Meat Aroma

Oxazoles have been found in relatively few cooked foods, although over 30 have been reported in coffee and cocoa, and 9 in cooked meat. Oxazolines have been found in cooked meat and roast peanuts, but not to any extent in other foods. 2,4,5-Trimethyl-3-oxazoline has been regularly detected in cooked meat [26], and when it was first identified in boiled beef [27] it was thought that the compound possessed the characteristic meat aroma however, on synthesis it was shown to have a woody, musty, green flavour with a threshold value of 1 mg/kg [28]. Other 3-oxazolines have nutty, sweet or vegetable-like aromas and the oxazoles also appear to be green and vegetable-like [28]. The contribution of these compounds to the overall aroma of heated foods is probably not as important as the closely related thiazoles and thiazolines. 

Meat aroma is not the result of one chemical constituent but the sum of the sensory effects of many of these volatiles. Over 90% of the volume of volatile constituents from freshly roasted beef is from lipid, but approximately 40 percent of the volatiles from the aqueous fraction are thought to be heterocyclic compounds, many resulting from Maillard reaction products or their interactions with other ingredients. 

Although exact mechanisms have not been described for the formation of other furanoid compounds through amine-carbohydrate interactions, probably many of the 32 furans described by Ohloff and Flament (23) from meat aroma mixtures are from this source. Shiba-moto (24) described many of the same components from mixtures producing meat odors. 

New compound identifications are also presented. Werkhoff et al described studies Involving reaction mixtures of cysteine, thiamine, glutamate, and ascorbate. Their study produced a large variety of unique mixed heterocyclic mono- and disulfides possessing roasted and meaty character. Many of these compounds were subsequently Identified 1n actual meat aroma systems. 

Volatile Precursors. Investigations involving model systems for meat aromas have been revieved (31-34). More than 600 volatiles have been identified from meat or simulated meat precursors. 

Figure 4. Formation of important meat aroma polysulfide heterocyclics by heating acetaldehyde and hydrogen sulfide. (Reprinted from ref. 39. Copyright 1976 American Chemical Society.)...

Other investigators (7-9) have identified a large number of carbonyls from heated fat. The remaining meat aroma components derived by heating lipids are esters, lactones, alkan-2-ones (methyl ketones), benzenoids and other alkylfurans. Several investigators have analyzed volatile compounds formed during thermal degradation of fatty acids (10-12). 

More than 600 components have been isolated [8] from natural beef aroma. We have estimated that only 94 of these volatiles find their origin in the MaiUard reaction and of these 50% are pyrazine derivatives which contribute more to a roasted aroma than to a meat aroma. ... 

By way of contrast, a total of 70 sulfur-containing compounds were identified in the volatile components isolated from our model meat flavor system. A rough survey of the chemical classes represented in the processed meat aroma is shown in Table I. 

Reduction of desirable meat aroma remains as a serious impediment to addition of soy protein. When highly purified soy protein is added to ground patties, thermally generated meat aroma intensity is decreased. Adsorption of flavor compounds onto vegetable protein is a primary mechanism for this aroma loss (5-7). 

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. 

In this model system of soy protein with meat aroma precursors, there was a significant reduction in alkyl substituted pyrazine content with an increase in soy protein content. The percentage loss based on the control for thermally generated pyrazines in the presence of 100 and 500 mg soy protein is shown in Table I. 

Frying temperature was found to be the crlterial parameter that determined the flavor quality in Chinese pork bundle. Cooked meat aroma increased as the heating temperature varied from 134°C to 172°C., as shown in Figure 3. Below 130°C neither cooked meat aroma nor brown color developed. Slightly higher temperatures have been reported for the optimum flavor formation in fried potato chips at 180°C (2), and roasted beans at 200°C (3). 

Figure 2. The effect of temperature and lard content on the raw meat aroma of Chinese fried pork bundle.

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. 

Thiamine degradation has a good share in meat aroma formation [17,64]. Neutral and acidic conditions favour the formation of 13 [65], which is a key component in boiled meat [66, 67[. It has already earlier been identified in a meat-like process flavouring [68[, prepared from cysteine, thiamine, hydrolysed vegetable protein and water [69]. Bolton and co-workers [70] showed that in model experiments with thiamine, [ S]-cysteine, glucose and xylose, only 8% of 13 contained sulphur from cysteine. They concluded that thiamine (43) was the primary precursor for the generation of 13 in this system. 

The odor threshold given by the authors is 0.01 ppb in water, with a cooked-meat aroma from 0.05-0.5 ppb becoming thiamine-like at higher concentrations. At a concentration of 0.3 ppm it has a roasted, meaty, rubbery, burnt flavor (Chemisis, 1996). 

Ohloff G. and Flament I. (1978) Heterocyclic constituents of meat aroma. Heterocycles 11, 663-95. 

Some reaction systems, which have been described in the patent literature for the production of meat aromas, regard thiamine as precursor. 3-Methyl-2-butene-l-thiol is one of the roast odorants of coffee (cf. 21.1.3.3.7) and can cause on off-flavor in beer (cf. Table 5.5). In general, only very small amounts are formed which are still aroma active on account of the very low odor threshold (Table 5.21). The formation of the thiol is explained by the fact that the 3-methyl-2-butene radical is formed from terpenes by photolysis (beer) or under the drastic conditions of the roasting process (coffee). This radical then meets a SH -radical formed from cysteine under these conditions. In the case of beer, humulons (cf. 20.1.2.3.2) are under discussion as the source of the alkyl radical. In coffee 3-methyl-2-butene-l-ol (prenyl alcohol) is also a possible precursor, which yields the thiol after water elimination and hydrogen sulfide addition. 

Meat from young cattle (ca. 4 months) with a body weight up to 150 kg when slaughtered. Color pale red. The meat aroma is weaker than that of beef. The meat is hung for 8 days before use. 

Meat aroma consists of (a) nonvolatile taste substances, (b) taste enhancers and (c) aroma constituents. The latter compounds or their precursors originate essentially from the water-soluhle fraction. The constituents listed in Table 12.22 have been identified as the taste substances of beef broth and roasted meat juice. Solutions of these substances in the given concentrations (Table 12.22) give the typical taste profiles, which are composed of sweet, sour, salty, and glutamate-Uke (umami) notes. The meat note is produced by odorants. 

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