Research on the aromas. On the aroma of coffee. II. Pyrazines and pyridines

Pyrazines and pyridines occurring in a coffee concentrate are analyzed by two procedures. 24 compounds have been identified and the presence of some 10 more is revealed. The syntheses, mass and infrared spectral data of reference compounds are given.     

Analytical techniques for the investigation of coffee aroma

A review is provided on instrumental measurement techniques used in coffee aroma analysis comprising sample preparation and identification techniques. In addition, a brief survey of the complex nature of coffee aroma is given.     

Rapid synthesis of kahweofuran and its derivatives, the coffee aroma components

Kahweofuran, as an impact flavor component of roasted coffee and possesses the 6-methyl-2,3-dihydrothieno[2,3-c]furan structure, was rapidly synthesized from 2-acetyl-3-hydroxymethylthiophene by the formal reductive cyclization using the Wilkinson’s catalyst. Similarly, the syntheses of the 4-methyl, 6-ethyl and 4,6-dimethyl derivatives were also achieved in favorable yields.     

Use of computerized pattern recognition in the analysis of stress induced changes in coffee aroma

The aim of the study was to evaluate changes in the aroma of coffee that has been exposed to heat for some time. Coffee grinds were extracted with water. The coffee was kept hot and sampled periodically using a continuous gas phase extraction method. Gas chromatography/mass spectrometry was used to follow changes in chromatographic profiles. Data were subjected to pattern recognition. About 20 substances were found that significantly changed when exposed to heat.     

Developing qualitative extraction profiles of coffee aromas utilizing polymeric ionic liquid sorbent coatings in headspace solid-phase microextraction gas chromatography-mass spectrometry

Two solid-phase microextraction (SPME) sorbent coatings based on polymeric ionic liquids (PILs) have been utilized for the analysis of complex coffee aroma samples. The PIL-based SPME coatings examined, namely, poly(1-(4-vinylbenzyl)-3-hexadecylimidazolium bis[(trifluoromethyl)sulfonyl]imide) [poly(VBHDIm⁺ NTf₂⁻)], with ∼14-μm thickness, and poly(1-vinyl-3-hexylimidazolium chloride) [poly(ViHIm⁺ Cl⁻)], with ∼8-μm thickness, were employed for the headspace determination of up to 49 analytes from four different coffee beans: two French roast coffees of different brands, Sumatra coffee, and decaffeinated Sumatra coffee. The analysis was conducted using gas chromatography coupled to mass spectrometry. For comparative purposes, the commercial polyacrylate (PA, 85-μm film thickness) SPME coating was utilized under the same extraction conditions. The three SPME coatings tested behaved quite differently as a function of the families of compounds extracted. Thus, the poly(VBHDIm⁺ NTf₂⁻) coating was extremely selective for aldehydes while also exhibiting good extraction efficiencies for acids. The poly-(ViHIm⁺ Cl⁻) coating exhibited superior performance for aromatic alcohols, and the PA coating worked better for heterocyclic aromatics. Both PIL-based SPME sorbent coatings demonstrated exceptional selectivity and extraction efficiency when dealing with complex coffee aromas in spite of their small film thicknesses.     

On the 60th Birthday of F. I. Danilov

Russian Journal of Electrochemistry -     

Reliable characterization of coffee bean aroma profiles by automated headspace solid phase microextraction-gas chromatography-mass spectrometry with the support of a dual-filter mass spectra library

This investigation is based on the automated solid phase microextraction GC-MS analysis of the volatile fraction of a variety of coffee bean matrices. Volatile analytes were extracted by headspace (HS)-SPME which was achieved with the support of automated instrumentation. The research was directed towards various important aspects relating to coffee aroma analysis: monitoring of the volatile fraction formation during roasting; chromatographic differentiation of the two main coffee species (Arabica and Robusta) and of a single species from different geographical origins; evaluation of the influence of specific industrial treatments prior to roasting. Reliable peak assignment was carried out through the use of a recently laboratory-constructed "flavour and fragrance" library and a dual-filter MS spectral search procedure. Further emphasis was placed on the automated SPME instrumentation and on its ability to supply highly repeatable chromatographic data.     

