Warmed-over flavor is an unpleasant characteristic usually associated withmeat which has been cooked and then refrigerated. The deterioration of meat flavor is most noticeable upon reheating. As cooking and subsequent refrigeration is the case with mostconvenience foods containing meat, it is a significant challenge to theprocessed foodindustry. The flavor is variously described as "rancid," "stale," and like "cardboard," and even compared to "damp dog hair."[1] Warmed-over flavor is caused by theoxidativedecomposition oflipids (fatty substances) in the meat into chemicals (short-chainaldehydes orketones) which have an unpleasant taste or odor. This decomposition process begins after cooking or processing and is aided by the release of naturally occurringiron in the meat.[1]
The occurrence of warmed-over flavor begins as lipids, primarily lipids from thecell membrane of cells in the meat, are attacked byoxygen. This process is aided by the release ofiron from iron-containing proteins in the meat, includingmyoglobin andhemoglobin. The iron is released by the heat of cooking, or by mechanical grinding. The free iron then acts as acatalyst, or promoter, of oxidation reactions. The reactions break down some of the fats in the meat to form primary oxidation products. These chemicals are not directly responsible for the objectionable taste. Instead, they subsequently further decompose to secondary oxidation products including "alcohols,acids,ketones,lactones andunsaturated hydrocarbons which produce the [warmed-over flavor]." Many of these compounds, includingpentanal,hexanal,pentylfuran,2-pentylfuran,2-octenal and2,3-octanedione have a strong odor and can be tasted at concentrations as low as 1 part per billion.[2]
Warmed-over flavor can be prevented by the addition ofpreservatives to processed meat. Many of the preservatives areantioxidants, ranging fromtocopherols (related to vitamin E) toplum juice to industrial additives such asbutylated hydroxytoluene (BHT),butylated hydroxyanisole (BHA) andpropyl gallate.[1] Other preservatives such assodium pyrophosphate andsodium hexametaphosphate may work by binding iron and preventing it from catalyzing the chemical reactions which lead to warmed-over flavor; as these compounds are generally more soluble in water than the fat-soluble antioxidant preservatives, they may be more readily used to prevent oxidative decomposition in meat.[2]Nitrites, a curing agent for meat, may prevent the development of warmed-over flavor by preventing the release of iron during cooking.[3]