Contribution of linoleic acid to the bitter taste of poppy seeds (Papaver somniferum)

In lipids isolated from poppy seeds which tasted "burning-bitter" the off-taste was associated with the free fatty acids fraction. In this fraction linoleic acid predominates, while oxidized fatty acids were among the minor constituents. The taste threshold of linoleic acid emulsified in water with monolinolein lies in the range of 4.0-6.0 mumol/ml. On the basis of its high concentration and relatively low taste threshold we conclude that free linoleic acid contributes significantly to the "burning-bitter" off-taste in poppy seeds.     

Detection of Furanoid Fatty Acids in Soya-Bean Oil – Cause for the Light-Induced Off-Flavour

The following furanoid fatty acids were detected in soya-bean oil (SBO), wheat germ oil, rapeseed oil and corn oil: 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid(I),10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoid acid (II), 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic acid (III). A model experiment indicated that II and III were quickly photooxidized with formation of the intense flavour compound 3-methyl-2-4-nonanedione (MND) as secondary product. MND causes the light-induced off-flavour of SBO. A method for the quantification of the three furanoid fatty acids in vegetable oils was developed. The amounts of II and III were relatively high (0.02-0.04%) in unprocessed and refined SBO and in one sample of wheat germ oil and quite low (0.0015–0.0035%) in corn oil and rapeseed oil. The furanoid fatty acids I, II and III were absent on olive and sunflower oils.     

A Comparative Study of the Potent Odorants of Different Virgin Olive Oils

The flavour of virgin olive oil was investigated by means of an aroma extract dilution analysis. A comparative study of four oil samples differing in the flavour, indicated that the following odorants were mainly responsible for the odour notes given in brackets: (Z)-3-hexenol, hexanal, (E)-2-hexenal and (Z)-3-hexenal (green), ethyl 2-methylbutyrate, (Z)-3-hexenyl acetate and ethyl cyclohexanoate (fruity), (E,E)-2,4-decadienal, (E)- and (Z)-2-nonenal (fatty) and 4-methoxy-2-methyl-2-butanethiol (black currant-like).     

Visualizing 3D flow

We discuss volume line integral convolution (LIC) techniques for effectively visualizing 3D flow, including using visibility-impeding halos and efficient asymmetric filter kernels. Specifically, we suggest techniques for selectively emphasizing critical regions of interest in a flow; facilitating the accurate perception of the 3D depth and orientation of overlapping streamlines; efficiently incorporating an indication of orientation into a flow representation; and conveying additional information about related scalar quantities such as temperature or vorticity over a flow via subtle, continuous line width and color variations     

Buchbesprechungen

Ohne Zusammenfassung

---

Book reviews

     

Structure-odour-activity relationships of alkylpyrazines

 The odour thresholds (i.e. the lowest concentration at which an odour can be detected) of 80 alkylpyrazines, most of them synthesized, were determined by gas chromatography-olfactometry. Trimethylpyrazine (1) had the lowest threshold (50 ng/l air) amongst mono-, di-, tri- and tetramethylpyrazine. Substitution of the methyl group in position 2 of 1 by an ethyl group yielded 2-ethyl-3,5-dimethylpyrazine (2) showing a 4500-fold lower odour threshold than 1. The thresholds of 2-ethenyl-3,5-dimethylpyrazine (3), 2,3-diethyl-5-methylpyrazine (4) and 2-ethenyl-3-ethyl-5-methylpyrazine (5) were as low as that of 2. The threshold of 3-ethenyl-2-ethyl-5-methylpyrazine was 8000 times higher than that of 5, indicating that an ethenyl group was only tolerated in position 2, but not in position 3. A further increase in the odour threshold was found when the ethenyl or the ethyl group was located in position 5. Substitution of the ethyl group of 2 by a (Z)-1-propenyl group increased the threshold only by a factor of 5, whereas the (E)-isomer and the 2-propenyl group enhanced the threshold by factors of 160 and 27000, respectively. Also a propyl, butyl, pentyl, isobutyl or hexyl group in position 2 of 2 was too bulky, and in these molecules the odour threshold was at least 2200 times higher than that of 2. The geometrical structure of a theoretical receptor was obtained by superimposing the minimized structures of pyrazines with low thresholds (Chem-X force-field minimization). Sterically forbidden regions in the resulting model were found by superimposing pyrazines with high thresholds.     

Integrated design and control for robust performance: Application to an MSMPR crystallizer

The interplay of different types of performance constraints in an integrated design and control problem is studied by means of a case study. This integrated problem is based on a recent method for robust process design [M. Mönnigmann, W. Marquardt, Normal vectors on manifolds of critical points for parametric robustness of equilibrium solutions of ODE systems, J. Nonlinear Sci. 12 (2002) 85–112; M. Mönnigmann, W. Marquardt, Steady state process optimization with guaranteed robust stability and feasibility, AIChE J. 49 (12) (2003) 3110–3126; M. Mönnigmann, W. Marquardt, Steady state process optimization with guaranteed robust stability and flexibility: application to HDA reaction section, Ind. Eng. Chem. Res. 44 (2005) 2737–2753; W. Marquardt, M. Mönnigmann, Constructive nonlinear dynamics in process systems engineering, Comput. Chem. Eng. 29 (2005) 1265–1275; M. Mönnigmann, Constructive nonlinear dynamics methods for the design of chemical engineering processes, Ph.D. Thesis, RWTH Aachen University, 2003]. The design is found by means of a steady-state optimization problem accounting for process economics and performance requirements. In particular, the latter are represented by constraints which guarantee a user-specified performance of the design in spite of parametric uncertainties. For the first time, two types of dynamic performance constraints are used simultaneously within the adopted framework. These are constraints on time-domain performance indicators as well as on the asymptotic dynamic process behavior. Furthermore, the effect of uncertainty in both, design and model parameters, is accounted for. A key strength of the suggested framework is the direct quantification of the trade-offs between economics and dynamic performance requirements for a selection of uncertainty scenarios. A series of different integrated design and control problems are formulated and solved for a continuous mixed-suspension mixed-product removal (MSMPR) crystallizer. The process exhibits a complex nonlinear behavior and represents a challenging example. The results of the case study allow an in depth understanding of the interactions of design and control for the underlying process.