Irradiated beef, flavor

Knowledge of the volatile components of irradiated and nonir-radiated beef is reviewed. Concurrent and nonconcurrent irradiation procedures produce the same compounds but in different relative quantities. Storage of irradiated beef decreases irradiation flavor and the quantity of volatile constituents. Methional, 1-nonanal, and phenylacetaldehyde are of primary importance in beef irradiation off-flavor produced under the conditions described. 

A number of investigators (2, 5, 15, 21, 34, 41, 42, 48, 82, 53) have tried to isolate and to characterize the chemical compound or compounds which give rise to irradiation flavor in meat or to correlate irradiation flavor scores with the production of specific compounds or types of compounds during the irradiation of meat or meat fractions (3,4,32,44> 49,50). These investigations have indicated some probable and some improbable sources of irradiation flavor and the order of magnitude of the concentration of the compounds responsible for irradiation flavor. Wick et al. (53) have offered impressive chemical and organoleptic data connecting the 20 2 1 ratio of methional, 1-nonanal, and phenylacetaldehyde found in irradiated beef at the parts per million level with typical irradiation odor. 

A problem associated with beef sterilized by irradiation at approximately room temperature is the production of an unpleasant flavor and aroma. This paper summarizes knowledge of the volatile components of enzyme-inactivated irradiated and nonirradiated beef, reviews the effects of concurrent and nonconcurrent irradiation procedures and of storage on these components, and presents evidence that methional (3-methylmercaptopropion-aldehyde), 1-nonanal, and phenylacetaldehyde are of primary importance to irradiation off-odor in beef thus processed. 

Any basic study of the chemistry of irradiation flavor is complicated by the fact that volatile components of nonirradiated beef must be known. Otherwise, those components produced by irradiation (and thus may be responsible for off-flavor) and those which are normally present in nonirradiated beef cannot be determined. 

Merritt, as a result of elegant analytical work on raw beef, has suggested (8,10,12) that the series of n-alkanes and 1-alkenes produced during irradiation are responsible for irradiation flavor. In our work no evidence has been found which supports this suggestion. The reason for this contradiction may be the different conditions used during irradiation. Merritt worked with raw beef which was irradiated in vacuum or an inert atmosphere. Our beef, on the other hand, had been partially cooked during enzyme-inactivation and then irradiated in the presence of air. It may also be that 1-nonanal, methional, and phenylacetaldehyde are not the only substances which when mixed in correct proportions give rise to typical irradiation odor. 

Table I summarizes the various meats, meat constituents, and other related substances which have been analyzed, including substances reported on previously (6) as well as those for which new data are given. The substances chosen are intended to provide a cross-section of the type of inherently related material from which volatile irradiation odor and flavor compounds might be expected to form. Thus, in addition to several whole meats, the volatile irradiation products from a number of protein and lipid substances have been analyzed. Among the lipid substances included are typical whole fats and separate moieties such as triglycerides, fatty acid esters, and cholesterol, as an example of a steroid. Among the proteinaceous substances included are a protein, a polypeptide, and some individual amino acids. Finally, beef itself has been separated into a protein, a lipid, and a lipoprotein fraction, and these have been separated, irradiated, and analyzed.

Merritt (42) has carefully studied the yields of hydrocarbons on irradiation of meat and meat components and proposed mechanisms for their formation during irradiation. Despite this recent progress, the chemical characterization of irradiation flavor in meats is far from complete. Little is known about the radiation-induced chemical processes giving rise to the compounds proposed as important to irradiation flavor or the identity of the chemical precursors of these compounds. However, irradiation flavor in beef appears to be associated largely with the protein constituents in meat (21). 

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