Stable Isotope Dilution Assay Research Articles

Analysis of 13 Alternaria mycotoxins including modified forms in beer

A multi-mycotoxin LC-MS/MS method was developed to quantify 13 free and modified Alternaria toxins in different beer types by applying a combination of stable-isotope dilution assays (SIDAs) and matrix-matched calibration. With limits of detection (LODs) between 0.03 µg/L (alternariol monomethyl ether, AME) and 5.48 µg/L (altenuene, ALT), limits of quantitation (LOQs) between 0.09 µg/L (AME) and 16.24 µg/L (ALT), and recoveries between 72 and 113%, we obtained a sensitive and reliable method, which also covers the emerging toxins alternariol-3-glucoside (AOH-3-G), alternariol-9-glucoside (AOH-9-G), alternariol monomethyl ether-3-glucoside (AME-3-G) and alternariol-3-sulfate (AOH-3-S) and alternariol monomethylether-3-sulfate (AME-3-S). Furthermore, 50 different beer samples were analyzed, showing no contamination with Alternaria toxins apart from tenuazonic acid (TeA) in concentrations between 0.69 µg/L and 16.5 µg/L. According to this study, the exposure towards TeA through beer consumption can be considered as relatively low, as the threshold of toxicological concern (TTC) value of 1500 ng/kg body weight per day might not be reached when consuming reasonable amounts of beer.

Preliminary investigation of potent thiols in Cypriot wines made from indigenous grape varieties Xynisteri, Maratheftiko and Giannoudhi

Polyfunctional thiols have previously been shown to be key aroma compounds in Sauvignon blanc and more recently in Chardonnay wines. Their role in other wine varieties such as those made from three popular indigenous Cypriot grape varieties has remained unexplored. As an extension of a previous project that profiled the sensory and chemical characteristics of Cypriot wines and their comparison to Australian wines, this study aimed to investigate five potent thiols in Xynisteri, Maratheftiko, Giannoudhi, Pinot gris, Chardonnay and Shiraz wines. Wines were analysed utilising Stable Isotope Dilution Assay (SIDA) with derivatisation and High-Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC-MS/MS). The varietal thiols measured were 4-methyl-4-sulfanylpentan-2-one (4MSP) that has an aroma of “boxwood” and “cat urine” at high concentration, 3-sulfanylhexan-1-ol (3SH) which has been described as having a “grapefruit/tropical fruit” aroma, and 3-sulfanylhexyl acetate (3SHA) that has also been described as having an aroma of “passionfruit”. Additionally, two other potent thiols were measured including benzyl mercaptan (BM) that has an aroma of “smoke and meat” and furfuryl thiol (FFT) that has been described as having a “roasted coffee” like aroma. The reason these thiols are known as potent thiols are due to their very low aroma detection thresholds in the low ng/L (ppt) range. Of the thiols that were measured, 3SH was the only varietal thiol detected in the red wine samples. All of the white wine samples contained 3SH, BM and 3SHA, whereas 4MSP was only detected in Pinot gris and three Xynisteri wines. The potent thiol, FFT, was detected only in the Chardonnay and four of the Xynisteri wines. Interestingly the thiols that were present in the samples were found at concentrations above their aroma detection thresholds (determined in hydroalcoholic solutions), especially 3SH which was found in an order of magnitude above its aroma detection threshold. These findings provide early knowledge of the presence of these thiols in Cypriot wines, compared with Australian wines and establish any relationships between this chemical data with previous wine sensory profile data.

Chiral analysis of cis-2-methyl-4-propyl-1,3-oxathiane and identification of cis-2,4,4,6-tetramethyl-1,3-oxathiane in wine

