Identification of new strawberry sulfur volatiles and changes during maturation

Two Florida strawberry cultivars, 'Strawberry Festival' and 'Florida Radiance', were harvested at five fruit developmental stages (white, half red, three-quarter red, full ripe, and overripe) at four harvest dates. A static headspace solid-phase microextraction (SPME) sampling technique coupled with gas chromatography (GC) using pulsed flame photometric detection (PFPD) was employed to measure 16 sulfur volatiles in these strawberries. A total of 7 sulfur volatiles have been previously reported, and 9 are reported for the first time in strawberries. Newly identified sulfur volatiles include methyl thiopropionate, ethyl thiobutanoate, methyl thiohexanoate, methyl (methylthio)acetate, ethyl (methylthio)acetate, methyl 2-(methylthio)butyrate, methyl 3-(methylthio)propionate, ethyl 3-(methylthio)propionate, and methyl thiooctanoate. Identifications were based on matching sulfur peak linear retention indexes (LRIs) of unknowns with authentic standards and gas chromatography-mass spectrometry (GC-MS) data. Concentrations were determined using both internal and external standards. Most sulfur volatiles increased with increasing maturity, with only concentrations of hydrogen sulfide and methanethiol remaining relatively consistent at all five stages. At the white and half red stages, most sulfur volatiles consisted of various alkyl sulfides. At three-quarter red (commercial ripe), full ripe, and overripe stages, the majority of sulfur volatiles consisted of sulfur esters. Most sulfur volatiles increased dramatically between the commercial ripe, full ripe, and overripe stages, increasing as much as 100% between full ripe and overripe. Principal component analysis indicated that sulfur volatiles could be used to distinguish overripe from full ripe and commercial ripe berries.     

Identification based on quantitative measurements and aroma recombination of the character impact odorants in a Bavarian Pilsner-type beer

Application of aroma extract dilution analysis on the volatiles isolated from a Bavarian Pilsner-type beer revealed 40 odor-active constituents in the flavor dilution (FD) factor range of 16-2048, among which ethyl octanoate, (E)-beta-damascenone, 2- and 3-methylbutanoic acid, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone showed the highest FD factor of 2048. After quantitation of the 26 odorants showing FD factors > or =128 by stable isotope dilution analysis and determination of their odor thresholds in water, odor acitivity values (OAVs) were calculated. The results indicated ethanol, (E)-beta-damascenone, (R)-linalool, acetaldehyde, and ethyl butanoate with the highest OAVs, followed by ethyl 2-methylpropanoate and ethyl 4-methylpentanoate, which was previously unknown in beer. Finally, the overall aroma of the beer could be mimicked for the first time by recombining 22 reference odorants in the same concentrations as they occurred in the beer using ethanol/water as the matrix.     

Impact of growing environment on chickasaw blackberry (Rubus L.) aroma evaluated by gas chromatography olfactometry dilution analysis

The aroma extract of Chickasaw blackberry (Rubus L.) was separated with silica gel normal phase chromatography into six fractions. Gas chromatography-olfactometry (GCO) was performed on each fraction to identify aroma active compounds. Aroma extraction dilution analysis (AEDA) was employed to characterize the aroma profile of Chickasaw blackberries from two growing regions of the United States: Oregon and Arkansas. Comparative AEDA analysis showed that the berries grown in the two regions had similar aroma compositions; however, those odorants had various aroma impacts in each region. The compounds with high flavor dilution factors in Oregon's Chickasaw were ethyl butanoate, linalool, methional, trans,cis-2,6-nonadienal, cis-1,5-octadien-3-one, and 2,5-dimethyl-4-hydroxy-3(2H)-furanone, whereas in the Chickasaw grown in Arkansas, they were ethyl butanoate, linalool, methional, ethyl 2-methylbutanoate, beta-damascenone, and geraniol.     

