Chemoinformatic Exploration of "Bioinspired Metabolomes" Illuminates Diacetyl Assembly Pathways Toward Nesteretal A-Like Cage Molecules.

An appealing and challenging cage structure along with an unusual biosynthetic pathway prompted us to explore an expeditious bioinspired one-pot total synthesis of nesteretal A. An unconventional strategy was chosen, and a cascade reaction starting from diacetyl was studied. Under organocatalytic conditions mimicking an aldolase, nesteretal A and a related cage analogue were anticipated by in silico metabolization, detected, targeted, and characterized.

Off-flavors generated during long-term ambient storage of pasteurized drinking yogurt from skim milk.

Few studies have examined sensory quality changes during the storage of pasteurized drinking yogurt (PDY), and the cause of off-flavor development is unclear. Off-flavors generated during 90-d ambient storage (25 °C) of PDY from reconstituted skim milk were investigated by sensory evaluation, volatile component analysis with gas chromatography-mass spectroscopy, and gas chromatography-olfactometry. Rancid off-flavor was induced by increased fatty acid concentration due to fat decomposition by heat-stable lipase. Masking of off-flavors was inhibited by degradation of diacetyl, which originally contributed to yogurt-like flavors. Maillard reaction particular to ambient storage of PDY resulted in changes in the furaneol and sotolon levels, which may be involved in enhancement of off-flavors. Finally, our findings indicated that production of 4-vinylguaiacol may be involved in off-flavor development. The results of this study will contribute to the development of PDY with a longer shelf life and superior flavor.

Chiral Tertiary Amine Catalyzed Asymmetric [4 + 2] Cyclization of 3-Aroylcoumarines with 2,3-Butadienoate.

Coumarins and 2H-pyran derivatives are among the most commonly found structural units in natural products. Therefore, the introduction of 2H-pyran moiety into the coumarin structural unit, i.e., dihydrocoumarin-fused dihydropyranones, is a potentially successful route for the identification of novel bioactive structures, and the synthesis of these structures has attracted continuing research interest. Herein, a chiral tertiary amine catalyzed [4 + 2] cyclization of 3-aroylcoumarines with benzyl 2,3-butadienoate was reported. In the presence of Kumar's 6'-(4-biphenyl)-ß-iso-cinchonine, the desired dihydrocoumarin-fused dihydropyranone products could be obtained in up to 97% yield and 90% ee values.

Analysis of α-dicarbonyl compounds in coffee (Coffea arabica) prepared under various roasting and brewing methods.

This study investigated the correlations of α-dicarbonyl compounds (α-DCs), including glyoxal (GO), methylglyoxal (MGO) and diacetyl (DA), formed in coffee prepared under various roasting and brewing methods. The levels of α-DCs in Brazilian coffee beans (Coffea arabica) ranged from 28.3 to 178 µg/mL. Concentration ranges of GO, MGO and DA were 1.31-6.57, 25.5-159 and 1.50-12.9 µg/mL, respectively. The level of α-DCs increased with high roasting temperature, long roasting time, small coffee bean particles, mineral water and espresso brewing. In correlation analysis, the roasting temperature-time showed strong negative correlations with α-DCs in espresso (-0.886) and cold-brew coffee (-0.957). In espresso coffee, there was a strong negative correlation between the α-DCs and coffee bean particle size (-0.918).

Evaluation of the synergistic olfactory effects of diacetyl, acetaldehyde, and acetoin in a yogurt matrix using odor threshold, aroma intensity, and electronic nose analyses.

Despite intensive analyses of yogurt flavor, the synergistic effects of the key aroma compounds on sensory responses and their optimum concentration ranges remain less well-documented. This study investigated the odor thresholds, optimum concentration ranges, and perceptual actions of diacetyl, acetaldehyde, and acetoin in a yogurt matrix. Our results show that the odor thresholds of diacetyl, acetaldehyde, and acetoin in the yogurt matrix were 5.43, 15.4, and 29.0 mg/L, respectively, which were significantly higher than the corresponding values in water. The optimum diacetyl, acetaldehyde, and acetoin concentration ranges were found to be 6.65 to 9.12, 25.9 to 35.5, and 37.3 to 49.9 mg/L, respectively. In Feller's additive model, the addition of each compound led to a significant reduction in their odor threshold in the yogurt matrix, thus demonstrating the synergistic effects of the compounds. In the σ-τ plot, various concentrations of compounds were associated with various degrees of additive behavior with respect to the aroma intensity of the yogurt matrix, thus demonstrating the synergism among these compounds in increasing the overall aroma intensity. The optimal simultaneous concentration ratio of diacetyl:acetaldehyde:acetoin was determined to be 4.00:16.0:32.0 mg/L. The specific synergistic effects were also confirmed by an electronic nose analysis and aroma profile comparison. In summary, these 3 aroma compounds exhibited synergistic effects in a yogurt matrix, thus providing a theoretical basis for the enhancement of flavors in dairy products.