cis-2-Methyl-4-propyl-1,3-oxathiane (cis-2-MPO), arising from 3-sulfanylhexan-1-ol (3-SH) and acetaldehyde, was recently identified in wine, but the enantiomeric distribution was unknown. Such information could reveal influences on wine aroma, given the impact of chirality on odorant molecules. Herein, a stable isotope dilution assay employing headspace solid-phase microextraction with chiral gas chromatography–mass spectrometry was developed, validated, and applied to a selection of wines. Studies with (3R)-3-SH revealed the elution order of the cis-2-MPO enantiomers and the concentrations of (2R,4S)-2-MPO and (2S,4R)-2-MPO in the studied wines ranged from undetected to 250 ng/L and 303 ng/L, respectively. Strong positive correlations were found between (3R)-3-SH and (2S,4R)-2-MPO (r = 0.654), and (3S)-3-SH and (2R,4S)-2-MPO (r = 0.860). Additionally, cis-2,4,4,6-tetramethyl-1,3-oxathiane, constituted from acetaldehyde and 4-methyl-4-sulfanylpentan-2-ol (4-MSPOH), was identified in wine for the first time. This new 1,3-oxathiane, which presents a novel fate for 4-MSPOH, was detected in wines as a single enantiomer at up to 28 ng/L.

Detection and Isolation of Emetic Bacillus cereus Toxin Cereulide by Reversed Phase Chromatography.

The emetic toxin cereulide is a 1.2 kDa dodecadepsipeptide produced by the food pathogen Bacillus cereus. As cereulide poses a serious health risk to humans, sensitive and specific detection, as well as toxin purification and quantification, methods are of utmost importance. Recently, a stable isotope dilution assay tandem mass spectrometry (SIDA–MS/MS)-based method has been described, and an method for the quantitation of cereulide in foods was established by the International Organization for Standardization (ISO). However, although this SIDA–MS/MS method is highly accurate, the sophisticated high-end MS equipment required for such measurements limits the method’s suitability for microbiological and molecular research. Thus, we aimed to develop a method for cereulide toxin detection and isolation using equipment commonly available in microbiological and biochemical research laboratories. Reproducible detection and relative quantification of cereulide was achieved, employing reversed phase chromatography (RPC). Chromatographic signals were cross validated by ultraperformance liquid chromatography–mass spectrometry (UPLC–MS/MS). The specificity of the RPC method was tested using a test panel of strains that included non-emetic representatives of the B. cereus group, emetic B. cereus strains, and cereulide-deficient isogenic mutants. In summary, the new method represents a robust, economical, and easily accessible research tool that complements existing diagnostics for the detection and quantification of cereulide.

Characterization of the Key Aroma Compounds in a Freshly Prepared Oat (Avena sativa L.) Pastry by Application of the Sensomics Approach.

Oat flour has a weak cereal-like, powdery aroma, which is significantly changed by a thermal process. Application of an aroma extract dilution analysis on a distillate obtained from oat pastry prepared under defined conditions led to the detection of 43 odor-active areas in the flavor dilution (FD) factor range of 2-8192. Among them, 3-(methylthio)propanal (cooked-potato-like), 2-acetyl-1-pyrroline (roasty, popcorn-like), vanillin (vanilla-like), 2-methoxy-4-vinylphenol (clove-like), 1-octen-3-one (mushroom-like), 2-propionyl-1-pyrroline (roasty, popcorn-like), and (E,E,Z)-2,4,6-nonatrienal (oat-like) were identified with the highest FD factors. Nine aroma compounds were identified for the first time in oats or oat products, and (E,E,Z)-2,4,6-decatrienal, also showing an oat-like odor quality, is reported for the first time in foods. Quantitation of the 36 most important compounds by means of stable isotope dilution assays followed by a calculation of odor activity values on the basis of odor thresholds in corn starch revealed 2-acetyl-1-pyrroline, vanillin, the tautomers 2-acetyl-3,4,5,6-tetra-hydropyridine and 2-acetyl-1,4,5,6-tetrahydropyridine, 3-(methylthio)propanal, 2-propionyl-1-pyrroline, and methanethiol as the key aroma-active compounds. An aroma recombinate prepared in odorless oat pastry material containing 30 odorants in the concentrations determined in the oat pastry was able to successfully mimic the overall aroma profile of the original oat pastry.

Changes in the Concentrations of Key Aroma Compounds in Oat (Avena sativa) Flour during Manufacturing of Oat Pastry.

