Sensomics analysis of taste compounds in balsamic vinegar and discovery of 5-acetoxymethyl-2-furaldehyde as a novel sweet taste modulator

Maillard reaction intermediates in Chinese Baijiu and their effects on Maillard reaction related flavor compounds during aging

This study investigated the Maillard reaction in Baijiu and the effects of extended aging in the presence of Maillard reaction intermediates (MRIs) on aromatic compounds, particularly focusing on heterocyclic changes. MRIs with different aroma types in Baijiu aged 1-18 years and force-aged for 6 weeks were determined. Results revealed that MRIs in soy sauce aroma-type Baijiu were significantly more abundant than those in other types of Baijiu. Changes in MRIs were observed and compared in aging and forced-aging Baijiu. Additionally, the distribution and variation of heterocycles in Baijiu were examined, which revealed an increase in N-heterocycle levels but a decrease in S- and O-heterocycle levels to a certain extent. The results of this study demonstrate that the Maillard reaction during the aging of Baijiu influences heterocycle concentrations, thereby improving flavor of aged Baijiu. Research into heterocycles and the Maillard reaction may help elucidate the aromatic evolution of Baijiu with aging and provide guidance for Baijiu storage.

Chemical Characterization of Red Wine Polymers and Their Interaction Affinity with Odorants

In order to characterize red wine polymers with regard to their binding properties to aroma compounds (odorants), a qualitative and quantitative analysis of chemical degradation products after different chemical treatments (thiolytic, acidic, and alkaline depolymerization) of high -molecular-weight (HMW) fractions of red wine was performed. Using 1H NMR, LC-ToF-MS, LC-MS/MS, and HPIC revealed key structural features such as carbohydrates, organic acids, phenolic compounds, anthocyanins, anthocyanidins, amino acids, and flavan-3-ols responsible for odorant-polymer interactions. Further, NMR-based interaction studies of the selected aroma compounds 3-methylbutanol, cis-whisky lactone, 3-methylbutanoic acid, and 3-isobutyl-2-methoxypyrazine with HMW polymers after chemical treatment demonstrated a reduced interaction affinity of the polymer compared to the native HMW fractions, and further, the importance of aromatic compounds such as flavan-3-ols for the formation of odorant polymer interactions. In addition, these observations could be verified by human sensory experiments. For the first time, the combination of a compositional analysis of red wine polymers and NMR-based interaction studies with chemically treated HMW fractions enabled the direct analysis of the correlation of the polymer's structure and its interaction affinity with key odorants in red wine.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Preparation of 5-(Acyloxymethyl)furfurals from Carbohydrates Using Zinc Chloride/Acetic Acid Catalyst System and Their Synthetic Value Addition

5-(Acyloxymethyl)furfurals (AMFs) have received considerable attention as hydrophobic, stable, and halogen-free congeners of 5-(hydroxymethyl)furfural (HMF) for synthesizing biofuels and biochemicals. In this work, AMFs have been prepared directly from carbohydrates in satisfactory yields using the combination of ZnCl₂ as the Lewis acid catalyst and carboxylic acid as the Brønsted acid catalyst. The process was initially optimized for 5-(acetoxymethyl)furfural (AcMF) and then extended to producing other AMFs. The effects of reaction temperature, duration, loading of the substrate, and dosage of ZnCl₂ on AcMF yield were explored. Fructose and glucose provided AcMF in 80% and 60% isolated yield, respectively, under optimized parameters (5 wt % substrate, AcOH, 4 equiv ZnCl₂, 100 °C, 6 h). Finally, AcMF was converted into high-value chemicals, such as 5-(hydroxymethyl)furfural, 2,5-bis(hydroxymethyl)furan, 2,5-diformylfuran, levulinic acid, and 2,5-furandicarboxylic acid in satisfactory yields to demonstrate the synthetic versatility of AMFs as carbohydrate-derived renewable chemical platforms.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Identification of volatile compounds correlated with consumer acceptability of strawberry preserves: Untargeted GC-MS analysis

Volatile compounds that impact the acceptability of strawberry preserves were investigated by untargeted GC-MS flavoromics analysis. Chemical profiles for fifteen strawberry preserves were modeled against consumer liking scores by orthogonal partial least squares (OPLS) with good fit (R²Y = 0.998) and predictive ability (Q² = 0.853). Ten highly predictive compounds were selected, nine of which were identified, and eight of which were quantified using tandem mass spectrometry. Sensory recombination difference testing revealed that the addition of predictive compounds to an average-liked preserve at levels found in the most-liked preserve induced a perceptible difference to frequent consumers of strawberry jams. One of the highly predictive compounds was identified (MS and synthesis) as a novel linalool oxide product 2-methyl-2-vinyl-tetrahydrofuran with a fruity, herbal-minty, piney aroma and a low odor threshold value.

