Effect of lipid composition on meat-like model systems containing cysteine, ribose, and polyunsaturated fatty acids

This paper compares the volatile constituents of model systems containing the important meat aroma precursors cysteine and ribose, with and without either methyl linoleate, an n-6 fatty acid, or methyl alpha-linolenate, an n-3 acid, both of which are present in meat. Many of the volatile compounds formed from the reaction between cysteine and ribose were not formed, or formed in lower amounts, when lipid was present. This may be due to the reaction between hydrogen sulfide, formed from the breakdown of cysteine, and lipid degradation products. In addition, cysteine and ribose modified lipid oxidation pathways, so that alcohols and alkylfurans were formed rather than saturated and unsaturated aldehydes. Several volatile compounds, which have been found at elevated levels in cooked meat from animals fed supplements high in n-3 acids, were formed when methyl alpha-linolenate reacted with cysteine and ribose. The possible effects of increasing the n-3 content of meat upon flavor formation during cooking are discussed.     

Aroma components of cooked tail meat of American lobster (Homarus americanus)

Key aroma components of cooked tail meat of American lobster (Homarus americanus) were studied by gas chromatography-olfactometry (GCO) techniques. Components of low and intermediate volatility were evaluated by aroma extract dilution analysis of solvent extracts prepared by direct solvent extraction-high vacuum distillation and vacuum steam distillation-solvent extraction, whereas headspace volatile components were assessed by GCO of decreasing headspace (static and dynamic modes) samples. Forty-seven odorants were detected by all techniques. 3-Methylbutanal (chocolate, malty), 2,3-butanedione (buttery), 3-(methylthio)propanal (cooked potato), 1-octen-3-one (mushroom), 2-acetyl-1-pyrroline (popcorn), and (E,Z)-2,6-nonadienal (cucumber), were identified as predominant odorants by all four isolation methods. The highly volatile compounds methanethiol (rotten, sulfurous) and dimethyl sulfide (canned corn) were detected by headspace methods only. These eight odorants along with three unknown compounds with crabby, amine, fishy odors were found to predominate in the overall aroma of cooked lobster tail meat.     

Characterization of aroma-active compounds in raw and cooked pine-mushrooms (Tricholoma matsutake Sing.)

The characteristic aroma-active compounds in raw and cooked pine-mushrooms (Tricholoma matsutake Sing.) were investigated by gas chromatography-olfactometry using aroma extract dilution analysis. 1-Octen-3-one (mushroom-like) was the major aroma-active compound in raw pine-mushrooms; this compound had the highest flavor dilution factor, followed by ethyl 2-methylbutyrate (floral and sweet), linalool (citrus-like), methional (boiled potato-like), 3-octanol (mushroom-like and buttery), 1-octen-3-ol (mushroom-like), (E)-2-octen-1-ol (mushroom-like), and 3-octanone (mushroom-like and buttery). By contrast, methional, 2-acetylthiazole (roasted), an unknown compound (chocolate-like), 3-hydroxy-2-butanone (buttery), and phenylacetaldehyde (floral and sweet), which could be formed by diverse thermal reactions during the cooking process, together with C8 compounds, were identified as the major aroma-active compounds in cooked pine-mushrooms.     

Heterocyclic volatiles formed by heating cysteine or hydrogen sulfide with 4-hydroxy-5-methyl-3(2H)-furanone at pH 6.5

The reaction of 4-hydroxy-5-methyl-3(2H)-furanone (HMF) with cysteine or hydrogen sulfide at pH 6.5 for 60 min at 140 degrees C produced complex mixtures of volatile compounds, the majority of these containing either sulfur or nitrogen. Of the 68 compounds detected, 63 were identified, some tentatively, by GC-MS. Among the identified compounds were thiophenes (10), thiophenones (6), thienothiophenes (5), thiazoles (5), trithiolanes (4), pyrazines (6), and oxazoles (4). More compounds were produced in the reaction of HMF with cysteine (63) than were formed in the reaction with hydrogen sulfide (33). In both systems, thiophenones were major reaction products, accounting for 25-36% of the total volatiles formed. Possible reasons for the differences in the composition of the two systems are discussed. The contributions of these reactions, and their products, to the flavor of heated foods are considered.     

