Beef, flavor precursors

The alicyclic ketones have been identified as being important flavor precursors by Flament et al. (15) and more recently by MacLeod and Ames (44), who identified a similar compound (3-methyl-cyclo-pentanone) in heated ground beef. Flament et al. (15) singled out the importance of these compounds, particularly in the presence of alhylpyrazines. Nishimura et al. (41) produced a meaty odor by heating 2-hydroxy-3-methylcyclopent-2-enone with cyclotene and HaS. Two volatile compounds described as having meaty odor were 2-methyl-cyclopentanone and 3-methylcyclopentanone. Thus, cyclotene appears to be a key precursor of "roast beef" flavor. 

Mabrouk, A.F., Jarboe, J.K., O Connor, E.M. Water-soluble flavor precursors of beef Extraction and fractionation. J. Agric. Food Chem. 1969,11, 5-9. 

In 1986, a review of the analysis of meat volatiles by Shahidi and colleagues (10) listed 995 compounds that have been found in meat. Mechanistic studies that have combined various amino acids and sugars have predicted the presence of even more compounds that have yet to be observed (77). The formation of flavor-producing compounds results from the complex interaction of numerous precursors and treatments. Some factors involved in beef flavor production are diet, postmortem aging, storage time and temperature, and cooking method. Additionally, it has recently been shown by Block et al. (72, 13) and others (74) that the method used to analyze flavor compounds may, in the process, create new flavor compounds. 

Wasserman, A.E., N. Gray, Meat flavor. I. Fractionation of water-soluble flavor precursors of beef, J. Food ScL, 1965. 30, 5, p. 801. 

Table 1 Concentrations of Some Water-Soluble Flavor Precursors in Beef from Animals Raised on Grass and Concentrate Diets, Showing the Range of Values ( = 24)...

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). 

This important flavor compound was identified in the head-space volatiles of beef broth by Brinkman, et al. (43) and although it has the odor of fresh onions, it is believed to contribute to the flavor of meat. This compound can be formed quite easily from Strecker degradation products. Schutte and Koenders (49) concluded that the most probable precursors for its formation were etha-nal, methanethiol and hydrogen sulfide. As shown in Figure 5, these immediate precursors are generated from alanine, methionine and cysteine in the presence of a Strecker degradation dicarbonyl compound such as pyruvaldehyde. These same precursors could also interact under similar conditions to give dimethyl disulfide and 3,5-dimethyl-l,2,4-trithiolane previously discussed. 

In addition to simple model systems, more complex systems which are closer to actual foodstuffs have been used to investigate the formation of flavor chemicals in the Maillard reaction. Sixty-three volatile chemicals were isolated and identified from starch heated with glycine (4). When beef fat was used as a carbonyl compound precursor in a Maillard model system with glycine, 143 volatile chemicals were identified (6). These included fifteen n-alkanes, twelve n-alkenes, thirteen n-aldehydes, thirteen 2-ketones, twelve n-alcohols, and eleven n-alkylcyclohexanes. Recently, the effect of lipids and carbohydrates on the thermal generation of volatiles from commercial zein was studied (7). 

Diffusate powder prepared by freeze-drying dialyzable water-soluble solutes from beef is undoubtedly the best precursor mixture for producing "meaty" odor and flavor since it is these ingredients that are largely responsible for the flavor of cooked meat. 

Hodge et al. (45) discussed mechanisms for formation of methyl furanones and related substances from Amadori compounds. They have been produced by heating D-ribose and D-ribose phosphate with ammonia (46 47). Hicks and Feather (48) demonstrated that the Amadori compound 1-benzylamino-l-deoxy-D-threo-pentulose dehydrates to 4-hy-droxy-5-methyl-3(2H)-furanone and it has also been identified as a degradation product of L-ascorbic acid. This compound is believed to be formed from ribose-5-phosphate, and gained prominence when it was isolated from beef by Tonsbeck et al. (49). It became more apparent as a precursor of meat flavor when Van den Ouweland and Peer (50) reacted it and its thio analog with HaS to produce a number of sulfur compounds, some of which had meaty odors. 

