Flavor Perception and Formation Mechanism of Empty Cup Aroma in Soy Sauce Aroma Type Baijiu.

The research focused on the distinctive empty cup aroma, with the aim of identifying the key aroma compounds and the formation mechanism of empty cup aroma in soy sauce aroma type baijiu (SSB). The lasting times of SSB is significantly longer than that of other types of baijiu, with an average duration of 28 days. Key compounds such as 2,3-dimethyl-5-ethylpyrazine, phenylethyl alcohol, p-cresol, sotolon, benzeneacetic acid were identified in empty cup aroma due to their highest flavor dilution factor. Molecular dynamics (MD) simulation was performed to study the mechanism of empty cup aroma on the liquid-gas interface and solid-gas interface. The results revealed the existence of hydrogen bonding and van der Waals forces between sotolon and lactic acid, a representative nonvolatile compound, which are speculated to be an important reason for the empty cup aroma.

Sotolon and (2E,4E,6Z)-Nona-2,4,6-trienal Are the Key Compounds in the Aroma of Walnuts.

Fresh kernels of the walnut tree (Juglans regia L.) show a characteristic and pleasant aroma, the molecular basis of which was unknown. The application of an aroma extract dilution analysis resulted in 50 odor-active compounds. Among them, 37 had not been reported as fresh walnut kernel volatiles before, including the two odorants with the highest flavor dilution factors, namely, fenugreek-like smelling 3-hydroxy-4,5-dimethylfuran-2(5H)-one (sotolon) and oatmeal-like smelling (2E,4E,6Z)-nona-2,4,6-trienal. Quantitations revealed 17 odorants with concentrations in the walnuts that exceeded their odor threshold concentrations. Aroma reconstitution and omission experiments finally showed that the characteristic aroma of fresh walnuts is best represented by a binary mixture of sotolon and (2E,4E,6Z)-nona-2,4,6-trienal. Of both, the natural concentration was ∼10 µg/kg. Further sensory studies showed that the walnut character is intensified when their concentrations are in parallel increased to ∼100 µg/kg. This finding may guide the future breeding of new walnut cultivars with improved aroma.

Optimization and Validation of a Method to Determine Enolones and Vanillin Derivatives in Wines-Occurrence in Spanish Red Wines and Mistelles.

Understanding the chemical nature of wine aroma demands accurate quantitative determinations of different odor-active compounds. Quantitative determinations of enolones (maltol, furaneol, homofuraneol, and sotolon) and vanillin derivatives (vanillin, methyl vanillate, ethyl vanillate, and acetovanillone) at low concentrations are complicated due to their high polarity. For this reason, this paper presents an improved and automated version for the accurate measure of these common trace wine polar compounds (enolones and vanillin derivatives). As a result, a faster and more user-friendly method with a reduction of organic solvents and resins was developed and validated. The optimization of some stages of the solid phase extraction (SPE) process, such as washing with an aqueous solution containing 1% NaHCO3 at pH 8, led to cleaner extracts and solved interference problems. Due to the polarity of these type of compounds, an optimization of the large volume injection was also carried out. Finally, a programmable temperature vaporization (PTV) quartz glass inlet liner without wool was used. The injector temperature was raised to 300 °C in addition to applying a pressure pulse of 180 kPa for 4 min. Matrix effects were solved by the use of adequate internal standards, such as ethyl maltol and 3',4'-(methylenedioxy)acetophenone. Method figures of merit were highly satisfactory: good linearity (r2 > 0.98), precision (relative standard deviation, RSD < 10%), high recovery (RSD > 89%), and low detection limits (<0.7 µg/L). Enolones and vanillin derivatives are associated with wine aging. For this reason, the methodology was successfully applied to the quantification of these compounds in 16 Spanish red wines and 12 mistelles. Odor activity values (OAV) indicate that furaneol should be considered an aroma impact odorant in red wines and mistelles (OAV > 1) while homofuraneol and sotolon could also produce changes in their aroma perceptions (0.1 < OAV < 1).

Tackling Virulence of Pseudomonas aeruginosa by the Natural Furanone Sotolon.