Investigation of the reaction between 4-hydroxy-5-methyl-3(2H)-furanone and cysteine or hydrogen sulfide at pH 4.5

Reaction of 4-hydroxy-5-methyl-3(2H)-furanone (HMF) with cysteine or hydrogen sulfide at pH 4.5 for 60 min at 140 degrees C produced complex mixtures of volatile compounds, the majority of which contained sulfur. Sixty-nine compounds were identified, some tentatively, by GC/MS. These included disulfides (26), thiols (7), dithiolanones (6), thiophenones (4), dithianones (3), and thienothiophenes (6). The main non-sulfur compounds were 2, 3-pentanedione, 2,4-pentanedione, and 3,4-hexanedione. Both systems produced approximately the same total quantity of volatile compounds, but the reaction containing cysteine gave the larger number of individual compounds, with thiols quantitatively the dominant components. By comparison, the major products formed in the reaction with hydrogen sulfide were the dithiolanones. Reaction pathways are presented for the major products and, where applicable, possible reasons for the differences in composition of the two systems are discussed. The contribution of these reactions, and their products, to the flavor of roasted foods is considered.     

An improved cooked meat medium for the detection of Clostridium botulinum.

A new medium composed of cooked meat and fluid thioglycolate broth was tested with 20 proteolytic and 11 saccharolytic strains of Clostridium botulinum. All of the proteolytic strains produced a black ring at the surface of the broth, presumably due to hydrogen sulfide production, while the saccharolytic strains produced white opaque rings. Since the black ring is formed rapidly and is easily seen, the new medium may be useful for the rapid identification of proteolysis in unknown isolates. Growth and toxin production were better in the new medium than in the usual cooked meat medium or in cooked meat medium plus 0.5% glucose. These results suggest that the new medium will be useful in facilitating identification of C. botulinum.     

Characterization of the most odor-active compounds of Iberian ham headspace

Gas chromatography-olfactometry (GC-O) based on detection frequency (DF) was used to characterize the most odor-active compounds from the headspace of Iberian ham. Twenty-eight odorants were identified by GC-O on two capillary columns, including aldehydes (11), sulfur-containing compounds (7), ketones (5), nitrogen-containing compounds (2), esters (2), and an alcohol. Among them, the highest odor potencies (DF values) were found for 2-methyl-3-furanthiol, 2-heptanone, 3-methylbutanal, methanethiol, hexanal, hydrogen sulfide, 1-penten-3-one, 2-methylpropanal, ethyl 2-methylbutyrate, and (E)-2-hexenal. Nine of the 28 most odor-active compounds were identified for the first time as aroma components of dry-cured ham, including hydrogen sulfide, 1-penten-3-one, (Z)-3-hexenal, 1-octen-3-one, and the meaty-smelling compounds 2-methyl-3-furanthiol, 2-furfurylthiol, 3-mercapto-2-pentanone, 2-acetyl-1-pyrroline, and 2-propionyl-1-pyrroline.     

Carbonyl odorants contributing to the in-oven roast beef top note

Among the few papers related to the gas chromatography (GC)-olfactometric determination of important odorants in cooked beef aroma, only one uses roasting conditions, but none of them investigates the appealing aroma during the cooking of the piece of meat. The present paper investigates this top note as perceived from the oven, by analyzing the oven headspace using GC-"SNIF", a GC-olfactometric technique. From the different functional classes of odorants participating in overall in-oven aroma, this first paper focuses only on the role of aldehydes and ketones, as they represent the majority of aroma compounds formed during cooking. To ascertain the identification of these odorants, a microderivatization technique was used, based on (2,3,4,5,6-pentafluorophenyl)hydrazine. The resulting hydrazones exhibit very specific mass spectrometric fragments, leading to a sensitive and specific detection. A total of 23 carbonyl compounds were shown to contribute to the roast beef top note.     

