There are many chemicals that contribute to the aroma and flavor of rice. 1-butanal, 1-hexanal, 1-heptanal, methyl ethyl ketone, 1-pentanal and propanal are responsible for what is known as the ‘old’ or ‘stale’ aroma of stored rice, while 1-butanal and 1-heptanan are involved in the aroma of ‘refresh’ rice.
The stale flavors associated with old rice that had been stored at warm temperatures for some time before cooking has been attributed to the formation of free fatty acids by lipase activity and to lipid oxidation, not to these aroma compounds.
The lipid oxidation products, pentanal, and hexanal, have been implicated in stale rice flavor. These aldehydes can be formed by lipoxygenase activity on linoleic and linolenic acids.
There is no single compound found in cooked rice that can described as ‘cooked rice’ and the aroma probably arises from a mixture of several compounds. The majority of compounds in the headspace cooked rice are lipid oxidation products.
Rice flavor compounds