Evaluation of aroma differences between hand-squeezed juices from Valencia late and Navel oranges by quantitation of key odorants and flavor reconstitution experiments

Twenty-five odor-active compounds were quantified in hand-squeezed juices of Valencia late and Navel oranges using stable isotope dilution assays. Odor activity values (OAVs, ratio of the concentration to odor thresholds) based on odor thresholds in water were calculated for the entire set of aroma compounds in both varieties. It was shown that due to their high OAVs, the fruity-smelling esters ethyl 2-methylpropanoate, ethyl butanoate, (S)-ethyl 2-methylbutanoate, and 3a,4,5,7a-tetrahydro-3,6-dimethyl-2(3H)-benzofuranone (wine lactone), the grassy smelling (Z)-hex-3-enal, and the citrus-like decanal were the most potent odorants in both juices. The weaker fruity note in the Navel oranges was clearly correlated with significantly lower OAVs of all fruity-smelling esters but a higher OAV of (Z)-3-hexenal compared to Valencia late. Model solutions simulating the odor of both orange varieties confirmed the findings of the quantitation studies.     

Characterization of the key aroma compounds in an american bourbon whisky by quantitative measurements, aroma recombination, and omission studies

Thirty-one of the 45 odor-active compounds previously identified by us in an American Bourbon whisky were quantified by stable isotope dilution assays. Also for this purpose, new synthetic pathways were developed for the synthesis of the deuterium-labeled whisky lactone as well as for gamma-nona- and gamma-decalactone. To obtain the odor activity values (OAVs), the concentrations measured were divided by the odor thresholds of the odorants determined in water/ethanol (6:4 by vol.). Twenty-six aroma compounds showed OAVs >1, among which ethanol, ethyl (S)-2-methylbutanoate, 3-methylbutanal, 4-hydroxy-3-methoxybenzaldehyde, (E)-beta-damascenone, ethyl hexanoate, ethyl butanoate, ethyl octanoate, 2-methylpropanal, (3S,4S)- cis-whiskylactone, (E, E)-2,4-decadienal, 4-allyl-2-methoxyphenol, ethyl-3-methylbutanoate, and ethyl 2-methylpropanoate showed the highest values. The overall aroma of the Bourbon whisky could be mimicked by an aroma recombinate consisting of the 26 key odorants in their actual concentrations in whisky using water/ethanol (6:4 by vol.) as the matrix. Omission experiments corroborated the importance of, in particular, 4-hydroxy-3-methoxybenzaldehyde, (3S,4S)-cis-whiskylactone, ethanol, and the entire group of esters for the overall aroma of the Bourbon whisky.     

Characterization of the key aroma compounds in soy sauce using approaches of molecular sensory science

Application of aroma extract dilution analysis (AEDA) to the volatiles isolated from a commercial Japanese soy sauce revealed 30 odor-active compounds in the flavor dilution (FD) factor range of 8-4096, among which 2-phenylethanol showed the highest FD factor of 4096, followed by 3-(methylsulfanyl)propanal (methional), the tautomers 4-hydroxy-5-ethyl-2-methyl- and 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone (4-HEMF), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (4-HDF), and 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolone), all showing FD factors of 1024. Thirteen odorants were quantified by stable isotope dilution assays, and their odor activity values (OAVs) were calculated as ratio of their concentrations and odor thresholds in water. Among them, 3-methylbutanal (malty), sotolone (seasoning-like), 4-HEMF (caramel-like), 2-methylbutanal (malty), methional (cooked potato), ethanol (alcoholic), and ethyl 2-methylpropanoate (fruity) showed the highest OAVs (>200). An aqueous model aroma mixture containing 13 odorants, which had been identified with the highest OAVs, in concentrations that occur in the soy sauce showed a good similarity with the overall aroma of the soy sauce itself. Heat treatment of the soy sauce resulted in a clear change of the overall aroma. Quantitation of selected odorants revealed a significant decrease in sotolone and, in particular, increases in 2-acetyl-1-pyrroline, 4-HDMF, and 4-HEMF induced by heating.     

Influence of strawberry yogurt composition on aroma release

The primary objective of this study was to determine how yogurt ingredients affect aroma release in the mouth during eating. A model strawberry flavor consisting of ethyl butanoate, ethyl 3-methylbutanoate, (Z)-hex-3-enol, 2-methylbutanoic acid, 5-hexylhydro-2(3H)-furanone, and 3-methyl-3-phenylglycidic acid ethyl ester was added to unflavored, unsweetened yogurt that had different added sweeteners and hydrocolloids. In all, 12 yogurt formulations were examined to determine the effects of gelatin, modified food starch, pectin, sucrose, high-fructose corn syrup, and aspartame on aroma release. Aroma release was monitored by breath-by-breath analysis (proton-transfer reaction-mass spectrometry) during eating of the test yogurts. Results showed aroma release of the ethyl butanoate, (Z)-hex-3-enol, and ethyl 3-methylbutanoate to be suppressed by sweeteners, with 55 DE high-fructose corn syrup having the greatest effect. Addition of thickening agents had no significant effect on the aroma release profiles of the compounds under study.     

