Meaty aromas

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

Evers, et al. (34) identified several S-substituted furans having meaty aroma including 3-mercapto-2-methylfuran and 3-mer-capto-2,5-dimethylfuran from Maillard reaction mixtures. These compounds were readily oxidized to sulfides, some of which retained meaty odors. All furans having the sulfur atom bound to the 8-carbon had meaty aromas, whereas those with sulfur bound to the a-carbon had hydrogen sulfide-like odors. 

It appears, then, that there is a general, meaty aroma, common to cooked beef, pork, and lamb (and probably poultry), attributable to the pyrolysis of the mixture of low molecular weight nitrogenous and carbonyl compounds extracted from the lean meat by cold water. But the aromas of roast beef, roast pork, roast lamb, and roast chicken are unmistakably different. The chemical composition of the muscular fat deposits of these animals differ appreciably, and it is to these lipid components that we must look to account for the specific flavor differences. Heating the carefully separated fat alone does not give a meaty aroma at all, much less an animal-specific one. It is the subsequent reactions of pyrolysis products of nonlipid components that give the characteristic aromas and flavors of roasted meats (20). 

The effect of water content on the reaction yield is shown graphically in Figure 1. The sample prepared at 757. water content provided the highest yield. It also had the most balanced, meaty aroma. In contrast, the samples with 0%, 10% and 25% water had a biting aroma. The 50% water sample had a blended onion aroma at 75% water the aroma was pot-roasted, roasted, meaty and clean, while the 100% water sample was roasted and pot-roasted but also burnt. 

Ethylkahweofuran 9 has a sulfury, meaty aroma and a threshold of 5 ppb. The dimethyl derivative was perceived... 

A heterocyclic sulfur-containing compound, 2-methyl-thiophene, was identified in boiled crayfish tail meat and pasteurized crabmeat. Thiazole and 3-methylthiopropanal were identified in the crayfish hepatopancreas. Heterocyclic sulfur-containing compounds play important roles in generating meaty aromas in a variety of meat products and are considered important volatile aroma components of marine crustaceans (12— 14). The 2-methylthiophene could be an important flavor cemponent in boiled crayfish tail meat. Both thiazole find 3-methylthiopropanal were important contributors to the desirable meaty aroma associated with crayfish hepatopancreas. The 3-methyl-thiopropanal, identified in boiled crayfish hepatopancreas, is derived from Strecker degradation of methionine (15), and has been considered to be an important cemponent in basic meat flavor (16). Pyridine was detected in the headspace of the hepatopancreas from freshly boiled crayfish. Pyridine and 2-ethylpyridine have been previously reported as components in the atmospheric distillate from a sample of crayfish hepatopancreas frozen for three months (2). 

Several S-substituted furans have been identified from Halliard reaction mixtures which possess meaty aromas including 3-mercapto-2-methylfuran and 3-mercapto-2,5-dimethyl furan (38). 

A thorough study of the aromas produced from over 400 model Maillard reaction systems vas performed (44). Combinations of 21 amino adds and 8 sugars were evaluated under different conditions of temperature and humidity. Table II lists beefy or meaty aromas produced from thermal interactions between glucose and eight amino acids. 

Browning of glucose and simple mixtures of amino acids did not produce authentic meaty aromas, but heating a synthetic mixture of all compounds identified in beef extract in the appropriate concentration, including alanine, glutamic acid, asparagine, taurine, carnosine, anserine, histidine, cystine, creatinine, hypoxanthine, lactic and succinic acid, produced a highly desirable meaty odor. 

Heterocyclic compounds are dominant among the aroma compounds produced in the Maillard reaction, and sulfur-containing heterocyclics have been shown to be particularly important in meat-like flavors. In a recent review, MacLeod (6) listed 78 compounds which have been reported in the literature as possessing meaty aromas seven are aliphatic sulfur compounds, the other 71 are heterocyclic of which 65 contain sulfur. The Strecker degradation of cysteine by dicarbonyls is an extremely important route for the formation of many heterocyclic sulfur compounds hydrogen sulfide and mercaptoacetaldehyde are formed by the decarboxylation and deamination of cysteine and provide reactive intermediates for interaction with other Maillard products. 

The observations on the aromas from cysteine + ribose reaction mixtures have been extended to compare the effect of different lipids triglycerides and phospholipids extracted from beef, and commercial egg lecithin (phosphatidylcholine) and egg cephalin (phosphatidylethanolamine) (L.J. Salter D.S Mottram, unpublished data). The inclusion of the beef triglycerides (TG) did not appear to have any effect on the aroma of the cysteine + ribose reaction mixture, which was sulfurous with an underlying meatiness. However, when beef phospholipids (FL) were used the meaty aroma increased markedly. Similarily, addition of egg lecithin (LEC) or egg cephalin (CEPH) to the cysteine + ribose reaction mixture gave increased meatiness, with the cephalin-containing mixture being judged to have the most meaty character. 

