Synergistic inhibition effect of 2-phenylethanol and ethanol on bioproduction of natural 2-phenylethanol by Saccharomyces cerevisiae and process enhancement

Natural 2-phenylethanol (PEA) could be produced on a large scale by way of bioconversion with yeast from l-phenylalanine. In this work the synergistic inhibition effect of the target product PEA and the byproduct ethanol on the bioconversion rate by Saccharomyces cerevisiae R-UV3 was systematically studied and a new kinetic model with an item representing the synergistic effect was proposed. Optimization strategies to repress the inhibition effect of PEA and ethanol were carried out in the mode of fed-batch culture with ISPR. The glucose concentration was regulated at the level of 0.2±0.1g/L by controlling a suitable respiratory quotient on line, which could limit the accumulation of the ethanol lower than 10g/L. In the presence of resin FD0816 with a weight of 10% of the medium, PEA was removed from the broth and the overall PEA concentration and the space-time yield reached 13.7g/L and 0.39g L(-1) h(-1) respectively. The semi-continuous process with ISPR was performed, in which the replacement of the resin was operated repeatedly when the aqueous PEA was over 2.7g/L and bioconversion continued until the bioactivity of the yeast cells declined, consequently achieving a final overall PEA concentration of 32.5g/L and a space-time yield of 0.45g L(-1) h(-1).     

Adsorption of volatile aroma compound 2-phenylethanol from synthetic solution onto granular activated carbon in batch and continuous modes

This paper reports a study on the adsorption of the aroma component 2-phenylethanol from an aqueous solution onto granular activated carbon, derived from coconut husks, using batch and continuous (packed-bed column) systems. In the batch mode, the contact time required to attain the adsorption equilibrium was 90 min. The adsorption isotherms were evaluated at 20.0 °C, 30.0 °C and 40.0 °C. In the continuous mode, the effects of flow rate and bed length were studied. Experimental data showed that the breakthrough and exhaustion times decreased with higher flow rates and increased with higher packed beds. The adsorption in the fixed-bed column was more efficient under the following conditions: flow rate of 3.5 mL min⁻¹ and bed length of 11 cm. Based on the data acquired, adsorption appears to represent a promising method for the recovery of 2-phenylethanol lost during the instant coffee production process.     

Kinetics and equilibrium for thermolysin-catalyzed syntheses of dipeptide precursors in aqueous/organic biphasic systems

The initial kinetics for the syntheses of N-(benzyloxycarbonyl)-L-alanyl-L-phenylalanine methyl ester (ZAPM) and N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methyl ester (ZDPM) in an aqueous/organic biphasic system, using free thermolysin were elucidated, both experimentally and theoretically. As model organic solvents, ethyl acetate and tert-amyl alcohol were used. The substrate concentration dependencies of the initial rate of syntheses for ZAPM and ZDPM observed in the biphasic system were well simulated using the overall partition coefficients of the substrates and product taking into consideration the effect of the formation of ion-pair complexes between the acid and amine components of the substrate, the initial rate equations determined in an aqueous buffer saturated with the organic solvent, and the pH dependence of the rate constant. The equilibrium yield for the synthesis of ZDPM was also in good agreement with the calculated result using the overall partition coefficients and equilibrium constant measured in the aqueous buffer.     

Analysis for partition equilibrium of amino acid derivatives in aqueous/organic biphasic systems

The overall partition coefficients of the acid and amine components of amino acid derivatives, the substrates for proteinase-catalyzed synthesis of oligopeptide precursors, in an aqueous/organic biphasic system were studied both experimentally and theoretically. In a single-component system containing either an acid or amine component, the overall partition coefficient was well expressed by a model using the acid dissociation constant and partition coefficients for the non-ionized and ionized forms of the component. The overall partition coefficient in a binary-component system containing both acid and amine components was well simulated by the model when the formation of ion-pair complexes in the organic solvent phase was taken into consideration in addition to the partitioning of the non-ionized and ionized forms of the components. The formation of ion-pair complexes in the organic solvent phase was indicated by an analysis using Fourier transform infrared ray spectroscopy (FT-IR). In addition to the partition equilibrium, the aqueous-phase pH change after partitioning could be predicted by the model.     