The flavor industry has introduced, over the years, methods of developing meat flavors by processing appropriate precursors under carefully controlled reaction conditions. As a result, meat flavors having a remarkably genuine meat character in the beef, chicken and pork tonalities are available for the food industry. It has repeatedly been stated that the Maillard reaction is particularly important for the formation of meat flavors. However, of the 600 volatile compounds isolated from natural beef aroma, only 12% of them find their origin in sugar/amino acid interactions and of these 70% are pyrazine derivatives. 

In this study the physical parameters involved in interaction of a major class of meat flavorants, methyl pyrazines, with soy proteins were determined at meat roasting temperatures. Beef diffusate, the water soluble, low molecular weight fraction that constitutes about IX of beef, was shown to contain the necessary precursors to obtain a desirable, thermally generated meat aroma (8). Diffusate was heated under controlled conditions and generated volatiles were transferred to a gas chromatograph for separation and quantitation. Methyl pyrazines, either from heated diffusate or from standard solutions, were measured in the presence of purified soy proteins and the thermodynamics of binding were determined. 

Raw meat has only a weak sweet aroma resembling serum, and a salty, metallic, bloody taste. However, it is a rich reservoir of compounds with taste properties and aroma precursors (24). Each meat has a distinct flavor characteristic. The flavors of distinct meat species or species-specific flavors are often carried by the lipid fraction (2S). For example 4-methyloctanoic and 4-methylnonanoic acids are specific to mutton while (E,E)-2,4-decadienal is specific to poultry meat. 12-Methyltridecanal has been identified as species-specific odorant in stewed beef, and is responsible for the tallowy and beef-like smell (26). The distinctive pork-like or piggy flavor noticeable in lard has in part been attributed to p-cresol and isovaleric acid (27,28,29). 

Recent studies of photooxidized butter and butter oil identified by aroma extract dilution analysis, 3-methylnonane-2,4-dione, a potent volatile compound derived from furanoid fatty acids (see Section C.4) (Figure 11.7). Six different furanoid fatty acids were established as dione precursors, and were found in various samples of butter made from either sweet cream (116 76 mg/ kg), or from sour cream (153-173 mg/kg), or from butter oil (395 mg/kg). Similar precursors of the dione were identified in stored boiled beef and vegetable oils. This flavor defect arising by photooxidation of butter or butter oil is apparently different from the light-activated flavor in milk,that involves the interaction of sulfur-containing proteins and riboflavin. However, more sensory comparisons are needed to distinguish between these two flavor defects due to light oxidation. 

Z)-4-heptenal), which occurs in beef and mutton and often in butter (odor threshold in Table 3.32). Also, the processing of oil and fat can provide an altered fatty acid profile. These can then provide new precursors for a new set of carbonyls. For example, (E)-6-nonenal, the precursor of which is octadeca-(Z,E)-9,15-dienoic acid, is a product of the partial hydrogenation of linolenic acid. This aldehyde can be formed during storage of partially hardened soya and linseed oils. The aldehyde, together with other compounds, is responsible for an off-flavor denoted as hardened flavor . Several reaction mechanisms have been suggested to explain the formation of volatile carbonyl compounds. The most probable mechanism is the P-scission of monohydroperoxides with formation of an intermediary short-lived alkoxy radical (Fig. 3.26). Such P-scission is catalyzed by heavy metal ions or heme(in) compounds (cf. 3.7.2. L7). 

HLA Tarr. The MaiUard reaction in flesh foods. Food Technol 8 15-19, 1954. RL Macy, HD Naumann, ME Bailey. Water-soluble flavor and odor precursors of meat. I. Qualitative study of certain amino adds, carbohydrates, non-amino acid nitrogen compounds, and phosphoric acid esters of beef, pork, and lamb. J Food Sd 29 136-141, 1964. 

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