Metabolomics identify landscape of food sensory properties

Sensory evaluation is a key component of food production strategy. The classical food sensory evaluation method is time-consuming, laborious, costly, and highly subjective. Since flavor (taste and smell), texture, and mouthfeel are all related to the chemical properties of food, there has been a growing interest in how they affect the senses of food. In the past decades, emerging metabolomics has received much attention in the field of sensory evaluation, because it not only offers a broad picture of chemical composition for sensory properties but also revealed their changes and functions in food proceeding. This article reviewed food chemicals regarding the flavor, smell, and texture of foods, and discussed the advantages and limitations of applying metabolomics approaches to sensory evaluation, including GC-MS, LC-MS, and NMR. Taken together, this review gives a comprehensive, critical overview of the current state, future challenges, and trends in metabolomics on food sensory properties.

Identification and Quantitation of Taste-Active Compounds in Dried Scallops by Combined Application of the Sensomics and a Quantitative NMR Approach

Application of the sensomics concept on dried scallops, a Japanese specialty produced from the adductor muscle of scallops, revealed after activity-guided fractionation with subsequent (comparative) taste dilution analyses besides nucleotides, amino acids, organic acids, and inorganic ions, the presence of taste-modulating quaternary ammonium compounds and opines in highly taste-active fractions. In order to recreate the taste of dried scallops, two independent quantitation approaches were applied and compared. The first approach used multiple targeted UHPLC-MS/MS and high-performance ion chromatography methods. Besides already established quantitation methods for basic taste compounds, a new HILIC-UHPLC-MS/MS_MRM method for the quantitation of chromatographically challenging opines, using synthesized stable isotope-labeled standards, was developed. Furthermore, a qHNMR approach was applied, enabling a direct identification and quantitation of organic taste compounds in a food extract without prior fractionation using a reference ¹H NMR database. Both methods yielded similar quantitative results of taste-active compounds in dried scallop extracts and subsequent taste recombination experiments based on these data were able to recreate the taste of dried scallops.

A Rapid HPLC Method for the Simultaneous Determination of Organic Acids and Furans: Food Applications

Concerns over the potential adulteration of commercially produced foods give rise to a requirement for a simple and fast analytical method capable of quantifying potential adulterants. This work demonstrates a simple HPLC method tailored to detect major organic acids and furans within ingredients in commercial food products, for example, pomegranate molasses, balsamic vinegar, and apple cider vinegar. The relative importance of this method is in its simplicity and its use of an environmentally friendly aqueous mobile phase under isocratic conditions, providing results in a less than 20 min runtime. The chromatographic separation was achieved using an Acclaim® OA, 5 µm, 120 Å (4.0 × 250 mm) column; a UV-DAD detector set at 210 nm; and a 200 mM Na2SO4 mobile phase with 0.55 mL/L methanosulfonic acid as a pH modifier. The method was then validated by quantifying the concentration of acetic acid, formic acid, citric acid, and hydroxymethyl furfural (HMF) in pomegranate molasses, balsamic vinegar, and apple cider vinegar commercial products. The concentration of acetic acid and HMF in balsamic vinegar was 80.380 mg/mL (±1.272 mg/mL) and 2.153 mg/mL (±0.021 mg/mL), respectively. The apple cider vinegar was composed only of acetic acid with a concentration of 44.139 mg/mL (±0.053 mg/mL). The concentrations of citric acid and HMF were 123.425 mg/mL (±2.502 mg/mL) and 11.382 mg/mL (±0.582 mg/mL), respectively, in pomegranate molasses. Furthermore, this method is also capable of determining various organic acids and furans in biomass: levulinic acid, formic acid, furfurals, diformylfuran, and gamma-valerolactone.

Quantitative Proton NMR Spectroscopy for Basic Taste Recombinant Reconstitution Using the Taste Recombinant Database

The quantitative determination of putative taste active metabolites, the ranking of these compounds in their sensory impact based on dose-overthreshold (DoT) factors, followed by confirmation of their relevance by reconstitution and omission experiments enables the decoding of the non-volatile sensometabolome of certain foods. The identification and quantitation of target taste compounds by liquid chromatography-tandem mass spectrometry (LC-MS/MS), high-performance liquid chromatography-ultraviolet/visible (HPLC-UV/Vis) spectroscopy, or high-performance ion chromatography (HPIC) is often laborious and time-consuming. In this work, we present a novel quantitative ¹H NMR approach for reconstituting basic taste recombinants of different foods, including apple juice, balsamic vinegar, golden chanterelles, process flavor, and shrimp. Compound identification using the taste recombinant database, followed by absolute quantitation via quantitative ¹H NMR (qHNMR), enables a fast and direct reconstitution of basic taste recombinants. The taste profile analysis of basic taste recombinants was generated via qHNMR in less than 15 min and compared with literature data acquired by LC-MS/MS and/or HPLC-UV/Vis and revealed identical results for all taste qualities. A determination of limit of detection (LoD) values for S/N = 50 of various proton signals with different integrals and multiplicities demonstrated that taste recognition thresholds of all basic tastants are far above those of LoD concentrations under the chosen conditions. Therefore, our experimental setup is able to detect basic taste-active compounds well below their taste recognition thresholds.