油酸-甘油-无水乙醇共混体系与超临界CO2的相平衡

旨在为生物柴油后处理阶段的超临界CO₂提纯工艺提供参考数据,以生物柴油生产过程中后处理阶段体系所含的油酸、无水乙醇及甘油为原料,通过在SYLG-01型超临界流体相平衡实验装置中,观察油酸-甘油-无水乙醇共混体系在温度为308 K下与CO₂达到相平衡状态的过程。结果表明,油酸-甘油-无水乙醇共混体系为液-液两相,与CO₂在相平衡实验装置内最开始是气-液-液态,随着压力的增加,当CO₂达到超临界状态时,不同相之间的流动性和传递性增强,共混体系变成了均一态。因此,改变超临界CO₂的压力,有望将体系中的游离脂肪酸和副产物甘油同时萃取分离。     

Fate of salmonellae in citrus oils and aqueous aroma

The manufacture of orange juice sometimes involves the use of flavor fractions recovered from oranges. The impact of such flavor fractions on Salmonella viability was investigated. A five-strain cocktail of salmonellae was challenged with a singlefold cold-pressed peel oil (CPO), a fivefold CPO, a terpeneless CPO, and an aqueous orange aroma stored at 4 and 25 degrees C. The results obtained in this study indicate that the test compounds possess substantial antimicrobial activity and can cause population reductions larger than the 5-log10 performance standard required by the U.S. Food and Drug Administration's juice hazard analysis critical control point rule (21 CFR 120). The times required to achieve 5-log10 reductions in Salmonella populations ranged from 0.03 to 42.8 h. In general, levels of antimicrobial activity for the test substances were in the following order: terpeneless CPO > five-fold CPO > single-fold CPO > aqueous aroma.     

Analysis of a chiral aroma compound by complexation gas chromatography

Summary Complexation gas chromatography with Ni(II)-bis[3-heptafluorobutyryl-(1R)-camphorate] as a chiral stationary phase is an efficient analytical method to resolve some racemic 1,3-oxathianes quantitatively into their enantiomers without derivatization. Configurations of 1,3-oxathiane enantiomers were assigned by optically pure reference substances.

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Analyse eines chiralen Aromastoffs mittels Komplexierungsgaschromatographie

Zusammenfassung Durch Komplexierungs-Gaschromatographie an. Ni(II)-bis [3-heptafluorbutyryl-(1R)-campherat] als chiraler stationärer Phase werden die racemischen Gemische einiger 1,3-Oxathiane ohne Derivatisierung quantitativ getrennt. Die Konfiguration der getrennten 1,3-Oxathiarl-Enantiomere wird mittels optisch reiner Vergleichssubstanzen zugeordnet.

     

Efficient photochemical decomposition of long-chain perfluorocarboxylic acids by means of an aqueous/liquid CO2 biphasic system

Photochemical decomposition of persistent and bioaccumulative long-chain (C9-C11) perfluorocarboxylic acids (PFCAs) with persulfate ion (S2O8(2-)) in an aqueous/liquid CO2 biphasic system was examined to develop a technique to neutralize stationary sources of the long-chain PFCAs. The long-chain PFCAs, namely, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUA), which are used as emulsifying agents and as surface treatment agents in industry, are relatively insoluble in water but are soluble in liquid CO2; therefore, introduction of liquid CO2 to the aqueous photoreaction system reduces the interference of colloidal PFCA particles. When the biphasic system was used to decompose these PFCAs, the extent of reaction was 6.4-51 times as high as that achieved in the absence of CO2. In the biphasic system, PFNA, PFDA, and PFUA (33.5-33.6 micromol) in 25.0 mL of water were 100%, 100%, and 77.1% decomposed, respectively, after 12 h of irradiation with a 200-W xenon-mercury lamp; F- ions were produced as a major product, and short-chain PFCAs, which are less bioaccumulative than the original PFCAs, were minor products. All of the initial S2O8(2-) was transformed to SO42-. The system also efficiently decomposed PFCAs at lower concentrations (e.g., 4.28-16.7 micromol of PFDA in 25.0 mL) and was successfully applied to decompose PFNA in floor wax.     