The bacterial resistance development due to the incessant administration of antibiotics has led to difficulty in their treatment. Natural adjuvant compounds can be co-administered to hinder the pathogenesis of resistant bacteria. Sotolon is the prevailing aromatic compound that gives fenugreek its typical smell. In the current work, the anti-virulence activities of sotolon on Pseudomonas aeruginosa have been evaluated. P. aeruginosa has been treated with sotolon at sub-minimum inhibitory concentration (MIC), and production of biofilm and other virulence factors were assessed. Moreover, the anti-quorum sensing (QS) activity of sotolon was in-silico evaluated by evaluating the affinity of sotolon to bind to QS receptors, and the expression of QS genes was measured in the presence of sotolon sub-MIC. Furthermore, the sotolon in-vivo capability to protect mice against P. aeruginosa was assessed. Significantly, sotolon decreased the production of bacterial biofilm and virulence factors, the expression of QS genes, and protected mice from P. aeruginosa. Conclusively, the plant natural substance sotolon attenuated the pathogenicity of P. aeruginosa, locating it as a plausible potential therapeutic agent for the treatment of its infections. Sotolon can be used in the treatment of bacterial infections as an alternative or adjuvant to antibiotics to combat their high resistance to antibiotics.

An accurate single-step LLE method using keeper solvent for quantification of trace amounts of sotolon in Port and white table wines by HPLC-DAD.

Sotolon has been reported to play an important role in the typical aroma of aged Port wines. A simple and cheap single-step liquid-liquid extraction (LLE) using glycerol as a keeper for liquid chromatography/ultra-violet absorption quantification of sotolon in Port wines is proposed in this work. The glycerol plays a protective role during the concentration of the extracts increasing the sotolon recovery as well the method repeatability. The proposed method yields chromatograms without interfering compounds and a forty-fold enrichment of sotolon. The detection and quantification limits were far below the sotolon odour threshold in Port wine (19 µg/L). The method was also validated for dry white table wines with good validation parameters. The methodology was successfully applied to selected commercial Tawny, Ruby, and White Port wines, being reported the presence of sotolon in young Ruby and White Port wines for the first time, although below the olfactory detection threshold.

Sotolon is a natural virulence mitigating agent in Serratia marcescens.

Serratia marcescens is an emerging opportunistic bacterium that can cause healthcare-associated infections. The high rate of multidrug resistance and the ability to produce a set of virulence factors, by which it can produce infectious diseases makes it urgent to find an alternative approach to the treatment of such infections. Disarming of virulence by targeting of quorum sensing (QS) as the regulating mechanism of virulence is a promising approach that has no effect on bacterial growth that is considered a key factor in emergence of resistance. This study was designed to investigate the ability of sub-inhibitory concentrations (sub-MICs) of sotolon to attenuate virulence of a clinical isolate of S. marcescens. Sotolon at 25 and 50 µg/ml inhibited 35.2 and 47.5% of biofilm formation, respectively. The inhibition of swimming motility were 41.4 and 69.3%, while that of swarming motility were 77.6 and 86.8% at 25 and 50 µg/ml, respectively. Moreover, sotolon reduced prodigiosin production by 76.6 and 87.6% at concentrations of 25 and 50 µg/ml, respectively. Protease activity was reduced by 25 µg/ml of sotolon by 54.8% and was completely blocked at 50 µg/ml. The relative expression of genes regulating virulence factors decreased by 40% for fimA, 29% for fimC, 59% for flhC, 57% for flhD, 39% for bsmB, 37% for rssB, 49% for rsmA, 54% for pigP, and 62% for shlA gene in the presence of 50 µg/ml sotolon. In conclusion, sotolon is an anti-virulence agent that could be used for the treatment of S.marcescens hospital-acquired infections.

Characterization of the potent odorants in Tibetan Qingke Jiu by sensory analysis, aroma extract dilution analysis, quantitative analysis and odor activity values.