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. 

In our opinion, the predominant contribution to flavor seems to come from sulfurous and carbonyl-containing volatiles. While many of the sulfur-containing volatiles are known to have meaty aromas, volatile carbonyl compounds generally are formed by lipid autoxidation/degradation and do not possess meaty flavor notes. However, it has been indicated that the carbonyl compounds are responsible for the "chickeny" aroma of cooked chicken (17). Thus, lipid autoxldatlon appears to yield the character impact compounds for chicken (18). 

Volatiles with a meaty flavor note generally present in meats from different species are perhaps qualitatively the same, however, their quantities vary from one species to another (25.261. To date, only 13 non-sulfurous volatiles with meaty aromas have been identified in meats and some may indeed be artifacts (Table II). 

TABLE II. Meat Flavor Volatiles with "Meaty" Aroma... 

Sun, B., Tian, H., Zheng, R, Liu, Y., Xie, J., Meaty aromas characteristic structural unit of sulfur-containing compounds with a basic meat flavor. Perf. Flav. 30(1), 36-45 (2003)... 

Lipid oxidation starts in raw beef and continues during cooking. Mottran et al. (21) demonstrated that the intramuscular lipids (not the adipose tissues) are responsible for the formation of most of the lipid-derived volatiles. Intramuscular lipids consist of marbling fat made primarily of triglycerols and structural or membrane lipids made of phospholipids. The phospholipids contain relatively high amount of unsaturated fatty acids more prone to oxidation. In beef, the intramuscular tissue phospholipids are sufficient in imparting a full meaty aroma (22). 

Meat flavor is due to a great number of volatiles from different chemical classes. However, most of the odorants described as meaty aroma contain sulfur. The two most important reactions which generate meaty aroma compounds are the reactions between sulfur containing amino acids and reducing sugars (Maillard reaction) and the thermal degradation of thiamin [35], Sulfur-containing furans are the basic chemicals responsible for the aroma of thermally treated meat. 

In a further trial 46 ales (OG 1030-1050) from 5 brewing companies were examined by sensory profile analysis and by instrumental analysis [54]. The most important variables in the discriminant analysis were (/) iso-amyl alcohol content (instrumental), (ii) caprylic flavour (sensory), (Hi) sodium content (instrumental), (iv) meaty aroma (sensory), (v) ethyl acetate content... 

Acetaldehyde can undergo various interactions with butanedione, hydrogen sulfide, methanethiol and ammonia to give various aliphatic sulfur compounds, thiazoles, thiadiazines and dithiazines as shown in Fig. 1. Compounds identified in YEs are indicated by ( ) (29). The involvement of alternative aldehydes, such as formaldehyde in place of acetaldehyde or mixtures of aldehydes, will lead to the corresponding homologues, some of which have also been reported in YEs. Another aldehyde, 3-methylbutanal, reacts with hydrogen sulfide and methanethiol to give the hemidithioacetal, l-methylthio-3-methyl-l-butanethiol which has been reported in YEs (14). Compounds of this class possess characterisitic meaty aromas with an onion note (14). 

Some of the compounds identified in YEs which are formed either by the thermal degradation of thiamine or on the interaction of thiamine degradation products with other components are shown in Fig. 2. They include aliphatic sulfur compounds, furans, thiophenes and thiazoles. 2-Methyl-3-furanthiol and 2-methyl-3-thiophenethiol have been identified in YEs 9,13 14) and are well known thermal degradation products of thiamine (29). As well as possessing meaty aromas and low odor threshold values 34), these compounds are key precursors of several other sulfur-substituted furans and thiophenes, including the derivatives in Fig. 2. Most possess meaty aromas at low concentrations and several have been identified in YEs (see Tables I and III). 

The investigation of characteristic flavors associated with cooked meats has been the subject of much research over the past four decades but, although compounds with "meaty" aromas had been synthesized, compounds with such characteristics were not found in cooked meats until recently (1). In the search for compounds with characteristic aromas it was found that furans and thiophenes with a thiol group in the 3-position possessed meat-like aromas (2). The corresponding disulfides formed by oxidation of furan and thiophene thiols were also found to have meat-like characteristics, and exceptionally low odor threshold values (3). A number of such compounds are formed in heated model systems containing hydrogen sulfide or cysteine and pentoses or other sources of carbonyl compounds (4,5), The thermal degradation of thiamine also produces 2-methyl-3-fiiranthiol and a number of sulfides and disulfides (6J). 

---