Production of fermented tea petal decoction with insights into in vitro biochemical tests, antioxidant assay and GC-MS analysis

Abstract

This research work was designed to attempt and propose the first report on production and biochemical characterization of fermented tea flower petal decoction or simply tea petal wine. The tea petal decoction and brewer’s yeast or Saccharomyces cerevisiae were co-cultured for fermentation. Antioxidant activity and chromatographic separation of potential candidates were assessed. Primary investigations for qualitative characters on this fermented broth revealed the presence of steroids, tannin, flavonoids, phenol, cardiac glycosides, coumarin, caffeine etc. Our manufactured fermented broth showed high free radical scavenging activity after 2 months of aging. High DPPH scavenging activities were also observed in solvent fractions of acetone, ethanol and methanol. The antioxidant activity, alcohol percentage and other qualities were seen to be gradually increased during aging. Gas chromatography-mass spectrometry analysis revealed the presence of 44 compounds including many potential antioxidant molecules and other bioactive agents. Hopefully, presence of alcohol with medicinally active compounds and antioxidant activity will make it as acceptable as a good wine and tea flower as economically functional.

Graphical abstract

Sensomics-Assisted Flavor Decoding of Dairy Model Systems and Flavor Reconstitution Experiments

The whole sensometabolome of a typical dairy milk dessert was decoded to potentially serve as a blueprint for further flavor optimization steps of functional fat-reduced food. By applying the sensomics approach, a wide range of different dairy volatiles, semi and nonvolatiles, were analyzed by ultrahigh-performance liquid chromatography tandem mass spectrometry with or without derivatization presteps. While for volatile sulfur compounds with low odor thresholds, headspace solid-phase microextraction gas chromatography was established, abundant carbohydrates and organic acids were quantified by quantitative ¹H nuclear magnetic resonance spectroscopy. Validated quantitation, sensory reconstitution, and omission studies highlighted eight flavor-active compounds, namely, diacetyl, δ-tetra-, δ-hexa-, and δ-octadecalactone, sucrose, galactose, lactic acid, and citric acid as indispensable for flavor recombination. Furthermore, eight odorants (acetaldehyde, acetic acid, butyric acid, methanethiol, phenylacetic acid, dimethyl sulfide, acetoin, and hexanoic acid), all with odor activity values >1, additionally contributed to the overall flavor blueprint. Within this work, a dairy flavor analytical toolbox covering four different high-throughput methods could successfully be established showing potential for industrial applications.

Pharmacology of TAS1R2/TAS1R3 Receptors and Sweet Taste

The detection of energy-rich sweet food items has been important for our survival during evolution, however, in light of the changing lifestyles in industrialized and developing countries our natural sweet preference is causing considerable problems. Hence, it is even more important to understand how our sense of sweetness works, and perhaps even, how we may deceive it for our own benefit. This chapter summarizes current knowledge about sweet tastants and sweet taste modulators on the compound side as well as insights into the structure and function of the sweet taste receptor and the transduction of sweet signals. Moreover, methods to assess the activity of sweet substances in vivo and in vitro are compared and discussed.

Identification and Quantitation of Reaction Products from Quinic Acid, Quinic Acid Lactone, and Chlorogenic Acid with Strecker Aldehydes in Roasted Coffee

To gain comprehensive insight into the interactions of key coffee odorants, like the Strecker aldehydes, acetaldehyde, propanal, methylpropanal, 2- and 3-methylbutanal, and methional, and the nonvolatile fraction of coffee, an untargeted metabolomics approach was applied. Ultra performance liquid chromatography (UPLC)-time of flight (TOF)-mass spectrometry (ESI^-) profiling followed by statistical data analysis revealed a marker substance for a coffee beverage spiked with acetaldehyde with an accurate mass of 217.0703 [M - H]^-. This compound could be identified as a reaction product of quinic acid (QA) and acetaldehyde linked by acetalization at the cis-diol function of QA. Consequently, the acetalization of aldehydes, QA, 5-O-caffeoyl quinic acid (CQA), and quinic acid γ-lactone (QAL) was investigated by means of model reactions, followed by synthesis, isolation, and structure elucidation via UPLC-TOF-MS and 1D and 2D NMR techniques. UHPLC-MS/MS_MRM screening and the quantification of aldehyde adducts in coffee beverages revealed the presence of QA/acetaldehyde, -/propanal, -/methylpropanal, and -/methional reaction products and CQA/acetaldehyde, -/propanal, -/methylpropanal, -/2- and 3-methylbutanal, and -/methional and QAL/acetaldehyde adducts for the first time, in concentrations of 12-270 μg/L for QA/aldehydes, 5-225 μg/L for CQA/aldehydes, and 62-173 μg/L for QAL/acetaldehyde. The sensory characterization of the identified compounds showed bitter taste recognition thresholds of 48-297 μmol/L for CQA adducts and 658 μmol/L for QAL/acetaldehyde, while the QA adducts showed no bitter taste (<2000 μmol/L).