Micelle-stabilized Olfactory Receptors for a Bioelectronic Nose Detecting Butter Flavors in Real Fermented Alcoholic Beverages.

A bioelectronic nose device based on micelle-stabilized olfactory receptors is developed for the selective discrimination of a butter flavor substance in commercial fermented alcoholic beverages. In this work, we have successfully overexpressed ODR-10, a type of olfactory receptor, from Caenorhabditis elegans using a bacterial expression system at a low cost and high productivity. The highly-purified ODR-10 was stabilized in micelle structures, and it was immobilized on a carbon nanotube field-effect transistor to build a bioelectronic nose for the detection of diacetyl, a butter flavor substance, via the specific interaction between diacetyl and ODR-10. The bioelectronic nose device can sensitively detect diacetyl down to 10 fM, and selectively discriminate it from other substances. In addition, this sensor could directly evaluate diacetyl levels in a variety of real fermented alcoholic beverages such as beer, wine, and makgeolli (fermented Korean wine), while the sensor did not respond to soju (Korean style liquor without diacetyl). In this respect, our sensor should be a powerful tool for versatile food industrial applications such as the quality control of alcoholic beverages and foods.

Identification and analysis of new α- and ß-hydroxy ketones related to the formation of 3-methyl-2,4-nonanedione in musts and red wines.

The formation of 3-methyl-2,4-nonanedione (MND) during red wine aging can contribute to the premature evolution of aroma, characterized by the loss of fresh fruit and development of dried fruit flavors. The identification of two new hydroxy ketones, 2-hydroxy-3-methylnonan-4-one (syn- and anti-ketol diastereoisomers) and 3-hydroxy-3-methyl-2,4-nonanedione (HMND), prompted the investigation of the precursors and pathways through which MND is produced and evolves. An HS-SPME-GC-MS method was optimized for their quantitation in numerous must and wine samples, providing insight into the evolution of MND, HMND, and ketols through alcoholic fermentation and wine aging. Alcoholic fermentation resulted in a significant decrease in MND and HMND and the simultaneous appearance of ketol diastereoisomers. The analysis of 167 dry red wines revealed significant increases in MND and anti-ketol contents through aging and a significant positive correlation between MND and anti-ketols. Additional experiments demonstrated that ketols are precursors to MND during red wine oxidation.

Preparation, characterization and comparison of biological potency in two new Zn(II) and Pd(II) complexes of butanedione monoxime derivatives.

A novel Schiff base ligand (2-iminothiophenol-2,3-butanedione monoxime, ITBM) and its complexes with Pd(II) and Zn(II) metal ions ([M(ITBM)2]Cl2) were synthesized and characterized in the present study. The formulated complexes were evaluated for in vitro antioxidant activity as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH•). According to the results, antioxidant activity of Pd complex (IC50=36 mg L-1) was more effective than that of Zn(II) complex (IC50=72 mg L-1). Biophysical techniques along with computational modeling were employed to examine the binding of these complexes with human serum albumin (HSA) as the model protein. The trial findings revealed an interaction between Schiff base complexes and HSA with a modest binding affinity [Kb=6.31(±0.11)×104 M-1 for Zn(II) complex and 0.71(±0.05)×104 M-1 for Pd(II) complex at 310 K]. An intense fluorescence quenching of protein through a static quenching mechanism was occurred due to the binding of both complexes to HSA. Hydrogen bonds and van der Waals forces in both examined systems were the main stabilizing forces in the development of drug-protein complex. Based on far-UV-CD observations, the content of α-helical structure in the protein was reduced through induction by both complexes. Analysis of protein-ligand docking demonstrated binding of the two Schiff base complexes to residues placed in the IIA subdomain of HSA. In addition, Zn complex with HSA showed a stronger binding ability than that of Pd complex.Communicated by Ramaswamy H. Sarma.

Cinnamil- and Quinoxaline-Derivative Indicator Dyes for Detecting Volatile Amines in Fish Spoilage.