Characterization of the key aroma compounds in the beverage prepared from Darjeeling black tea: quantitative differences between tea leaves and infusion

By application of the aroma extract dilution analysis on the volatile fraction isolated from a black tea infusion (Darjeeling Gold Selection), vanillin (vanilla-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel), 2-phenylethanol (flowery), and (E,E,Z)-2,4,6-nonatrienal (oat-flake-like) were identified with the highest flavor dilution (FD) factors among the 24 odor-active compounds detected in the FD factor range of 4-128. Quantitative measurements performed by means of stable isotope dilution assays and a calculation of odor activity values (OAVs; ratio of concentration to odor threshold in water) revealed, in particular, the previously unknown tea constituent (E,E,Z)-2,4,6-nonatrienal as a key odorant in the infusion and confirmed the important role of linalool and geraniol for the tea aroma. An aroma recombinate performed by the 18 odorants for which OAVs > 1 were determined in their "natural" concentrations matched the overall aroma of the tea beverage. In the black tea leaves, a total of 42 odorants were identified, most of which were identical with those in the beverage prepared thereof. However, quantitative measurements indicated that, in particular, geraniol, but also eight further odorants were significantly increased in the infusion as compared to their concentration in the leaves.     

Identification of aroma-active compounds in Jiashi muskmelon juice by GC-O-MS and OAV calculation

To identify aromatic compounds in Jiashi melon juice, gas chromatography-mass spectrometry-olfactometry (GC-MS-O) analysis was used. Odor activity values (OAVs) were also calculated on the basis of the qualitative and quantitative analysis of volatile compounds. Results showed that 42 volatiles were identified, among which 4 compounds, namely, diethyl carbonate, isophorone, 2-butoxyethyl acetate, and menthol, were identified or tentatively identified for the first time as volatiles in melon fruit. Twelve compounds, namely, (2E,6Z)-nona-2,6-dienal, (3Z,6Z)-nona-3,6-dien-1-ol, ethyl butanoate, ethyl 2-methylbutyrate, ethyl 2-methylpropanoate, (Z)-non-6-enal, (E)-2-nonenal, heptanal, methyl 2-methylbutyrate, nonanal, hexanal, and 2-methylpropyl acetate, were identified as the potent odorants of Jiashi melon juice by both OAV and detection frequency analysis (DFA). In addition, seven odorants were detected by all of the panelists and showed higher OAVs, indicating that DFA and OAV resulted in relatively similar "Jiashi" melon aroma patterns.     

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.     

Characterization of the aroma-active compounds in pink guava (Psidium guajava, L.) by application of the aroma extract dilution analysis

The volatiles present in fresh, pink-fleshed Colombian guavas ( Psidium guajava, L.), variety regional rojo, were carefully isolated by solvent extraction followed by solvent-assisted flavor evaporation, and the aroma-active areas in the gas chromatogram were screened by application of the aroma extract dilution analysis. The results of the identification experiments in combination with the FD factors revealed 4-methoxy-2,5-dimethyl-3(2 H)-furanone, 4-hydroxy-2,5-dimethyl-3(2 H)-furanone, 3-sulfanylhexyl acetate, and 3-sulfanyl-1-hexanol followed by 3-hydroxy-4,5-dimethyl-2(5 H)-furanone, ( Z)-3-hexenal, trans-4,5-epoxy-( E)-2-decenal, cinnamyl alcohol, ethyl butanoate, hexanal, methional, and cinnamyl acetate as important aroma contributors. Enantioselective gas chromatography revealed an enantiomeric distribution close to the racemate in 3-sulfanylhexyl acetate as well as in 3-sulfanyl-1-hexanol. In addition, two fruity smelling diastereomeric methyl 2-hydroxy-3-methylpentanoates were identified as the ( R,S)- and the ( S,S)-isomers, whereas the ( S,R)- and ( R,R)-isomers were absent. Seven odorants were identified for the first time in guavas, among them 3-sulfanylhexyl acetate, 3-sulfanyl-1-hexanol, 3-hydroxy-4,5-dimethyl-2(5 H)-furanone, trans-4,5-epoxy-( E)-2-decenal, and methional were the most odor-active.     