Tibetan Qingke Jiu is the most important alcoholic beverage in the daily life of Tibetan people due to its unique flavor and rich nutrients. In this study, the aromatic characteristics of Qingke Jiu were studied by sensory analysis, aroma extract dilution analysis (AEDA), quantitative analysis, and odor activity values (OAVs). Sensory evaluation demonstrated that Qingke Jiu had fruity, cooked potato, honey, sour, sweet, and caramel-like aroma. A total of 66 aroma compounds were identified by AEDA and gas chromatography-mass spectrometry, with flavor dilution (FD) factors ranging from 4 to 2048. Among them, methional, acetic acid, ethyl butanoate, phenylacetaldehyde and ß-phenylethanol appeared with the highest FD factors. The concentration of these aroma-active compounds was further quantitated by combination of four different quantitative measurements, and 17 odorants had concentrations higher than their odor thresholds. Based on the OAVs, phenylacetaldehyde, ß-phenylethanol, ethyl phenylacetate, sotolon, furaneol, methional, methionol, γ-nonalactone, ethyl 2-methylbutanoate, ß-damascenone, ethyl 3-methylbutanoate, ethyl acetate, ethyl butanoate, and acetic acid could be potentially important to the overall aroma profile of Qingke Jiu.

Creation and Acceptability of a Fragrance with a Characteristic Tawny Port Wine-Like Aroma.

Port wine, the ultimate expression of the Demarcated Douro Region's (DDR's) history, cultural heritage experience, and art, was born on the slopes of the Douro river valley. One of the categories of port wine that is much appreciated by consumers is tawny port wine. This category of wine is aged in oak barrels and is characterized by oxidative aromas. Thus, the objective of the present work was to develop a tawny port wine-like fragrance, the first according to the literature. First, a group of 50 consumers in an informal environment and using two samples of tawny port wine (13 and over 40 years of aging in wood, respectively) was asked about the pleasantness of the aromas and the possible use of a tawny port wine-like fragrance. More than 80% of the group stated that they would use the fragrance as an air freshener (scent marketing in restaurants) or even in personal-use products. Then, a sensory panel of 12 participants (3 men and 9 women) was trained, and using tawny port wines of various brands and ages, the panel selected six descriptors to aromatically describe this type of wine. For the descriptors, seven aromatic chemical compounds were appointed and fragrances were developed with contributions from the panel. After several sessions with the sensory panel, three fragrances were selected, created with only three of the aromatic compounds initially used: benzaldehyde, sotolon, and vanillin. Afterward, the levels of consumer acceptability (150 individuals) for the three developed fragrances were studied and the optimization of their sensory characteristics was evaluated using a "just about right" (JAR) scale. It was found that male individuals assigned higher ratings and preferred fragrance 5.1, which was a statistically significant result (p < 0.001). Regarding age, Tukey's test showed significant differences in responses to fragrance 5.3 between young adults and middle-aged adults (p = 0.018). Young adults gave higher scores for this fragrance. Additionally, consumers considered that the intensity of the tawny port wine aroma was ideal in the three fragrances, however, the fragrance color was not very intense. The use of the three compounds (benzaldehyde, sotolon, and vanillin) seems to be enough to obtain a tawny port wine-like fragrance.

Identification of key odorant compounds in starch-based polymers intended for food contact materials.

Biopolymers used for food contact materials must be evaluated in order to ensure food safety and quality. In this work, the aroma profile of starch-based packaging materials, presented as pellets and films has been characterized. Headspace solid phase microextraction (HS-SPME) technique and gas chromatography coupled to both mass spectrometry and a sniffing port (GC-MS-O) were used for identification. In total, 35 odorant compounds were detected. The results showed that aldehydes were the odorants with the highest aromatic impact in starch-based films. Eight odorant compounds, such as trimethylamine, 1-octen-3-one, sotolon, (Z) and (E)-2-nonenal, p-vinylguaiacol, eugenol and 1-undecanol, defined as aroma-impact compounds, obtained modified frequency values (MF%) above 60% in at least 3 out of 4 films. A sensory panel evaluated the toasted, sweet/fruity, green, flower, distasteful, fat and spices notes in the films and it was observed that the quality of all samples decreased when the toasted and spices notes increased.

Key volatile aroma compounds of lactic acid fermented malt based beverages - impact of lactic acid bacteria strains.