Molecularization of Bitter Off-Taste Compounds in Pea-Protein Isolates (Pisum sativum L.)

Activity-guided fractionations, combined with taste dilution analyses (TDA), were performed to locate the key compounds contributing to the bitter off-taste of pea-protein isolates (Pisum sativum L.). Purification of the compounds perceived with the highest sensory impact, followed by 1D/2D-NMR, (LC-)MS/MS, LC-TOF-MS, and MSE experiments, led to the identification of 14 lipids and lipid oxidation products, namely, 9,10,13-trihydroxyoctadec-12-enoic acid, 9,12,13-trihydroxyoctadec-10-enoic acid, 9,10,11-trihydroxyoctadec-12-enoic, 11,12,13-trihydroxyoctadec-9-enoic acid, (10E,12E)-9-hydroxyoctadeca-10,12-dienoic acid, (9Z,11E)-13-hydroxyoctadeca-9,11-dienoic acid, (9E,11E)-13-hydroxyoctadeca-9,11-dienoic acid, 1-linoleoyl glycerol, α-linolenic acid, 2-hydroxypalmitic acid, 2-hydroxyoleic acid, linoleic acid, (9Z,11E)-13-oxooctadeca-9,11-dienoic acid, and octacosa-6,9,19,22-tetraen. Herein, we present the isolation, structure determination, and sensory activity of these molecules. Depending on their structure, the isolated compounds showed human bitter recognition thresholds between 0.06 and 0.99 mmol/L in water.

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.

Perception of Bitter Taste through Time-Intensity Measurements as Influenced by Taste Modulation Compounds in Steviol Glycoside Sweetened Beverages

To limit sugar consumption and maintain sweetness levels in the diet, food and beverage developers often use high potency sweeteners (HPSs) as alternatives. Steviol glycosides are considered a consumer-friendly alternative but they are perceived to have a bitter taste accompanied by sweet and bitter lingering. Recently, taste modulators have been discovered that help to alleviate negative attributes like bitterness of HPSs. To show that taste modulation compounds (TMCs) decrease perceived bitterness associated with steviol glycosides, a trained descriptive panel (n = 9) performed a single-attribute time-intensity (TI) assessment over 2 min. Analysis of Variance (ANOVA) was used to analyze TI curves and curve parameters (AUC, Imax and Tmax). Principal components analysis (PCA) was also used to assess TI curves. Results showed that statistically significant results depended on the analysis method. Bitterness perception was shown to persist less over 2 min for steviol glycosides with TMCs when assessing raw scores and parameters. The same was not found using differences from control curves or weighted curves from PCA. These findings demonstrate that particular TMCs may subtly decrease perceived bitterness of steviol glycosides. However, business objectives of TMC use may dictate what kind of analysis method to use when analyzing perceived bitter perception of TMCs over time.

Discovery of a Thiamine-Derived Taste Enhancer in Process Flavors

Targeted quantitation of 48 basic taste-active compounds in commercial meatlike process flavors, calculation of dose-overthreshold factors, and basic taste re-engineering, followed by activity-guided fractionation, revealed, next to l-glutamate and 5'-ribonucleotides, a series of N-acetylated amino acids and S-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteine as taste-modulating compounds. The N-acetylated amino acids imparted kokumi enhancement with rather high taste thresholds ranging up to 1800 μmol/L ( N-acetylmethionine) in model broth. In comparison, S-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteine, found to be formed by a Maillard-type reaction of thiamine and cysteine, is reported for the first time to exhibit strong kokumi enhancement above a low threshold concentration of 120 μmol/L (model broth). These results will open new avenues toward a knowledge-based optimization of thiamine-containing process flavors.

Beyond the Flavour: The Potential Druggability of Chemosensory G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) belong to the largest class of drug targets. Approximately half of the members of the human GPCR superfamily are chemosensory receptors, including odorant receptors (ORs), trace amine-associated receptors (TAARs), bitter taste receptors (TAS2Rs), sweet and umami taste receptors (TAS1Rs). Interestingly, these chemosensory GPCRs (csGPCRs) are expressed in several tissues of the body where they are supposed to play a role in biological functions other than chemosensation. Despite their abundance and physiological/pathological relevance, the druggability of csGPCRs has been suggested but not fully characterized. Here, we aim to explore the potential of targeting csGPCRs to treat diseases by reviewing the current knowledge of csGPCRs expressed throughout the body and by analysing the chemical space and the drug-likeness of flavour molecules.

Kaempferol 3- O-(2‴- O-Sinapoyl-β-sophoroside) Causes the Undesired Bitter Taste of Canola/Rapeseed Protein Isolates

By means of activity-guided fractionation using taste dilution analysis, liquid chromatography-tandem mass spectrometry (LC-MS/MS), liquid chromatography-time-of-flight mass spectrometry, one-/two-dimensional nuclear magnetic resonance spectroscopy, LC-MS/MS quantitation, dose-over-threshold considerations, and sensory spiking experiments, kaempferol 3- O-(2‴- O-sinapoyl-β-sophoroside), exhibiting a bitter taste above the low threshold concentration of 3.4 μmol/L, was found for the first time as the key molecule contributing to the unpleasant bitter taste of rapeseed (canola) protein isolates. This finding opens new avenues for a biorefinery approach targeting an off-taste removal.