Application of the aroma extract dilution analysis on the volatiles isolated from oat flour revealed 30 aroma-active compounds in the flavor dilution (FD) factor range of 2-8192, among which oat-flour-like smelling (E,E,Z)-2,4,6-nonatrienal showed by far the highest FD factor. Quantitation performed by stable isotope dilution assays and a calculation of odor activity values (OAV; ratio of the concentration to odor threshold) of 23 odorants showed an OAV of above 1. Among them, vanillin, (E,E,Z)-2,4,6-nonatrienal, 2-acetyl-1-pyrroline, 3-methylbutanoic acid, and 2-methoxy-4-vinylphenol showed the highest OAVs. In a heated (70 °C for 30 min) oat dough prepared by kneading the oat flour in the presence of sucrose and water, 34 aroma-active compounds were identified, among which 17 compounds appeared with an OAV of ≥1. During frying, the weak cereal-like aroma of the oat flour and the oat dough was changed with the generation of an intense roasty, popcorn-like aroma attribute. A comparison to recently published data on oat pastry prepared by toasting of the same dough showed a clear increase in the overall aroma intensity from flour to pastry, in particular, in the popcorn-like, roasty odor impression. Especially considerable increases in the concentrations of the popcorn-like smelling compounds 2-acetyl-1-pyrroline, 2-acetyl-3,4,5,6- and 2-acetyl-1,4,5,6-tetrahydropyridine, 2-propionyl-1-pyrroline, and 2-acetyl-2-thiazoline were measured. In addition, the concentrations of the Strecker aldehydes 2- and 3-methylbutanal, phenylacetaldehyde, and 3-(methyldithio)propanal were also much increased during the toasting process. In contrast, in line with the overall aroma profile, particularly the concentration of the oat-like smelling compound (E,E,Z)-2,4,6-nonatrienal was decreased during processing. The formation and precursors of the key aroma compounds are discussed.

Exploring the Characteristic Aroma of Beef from Japanese Black Cattle (Japanese Wagyu) via Sensory Evaluation and Gas Chromatography-Olfactometry.

Beef from Japanese Black cattle (Japanese Wagyu) is renowned for its flavor characteristics. To clarify the key metabolites contributing to this rich and sweet aroma of beef, an omics analysis combined with GC-olfactometry (GC-O) and metabolomics analysis with gas chromatography–mass spectrometry (GC-MS) were applied. GC-O analysis identified 39 odor-active odorants from the volatile fraction of boiled beef distilled by solvent-assisted flavor evaporation. Eight odorants predicted to contribute to Wagyu beef aroma were compared between Japanese Black cattle and Holstein cattle using a stable isotope dilution assay with GC–tandem quadrupole mass spectrometry. By correlating the sensory evaluation values of retronasal aroma, γ-hexalactone, γ-d2ecalactone, and γ-undecalactone showed a high correlation with the Wagyu beef aroma. Metabolomics data revealed a high correlation between the amounts of odorants and multiple metabolites, such as glutamine, decanoic acid, lactic acid, and phosphoric acid. These results provide useful information for assessing the aroma and quality of beef.

Risk screening of mycotoxins and their derivatives in dairy products using a stable isotope dilution assay and LC-MS/MS.

An liquid chromatography-tandem mass spectrometry method coupled with a stable isotope dilution assay was established for the simultaneous detection of 17 mycotoxins and their derivatives (aflatoxins B1 , B2 , G1 , G2 , M1 , and M2 ; fumonisins B1 and B2 ; ochratoxin A; zearalenone; zearalanone; α-zearalanol; α-zearalenol; T-2 toxin; deoxynivalenol; deepoxy-deoxynivalenol; and sterigmatocystin) in milk and dairy products. The mycotoxins were extracted with acidified acetonitrile and the lipids were removed using a Captiva EMR-lipid column. The average recoveries of the target compounds from samples spiked at three different concentrations were 67-102%, and the relative standard deviations of the peak areas were less than 10%. Limits of quantification (S/N=10) of 0.004-1.25 μg/kg were achieved, which are significantly lower than the maximum levels allowed in various countries and regions for each regulated mycotoxin. Milk and yogurt products from local markets and e-commercial platforms were analyzed using the optimized method. The screening showed that aflatoxin M1 , deoxynivalenol, fumonisins B1 and B2 , and zearalenone could be found in milk and yogurt products, especially those products also containing grains or jujube ingredients, indicating that there is a risk of mycotoxins in dairy products.

