Volatile cooked meat

The symmetrical compounds (17, R = R = R ) are formed from an aldehyde and ammonium sulfide (2,29,35) or hydrogen sulfide and ammonia (33), Thialdine (17, R - R - R = Me) is an important aroma compound found in the volatiles of beef broth (48), pressure-cooked meat (49), and fried chicken (50), It is also obtained from acetaldehyde (2,29,37) or from B-mercaptoacetaldehyde and ammonium sulfide (37), In our experiments, it was synthesized as a white powder from a reaction of acetaldehyde with ammonium sulfide in 60% yield. 

Paralleling the studies of the volatile products of roasted cacao beans and of baked cereal products, and using the same techniques, a great deal of effort has gone into the determination of the compounds present in the volatile fractions of cooked meat. Most of these have been concerned only with beef, either roasted or boiled, but chicken has also received appreciable attention (21). Several lists of compounds isolated from the volatiles of cooked beef have been published (22-24), both cumulative and newly isolated ones. The totals for chicken (as of 1972) and for beef (as of 1977) are more than two hundred each. It... 

Many pyrazines were isolated and identified in cooked foods, especially in cooked meats (27). Pyrazines comprised over 40% of the volatile compounds found in cooked pork liver (28). Two pyrazines, 2-methyl-3(or 6)-pentylpyrazine and 2,5-dimethyl-3-pentylpyrazine were among 52 volatiles identified as lipid-protein-carbohydrate interaction products in a zein regular or waxy corn starch-corn oil model system (7). 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

The volatiles from cooked meat contain large numbers of aliphatic compounds including aldehydes, alcohols, ketones, hydrocarbons and acids. These are derived from lipids by thermal degradation and oxidation (J7) and many may contribute to desirable flavor. In addition, the aldehydes, unsaturated alcohols and ketones produced in these reactions, as well as the parent unsaturated fatty acids, are reactive species and under cooking conditions could be expected to interact with intermediates of the Maillard reaction to produce other flavor compounds. 

In summary, model studies are very efficient for the identification and structure elucidation of important flavor components. Most of the compounds reported here have not been identified in meat and have not yet been reported as constituents of food volatiles. Nevertheless, there are good reasons to believe that minute traces of these sulfur-containing components are present in roasted and/or cooked meat volatiles because our model system was based solely on naturally occurring precursors. We believe that only minute trace amounts of these types of components need to be present in natural products to be of prime significance due to their extremely low odor threshold values. 

The basic fraction of the volatiles identified in the fried pork bundle contained 16 alkylpryazines. Among them, methylpyrazine (nutty, roasted), 2,5-dimethylpyrazine (grilled chicken, roasted peanut), 2,6-dimethylpyrazine (ether-like), 2,3,5-trimethylpyrazine (nutty, roasted) and 2-ethyl-6-methylpyrazine (grassy) were predominant. The combination of these alkylpyrazines may cause the characteristic cooked meat aroma of Chinese fried pork bundle. Quantitative analyses showed that alkylpyrazine formed during the final frying stages, as shown in Table II. 

Of the different types of lipids in foods, the phospholipids, being more unsaturated, are particularly important in relation to aroma formation in meat.151 The aroma of cooked meat was not affected by the prior extraction of triglycerides with hexane, but the use of a more polar solvent (chloroform-methanol), which extracts all lipids, including phospholipids, resulted, after cooking, in the replacement of the meaty aroma by a roast or biscuit-like one. This was reflected in the volatiles, the dominant aliphatic aldehydes and alcohols being replaced by alkylpyrazines. This implies that the participation of the lipids in the Maillard reactions inhibited the formation of heterocyclic compounds. 

The spectrvun of volatile flavor components of cooked meats from different species was Investigated. 

