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.

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.

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.

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.

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.

Increased sensitivity of OSHA method analysis of diacetyl and 2,3-pentanedione in air.

Gas chromatography/mass spectrometry (GC/MS) operated in selected ion monitoring mode was used to enhance the sensitivity of OSHA Methods 1013/1016 for measuring diacetyl and 2,3-pentanedione in air samples. The original methods use flame ionization detection which cannot achieve the required sensitivity to quantify samples at or below the NIOSH recommended exposure limits (REL: 5 ppb for diacetyl and 9.3 ppb for 2,3-pentanedione) when sampling for both diacetyl and 2,3-pentanedione. OSHA Method 1012 was developed to measure diacetyl at lower levels but requires an electron capture detector, and a sample preparation time of 36 hours. Using GC/MS allows detection of these two alpha-diketones at lower levels than OSHA Method 1012 for diacetyl and OSHA Method 1016 for 2,3-pentanedione. Acetoin and 2,3-hexanedione may also be measured using this technique. Method quantification limits were 1.1 ppb for diacetyl (22% of the REL), 1.1 ppb for 2,3-pentanedione (12% of the REL), 1.1 ppb for 2,3-hexanedione, and 2.1 ppb for acetoin. Average extraction efficiencies above the limit of quantitation were 100% for diacetyl, 92% for 2,3-pentanedione, 89% for 2,3-hexanedione, and 87% for acetoin. Mass spectrometry with OSHA Methods 1013/1016 could be used by analytical laboratories to provide more sensitive and accurate measures of exposure to diacetyl and 2,3-pentanedione.

Simple and Clean Photoinduced Aromatic Trifluoromethylation Reaction.

We describe a simple, metal- and oxidant-free photochemical strategy for the direct trifluoromethylation of unactivated arenes and heteroarenes under either ultraviolet or visible light irradiation. We demonstrated that photoexcited aliphatic ketones, such as acetone and diacetyl, can be used as promising low-cost radical initiators to generate CF3 radicals from sodium triflinate efficiently. The broad utility of this strategy and its benefit to medicinal chemistry are demonstrated by the direct trifluoromethylation of unprotected bidentate chelating ligand, xanthine alkaloids, nucleosides, and related antiviral drug molecules.

Modification of CO2 avoidance behaviour in Drosophila by inhibitory odorants.

The fruitfly Drosophila melanogaster exhibits a robust and innate olfactory-based avoidance behaviour to CO(2), a component of odour emitted from stressed flies. Specialized neurons in the antenna and a dedicated neuronal circuit in the higher olfactory system mediate CO(2) detection and avoidance. However, fruitflies need to overcome this avoidance response in some environments that contain CO(2) such as ripening fruits and fermenting yeast, which are essential food sources. Very little is known about the molecular and neuronal basis of this unique, context-dependent modification of innate olfactory avoidance behaviour. Here we identify a new class of odorants present in food that directly inhibit CO(2)-sensitive neurons in the antenna. Using an in vivo expression system we establish that the odorants act on the Gr21a/Gr63a CO(2) receptor. The presence of these odorants significantly and specifically reduces CO(2)-mediated avoidance behaviour, as well as avoidance mediated by 'Drosophila stress odour'. We propose a model in which behavioural avoidance to CO(2) is directly influenced by inhibitory interactions of the novel odours with CO(2) receptors. Furthermore, we observe differences in the temporal dynamics of inhibition: the effect of one of these odorants lasts several minutes beyond the initial exposure. Notably, animals that have been briefly pre-exposed to this odorant do not respond to the CO(2) avoidance cue even after the odorant is no longer present. We also show that related odorants are effective inhibitors of the CO(2) response in Culex mosquitoes that transmit West Nile fever and filariasis. Our findings have broader implications in highlighting the important role of inhibitory odorants in olfactory coding, and in their potential to disrupt CO(2)-mediated host-seeking behaviour in disease-carrying insects like mosquitoes.

Condensation of Diacetyl with Alkyl Amines: Synthesis and Reactivity of p-Iminobenzoquinones and p-Diiminobenzoquinones.

Condensation reactions between diacetyl and α-branched primary alkylamines under mild and neutral conditions provided a mixture of 2,5-dimethylbenzoquinone(alkylimines), 2,5-dimethylbenzoquinone(bis-alkyldiimines), and N,N'-dialkyl-2,5-dimethylbenzene-1,4-diamines, which were efficiently separated as pure products by column chromatography. Both 2,5-dimethylbenzoquinone(alkylimines) and 2,5-dimethylbenzoquinone(bis-alkyldiimines) underwent an interchange of the alkylimino group when treated with anilines, followed by reductive aromatization, to provide diarylamines and 1,4-dianilinobenzenes, respectively. Evaluation was also made of the reactivity and selectivity of these compounds in the presence of anilines, thiophenols and alkylhalides.

Identification and characterization of a mycobacterial NAD⁺-dependent alcohol dehydrogenase with superior reduction of diacetyl to (S)-acetoin.