Discovery of taste modulating octadecadien-12-ynoic acids in golden chanterelles (Cantharellus cibarius)

Activity-guided fractionation in combination with taste dilution and comparative taste dilution analysis, followed by LC-MS and 1D/2D-NMR experiments, enabled the identification of several C₁₈-acetylenic acids in chanterelles among which (9Z,15E)-14,17,18-trihydroxy-9,15-octadecadien-12-ynoic acid, (9Z,15E)-14-oxo-9,15-octadecadien-12-ynoic acid, (10E,15E)-9-hydroxy-14-oxo-10,15-octadecadien-12-ynoic acid, (10E,15E)-9-hydroperoxy-14-oxo-10,15-octadecadien-12-ynoic acid, (10E,15E)-9,14-dioxo-10,15-octadecadien-12-ynoic acid, (9Z,15E)-14-oxo-9,15-octadecadien-12-ynoic acid methyl ester, (9Z,15E)-17(18)-epoxy-14-oxo-9,15-octadecadien-12-ynoic acid methyl ester and (10E,14Z)-9-hydroperoxy-10,14-octadecadien-12-ynoic acid have not yet been reported in literature. Sensory evaluation in a basic taste recombinant revealed taste modulating thresholds for the octadecadien-12-ynoic acids in the range of 19-105 µmol/l. In comparison, three isolated octadecadienoic acids, namely (10E,14Z)-12-hydroxy-10,14-octadecadienoic acid, (9Z,11Z)-14,18-dihydroxy-9,11-octadecadienoic acid, and (9Z,11Z)-14,17,18-trihydroxy-9,11-octadecadienoic acid, respectively, did not show any taste modulating activity, thus pinpointing the putative key role of the acetylene moiety for kokumi enhancement.

Salt Taste Enhancing l-Arginyl Dipeptides from Casein and Lysozyme Released by Peptidases of Basidiomycota

Some l-arginyl dipeptides were recently identified as salt taste enhancers, thus opening the possibility to reduce dietary sodium uptake without compromising palatability. A screening of 15 basidiomycete fungi resulted in the identification of 5 species secreting a high peptidolytic activity (>3 kAU/mL; azocasein assay). PFP-LC-MS/MS and HILIC-MS/MS confirmed that l-arginyl dipeptides were liberated when casein or lysozyme served as substrate. Much higher yields of dipeptides (42-75 μmol/g substrate) were released from lysozyme than from casein. The lysozyme hydrolysate generated by the complex set of peptidases of Trametes versicolor showed the highest l-arginyl dipeptide yields and a significant salt taste enhancing effect in a model cheese matrix and in a curd cheese. With a broad spectrum of novel specific and nonspecific peptidases active in the slightly acidic pH range, T. versicolor might be a suitable enzyme source for low-salt dairy products.

Current Status and Future Perspectives in Flavor Research: Highlights of the 11th Wartburg Symposium on Flavor Chemistry & Biology

The 11th Wartburg Symposium on Flavor Chemistry & Biology, held at the hotel "Auf der Wartburg" in Eisenach, Germany, from June 21 to 24 in 2016, offered a venue for global exchange on cutting-edge research in chemistry and biology of odor and taste. The focus areas were (1) functional flavor genomics and biotechnology, (2) flavor generation and precursors, (3) new approaches and precursors, (4) new approaches and technologies, (5) new molecules and structure/activity relationships, (6) food-borne bioactives and chemosensory health prevention, and (7) chemosensory reception, processing, and perception. Selected from more than 250 applicants, 160 distinguished scientists and rising stars from academia and industry from 24 countries participated in this multidisciplinary event. This special issue comprises a selection of 33 papers from oral presentations and poster contributions and is prefaced by this symposium introduction to carve out essential achievements in odor and taste chemistry and to share future research perspectives.

Food-Grade Synthesis of Maillard-Type Taste Enhancers Using Natural Deep Eutectic Solvents (NADES)

The increasing demand for healthier food products, with reduced levels of table salt, sugar, and mono sodium glutamate, reinforce the need for novel taste enhancers prepared by means of food-grade kitchen-type chemistry. Although several taste modulating compounds have been discovered in processed foods, their Maillard-type ex food production is usually not exploited by industrial process reactions as the yields of target compounds typically do not exceed 1–2%. Natural deep eutectic solvents (NADES) are reported for the first time to significantly increase the yields of the taste enhancers 1-deoxy-d-fructosyl-N-β-alanyl-l-histidine (49% yield), N-(1-methyl-4-oxoimidazolidin-2-ylidene) aminopropionic acid (54% yield) and N²-(1-carboxyethyl) guanosine 5′-monophosphate (22% yield) at low temperature (80–100 °C) within a maximum reaction time of 2 h. Therefore, NADES open new avenues to a “next-generation culinary chemistry” overcoming the yield limitations of traditional Maillard chemistry approaches and enable a food-grade Maillard-type generation of flavor modulators.