Aroma properties of a homologous series of 2,3-epoxyalkanals and trans-4,5-epoxyalk-2-enals

A few odor-active epoxyaldehydes, formed during lipid peroxidation, have recently been reported as intense aroma compounds in foods. However, very little is known about their flavor properties in general. Syntheses of homologous trans-2,3-epoxyalkanals (C(6)-C(12)) and trans-4,5-epoxy-(E)-2-alkenals (C(7)-C(12)) followed by structural characterization using mass spectrometry (MS/EI; MS/CI) and (1)H NMR measurements were performed. An evaluation of their odor qualities and odor thresholds by gas chromatography-olfactometry revealed the following: within the trans-2,3-epoxyalkanals, the odor quality changed from grassy for the compounds with six and seven carbon atoms to citrus-like or soapy for aldehydes with eight and more carbon atoms. The odor thresholds lay in the range of 3-15 ng/L (in air) and were nearly identical within the series; however, a slight minimum was measured for trans-2,3-epoxyoctanal to trans-2,3-epoxydecanal. In the series of the trans-4,5-epoxyalk-(E)-2-enals the C(10) compound was characterized by the lowest odor threshold of 0.6-2.5 pg/L of air. However, all trans-4,5-epoxy-alk-(E)-2-enals smelled intensely metallic.     

Plant extracts, spices, and essential oils inactivate Escherichia coli O157:H7 and reduce formation of potentially carcinogenic heterocyclic amines in cooked beef patties

Meats need to be heated to inactivate foodborne pathogens such as Escherichia coli O157:H7. High-temperature treatment used to prepare well-done meats increases the formation of carcinogenic heterocyclic amines (HCAs). We evaluated the ability of plant extracts, spices, and essential oils to simultaneously inactivate E. coli O157:H7 and suppress HCA formation in heated hamburger patties. Ground beef with added antimicrobials was inoculated with E. coli O157:H7 (10(7) CFU/g). Patties were cooked to reach 45 °C at the geometric center, flipped, and cooked for 5 min. Samples were then taken for microbiological and mass spectrometry analysis of HCAs. Some compounds were inhibitory only against E. coli or HCA formation, while some others inhibited both. Addition of 5% olive or apple skin extracts reduced E. coli O157:H7 populations to below the detection limit and by 1.6 log CFU/g, respectively. Similarly, 1% lemongrass oil reduced E. coli O157:H7 to below detection limits, while clove bud oil reduced the pathogen by 1.6 log CFU/g. The major heterocyclic amines 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were concurrently reduced with the addition of olive extract by 79.5% and 84.3% and with apple extract by 76.1% and 82.1%, respectively. Similar results were observed with clove bud oil: MeIQx and PhIP were reduced by 35% and 52.1%, respectively. Addition of onion powder decreased formation of PhIP by 94.3%. These results suggest that edible natural plant compounds have the potential to prevent foodborne infections as well as carcinogenesis in humans consuming heat-processed meat products.     

Difference in the volatile composition of pine-mushrooms (Tricholoma matsutake Sing.) according to their grades