Colorimetric indicators are versatile for applications such as intelligent packaging. By interacting with food, package headspace, and/or the ambient environment, color change in these indicators can be useful for reflecting the actual quality and/or monitoring distribution history (e.g., time and temperature) of food products. In this study, indicator dyes based on cinnamil and quinoxaline derivatives were synthesized using aroma compounds commonly present in food: diacetyl, benzaldehyde, p-tolualdehyde and p-anisaldehyde. The identities of cinnamil and quinoxaline derivatives were confirmed by Fourier transform infrared (FT-IR) spectroscopy, mass spectrometry (MS), 1H nuclear magnetic resonance (NMR) and 13C NMR analyses. Photophysical evaluation showed that the orange-colored cinnamil derivatives in dimethylsulfoxide (DMSO) turned to dark brownish coloration when exposed to strong alkalis. The cinnamil and acid-doped quinoxaline derivatives were sensitive to volatile amines commonly present during the spoilage in seafood. Quinoxaline derivatives doped by strong organic acid were effective as pH indicators for volatile amine detection, with lower detection limits than cinnamil. However, cinnamil exhibited more diverse color profiles than the quinoxaline indicators when exposed to ammonia, trimethylamine, triethylamine, dimethylamine, piperidine and hydrazine. Preliminary tests of acid-doped quinoxaline derivatives on fresh fish demonstrated their potential as freshness indicators in intelligent packaging applications.

Melanoidins from Coffee, Cocoa, and Bread Are Able to Scavenge α-Dicarbonyl Compounds under Simulated Physiological Conditions.

Free amino residues react with α-dicarbonyl compounds (DCs) contributing to the formation of advanced glycation end products (AGEs). Phenolic compounds can scavenge DCs, thus controlling the dietary carbonyl load. This study showed that high-molecular weight cocoa melanoidins (HMW-COM), HMW bread melanoidins (HMW-BM), and especially HMW coffee melanoidins (HMW-CM) are effective DC scavengers. HMW-CM (1 mg/mL) scavenged more than 40% DCs within 2 h under simulated physiological conditions, suggesting some physiological relevance. Partial acid hydrolysis of HMW-CM decreased the dicarbonyl trapping capacity, demonstrating that the ability to react with glyoxal, methylglyoxal (MGO), and diacetyl was mainly because of polyphenols bound to macromolecules. Caffeic acid (CA) and 3-caffeoylquinic acid showed a DC-scavenging kinetic profile similar to that of HMW-CM, while mass spectrometry data confirmed that hydroxyalkylation and aromatic substitution reactions led to the formation of a stable adduct between CA and MGO. These findings corroborated the idea that antioxidant-rich indigestible materials could limit carbonyl stress and AGE formation across the gastrointestinal tract.

Mapping the location of DATEM in multi-phase systems: Synthesis and characterization of spin-label probe analogues.

Electron paramagnetic resonance (EPR) spectroscopy has emerged as a fast, reliable, non-invasive and sensitive method to determine the distribution, localization and reactivity of labelled ingredients in micro-heterogeneous systems. However, the commercially available probe molecules are very limited. In the present work, five new nitroxide [(4-hydroxy-2, 2, 6, 6-tetramethylpiperidin-1-oxyl (TEMPOL)] derivatives (1b-5b) of diacetyl tartaric acid esters of monoglycerides (DATEM) (1a-5a), a widely used food emulsifier, were synthesized under Steglich conditions and characterized by MS (mass-spectrometry), FT-IR (Fourier-transform infrared spectroscopy), EPR, NMR (nuclear magnetic resonance spectroscopy), fluorescence spectroscopy, and DSC (differential scanning calorimetry) analysis. Phase partitioning studies proved that the new spin labels are adequately capable of describing the localizations and partitioning of the corresponding DATEM in multi-phase systems. Findings disclosed in this work will provide new knowledge on ingredient reactivity and localization in multi-phase systems; which is vital to aid the design of more efficient delivery systems for bioactive compounds.

An enzyme-linked immunosorbent assay for the detection of diacetyl (2,3-butanedione).

Diacetyl (2,3-butanedione) is an important metabolic marker of several cancers, as well as an important off-flavour component produced during fermentation. As a small molecule in a complex mixture with many other analytes, existing methods for identification and quantitation of diacetyl invariably involves a chromatographic separation step followed by signal integration with an appropriate stoichiometric detector. Here we demonstrate that the chemical reaction of diacetyl with a 1,2-phenylenediamine derivative yields a chemical adduct, 1,4-quinoxaline which can be conjugated on BSA. The BSA-diacetyl adduct can be used to select an adduct-specific monoclonal antibody in a Fab-format from a 45-billion member phage-display library. The availability of this antibody allowed the development of an enzyme-linked immunosorbent assay for diacetyl, based on the 1,4-quinoxaline competition for the antibodies with the diacetyl adduct immobilized on the plate. The described ELISA assay can detect the captured diacetyl in micromolar concentrations, both in water samples and in cell culture medium.