Sensomics-Based Molecularization of the Taste of Pot-au-Feu, a Traditional Meat/Vegetable Broth

Targeted quantification of 49 basic taste-active molecules, followed by the calculation of dose-over-threshold (DoT) factors, and taste re-engineering experiments revealed minerals, nucleotides/nucleosides, amino acids, organic acids, and carbohydrates as the key compounds of Pot-au-Feu, a traditional broth preparation from beef cuts and vegetables. Moreover, the dipeptide carnosine was identified to be the key inducer for the white-meaty and thick-sour orosensation of the broth, next to anserine and 1-deoxy-d-fructosyl-N-β-alanyl-l-histidine, the latter of which has been identified for the first time by means of a sensory-guided fractionation. Sensory studies revealed the threshold concentration of carnosine in model broth to decrease by a factor of 5 upon nonenzymatic glycosylation to reach 4.4 mmol/L for its Amadori product 1-deoxy-d-fructosyl-N-β-alanyl-l-histidine.

The Cyclic Diarylheptanoid Asadanin as the Main Contributor to the Bitter Off-Taste in Hazelnuts (Corylus avellana L.)

Activity-guided fractionation and taste dilution analysis (TDA), followed by LC-MS/MS, LC-TOF-MS, and 1D/2D-NMR spectroscopy, led to the identification of the cyclic diarylheptanoid asadanin exhibiting a human bitter recognition threshold of 13 μmol/kg, as the major inducer of the sporadic bitter off-taste of hazelnut kernels (Corylus avellana L.). Sensory analysis of hazelnut samples from two origins (Ordu/2013 and Akçakoca/2014) and from Cimiciato-infected hazelnut kernels, followed by LC-MS/MS quantitation of 1 and calculation of dose-over-threshold (DoT) factors, showed established evidence for the Cimiciato infection as the major inductor of asadanin biosynthesis in hazelnut kernels and, as a consequence, as the reason for bitter off-taste development.

Vinegar Metabolomics: An Explorative Study of Commercial Balsamic Vinegars Using Gas Chromatography-Mass Spectrometry

Balsamic vinegar is a popular food condiment produced from cooked grape must by two successive fermentation (anaerobic and aerobic) processes. Although many studies have been performed to determine the composition of major metabolites, including sugars and aroma compounds, no study has been undertaken yet to characterize the comprehensive metabolite composition of balsamic vinegars. Here, we present the first metabolomics study of commercial balsamic vinegars by gas chromatography coupled to mass spectrometry (GC-MS). The combination of three GC-MS methods allowed us to detect >1500 features in vinegar samples, of which 123 metabolites were accurately identified, including 25 amino acids, 26 carboxylic acids, 13 sugars and sugar alcohols, four fatty acids, one vitamin, one tripeptide and over 47 aroma compounds. Moreover, we identified for the first time in vinegar five volatile metabolites: acetin, 2-methylpyrazine, 2-acetyl-1-pyroline, 4-anisidine and 1,3-diacetoxypropane. Therefore, we demonstrated the capability of metabolomics for detecting and identifying large number of metabolites and some of them could be used to distinguish vinegar samples based on their origin and potentially quality.

Sensomics-Assisted Elucidation of the Tastant Code of Cooked Crustaceans and Taste Reconstruction Experiments

Sensory-guided fractionation by means of ultrafiltration and cation-exchange chromatography, followed by MS/MS quantitation, and taste re-engineering experiments revealed the key taste molecules coining the characteristic taste profile of the cooked meat of king prawns. Furthermore, quantitative analysis demonstrated that the taste differences between crustaceans are due to quantitative differences in the combinatorial code of tastants, rather than to qualitative differences in the tastant composition. Besides the amino acids glycine, L-proline, and L-alanine, the characteristic seafood-like sweet profile was found to be due to the sweet modulatory action of quaternary ammonium compounds, among which betaine, homarine, stachydrin, and trimethylamine-N-oxide were found as the key contributors on the basis of dose-activity considerations. Knowledge of this combinatorial tastant code provides the foundation for the development of more sophisticated crustacean flavors that are lacking any heavy metal ions and allergenic proteins present when using crustacean extracts for food flavoring.

Discovery of kokumi peptide from yeast extract by LC-Q-TOF-MS/MS and sensomics approach

BACKGROUND

Yeast extract can impart thickness, complexity and long-lasting taste impression, coined kokumi taste, to blank chicken broth. In this research, the kokumi-active peptide in yeast extract was discovered by ultrafiltration, liquid chromatographic and quadrupole-time-of-flight-tandem mass spectrometric technologies. Furthermore, the sensory characters of these peptides were evaluated by a sensomics approach.