Partition efficiency of cytochrome c with alcohol/salt aqueous biphasic flotation system

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Persistence of aroma compounds in human breath after consuming an aqueous model aroma mixture

Persistence of aroma compounds in the breath was studied from a model mixture containing five chemicals in an aqueous medium at two concentration levels. The breath of five subjects was monitored by atmospheric pressure ionization-mass spectrometry (API-MS) and the persistence of each compound computed as the ratio of instrumental responses between first and second breaths. Persistence was modelled, based on relevant physicochemical parameters of the compounds in the mixture. Vapour pressure was found to be the most significant parameter. Persistence was not influenced by panellists, volatile concentration levels or replications within subjects, although there were large differences in persistence among chemicals.     

Simulation of retronasal aroma of white and red wine in a model mouth system. Investigating the influence of saliva on volatile compound concentrations

The influence of saliva on aroma release from white and red wines was studied in a model mouth system. Aroma compounds were analysed in the dynamic headspace of wines by solid phase micro extraction/gas chromatography with flame ionization detection. Volatile compounds were identified by solid phase micro extraction/gas chromatography-mass spectrometry, resulting in a total of 43 compounds in white wine and 41 in red wine. The results showed a greater influence of saliva on aroma release in white wine than red wine. In white wine treated with human saliva, esters and fusel alcohols, responsible for fruity and fusel oil odours, were reduced of 32–80%; by contrast, the concentration of 2-phenylethanol and furfural, responsible for rose and toasted almond notes, increased by 27% and by 155%, respectively. In red wine, treated with human saliva, only a few esters decrease, with a reduction of 22–51% due to protein-binding ability of polyphenols that are able to inhibit the activity of the saliva. C-13 norisoprenoids, vitispirane (eucalyptol) and TDN (kerosene), decreased both in white and red wine, showing a comparable variation while, for β-damascenone, the variation was insignificant.     

Investigations into the stabilization of a volatile aroma compound using a combined emulsification and spray drying process

The aromatic compound 3-methylbutyraldehyde (3-mba) was stabilized using a combined emulsification (W₁/O/W₂) and spray drying process. The process suitability and the encapsulation properties of eight materials were evaluated. Whey protein concentrate (WPC), sodium octenyl succinate modified starch (modified starch 1), maltodextrin, and gum Arabic (GA) were found to be the best process-adapted microencapsulation materials. These materials were chosen for further experiments in which the influence of the solids content on flavor intensity and flavor retention during storage were determined. The amount of encapsulated 3-mba increased with increasing solids content from 40–50% using WPC, modified starch 1, and maltodextrin. Microcapsules with GA reached the maximum value of encapsulated 3-mba at 45% solids. After 11 days of storage, flavor retention decreased in the following order: GA > modified starch 1 > WPC ∼ maltodextrin. Finally, the spray drying process was optimized by design of experiments (DoE). The optimized parameters were a feed temperature of 40 °C, a dry mass in W₂ of 60%, and an amount of W₁/O of 40% using modified starch 1.     

Analysis of the chiral aroma compound filbertone by inclusion gas chromatography

Summary By inclusion gas chromatography on (2,6-di-O-methyl-3-O-perfluoroacyl)--cyclodextrins (perfluoroacyl=trifluoroacetyl or heptafluorobutanoyl), the aroma compound of hazelnuts,E-5-methyl-hept-2-en-4-one, filbertone, was quantitatively separated into its enantiomers without derivatization. The method is used for the screening of the enantiomeric composition of filbertone in foodstuffs.