This study aims to define the aroma composition and key aroma compounds of barley malt wort beverages produced from fermentation using six lactic acid bacteria (LAB) strains. Gas chromatography mass spectrometry-olfactometry and flame ionization detection was employed; key aroma compounds were determined by means of aroma extract dilution analysis. Fifty-six detected volatile compounds were similar among beverages. However, significant differences were observed in the concentration of individual compounds. Key aroma compounds (flavor dilution (FD) factors ≥16) were ß-damascenone, furaneol, phenylacetic acid, 2-phenylethanol, 4-vinylguaiacol, sotolon, methional, vanillin, acetic acid, nor-furaneol, guaiacol and ethyl 2-methylbutanoate. Furthermore, acetaldehyde had the greatest odor activity value of up to 4266. Sensory analyses revealed large differences in the flavor profile. Beverage from L. plantarum Lp. 758 showed the highest FD factors in key aroma compounds and was correlated to fruity flavors. Therefore, we suggest that suitable LAB strain selection may improve the flavor of malt based beverages.

A fast and environment-friendly MEPSPEP/UHPLC-PDA methodology to assess 3-hydroxy-4,5-dimethyl-2(5H)-furanone in fortified wines.

Sotolon is widely associated with the quality of fortified aged wines, and has also been linked to premature oxidative aging (premox). Here we developed a single, fast and environmental-friendly microextraction by packed sorbent ultra-high pressure liquid chromatography analysis (MEPS/UHPLC-PDA) for sotolon quantification in different wines. The best extraction conditions (loading three times 250µL samples through the MEPSPEP sorbent and elution with 100µL of 50% MeOH) were combined with a fast UHPLC separation (5min separation using acidified 10% MeOH isocratic flow in a CORTECS C18 column) to allow unparalleled minimum sample and solvents volumes usage. The validated methodology showed good linearity (r(2)>0.993) and precision (<5.6%); high recovery (>81%) and detection limits (0.45-2.51µg/L) far below sotolon odor threshold for any type of wine. The methodology was successfully applied to selected white table and Madeira wines, encompassing therefore a wide range of alcohol and sugar contents. Furthermore, as far we may know, this is the first time a single methodology can be used to assess both wine aging or premox according to the type of wine.

How sotolon can impart a Madeira off-flavor to aged beers.

4,5-Dimethyl-3-hydroxy-2(5H)-furanone or sotolon is known to impart powerful Madeira-oxidized-curry-walnut notes to various alcoholic beverages. It has been much studied in oxidized Jura flor-sherry wines, aged Roussillon sweet wines, and old Port wines, in which it contributes to the characteristic "Madeira-oxidized" aroma of these beverages. No scientific paper describes how sotolon might be involved in the Madeira off-flavor found in aged beers. The specific extraction procedure applied here allowed us to quantify this lactone in 7 special beers, at levels sometimes well above its threshold (from 5 to 42 µg/L after 6, 12, 18, and 24 months of natural aging, while unquantifiable in fresh beer). Investigation of spiked beers led us to highlight the key role of pro-oxidants and acetaldehyde. Addition of ascorbic acid without sulfites should be avoided by brewers, as the former would intensify sotolon synthesis. Acetoin, a beer fermentation byproduct, also emerged as possible precursor in beer when combined with serine.

Determination of sotolon content in South African white wines by two novel HPLC-UV and UPLC-MS methods.

Sotolon has been reported to play an important role in the atypical ageing and aroma character of many wines. A number of analytical techniques for sotolon analysis in wine have been reported, but these often require extensive sample preparation. In this work we report a HPLC-UV method and a novel UPLC-MS method to determine sotolon concentrations in white wines with little sample preparation applied for the first time for the evaluation of sotolon levels in South African wines. The validation showed that the instrumental methods had good accuracy, repeatability and linearity, but the UPLC-MS method proved more sensitive. For both methods, quantification limits were lower than the sotolon odour threshold in wine (10µg/L), 0.86µg/L and 0.013µg/L, for HPLC-UV and UPLC-MS methods, respectively. Sotolon levels in 65 South African white wines were often found to be lower than the reported odour threshold, with the highest concentration being 9.11µg/L. However, for low levels (<1µg/L), unknown interferences in certain wines led to sotolon not being quantified with the HPLC-UV method, which made the UPLC-MS method more suitable.