Scalable synthesis of the aroma compounds d6-β-ionone and d6-β-cyclocitral for use as internal standards in stable isotope dilution assays

C13 Norisoprenoids are important aroma compounds in wine, giving positive attributes to the overall wine aroma even when found at very low levels. β-Ionone is considered one of the most important aroma compounds giving violet, woody and raspberry aromas to wine, fruits and vegetables in which it is found. Due to its potent aroma at low levels, precise analytical methods are desired for its quantification. Stable isotope dilution assay (SIDA) is one of the most important of these methods but requires the use of isotopically labelled standards. Herein, we describe the scalable synthesis of d6-β-ionone and d6-β-cyclocitral, another aroma compound with smokey and fruity notes, starting from the relatively inexpensive deuterated starting material d6-acetone.

Characterization of the Key Aroma Compounds in a Commercial Milk Chocolate by Application of the Sensomics Approach

Compared to dark chocolate, which is mainly produced from roasted cocoa and sucrose, milk chocolates contain different dairy products, such as milk powder, butter fat, or dairy cream. This difference in recipe renders a typical aroma attributed to this type of chocolate, often described as milky or creamy. To get an idea of the odorants responsible for this odor note, an aroma extract dilution analysis was applied on a distillate obtained by extraction and SAFE distillation of a commercial milk chocolate evaluated with an intense "milky, creamy" attribute. The identification experiments in combination with the flavor dilution (FD) factors revealed 48 odor-active compounds, among which phenylacetic acid (honey-like) and vanillin (vanilla-like) showed the highest FD factors followed by 2-methoxyphenol (smoky) and nonanoic acid (musty, pungent). The quantitation of 40 odorants by stable isotope dilution assays (SIDA) and a subsequent calculation of odor activity values (OAV; ratio of concentration to odor threshold) revealed dimethyl trisulfide (cabbage-like) and butanoic acid (sweaty) with the highest OAVs (>170), followed by 3-methylbutanoic acid (sweaty), acetic acid (vinegar-like), and phenylacetic acid. An aroma recombinate prepared with 39 reference odorants in the same concentrations as those determined for the compounds in the milk chocolate showed a good similarity with the overall aroma profile of the milk chocolate. A comparison of the results with the recent literature data on dark chocolates also evaluated by the Sensomics approach suggested that, in particular, methanethiol and a series of lactones may contribute to the milky, creamy odor note because these were reported with much lower odor activities in the dark chocolates.

Quantification of Allyl Methyl Sulfide, Allyl Methyl Sulfoxide, and Allyl Methyl Sulfone in Human Milk and Urine After Ingestion of Cooked and Roasted Garlic.

Due to its characteristic flavor and positive effects on human health, garlic is a highly valued food ingredient. Consumption of garlic alters the quality of body odors, which may in some instances hinder social interaction but be beneficial in other contexts, as it is assumed to contribute to early flavor learning in the breastfeeding context, for example. In previous work, allyl methyl sulfide (AMS) has been identified as the major odor-active metabolite in urine and milk, being excreted together with the odorless metabolites allyl methyl sulfoxide (AMSO) and allyl methyl sulfone (AMSO2) after ingestion of raw garlic. The present work aimed to elucidate whether commonly used culinary thermal processing steps influence the excretion profiles of garlic-derived compounds. To this aim, urine (n = 6) and milk (n = 4) samples were donated before and after ingestion of roasted and cooked garlic and investigated by gas chromatography-olfactometry/mass spectrometry, and, in the case of milk, by aroma profile analysis. The concentrations of AMS, AMSO, and AMSO2 were determined by stable isotope dilution assays. Sensory evaluations revealed that a garlic-like odor was perceivable in milk samples donated after ingestion of roasted and cooked garlic. Besides AMS, AMSO, and AMSO2, no other odor-active or odorless compounds related to the ingestion of roasted or cooked garlic were detected in the urine and milk samples. Maximum concentrations of the metabolites were detected around 1–2 h after garlic intake. In some cases, a second maximum occurred around 6 h after ingestion of garlic. The cooking procedure led to a more important reduction of metabolite concentrations than the roasting procedure. These findings suggest that intake of processed garlic leads to a transfer of odor-active and odorless metabolites into milk, which contributes to early flavor learning during breastfeeding and may also have a physiological effect on the infant.