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Analyse des chiralen Aromastoffes Filberton mittels Inclusionsgaschromatographie

Zusammenfassung Durch Inclusions-Gaschromatographie an (2,6-Di-O-methyl-3-O-perfluoracyl)--cyclodextrinen (Perfluoracyl=Trifluoracetyl oder Heptafluorbutanoyl) wird der Aromastoff der Haselnüsse, E-5-Methyl-hept-2-en-4-on, Filberton, ohne Derivatisierung quantitativ in die Enantiomere getrennt. Die Methode wird zur Analyse der Enantiomerenzusammensetzung von Filberton in Brotaufstrich verwendet.

     

Antityrosinase and antimicrobial activities of 2-phenylethanol, 2-phenylacetaldehyde and 2-phenylacetic acid

The inhibition kinetics of 2-phenylethanol, 2-phenylacetaldehyde and 2-phenylacetic acid on the enzyme activity of mushroom tyrosinase have been investigated. The results showed that these aromatic compounds can lead to reversible inhibition of the enzyme; furthermore, 2-phenylacetaldehyde and 2-phenylacetic acid are uncompetitive inhibitors and 2-phenylethanol is a mixed-type inhibitor. The inhibition constants have been determined and the inhibiting ability was: 2-phenylacetaldehyde > 2-phenylacetic acid > 2-phenylethanol, indicating that the functional group on the benzene ring group played an important role in the inhibition of the enzyme. In addition, 2-phenylacetic acid and 2-phenylethanol were found to have effective antibacterial activities, and 2-phenylacetic acid was more effective against Escherichia coli and Ralstonia solanacearum than 2-phenylethanol, but 2-phenylacetaldehyde lacked of antibacterial activity.     

Temperature effect on solubility of aroma compounds in various aqueous solutions

Solubility of nine aroma compounds (methyl ketones, ethyl esters, aldehyde and alcohol) in various aqueous solutions was measured by the mutual solubility method from −10 to +10 °C. Influence of both, the nature (carbohydrates and polyols) and the substrate concentration (from 0 to 57.5g/100 g) on aroma solubility in aqueous solutions was studied. Aroma solubility in water decreased when aroma hydrophobicity increased. Aroma solubility in various aqueous solutions decreased when substrate concentration increased; their solubility was higher in polyols solutions than in polysaccharides ones. Temperature effect on aroma solubility showed a noncontinuous evolution for solutions without ice: from +25 to +4 °C, solubility decreased, then from +4 to −5 °C, solubility increased. Finally, from −5 to −10 °C solubility decreased once again. The same behavior was observed for all studied media. Comparison with other characteristics (such as density and water structure) of the aqueous solutions was done in order to better understand this temperature effect on aroma solubility.     

紫外分光光度法测定发酵液中的2-苯乙醇含量

建立了紫外分光光度法测定发酵液中2-苯乙醇含量的方法。用正庚烷萃取待测样品中的2-苯乙醇,然后直接测定正庚烷溶液258nm波长下的吸光度,根据标准曲线可直接计算出发酵样品中2-苯乙醇含量,方法的检出限为0.19g/L,样品加样回收率为100.4%,变异系数为1.66%。该方法具有准确度高、重现性好、操作简单等优点。     

Continuous enrichment and trace analysis of tetracyclines in bovine milk using dual-functionalized aqueous biphasic system combined with high-performance liquid chromatography

Two PPG₁₀₀₀ based temperature-sensitive magnetic ionic liquid were synthesized and characterized. The temperature-sensitive magnetic ionic liquid aqueous biphasic system combined with HPLC was applied for the continuous enrichment and trace analysis of tetracycline antibiotics (TC) in bovine milk for the first time. High enrichment factors were achieved and the detection was highly sensitive. The trace analysis of TC was rapid, free of organic solvent, recyclable and magnetically assisted for phase separation. Under optimum conditions, wide linear ranges of 0.25–300 ng/mL for all TC, high enrichment factors of 217.7–231.4, good precisions with relative standard deviation in the range of 0.74–3.97%, very low limits of detection of 0.031–0.067 ng/mL, limits of quantification of 0.103–0.223 ng/mL, and good recoveries of 94.28–99.76% were acquired for the proposed analytical method. Real milk analysis was satisfactory. This developed analytical method is showing great potential for trace analysis of targeted analytes in foods and drinks.