An enzyme capable of reducing acetoin in the presence of NADH was purified from Mycobacterium sp. B-009, a non-clinical bacterial strain of soil origin. The enzyme is a homotetramer and can be classified as a medium-chain alcohol dehydrogenase/reductase based on the molecular weight of the monomer. Identification of the structural gene revealed a limited distribution of homologous genes only among actinomycetes. In addition to its activity as a reductase specific for (S)-acetoin (EC 1.1.1.76), the enzyme showed both diacetyl reductase (EC 1.1.1.304) and NAD(+)-dependent alcohol dehydrogenase (EC 1.1.1.1) activities. (S)-Acetoin and diacetyl reductases belong to a group of short-chain alcohol dehydrogenase/reductases but do not have superior abilities to dehydrogenate monoalcohols. Thus, the purified enzyme can be readily distinguished from other enzymes. We used the dual functionality of the enzyme to effectively reduce diacetyl to (S)-acetoin, coupled with the oxidation of 1-butanol.

Aroma-active components of yeast extract pastes with a basic and characteristic meaty flavour.

BACKGROUND: Aroma-active compounds, together with sugars, amino acids, fat and nucleotides, are the main chemical species determining the characteristic aroma and taste of food. For selecting yeast extract pastes products with a less undesirable aroma, the aroma-active compounds that affect the overall consumer acceptance of yeast extract pastes products were analysed in this work. RESULTS: The aroma-active compounds of yeast extract pastes were extracted by using dynamic headspace extraction or simultaneous distillation extraction, and were detected by gas chromatography-olfactrometry-mass spectrometry in conjunction with dynamic headspace dilution analysis or aroma extract dilution analysis. Sensory results revealed that a meaty, roasted aroma was the dominant of overall aroma. The important aroma-active compounds referred in this work were mainly aldehydes, acids, ketones, furan derivatives, pyrazines, and sulfur-containing compounds. Of these, six volatile compounds such as 3-methylbutanal, 2,3-butanedione, 2,3,5-trimethyl-pyrazin, acetic acid ethenyl ester, 2-acetyl-1-pyrroline and (E,E)-2,4-decadienal had never been reported before as key aroma-active compounds of yeast extract pastes. CONCLUSIONS: The key aroma-active compounds were identified in basic and characteristic meaty flavour yeast extract pastes, and their characterisation was determined.

Is diacetyl a respiratory sensitizer? A reconsideration using QSAR, QMM, and competition experiments.

Concerns have been raised that diacetyl (DA) might be a respiratory sensitizer based on its LUMO energy similar to that of the respiratory allergen toluene-2,4-diisocyanate (TDI) and results of a local lymph node assay (LLNA) that reported an EC3 of 1.9%. To better understand the concerns, we performed a systematic literature review and experimental competition reactions between DA and TDI. The experimental evidence demonstrates that DA is at least 400-fold less reactive than TDI. The literature review finds evidence that the EC3 for DA is actually >11%. We conclude that DA is unlikely to have significant respiratory sensitization potential.

DMAP-catalyzed [3 + 2] and [4 + 2] cycloaddition reactions between [60]fullerene and unmodified Morita-Baylis-Hillman adducts in the presence of Ac2O.

One-step DMAP-catalyzed [3 + 2] and [4 + 2] cycloaddition reactions between C(60) and unmodified Morita-Baylis-Hillman adducts in the presence of Ac(2)O have been developed for the easy preparation of cyclopentene- and cyclohexene-fused [60]fullerene derivatives. When the MBH adducts bear an alkyl group, two different reaction pathways could be controlled selectively depending on the conditions.

Dissection of activation parameters in the bell-shaped α-effect following solvent modulation (DMSO-H2O media).

This paper comprises results of our investigation of the α-effect phenomenon for the reaction of O-p-nitrophenyl thionobenzoate (PNPTB) with butane-2,3-dione monoximate (Ox(-), α-nucleophile) and p-chlorophenoxide (p-ClPhO(-), normal-nucleophile) in DMSO-H2O mixtures of varying compositions at 15.0 °C, 25.0 °C, and 35.0 °C. The reactivity of Ox(-) and p-ClPhO(-) increases significantly as the DMSO content in the medium increases, although the effects of medium on reactivity are not the same for the reactions with Ox(-) and p-ClPhO(-). Ox(-) exhibits the α-effect in all solvent compositions and temperatures. The α-effect increases up to 50 mol % DMSO and then decreases thereafter, resulting in a bell-shaped α-effect profile. Dissection of the activation parameters (i.e., ΔH(‡) and TΔS(‡)) has revealed that the bell-shaped α-effect behavior is due to entropy of activation differences rather than enthalpy terms, although the enthalpy term controls almost entirely the solvent dependence of the reaction rate. Differences in the transition-state (TS) structures for the reactions with Ox(-) (a six-membered cyclic TS) and p-ClPhO(-) (an acyclic TS) are consistent with the entropy-dependent α-effect behavior.

Potentiation of the in vitro antistaphylococcal effect of oxacillin and tetracycline by the anti-inflammatory drug diacetyl rhein.