Flavor Is an Important sensory aspect of the overall acceptability of meat products. It Is perceived as the simultaneous stimulation of our taste and odor senses due to high molecular weight components and volatile chemicals present In cooked meats. The overwhelming effects of flavor volatiles has a tremendous effect on sensory acceptability of foods even before they are consumed. 

Fat portion of meats, particularly their phospholipid components, undergo autoxidation/degradation (2) and produce an overwhelming number of volatiles. Fats also serve as a depot of fat-soluble compounds that volatilize on heating and strongly affect flavor. Since compositional characteristics of lipids in meats, vary from one species to another, these factors may be responsible for the development of some species-specific flavor notes in cooked meats (8.9 ). Obviously presence of 4-methyloctanoic and 4-... 

Nearly 1000 compounds have so far been identified in the volatile constituents of meat from beef, chicken, mutton and pork (6). The largest number of volatiles has been determined in beef and these were representative of most classes of organic compounds. Hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, lactones, ethers, sulfur and halogenated compounds as well as different classes of heterocyclic substances (Figure 1) namely furans, pyrldlnes, pyrazines, pyrroles, oxazol(in)es, thiazol(in)es, thiophenes were present in cooked meat flavor volatiles as shown in Table I. Many of these compounds are unimportant to the flavor of meat and some may have been artifacts (16). 

Chemical structures of some heterocyclic flavor volatiles of cooked meats. 

The development of oxidative flavors and off-flavors is an Important factor in acceptance or rejection of cooked meats. One of the Important reactions Involved in the formation of volatile compovinds In meat, and meat products In general, is the autoxidatlon of unsaturated fatty acids. Phospholipid components of meats are generally rich in polyunsaturated fatty acids and hence are generally prone to autoxidatlon (27). 

Although autoxidatlon of lipids in foods is generally considered as unwanted, certain products of lipid autoxidatlon at low concentrations are necessary to the characteristic odor and aroma properties of meats from different species (8.9.28 >. Therefore, the concentration and relative abundance of these chemicals in meat volatiles determine whether they play a desirable or an undesirable role in flavor characteristics of cooked meats. Thus, the origin of flavor and off-flavors developments, which are somewhat species-specific, are perhaps the same. So, in freshly cooked meats the specific flavor of meat which is species-specific develops and progression of autoxidatlon results in the formation of undesirable warmed-over flavor in cooked meats upon storage. 

Propionic acid is used as a feed and com preservative, and as a chemical intermediate. It is also used to control fungi and bacteria in drinking water for livestock. Propionic acid has been qualitatively detected as a volatile component of baked potatoes and cooked meats. It has also been detected in other foods and beverages, including dairy products. Propionic acid is a major constituent (100-300 pg per cigarette) of the gas phase of the mainstream smoke of unfiltered cigarettes. 

Hartman G.J., Scheide J.D. and Ho C.T. (1984) Effect of water activity on the major volatiles produced in a model system approximating cooked meat. J. Food Sci. 49, 607-13. 

Classes of chemical compounds having different function groups and odor descriptors, some of which are useful to the flavor or perfume industries were selected for this initial study. For example, alcohols, aldehydes, pyrazines and various benzenoid compounds which have been isolated in the volatiles of cooked meat as reviewed by Hornstein (22) were studied. For each class of chemical compounds literature threshold values obtained only from one laboratory were used in order to prevent errors associated with technique or methodology between laboratories that occur for threshold determinations as discussed by Guadagni al. ) and Powers and Ware (23). 

Antioxidative Properties. When cooked meat is refrigerated, a rancid or stale flavor usually develops within 48 hrs. This character has been termed warmed-over flavor (WOF) and is generally attributed to the oxidation of lipids. Various synthetic and natural antioxidants have been used to reduce the development of WOF. Among the natural antioxidants used are the sulfur containing amino acid cysteine, and various Maillard reaction products. Eiserich and Shibamoto (Chapter 20) found that certain volatile sulfur heterocycles derived from Maillard reaction systems can function as antioxidants. 

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