Trace level and highly selective determination of urea in various real samples based upon voltammetric analysis of diacetylmonoxime-urea reaction product on the carbon nanotube/carbon paste electrode.

In this study an innovative method was introduced for selective and precise determination of urea in various real samples including urine, blood serum, soil and water. The method was based on the square wave voltammetry determination of an electroactive product, generated during diacetylmonoxime reaction with urea. A carbon paste electrode, modified with multi-walled carbon nanotubes (MWCNTs) was found to be an appropriate electrochemical transducer for recording of the electrochemical signal. It was found that the chemical reaction conditions influenced the analytical signal directly. The calibration graph of the method was linear in the range of 1 × 10-7- 1 × 10-2 mol L-1. The detection limit was calculated to be 52 nmol L-1. Relative standard error of the method was also calculated to be 3.9% (n = 3). The developed determination procedure was applied for urea determination in various real samples including soil, urine, plasma and water samples.

Aroma compound diacetyl suppresses glucagon-like peptide-1 production and secretion in STC-1 cells.

Diacetyl is a volatile flavour compound that has a characteristic buttery aroma and is widely used in the flavour industry. The aroma of a food plays an important role in food palatability and thus intake. This study investigates the effect of diacetyl on the satiety hormone, glucagon-like peptide (GLP-1), using the enteroendocrine cell line, STC-1. Diacetyl decreased proglucagon mRNA and total GLP-1 from glucose stimulated STC-1 cells. This dampening effect on GLP-1 appears to be mediated by increasing intracellular cAMP levels, increasing synthesis of the G protein coupled receptor, GPR120, and its recruitment to the cell surface. Voltage gated Ca2+ channels, K+ATP channels and the α-gustducin taste pathway do not appear to be involved. These findings demonstrate that components contributing to food palatability suppress GLP-1. This ability of diacetyl to reduce satiety signals may contribute to overconsumption of some palatable foods.

Nickel(II) diacetyl monoxime-2-pyridyl hydrazone complex can inhibit Ehrlich solid tumor growth in mice: A potential new antitumor drug.

The chief chemotherapeutic drug, cisplatin had common bad effects such as nephrotoxicity, ototoxicity and bone marrow depression. This led us to develop a new potential anticancer drug based on nickel metal ion that may be less toxic. Nickel(II) diacetyl monoxime-2-pyridyl hydrazone complex cytoprotective effect, superoxide dismutase (SOD)-like activity and anticancer activities were studied. In vitro, the complex showed SOD-like activity of 86.62%. It was capable to kill 90.2% of Ehrlich ascites carcinoma (EAC) cells and to protect 92.48% of human RBCs. In vivo, the complex lowered the tumor burden markedly in a concentration-dependent manner. Noticeably, solid tumor growth was suppressed; tumor volume and weight were reduced and mice life span was lengthened. The hematological indices were improved, catalase activity was re-elevated and malondialdehyde (MDA) level was reversed towards normal. Nucleic acids, cholesterol, triglycerides, liver enzymes, urea and creatinine contents were reduced to near normal ranges. Glutathione (GSH), SOD, albumin and total protein levels were increased. In conclusion, our results revealed that the complex has the ability to suppress Ehrlich solid tumor growth in mice with minimal side effects. This may possibly via its redox activity. Surprisingly, nickel complex antitumor activities were more potent than those of cisplatin.

Diacetyl and related flavorant α-Diketones: Biotransformation, cellular interactions, and respiratory-tract toxicity.

Exposure to diacetyl and related α-diketones causes respiratory-tract damage in humans and experimental animals. Chemical toxicity is often associated with covalent modification of cellular nucleophiles by electrophilic chemicals. Electrophilic α-diketones may covalently modify nucleophilic arginine residues in critical proteins and, thereby, produce the observed respiratory-tract pathology. The major pathway for the biotransformation of α-diketones is reduction to α-hydroxyketones (acyloins), which is catalyzed by NAD(P)H-dependent enzymes of the short-chain dehydrogenase/reductase (SDR) and the aldo-keto reductase (AKR) superfamilies. Reduction of α-diketones to the less electrophilic acyloins is a detoxication pathway for α-diketones. The pyruvate dehydrogenase complex may play a significant role in the biotransformation of diacetyl to CO2. The interaction of toxic electrophilic chemicals with cellular nucleophiles can be predicted by the hard and soft, acids and bases (HSAB) principle. Application of the HSAB principle to the interactions of electrophilic α-diketones with cellular nucleophiles shows that α-diketones react preferentially with arginine residues. Furthermore, the respiratory-tract toxicity and the quantum-chemical reactivity parameters of diacetyl and replacement flavorant α-diketones are similar. Hence, the identified replacement flavorant α-diketones may pose a risk of flavorant-induced respiratory-tract toxicity. The calculated indices for the reaction of α-diketones with arginine support the hypothesis that modification of protein-bound arginine residues is a critical event in α-diketone-induced respiratory-tract toxicity.