Comparison of three lychee cultivar odor profiles using gas chromatography-olfactometry and gas chromatography-sulfur detection

Odor volatiles in three major lychee cultivars (Mauritius, Brewster, and Hak Ip) were examined using gas chromatography-olfactometry, gas chromatography-mass spectrometry, and gas chromatography-pulsed flame photometric detection. Fifty-nine odor-active compounds were observed including 11 peaks, which were associated with sulfur detector responses. Eight sulfur volatiles were identified as follows: hydrogen sulfide, dimethyl sulfide, diethyl disulfide, 2-acetyl-2-thiazoline, 2-methyl thiazole, 2,4-dithiopentane, dimethyl trisulfide, and methional. Mauritius contained 25% and Brewster contained 81% as much total sulfur volatiles as Hak Ip. Cultivars were evaluated using eight odor attributes: floral, honey, green/woody, tropical fruit, peach/apricot, citrus, cabbage, and garlic. Major odor differences in cabbage and garlic attributes correlated with cultivar sulfur volatile composition. The 24 odor volatiles common to all three cultivars were acetaldehyde, ethanol, ethyl-3-methylbutanoate, diethyl disulfide, 2-methyl thiazole, 1-octen-3-one, cis-rose oxide, hexanol, dimethyl trisulfide, alpha-thujone, methional, 2-ethyl hexanol, citronellal, (E)-2-nonenal, linalool, octanol, (E,Z)-2,6-nonadienal, menthol, 2-acetyl-2-thiazoline, (E,E)-2,4-nonadienal, beta-damascenone, 2-phenylethanol, beta-ionone, and 4-vinyl-guaiacol.     

Quality assessment of strawberries (Fragaria species)

Several cultivars of strawberries (Fragaria sp.), grown under different conditions, were analyzed by both sensory and instrumental methods. The overall appreciation, as expressed by consumers, was mainly reflected by attributes such as sweetness and aroma. No strong correlation was obtained with odor, acidity, juiciness, or firmness. The sensory quality of strawberries can be assessed with a good level of confidence by measuring the total sugar level ( degrees Brix) and the total amount of volatile compounds. Sorting out samples using the score obtained with a hedonic test (called the "hedonic classification method") allowed the correlation between consumers' appreciation and instrumental data to be considerably strengthened. On the basis of the results obtained, a quality model was proposed. Quantitative GC-FID analyses were performed to determine the major aroma components of strawberries. Methyl butanoate, ethyl butanoate, methyl hexanoate, cis-3-hexenyl acetate, and linalool were identified as the most important compounds for the taste and aroma of strawberries.     

Characterization of the key odorants in raw Italian hazelnuts ( Corylus avellana L. var. Tonda Romana) and roasted hazelnut paste by means of molecular sensory science

The concentrations of 19 odorants, recently characterized by GC-olfactometry and aroma extract dilution analysis as the most odor-active compounds in raw hazelnuts, were quantitated by stable isotope dilution assays (SIDA). Calculation of odor activity values (OAV) on the basis of odor thresholds in oil revealed high OAVs, in particular for linalool, 5-methyl-4-heptanone, 2-methoxy-3,5-dimethylpyrazine, and 4-methylphenol. A model mixture in sunflower oil containing the 13 odorants showing OAVs above 1 in their natural concentrations resulted in a good similarity compared to the overall nut-like, fruity aroma of the raw hazelnuts. Quantitation of the 25 most odor-active compounds in roasted hazelnut paste by SIDA showed clear changes in the concentrations of most odorants, and formation of new odor-active compounds induced by the roasting process was observed. The highest OAVs were calculated for 3-methylbutanal (malty), 2,3-pentanedione (buttery), 2-acetyl-1-pyrroline (popcorn), and (Z)-2-nonenal (fatty), followed by dimethyl trisulfide, 2-furfurylthiol, 2,3-butanedione, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone. The aroma of a model mixture containing the 19 odorants with OAVs above 1 in their actual concentrations in the roasted nut material was judged to elicit a very good similarity to the popcorn-like, coffee-like, and sweet-smoky aroma of the roasted hazelnut paste. New SIDAs were developed for the quantitation of 5-methyl-4-heptanone, 5-methyl-(E)-2-hepten-4-one, 2-thenylthiol, and 3,5,5-trimethyl-2(5H)-furanone.     

