only when the beef is heated over a long period of time (e.g. stewing). Briefly roasting the meet does not release the material. Hence, this gives the potential to create a boiled or stewed beef flavour well differentiated from fried or roasted beef.
Unsaturated The most important materials in this category are the “trans-2-alkenals,” in particular trans- 2-hexenal 5 (leaf aldehyde, F-3). A Union Carbide patent revealed a route using ethyl vinyl ether as “vinylic synthon.”