The differences in volatile components of pine-mushrooms (Tricholoma matsutake Sing.) according to their grades were observed by applying multivariate statistical methods to GC-MS data sets. A total of 35 and 37 volatile components were identified in raw and cooked pine-mushrooms, respectively. The volatile components in pine-mushrooms were primarily composed of C8 species, such as 3-octanol, 1-octen-3-ol, 1-octanol, (E)-2-octen-1-ol, 3-octanone, 1-octen-3-one, (E)-2-octenal, and octanoic acid. The levels of ethyl octanoate, junipene, and 3-methyl-3-buten-2-one were much higher in raw pine-mushroom of higher grades, whereas the reverse was true for C8 components. On the other hand, furfuryl alcohol, benzyl alcohol, phenylethyl alcohol, dihydro-5-methyl-2(3H)-furanone, 2(5H)-furanone, (E)-2-methyl-2-butenal, furfural, phenylacetaldehyde, benzoic acid methyl ester, camphene, and beta-pinene were the major components of cooked mushrooms. These volatile components formed by various thermal reactions could be mainly responsible for the difference in volatile components of cooked pine-mushrooms according to their grades.     

Identification of sulfur volatiles in canned orange juices lacking orange flavor

The purpose of this study was to understand why some canned orange juices are not perceived as orange juice. Sensory flavor profile data indicated that the primary odor (orthonasal) attributes were tropical fruit/grapefruit, cooked/caramel, musty, and medicine. By comparison fresh-squeezed juice lacked these odor attributes. GC-O analysis found 43 odor-active components in canned juices. Eight of these aroma volatiles were sulfur based. Four of the 12 most intense aroma peaks were sulfur compounds that included methanethiol, 1-p-menth-1-ene-8-thiol, 2-methyl-3-furanthiol, and dimethyl trisulfide. The other most intense odorants included 7-methyl-3-methylene-1,6-octadiene (myrcene), octanal, 2-methoxyphenol (guaiacol), 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone (homofuraneol), (E)-non-2-enal, (E,E)-deca-2,4-dienal, 4-hydroxy-3-methoxybenzaldehyde (vanillin), and alpha-sinensal. Odorants probably responsible for the undesirable sensory attributes included grapefruit (1-p-menth-1-ene-8-thiol), cooked [2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (Furaneol), and 3-(methylthio)propanal (methional)], musty [7-methyl-3-methylene-1,6-octadiene and (E)-non-2-enal], and medicine (2-methoxyphenol). The canned juices also lacked several aldehydes and esters normally found in fresh orange juice.     

Evaluation of the key aroma compounds in beef and pork vegetable gravies a la chef by stable isotope dilution assays and aroma recombination experiments

Although the aroma compounds of meat processed as such have been studied previously, data on complete homemade dishes containing beef and pork meat were scarcely studied. Recently, 38 odor-active compounds were characterized in beef and pork vegetable gravies using GC-olfactometry. In the present investigation, the most odor-active compounds were quantitated in a freshly prepared stewed beef vegetable gravy (BVG) as well as a stewed pork vegetable gravy (PVG) by means of stable isotope dilution assays. Calculation of odor activity values (OAVs; ratio of concentration to odor threshold) revealed 3-mercapto-2-methylpentan-1-ol, (E,E)-2,4-decadienal, (E,Z)-2,6-nonadienal, (E)-2-decenal, (E)-2-undecanal, and 3-hydroxy-4,5-dimethyl-2(5H)-furanone as the most potent odorants in both gravies. However, significantly different OAVs were found for 12-methyltridecanal, which was much higher in the BVG, whereas (E,Z)-2,4-decadienal showed a clearly higher OAV in the PVG. Aroma recombination experiments performed on the basis of the actual concentrations of the odorants in both gravies revealed a good similarity of the aromas of both model mixtures containing all odorants with OAVs > 1 with those of the original gravies.     

Important aroma compounds in freshly ground wholemeal and white wheat flour-identification and quantitative changes during sourdough fermentation