Characterization of odor-active compounds in guava wine

The volatile compounds of guava wine were isolated by continuous solvent extraction and analyzed by GC-FID and GC-MS. A total of 124 volatile constituents were detected, and 102 of them were positively identified. The composition of guava wine included 52 esters, 24 alcohols, 11 ketones, 7 acids, 6 aldehydes, 6 terpenes, 4 phenols and derivatives, 4 lactones, 4 sulfur-compounds, and 5 miscellaneous compounds. The aroma-active areas in the gas chromatogram were screened by application of the aroma extract dilution analysis and by odor activity values. Twelve odorants were considered as odor-active volatiles: (E)-β-damascenone, ethyl octanoate, ethyl 3-phenylpropanoate, ethyl hexanoate, 3-methylbutyl acetate, 2-methyltetrahydrothiophen-3-one, 2,5-dimethyl-4-methoxy-3(2H)-furanone, ethyl (E)-cinnamate, ethyl butanoate, (E)-cinnamyl acetate, 3-phenylpropyl acetate, and ethyl 2-methylpropanoate.     

Volatile compounds of selected strawberry varieties analyzed by purge-and-trap headspace GC-MS

Six strawberry (Fragaria x ananassa Duch.) varieties, Senga Sengana, Jonsok, Polka, Korona, Bounty, and Honeoye, were studied in relation to composition of their volatile headspace compounds collected by dynamic purge-and-trap concentration. Also, the influence of cultivation technique on the volatile compounds was tested by comparing conventionally and organically cultivated strawberry varieties. In addition, the effect of geographical origin on strawberry volatiles was investigated. The emphasis of this study was lay in the industrial utilization of strawberry. A total of 52 different volatile compounds were determined from frozen strawberries grown in 1997 and 1998. In addition to individual compounds, total areas of chromatogram profiles were compared. The major esters were found to be methyl butanoate, ethyl butanoate, methyl hexanoate, and ethyl hexanoate. With the application of principal component analysis and analysis of variance to the data matrix, the varieties were classified into three groups. Var. Honeoye was most different from the others. Organic cultivation had no effect on strawberry volatiles.     

Identification of potent odorants in different cultivars of snake fruit [Salacca zalacca (Gaert.) Voss] using gas chromatography-olfactometry

Three cultivars of snake fruits, Pondoh Hitam, Pondoh Super, and Gading, were freshly extracted using liquid-liquid extraction. The aroma compounds of the three samples were analyzed by GC-MS and GC-olfactometry using the nasal impact frequency (NIF) method. A total of 24 odor-active compounds were associated with the aroma of snake fruit. Methyl 3-methylpentanoate was regarded as the character impact odorant of typical snake fruit aroma. 2-Methylbutanoic acid, 3-methylpentanoic acid, and an unknown odorant with very high intensity were found to be responsible for the snake fruit's sweaty odor. Other odorants including methyl 3-methyl-2-butenoate (overripe fruity, ethereal), methyl 3-methyl-2-pentenoate (ethereal, strong green, woody), and 2,5-dimethyl-4-hydroxy-3[2]-furanone (caramel, sweet, cotton candy-like) contribute to the overall aroma of snake fruit. Methyl dihydrojasmonate and isoeugenol, which also have odor impact, were identified for the first time as snake fruit volatiles. The main differences between the aroma of Pondoh and Gading cultivars could be attributed to the olfactory attributes (metallic, chemical, rubbery, strong green, and woody), which were perceived by most of the panelists in the Pondoh samples but were not detected in the Gading samples. This work is a prerequisite for effective selection of salak genotypes with optimal aroma profiles for high consumer acceptance.     