On the rheology of cold drawing. I. Elastic materials

In this, the first paper in a series on neck formation and steady-state drawing of polymeric fibers and films under uniaxial tension, the emphasis is laid on those aspects of the mechanics of cold drawing that are not sensitive to viscoelastic effects and, therefore, can be treated by use of constitutive assumptions appropriate to elastic materials. It is here shown that a unidimensional theory which has been employed to model the mechanics of slender bars in tension₆ can be derived as an approximation for three-dimensional bars and, in a sense which can be made precise, is valid to within an error of the order of the fourth power of the thickness. A particular constitutive equation for incompressible, three-dimensional, elastic materials is explored in detail and is found to yield, for such slender bars as thin fibers and wide (but thin) strips of film, equations of equilibrium whose solutions are in good qualitative accordance with the necks and drawing configurations observed in practice.     

On the Use of the Knox Equation. I. the Fit Problem

Abstract

To obtain significant A, B, and C parameters of the Knox equation, which corresponds to the plot of the reduced plate height, h, versus the reduced linear velocity, v, actual results must be fitted correctly. The Knox equation is analyzed, the rôle of each individual parameter is shown. The equation producing the coordinates of the minimum plate height (maximum efficiency) is fully derived from the derivative of the Knox equation. Two tables giving the minimum coordinates for usual A, B, and C ranges are listed. The classical fit method is derived and analyzed. A graphical fit method which uses the remarkable graphical capabilities of modern spreadsheet packages is described. A synthetical set of data was fitted. It is demonstrated that each Knox parameter, obtained through fit procedures, must be given with the fitting confidence interval which is often in the 20% range.     

On the reaction of isothiosemicarbazides with heterocumulenes. Part I

Isothiosemicarbazides 2 react with acyl isothiocyanates under addition-cyclization to yield 1,3,4-thiadiazoline-2-imines 3 as well as the isomeric 2-amino-substituted 1,3,4-thiadiazolium-5-acylaminides 3′ . In a similar manner the 2-hydrazino-substituted 1,3-thiazoline 4 adds ethoxycarbonyl isothiocyanate to give the thiosemicarbazide 5 , which undergoes a rearrangement to the 1,3,4-thiadiazoline-2-imine 5′. The [2+2] cycloreversion of 3d involving ethoxycarbonyl iso(thio)cyanate and the thermal induced Dimroth rearrangement of 3′f and h are also discussed.     

On the photodecomposition of chlorophyll in vitro. I. Reaction rates

Abstract— Chlorophyll solutions are irreversibly bleached by light in the presence of oxygen. The action spectra parallel the absorption spectra for both chlorophyll a and b. The reaction is of second order with a Q₁₀ of 1.26. The reaction rates for chlorophylls a and b are of the same order of magnitude. Depending upon the light source, the initial rate for chlorophyll a is slightly higher, by a factor of 1.15 to 1.30. The rate for pheophytin is lowe 3 by several orders of magnitude. No pheophytin has been detected in the reaction products of the irradiated chlorophyll solutions in the absence of water.     

香米特征香味成分2-乙酰基-1-吡咯啉提取及检测方法研究进展

2-乙酰基-1-吡咯啉(2-AP)是目前已经探明的香米特征性香味成分,其含量的高低直接影响香米的品质与价格,但由于该成分在天然香米中的含量通常低至微克每千克,在采用现代分析检测方法测定时,还可能受到样品基质干扰、色谱分离共流出等问题的影响,因此,如何从稻米样品中高效提取该化合物并结合适当的检测方法进行精确测定具有一定的挑战性。该文综述了对稻米中2-AP进行测定时常用的样品前处理方法及仪器分析方法。样品前处理方法主要有蒸馏法、萃取法及顶空富集法等;仪器分析方法主要包括气相色谱及气相色谱-质谱法、气相色谱-嗅觉测试法,以及最新被开发出来的衍生化-高效液相色谱-串联质谱法。该综述将为食品贸易领域香米中2-AP的测定、农业领域香米的遗传育种及水肥管理、食品加工领域米香类稳定风味成分的开发等提供参考依据。