An investigation on the odor-active compounds of wholemeal (WWF) and white wheat flour (WF 550) by aroma extract dilution analysis (AEDA) and by quantitative studies using stable isotope dilution assays (SIDA) revealed a significant number of odor-active compounds, such as (E)-2-nonenal, (E,Z)- and (E,E)-2,4-decadienal, (E)-4,5-epoxy-(E)-2-decenal, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, and vanillin, with high odor activities in both wheat flours. The amounts and, consequently, the aroma potencies of vanillin, (E,E)-2,4-decadienal, and 3-(methylthio)propanal were much higher in the WWF than in the WF 550 samples. Fermentation of suspensions of both flours with lactic acid bacteria did not generate new odorants; however, many compounds, such as acetic acid or 3-methylbutanal, were increased, whereas aldehydes (formed from the degradation of unsaturated fatty acids) were decreased. Comparing the odorant concentrations present before and after fermentation gave evidence that the main influence of the microorganisms on sourdough aroma is to either enhance or decrease specific volatiles already present in the flour. A comparison with literature data indicated that most of these odorants are also important for the bread crumb aroma present after baking of the dough.     

Precursors of chicken flavor. II. Identification of key flavor precursors using sensory methods

Sensory evaluation was used to identify flavor precursors that are critical for flavor development in cooked chicken. Among the potential flavor precursors studied (thiamin, inosine 5'-monophosphate, ribose, ribose-5-phosphate, glucose, and glucose-6-phosphate), ribose appears most important for chicken aroma. An elevated concentration (added or natural) of only 2-4-fold the natural concentration gives an increase in the selected aroma and flavor attributes of cooked chicken meat. Assessment of the volatile odor compounds by gas chromatography-odor assessment and gas chromatography-mass spectrometry showed that ribose increased odors described as "roasted" and "chicken" and that the changes in odor due to additional ribose are probably caused by elevated concentrations of compounds such as 2-furanmethanethiol, 2-methyl-3-furanthiol, and 3-methylthiopropanal.     

Aroma extract dilution analysis of Cv. Marion (Rubus spp. hyb) and Cv. Evergreen (R. laciniatus L.) blackberries

Cultivar Marion and Evergreen blackberry aromas were analyzed by aroma extract dilution analysis. Sixty-three aromas were identified (some tentatively) by mass spectrometry and gas chromatography-retention time; 48 were common to both cultivars, and 27 have not been previously reported in blackberry fruit. A comparison of cultivars shows that both have comparable compound types and numbers but with widely differing aroma impacts, as measured by flavor dilution (FD) factors. Ethyl 2-methylbutanoate, ethyl 2-methylpropanoate, hexanal, furanones (2,5-dimethyl-4-hydroxy-3-(2H)-furanone, 2-ethyl-4-hydroxy-5-methyl-3-(2H)-furanone, 4-hydroxy-5-methyl-3-(2H)-furanone, 4,5-dimethyl-3-hydroxy-2-(5H)-furanone, and 5-ethyl-3-hydroxy-4-methyl-2-(5H)-furanone), and sulfur compounds (thiophene, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 2-methylthiophene, and methional) were prominent in Evergreen (FD 512-2048). Except for ethyl 2-methylpropanoate, these same compounds were also prominent in Marion, but the FD factors varied significantly (FD 8-256) from Evergreen. The aroma profile of blackberry is complex, as no single volatile was unanimously described as characteristically blackberry.     

Analysis of volatiles in meat from Iberian pigs and lean pigs after refrigeration and cooking by using SPME-GC-MS

The volatile compounds generated in meat from Iberian and lean pigs after four different treatments (raw, refrigerated, cooked, and refrigerated cooked meat) were analyzed. The different treatments showed different volatile profiles. Methyl alcohols and ketones (such as 2-ethyl-hexan-1-ol, 2-methyl-butan-1-ol, 3-methyl-butan-1-ol, and 3-hydroxy-butan-2-one) were the most representative in refrigerated meat because of the degradation of carbohydrates and proteins together with the Strecker degradation pathway. Lipid-derived volatiles were the most abundant in cooked meat and refrigerated cooked meat. Meat from different pig breeds presented different volatile profiles, probably due to different enzymatic and oxidative deterioration susceptibility. Otherwise, the fat content and its compositional characteristics also played an important role in the generation of volatiles. As compared to samples from lean pigs, muscles from Iberian pigs showed a higher content of heme iron that may have promoted the generation of higher content of total lipid-derived volatiles during the refrigeration of cooked meat. Despite that, the formation of volatiles with low thresholds and related to intense rancidity perception likely to be derived from polyunsaturated fatty acids was higher in lean pork than in meat from Iberian pigs. This might be expected to lead to a more intense development of a warmed over flavor during refrigeration of cooked samples from lean pigs.     