RESULTS

A total of 10 kokumi peptides were identified from yeast extract. They were γ-Glu-Cys-Gly, γ-Glu-Leu, γ-Glu-Val, γ-Glu-Tyr, Leu-Lys, Leu-Gln, Leu-Ala, Leu-Glu, Leu-Thr and Ala-Leu. Apart from the well-known kokumi-active glutathione and γ-glutamyl dipeptides, five leucyl dipeptides were first proposed having kokumi activity. Among them, Ala-Leu was found to have the highest kokumi threshold concentration (1.5 mmol L(-1) ) in the blank chicken broth, while Leu-Glu was the lowest (0.3 mmol L(-1) ). A subsequent dose-response experiment indicated that the bitter-tasting leucyl dipeptides could impart kokumi taste to chicken broth at low concentrations (less than bitter threshold concentrations). Interestingly, the kokumi sensation began to decrease when such peptides exceeded the threshold concentration by approximately 16-fold in the blank chicken broth.

CONCLUSION

Key kokumi-active fractions were purified from yeast extract. Among them, ten important kokumi peptides from yeast extract were identified.

Applicability of salt reduction strategies in pizza crust

In an effort to reduce population-wide sodium intake from processed foods, due to major health concerns, several different strategies for sodium reduction in pizza crust without any topping were evaluated by sensory analyses. It was possible to reduce sodium by 10% in one single step or to replace 30% of NaCl by KCl without a noticeable loss of salty taste. The late addition of coarse-grained NaCl (crystal size: 0.4-1.4 mm) to pizza dough led to an enhancement of saltiness through taste contrast and an accelerated sodium delivery measured in the mouth and in a model mastication simulator. Likewise, the application of an aqueous salt solution to one side of the pizza crust led to an enhancement of saltiness perception through faster sodium availability, leading to a greater contrast in sodium concentration. Each of these two strategies allowed a sodium reduction of up to 25% while maintaining taste quality.

Application of 2D-HPLC/taste dilution analysis on taste compounds in aniseed (Pimpinella anisum L.)

This is the first application of fully automated, preparative, two-dimensional HPLC combined with sensory analysis for taste compound discovery using a sweet and licorice-like bitter-tasting aniseed extract as an example. Compared to the traditional iterative fractionation of food extracts by sensory-guided sequential application of separation techniques, the fully automated 2D-HPLC allowed the comprehensive separation of the aniseed extract into 256 subfractions and reduced the fractionation time from about 1 week to <1day. Using a smart sensory strategy to locate high-impact fractions, e.g., by evaluating first-dimension fractions by reconstituting them from second-dimension subfractions, followed by straightforward application of the taste dilution analysis on the individual second-dimension subfractions revealed the sweet-tasting trans-anethole and the bitter-tasting trans-pseudoisoeugenol 2-methylbutyrate, showing recognition thresholds of 70 and 68 μmol/L, respectively, as the primary orosensory active compounds in aniseed. 2D-HPLC combined with smart sensory analysis seems to be a promising strategy to speed the discovery of the key players imparting the attractive taste of foods.

Nature's chemical signatures in human olfaction: a foodborne perspective for future biotechnology

The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.

Phenolic composition of vinegars over an accelerated aging process using different wood species (acacia, cherry, chestnut, and oak): effect of wood toasting

Wood shavings are widely employed in vinegar making to reduce aging time. Accordingly, this study aims to evaluate the effects of using shavings from different wood species (acacia, cherry, chestnut, and oak) and of toasting on the release of phenolic compounds into vinegar during the aging process. The study involved aging vinegars using previously toasted shavings and untoasted ones, at 0.5% and 1% (w/v), and collecting samples at 15 and 30 days. The phenolic compounds were analyzed by LC-DAD during the aging process. As a result, wood markers naringenin and kaempferol (cherry), robinetin and fustin (acacia), and isovanillin (oak) were identified for the first time in vinegars. The results also showed that toasting wood shavings decreases the concentration of most flavonoid wood markers (e.g., (+)-taxifolin, naringenin, and fustin) in vinegar, but that it is essential for the highest releases of aldehyde compounds (syringaldehyde, protocatechualdehyde, and vanillin). Remarkably, 15 days was sufficient to obtain the highest increases of most polyphenol compounds in the vinegar. Statistical analysis (linear discriminant analysis) proved that the phenolic compounds identified in vinegars are useful for discriminating vinegars regarding the wood species of the shavings used to accelerate aging.