Changes in the key aroma compounds of matsutake mushroom (Tricholoma matsutake Sing.) from Canada during pan-frying elucidated by application of the sensomics approach

A distillate obtained by solvent extraction and solvent-assisted flavor evaporation (SAFE) from raw, unprocessed matsutake mushrooms (Tricholoma matsutake Sing.) from Canada were analyzed by application of the aroma extraction dilution analysis (AEDA). Twenty-eight aroma-active compounds were detected in the flavor dilution (FD) factor range of 4–4096 among which (E)-methyl cinnamate (sweet, fruity), 4-methylquinazoline (minty), 1-octen-3-one (mushroom-like), trans-4,5-epoxy-(E)-2-decenal (metallic), and 3-methylbutanoic (sweaty) appeared with the highest FD factors. Quantitation of 18 odour-active compounds by stable isotope dilution assays, and a calculation of odour activity values (OAV ratio of concentration to odour threshold) confirmed 1-octen-3-one and (E)-methyl cinnamate as well as (E,E)-2,4-nonadienal, and 3-methylbutanal with OAVs ≥ 390 as key aroma compounds of the raw matsutake. A quantitative study on changes in the concentrations of (E)-methyl cinnamate over time suggested its rapid enzymatic formation within a few minutes. After pan-frying, among the 36 odour-active compounds located by AEDA, the highest FD factors were determined for 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like), (E)-methyl cinnamate, 4-methylquinazoline, 2H-chromen-2-one (woodruff, almond-like), 1-octen-3-one, (Z)-methyl cinnamate (fruity), trans-4,5-epoxy-(E)-2-decenal, and 2-aminoacetophenone (foxy). Based on the quantitative data, the highest OAVs ≥ 278 were calculated for (E)-methyl cinnamate, (E,E)-2,4-nonadienal, (Z)-1,5-octadien-3-one, and 3-methylbutanal. The overall aroma profile of the pan-fried matsutake could be simulated by an aroma recombinate of 17 odorants in their natural concentrations occurring in the mushrooms. A total of 14 compounds were newly identified in matsutake.

Key Odorants from Daldinia childiae

AbstractAn investigation to identify odorants responsible for a pleasant woody perfume‐like aroma produced in the fermentation broth of the fungus Daldinia childiae (JD Rogers & YM Ju) was conducted. Thirty odorants were identified from 30‐day‐old fermentations employing solvent‐assisted flavour evaporation (SAFE) and aroma extract dilution analysis (AEDA). Eleven odorants with flavour dilution (FD) factors ≥16 were quantitated using stable isotope dilution assays (SIDA), and odour activity values (OAV) determined. Odorants with the highest OAVs included guai‐11‐en‐10‐ol (woody, OAV 102689), 1‐octen‐3‐one (mushroom, OAV 9025), sotolon (maple, OAV 458), and (2E)‐non‐2‐enal (fatty, OAV 70). An odour simulation model formulated using odorants with OAV ≥ 1 closely matched the sensory attributes of natural D childiae fermentations. Guai‐11‐en‐10‐ol, a component of patchouli essential oil used widely in perfumery and cosmetics, was identified as the key impact odorant driving the pleasant woody perfume‐like aroma in D childiae fermentations. The findings from this investigation lay the groundwork for future studies on D childiae as a source for the sustainable biotechnological production of guai‐11‐en‐10‐ol with potential applications in the flavour and fragrance industry.

Comparative quantitative LC\u2013MS/MS analysis of 13 amylase/trypsin inhibitors in ancient and modern Triticum species

Amylase/trypsin inhibitors (ATIs) are major wheat allergens and they are also implicated in causing non-celiac gluten sensitivity and worsening other inflammatory conditions. With only few studies on ATI contents in different Triticum species available so far, we developed a targeted liquid chromatography-tandem mass spectrometry (LC–MS/MS) method based on stable isotope dilution assays to quantitate the 13 most important ATIs in a well-defined sample set of eight cultivars of common wheat and durum wheat (modern species), as well as spelt, emmer and einkorn (ancient species) grown at three locations in Germany, respectively. Only few ATIs with low contents were detected in einkorn. In contrast, spelt had the highest total ATI contents. Emmer and common wheat had similar total ATI contents, with durum wheat having lower contents than common wheat. Due to the lack of correlation, it was not possible to estimate ATI contents based on crude protein contents. The wheat species had a higher influence on ATI contents than the growing location and the heritability of this trait was high. Despite comparatively low intra-species variability, some cultivars were identified that may be promising candidates for breeding for naturally low ATI contents.