Identification and quantitation of key aroma compounds formed in Maillard-type reactions of fructose with cysteamine or isothiaproline (1,3-thiazolidine-2-carboxylic acid)

Fructose was reacted in the presence of either cysteamine (model A) or isothiaproline (model B) in aqueous buffer at 145 degrees C and pH 7.0. Application of an aroma extract dilution analysis on the bulk of the volatile compounds formed in model A revealed 5-acetyl-3,4-dihydro-2H-1,4-thiazine (19), N-(2-mercaptoethyl)-1,3-thiazolidine (16), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (15), and 2-acetyl-2-thiazoline (11) as the key aroma compounds among the 10 odorants detected. A similar set of aroma compounds was formed when isothiaproline was reacted (model B), but the flavor dilution factors were generally lower. Substitution of the buffer by silica gel/water (9 + 1 w/w) in both models and application of 150 degrees C for 10 min also gave the same key odorants from both thio compounds; however, under these conditions isothiaproline was the better precursor of, in particular, 19 and 11. Quantitative measurements performed by means of stable isotope dilution assays revealed a significant effect of the pH on odorant formation. For example, in model A, formation of 19 as well as of 11 was suppressed at pH values <5.0. A clear maximum was, however, found for 19 at pH 7.0 (approximately 1 mol % yield), whereas 11 increased with increasing pH from 7.0 to 9.0.     

Effect of heated sunflower oil and dietary supplements on the composition, oxidative stability, and sensory quality of dark chicken meat

A factorial design was used to study the effect of dietary oxidized sunflower oils (fresh, heated at low temperatures, and heated at high temperatures), DL-alpha-tocopheryl acetate (0 or 100 mg/kg), and Zn supplementation (0 or 600 mg/kg) on the composition, oxidative stability, and sensory quality of dark chicken meat with skin from animals fed with a Se supplement (Se-enriched yeast, 0.6 mg of Se/kg). The positional and geometrical isomers of linoleic acid were increased in raw meat from chickens fed oils oxidized at high temperatures. In addition, supplementation with alpha-tocopheryl acetate increased the alpha-tocopherol content, whereas 2-thiobarbituric acid (TBA) values and lipid hydroperoxide content were reduced. Likewise, TBA values, rancid aroma, and rancid flavor also decreased in cooked dark meat. However, none of the dietary factors studied affected consumer acceptability scores of cooked meat. Furthermore, Zn supplementation increased the Se content in raw meat.     

Identification of characteristic aroma-active compounds from water dropwort (Oenanthe javanica DC.)

Characteristic aroma components of water dropwort (Oenanthe javanica DC.) were evaluated by aroma extract dilution analysis and solid-phase microextraction-gas chromatography-olfactometry. Alpha-Terpinolene (plastic/cucumber-like) was the most intense aroma-active compound in water dropwort. Other potent aroma-active compounds included p-cymene (kerosene-like), alpha-terpinene (lemon), (E)-caryophyllene (woody), (Z,E)-alpha-farnesene (woody), hexanal (green), (Z)-3-hexenol (green), phenylacetaldehyde (honey), (E)-2-nonenal (cucumber), bornyl acetate (cooked vegetable), and gamma-terpinene (lemon). Of these, p-cymene was believed to be primarily responsible for the distinct kerosene-like aroma note of water dropwort. The aroma property of p-cymene was dependent on its concentration and was described as kerosene-like at relatively high concentrations but changed to citrus and green aroma notes at low concentrations.