BACKGROUND: The anti-inflammatory drug diacetyl rhein has been found to possess promising antistaphylococcal effects against various drug-resistant strains in our previous study. In the present work, we explored the in vitro combinatory interactions of diacetyl rhein with oxacillin and tetracycline against 13 standard strains and clinical isolates of Staphylococcus aureus, including those resistant to erythromycin, methicillin and tetracycline. METHODS: Minimum inhibitory concentrations were determined by broth microdilution assay, and the effects of combinations were evaluated according to the sum of fractional inhibitory concentrations (ΣFICs). RESULTS: Synergistic or additive effects were observed against all S. aureus strains (ΣFIC 0.258-1), whereas diacetyl rhein-oxacillin appeared to be the most effective combination, synergistically inhibiting the growth of 4 strains tested. CONCLUSION: To our best knowledge, this is the first report on a synergistic antibacterial effect of diacetyl rhein. Our results suggest this promising compound for further evaluation of its synergistic anti-infective potential as an agent with a combined anti-inflammatory and synergistic antibacterial action.

Short communication: Reactivity of diacetyl with cleaning and sanitizing agents.

Diacetyl is used to impart a buttery flavor to numerous food products such as sour cream, cottage cheese, vegetable oil-based spreads, baked goods, and beverages. Recent studies have linked exposure to high concentrations of diacetyl and the onset of bronchiolitis obliterans. Due to the reported risks that diacetyl may pose, many food companies have altered practices to reduce worker exposure to diacetyl, including the use of personal respirators, improved air handling systems, and adequate cleaning practices. Commonly used cleaning and sanitizing agents may be reactive with diacetyl; however, the efficacy of these chemicals has not been studied in detail and remains unclear. The objective of this work was to study the reaction chemistry of diacetyl with common industrial cleaning and sanitizing chemicals. The reactions were assessed at equimolar concentrations and analyzed by gas chromatography-mass spectrometry. Peroxyacetic acid was most reactive with diacetyl (95% reduction in diacetyl), followed by sodium hypochlorite (76% reduction), and hydrogen peroxide (26% reduction). Benzalkonium chloride (BAC) did not react with diacetyl. Acetic acid was detected as the main product of reactions of diacetyl with peroxyacetic acid, sodium hypochlorite, and hydrogen peroxide. 1,1-Dichloro-2-propanone and 1,1,1-trichloropropanone were also identified as volatile reaction products in the sodium hypochlorite reactions.

Fluorescence and electrochemical recognition of nucleosides and DNA by a novel luminescent bioprobe Eu(III)-TNB.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (µs -ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A method is presented for determination of nucleosides using the effect of enhancement of fluorescence of the easily accessible europium(III)-TNB in presence of different nucleosides. The latter coordinates to Eu(III) -TNB and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. A similar method for the determination of DNA based on the quenching of Eu(III)-TNB has been established. The interaction of Eu(III)-4,4,4 trifluoro-1-(2-naphthyl)1,3-butanedione (TNB) complex with nucleosides (NS) (guanosine, adenosine, cytidine, inosine) and DNA has been studied using normal and time-resolved luminescence techniques. Binding constants were determined at 293 K, 298 K, 303 K, 308 K and 313 K by using Benesi-Hildebrand equation. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. The formation of binary and ternary complexes of Eu(III) with nucleosides and TNB has been studied potentiometrically at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol.dm(-3) (KNO3) . The formation of the 1:1 binary and 1:1:1 ternary complexes are inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the HYPERQUAD computer program. Electrochemical investigations for the systems under investigations have been carried out using cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon electrode in I = 0.1 mol/L p-toluenesulfonate as supporting electrolyte.

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.

Modification of citrulline residues with 2,3-butanedione facilitates their detection by liquid chromatography/mass spectrometry.

Citrullination is a post-translational modification (PTM) that results from the deimination of the amino acid arginine into citrulline by Peptidyl Arginine Deiminase enzymes and occurs in a wide range of proteins in health and disease. This modification causes a 1 Da mass shift, which can be used to identify citrullination sites in proteins by the use of mass spectrometry. However, other PTMs, such as deamidation from asparagine to aspartic acid or from glutamine to glutamic acid, can also cause a 1 Da mass shift, making correct interpretation of the data more difficult. We developed a chemical tagging strategy which, combined with an open source search application, allowed us to selectively pinpoint citrullinated peptides in a complex mixture after liquid chromatography/mass spectrometry (LC/MS) analysis. After incubation of a peptide mixture with 2,3 butanedione, citrulline residues were covalently modified which resulted in a 50 Da shift in singly charged mass. By comparison of the peptide mass fingerprint from a modified and an unmodified version of the same sample, our in-house search application was able to identify the citrullinated peptides in the mixture. This strategy was optimized on synthetic peptides and validated on a digest of in vitro citrullinated fibrinogen, where different proteolytic enzymes were used to augment the protein coverage. This new method results in easy detection of citrullinated residues, without the need for complex mass spectrometry equipment.