Nontargeted GC-MS approach for volatile profile of toasting in cherry, chestnut, false acacia, and ash wood

By using a nontargeted GC-MS approach, 153 individual volatile compounds were found in extracts from untoasted, light toasted and medium-toasted cherry, chestnut, false acacia, as well as European and American ash wood, used in cooperage for aging wines, spirits and other beverages. In all wood types, the toasting provoked a progressive increase in carbohydrate derivatives, lactones and lignin constituents, along with a variety of other components, thus increasing the quantitative differences among species with the toasting intensity. The qualitative differences in the volatile profiles allow for identifying woods from cherry (being p-anisylalcohol, p-anisylaldehyde, p-anisylacetone, methyl benzoate and benzyl salicylate detected only in this wood), chestnut (cis and trans whisky lactone) and false acacia (resorcinol, 3,4-dimethoxyphenol, 2,4-dihydroxy benzaldehyde, 2,4-dihydroxyacetophenone, 2,4-dihydroxypropiophenone and 2,4-dihydroxy-3-methoxyacetophenone), but not those from ash, because of the fact that all compounds present in this wood are detected in at least one other. However, the quantitative differences can be clearly used to identify toasted ash wood, with tyrosol being most prominent, but 2-furanmethanol, 3- and 4-ethylcyclotene, α-methylcrotonolactone, solerone, catechol, 3-methylcatechol and 3-hydroxybenzaldehyde as well. Regarding oak wood, its qualitative volatile profile could be enough to distinguish it from cherry and acacia woods, and the quantitative differences from chestnut (vanillyl ethyl ether, isoacetovanillone, butirovanillone, 1-(5-methyl-2-furyl)-2-propanone and 4-hydroxy-5,6-dihydro-(2H)-pyran-2-one) and ash toasted woods.

Kinetics of sodium release from wheat bread crumb as affected by sodium distribution

As a basis for sodium reduction in bread, the kinetics of sodium release from wheat bread crumb during chewing was investigated by three independent methods using two in-mouth techniques and a model mastication simulator, respectively. Complete sodium extraction in-mouth was achieved after 30 s. Using coarse-grained NaCl in breadmaking significantly accelerated sodium release and led to enhanced salt taste, allowing a sodium reduction in bread by 25% while maintaining taste quality. This salt taste enhancement by accelerated sodium delivery can be explained by the increasing contrast in sodium concentration, which is known to determine salt taste perception. For the first time, the resulting inhomogeneous salt distribution in bread prepared by using coarse-grained NaCl was visualized by means of confocal laser scanning microscopy using a sodium-selective, fluorescent dye.

Quantitation and bitter taste contribution of saponins in fresh and cooked white asparagus (Asparagus officinalis L.)

A sensitive HPLC-MS/MS method was developed enabling the simultaneous quantification of bitter-tasting mono- and bidesmosidic saponins in fresh and processed asparagus (Asparagus officinalis L.). Based on quantitative data and bitter taste recognition thresholds, dose-over-threshold factors were determined for the first time to determine the bitter impact of the individual saponins. Although 3-O-[α-L-rhamnopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranosyl]-(25R/S)-spirost-5-ene-3β-ol was found based on dose-over-threshold factors to be the predominant bitter saponin in raw asparagus spears, 3-O-[α-L-rhamnopyranosyl-(1 → 2)-{α-L-rhamnopyranosyl-(1 → 4)}-β-D-glucopyranosyl]-26-O-[β-D-glucopyranosyl]-(25R)-22-hydroxyfurost-5-ene-3β,26-diol, 3-O-[α-L-rhamnopyranosyl-(1 → 2)-{α-L-rhamnopyranosyl-(1 → 4)}-β-D-glucopyranosyl]-26-O-[β-D-glucopyranosyl]-(25S)-22-hydroxyfurost-5-ene-3β,26-diol, and (25R)- and (25S)-furost-5-en-3β,22,26-triol-3-O-[α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranoside]-26-O-β-D-glucopyranoside were found as key bitter contributors after cooking. Interestingly, the monodesmosidic saponins 5a/b were demonstrated for the first time to be the major contributor to the bitter taste of fresh asparagus spears, while the bidesmosides 1a/b and 2a/b may be considered the primary determinants for the bitter taste of cooked asparagus.

Compositional and sensory characterization of red wine polymers

After isolation from red wine by means of ultrafiltration and gel adsorption chromatography, the composition of the highly astringent tasting high-molecular weight polymers was analyzed by means of HPLC-MS/MS, HPLC-UV/vis, and ion chromatography after thiolytic, alkaline, and acidic depolymerization and, on the basis of the quantitative data obtained as well as model incubation experiments, key structural features of the red wine polymers were proposed. The structural backbone of the polymers seems to be comprised of a procyanidin chain with (-)-epicatechin, (+)-catechin, (-)-epicatechin-3-O-gallate units as extension and terminal units as well as (-)-epigallocatechin as extension units. In addition, acetaldehyde was shown to link different procyanidins at the A-ring via an 1,1-ethylene bridge and anthocyanins and pyranoanthocyanins were found to be linked to the procyanidin backbone via a C-C-linkage at position C(6) or C(8), respectively. Alkaline hydrolysis demonstrated the polymeric procyanidins to be esterified with various organic acids and phenolic acids, respectively. In addition, the major part of the polysaccharides present in the red wine polymeric fraction were found not to be covalently linked to procyanidins. Interestingly, sensory evaluation of individual fractions of the red wine polymers did not show any significant difference in the astringent threshold concentrations, nor in the astringency intensity in supra-threshold concentrations and demonstrated the mean degree of polymerization as well as the galloylation degree not to have an significant influence on the astringency perception.