Key Odorants from the American Matsutake, Tricholoma magnivelare.

The American Matsutake, Tricholoma magnivelare (Peck) Redhead, is an edible wild mushroom with a distinctive aroma described as mushroom and spice with subtle floral and citrus nuances. In this study, a total of 36 odorants were identified from T. magnivelare using solvent-assisted flavor evaporation and aroma extract dilution analysis. Stable isotope dilution assays were performed to quantitate 14 odorants with flavor dilution factors ≥64. Odorants with high odor activity values (OAVs) included 1-octen-3-one (OAV 2125), linalool (OAV 650), (2E,4E)-nona-2,4-dienal (OAV 304), and 1-octen-3-ol (OAV 206). An odor simulation model matched the odor profile of the fresh mushroom. Omission studies showed that linalool, hexanal, (2E,4E)-nona-2,4-dienal, methyl (E)-3-phenylprop-2-enoate, and 1-octen-3-one or 1-octen-3-ol were essential to the aroma of T. magnivelare. Chiral chromatography showed that α-pinene was a scalemic mixture of 34% (R)-(+) to 66% (S)-(-), while 1-octen-3-ol was present as 95% (R)-(-) to 5% (S)-(+), and linalool was 96% (R)-(-) to 4% (S)-(+). These results establish the base for future investigations into the aroma chemistry of other members of the genus Tricholoma.

Characterization of the Key Aroma Constituents in Fry Breads by Means of the Sensomics Concept.

The key aroma constituents in the volatile fractions isolated FROM two differently processed fry breads by solvent-assisted flavor evaporation were characterized by an aroma extract dilution analysis (AEDA). Twenty-two compounds were identified with flavor dilution (FD) factor ranges of 2–516. Among them, 13 compounds (FD ≥ 16) were quantified by stable isotope dilution assays and analyzed by odor activity values (OAVs). Of these, 11 compounds had OAVs ≥ 1, and the highest concentrations were determined for δ-decalactone and 2,3-butanedione. Two recombination models of the fry breads showed similarity to the corresponding fry breads. Omission tests confirmed that aroma-active constituents, such as δ-decalactone (oily/peach), 2-acetyl-1-pyrroline (roasty/popcorn-like), 3-methylbutanal (malty), methional (baked potato-like), 2,3-butanedione (buttery), phenyl acetaldehyde (flowery), (E,E)-2,4-decadienal (deep-fried), butanoic acid, and 3-methylbutanoic acid, were the key aroma constituents of fry bread. In addition, 3-methoxy-4-vinylphenol (smoky) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone were also identified as important aroma constituents of fry bread.

Development of a LC-MS/MS method using stable isotope dilution for the quantification of individual B6 vitamers in fruits, vegetables, and cereals

Vitamin B6 comprises an important set of molecules tightly interwoven with the human amino acid, fatty acid, and carbohydrate metabolism. Analytical methods striving for the quantification of individual B6 vitamers so far mostly rely on methods based on HPLC in combination with fluorescence detection, but their application encounters multiple difficulties due to the chemical divergence of the single vitamers. The present study describes the development of a method based on LC-MS/MS and stable isotope dilution assay (SIDA) for the simultaneous quantification of five vitamers (PN, PL, PM, PMP, and PNG) of the B6 group in food samples. [13C3]-PN, [13C3]-PL, and [13C6]-PNG were applied as internal standards for the analysis of PN, PL, and PNG. PM and PMP were quantified via matrix-matched calibration referring to [13C3]-PN. The developed method was validated using starch matrix. The limits of detection and quantification ranged from 0.0028 to 0.02 mg/kg and from 0.0085 to 0.059 mg/kg, respectively, for all analytes. Calculated recoveries varied from 92 to 111%. Intra-injection precisions ranged from 0 to 9%, inter-day precisions from 4 to 10%, and intra-day precisions from 4 to 10%. A total of 14 plant-based food samples including fruits, vegetables, and cereals were examined for their content of vitamin B6 using the validated method. Furthermore, the first quantitation of PNG without enzymatic steps or divergent internal standards was undertaken utilizing LC-MS/MS and SIDA.