Similarities in the aroma chemistry of Gewürztraminer variety wines and lychee (Litchi chinesis sonn.) fruit

GC/O analysis of canned lychees indicated that cis-rose oxide, linalool, ethyl isohexanoate, geraniol, furaneol, vanillin, (E)-2-nonenal, beta-damascenone, isovaleric acid, and (E)-furan linalool oxide were the most odor potent compounds detected in the fruit extracts. However, on the basis of calculated odor activity values (OAVs), cis-rose oxide, beta-damascenone, linalool, furaneol, ethyl isobutyrate, (E)-2-nonenal, ethyl isohexanoate, geraniol, and delta-decalactone were determined to be the main contributors of canned lychee aroma. When these results were compared with GC/O results of fresh lychees and Gewürztraminer wine, 12 common odor-active volatile compounds were found in all three products. These included cis-rose oxide, ethyl hexanoate/ethyl isohexanoate, beta-damascenone, linalool, ethyl isobutyrate, geraniol, ethyl 2-methylbutyrate, 2-phenylethanol, furaneol, vanillin, citronellol, and phenethyl acetate. On the basis of OAVs, cis-rose oxide had the highest values among the common odorants in the three products, indicating its importance to the aroma of both lychee fruit and Gewürztraminer wines. Other compounds that had significant OAVs included beta-damascenone, linalool, furaneol, ethyl hexanoate, and geraniol. This indicated that while differences exist in the aroma profile of lychee and Gewürztraminer, the common odorants detected in both fruit and wine, particularly cis-rose oxide, were responsible for the lychee aroma in Gewürztraminer wine. When headspace SPME was used as a rapid analytical tool to detect the levels of selected aroma compounds deemed important to lychee aroma in Gewürztraminer-type wines, cis-rose oxide, linalool, and geraniol were found to be at relatively higher levels in Gewürztraminers. No cis-rose oxide was detected in the control wines (Chardonnay and Riesling), while lower levels were detected in the Gewürztraminer-hybrid wine Traminette. Gewürztraminers produced in the Alsace region showed differences in the levels of the 3 monoterpenes when compared to those from New York State, which could be attributed to differences in viticultural and enological practices between regions.     

Comparison of odor-active compounds from six distinctly different rice flavor types

Using a dynamic headspace system with Tenax trap, GC-MS, GC-olfactometry (GC-O), and multivariate analysis, the aroma chemistry of six distinctly different rice flavor types (basmati, jasmine, two Korean japonica cultivars, black rice, and a nonaromatic rice) was analyzed. A total of 36 odorants from cooked samples were characterized by trained assessors. Twenty-five odorants had an intermediate or greater intensity (odor intensity >or= 3) and were considered to be major odor-active compounds. Their odor thresholds in air were determined using GC-O. 2-Acetyl-1-pyrroline (2-AP) had the lowest odor threshold (0.02 ng/L) followed by 11 aldehydes (ranging from 0.09 to 3.1 ng/L), guaiacol (1.5 ng/L), and 1-octen-3-ol (2.7 ng/L). On the basis of odor thresholds and odor activity values (OAVs), the importance of each major odor-active compound was assessed. OAVs for 2-AP, hexanal, ( E)-2-nonenal, octanal, heptanal, and nonanal comprised >97% of the relative proportion of OAVs from each rice flavor type, even though the relative proportion varied among samples. Thirteen odor-active compounds [2-AP, hexanal, ( E)-2-nonenal, octanal, heptanal, nonanal, 1-octen-3-ol, ( E)-2-octenal, ( E, E)-2,4-nonadienal, 2-heptanone, ( E, E)-2,4-decadienal, decanal, and guaiacol] among the six flavor types were the primary compounds explaining the differences in aroma. Multivariate analysis demonstrated that the individual rice flavor types could be separated and characterized using these compounds, which may be of potential use in rice-breeding programs focusing on flavor.     

Characterization of aroma compounds in apple cider using solvent-assisted flavor evaporation and headspace solid-phase microextraction

The aroma-active compounds in two apple ciders were identified using gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (MS) techniques. The volatile compounds were extracted using solvent-assisted flavor evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). On the basis of odor intensity, the most important aroma compounds in the two apple cider samples were 2-phenylethanol, butanoic acid, octanoic acid, 2-methylbutanoic acid, 2-phenylethyl acetate, ethyl 2-methylbutanoate, ethyl butanoate, ethyl hexanoate, 4-ethylguaiacol, eugenol, and 4-vinylphenol. Sulfur-containing compounds, terpene derivatives, and lactones were also detected in ciders. Although most of the aroma compounds were common in both ciders, the aroma intensities were different. Comparison of extraction techniques showed that the SAFE technique had a higher recovery for acids and hydroxy-containing compounds, whereas the HS-SPME technique had a higher recovery for esters and highly volatile compounds.