Models of toxicity of diacetyl and alternative diones.

Diacetyl (DA; 2,3-butanedione), with the chemical formula (CH3CO)2 is a volatile organic compound with a deep yellow color and a strong buttery flavor and aroma. These properties have made DA a particularly useful and common food flavoring ingredient. However, because of this increased occupational use, workers can be exposed to high vapor concentrations in the workplace. Despite being listed by the USFDA to be 'generally regarded as safe' (GRAS), multiple lines of evidence suggest that exposure to high concentrations of DA vapor causes long-term impairments in lung function with lung function testing indicating evidence of either restrictive or obstructive airway narrowing in affected individuals. A growing number of pre-clinical studies have now addressed the short and long-term toxicity associated with DA exposure providing further insight into the toxicity of DA and related diones. This review summarizes these observations.

Effect of Furan Fatty Acids and 3-Methyl-2,4-nonanedione on Light-Induced Off-Odor in Soybean Oil.

Soybean oil is one of the most widely consumed vegetable oils. However, under photooxidative conditions, this oil develops a beany and green off-odor through a mechanism that has not yet been elucidated. Upon photooxidation, 3-methyl-2,4-nonanedione (3-MND) produces a strong aroma. In this study, the effect of furan fatty acids and 3-MND on odor reversion in soybean oil was investigated. Our findings suggest that the observed light-induced off-odor was likely attributable to the furan fatty acids present in the oil through the generation of 3-MND. While 3-MND may not be directly responsible for the development of light-induced off-odor, this compound appears to be involved because off-odor was detected in canola oil samples containing added 3-MND. In addition, in the present work, 3-hydroxy-3-methyl-2,4-nonanedione, which is derived from 3-MND, was identified for the first time in light-exposed soybean oil and shown to be one of the compounds responsible for odor reversion.

The Effects of Egg and Diacetyl Tartaric Acid Esters of Monoglycerides Addition on Storage Stability, Texture, and Sensory Properties of Gluten-Free Sorghum Bread.

The impact of whole egg addition (as is) at 20%, 25%, or 30% (flour basis) on sorghum bread quality was evaluated. The use of the antistaling agent diacetyl tartaric acid esters of monoglycerides (DATEM) at 0.5% (flour basis) at each of the egg addition levels was also studied. Evaluated quality factors included color, specific volume, and crumb structure. Texture analysis was performed to evaluate the rate of quality loss based on changes in crumb hardness values over time. A trained sensory panel evaluated bread quality attributes by descriptive analysis. Sorghum breads with egg had larger specific volumes than the control, while DATEM had a negative effect on the volume of sorghum gluten-free bread. Inclusion of egg in the bread formula improved cell structure and produced darker crust (P < 0.05). The addition of egg reduced bread hardness and slowed the rate of quality loss over a 12-d storage period. Descriptive analysis confirmed the findings of texture analysis. Control breads were significantly harder (P < 0.05) than egg-containing bread at days 0 and 4. This research demonstrates that addition of eggs to a gluten-free sorghum bread formulation results in improved storage stability and better overall quality and acceptability of the product.

Fluorescent detection of dipicolinic acid as a biomarker of bacterial spores using lanthanide-chelated gold nanoparticles.

Gold nanoparticles (GNPs) functionalized with ethylenediamine-lanthanide complexes (Eu-GNPs and Tb-GNPs) were used for the selective fluorescent detection of dipicolinic acid (DPA), a unique biomarker of bacterial spores, in water. Particles were characterized by transmission electron microscopy and zeta potential measurements. The coordination of DPA to the lanthanides resulted in the enhancement of the fluorescence. A selective response to DPA was observed over the nonselective binding of aromatic ligands. The ligand displacement strategy were also employed for the ratiometric fluorescent detection of DPA. 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedion (TFNB) was chosen as an antenna to synthesize ternary complexes. The addition of DPA on EuGNP:TFNB ternary complex quenched the initial emission of the complex at 615nm and increased the TFNB emission at 450nm when excited at 350nm. The results demonstrated that the ratiometric fluorescent detection of DPA was achieved by ligand displacement strategy.