Quantitation and Taste Contribution of Sensory Active Molecules in Oat (Avena sativa L.).

A total of 59 taste-active molecules were quantitated and then rated for their individual taste impact on the basis of dose-over-threshold factors in oat flour (Avena sativa L.). A sensitive high-performance liquid chromatography-tandem mass spectrometry method was developed to quantitate bitter-tasting steroidal and furostanol saponins as well as avenanthramides. Four monoglycerides, five free fatty acids and four saponins were confirmed for the first time to be major contributors to the bitter off-taste of oats, among them 1-linoleoyl-rac-glycerol, 1-stearoyl-rac-glycerol, 1-oleoyl-rac-glycerol, 1-palmitoyl-rac-glycerol, linoleic acid, linolenic acid, oleic acid, palmitic acid, and stearic acid as well as avenacosides A and B and the recently identified furostanosides 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→3)-β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol and 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol. By means of a stable isotope dilution assay, quantitated avenanthramides 2c, 2p, 2f, 1p, 1c, 1f, and 3f were found in concentrations below their thresholds and, therefore, did not contribute to the bitter sensation of the tested oat flour.

Characterisation of the key aroma compounds in a Longjing green tea infusion (Camellia sinensis) by the sensomics approach and their quantitative changes during processing of the tea leaves

Longjing tea is one of China’s most renowned green teas and is enjoyed by tea enthusiasts all over the world. Although its unique aroma is the most important quality attribute, the key aroma compounds were not yet systematically analysed. A sensory-guided screening of the aroma distillate isolated from a high-grade Longjing green tea infusion by application of an aroma extract dilution analysis revealed 60 aroma-active domains in the gas chromatogram with flavour dilution (FD) factors in the range from 32 to the highest FD factor of 4098, as found for 3-methylnonane-2,4-dione (hay-like, aniseed-like) and vanillin (vanilla-like). A quantitation of the 42 aroma compounds eliciting the highest FD factors by means of stable isotope dilution assays (SIDA) followed by a calculation of odour activity values (OAV; ratio of concentration to odour threshold) showed that 30 aroma compounds exceeded their odour threshold in the tea beverage. By mixing 30 purified reference compounds of these odorants in water in exactly the same concentrations as determined in the tea beverage, the genuine aroma of the Longjing tea could successfully be simulated. In ensuing studies, quantitative changes during the traditional manufacturing process of the tea leaves as well as differences induced by the hot water treatment were systematically evaluated based on SIDAs. The results indicated the great importance of the initial pan-frying for the formation of key aroma compounds in the tea leaves. A comparison of the concentrations of selected key aroma compounds in the finished tea leaves and the tea infusion prepared thereof indicated further that large quantities of, for example, 2-methylbutanal, dimethyl sulphide, and 3-methylnonane-2,4-dione were obviously formed from yet unknown precursors by the hot water treatment.

Key Odorants from the Fragrant Bolete, Suillus punctipes.

The fragrant bolete, Suillus punctipes (Peck) Singer, is an edible mushroom with a unique aroma reminiscent of mushroom and citrus peel with an undertone of apricot. Thirty-five odorants were identified using solvent-assisted flavor evaporation (SAFE) and aroma extract dilution analysis (AEDA). Fourteen odorants including those with flavor dilution (FD) factors ≥64 were quantitated using stable isotope dilution assays (SIDA). Some odorants with high OAVs included 1-octen-3-one (OAV 164368), 1-octen-3-ol (OAV 3421), linalool (OAV 812), and nonanal (OAV 487). An odor simulation model was prepared closely matching the aroma of the mushroom. Omissions experiments revealed that 1-octen-3-one, 1-octen-3-ol, (2E)-oct-2-enal, linalool, δ-dodecalactone, and a mixture of three aldehydes, octanal, nonanal, and decanal, were essential odorants for the aroma profile. Enantiomeric ratios were determined for several odorants employing chiral chromatography. The results from this study lay the groundwork for future studies in the aroma chemistry of S. punctipes and other mushrooms from the Suillus genus.