Evaluation of potent odorants in heated egg yolk by aroma extract dilution analysis

Egg yolk was extracted using the method of Likens-Nickerson (simultaneous distillation/extraction). The resulting aroma extract, which smelled characteristic of heated egg yolk was analysed by aroma extract dilution analysis and gas chromatography–mass spectrometry. Of 41 odorants that were detected, 19 could be identified. Compounds with high flavour dilution factors were methional, phenyl acetaldehyde, 2-acetyl-1-pyrroline, heptanal, 1-octen-3-one and (E,E)-2,4-decadienal. Strecker degradation of methionine, phenylalanine and proline, as well as autoxidation of phospholipid-bound linoleic and arachidonic acids are proposed as the major factors for egg yolk flavour formation.     

Identification of key aroma compounds generated from cysteine and carbohydrates under roasting conditions

 Application of the aroma extract dilution analysis to volatile fractions obtained from dry-heated (180  °C for 6 min on silica) mixtures of cysteine and ribose (I), glucose (II) or rhamnose (III) revealed the following compounds with the highest flavour dilution factors: 2-furfurylthiol (FFT) and 2-acetyl-2-thiazoline in I; 2-acetyl-2-thiazoline, 2-propionyl-2-thiazoline and FFT in II; 5-methyl-2-furfurylthiol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 2-acetyl-2-thiazoline, 2-propionyl-2-thiazoline and (Z)-2-propenyl-3,5-dimethylpyrazine in III. A comparison of the data with results of previous studies, in which the same mixtures had been reacted under aqueous conditions (145  °C, 20 min) revealed that the dry-heating process favoured the formation of the roasty, popcorn-like smelling 2-acetyl- and 2-propionyl-2-thiazoline as well as the potato-chip-like 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine in all three reaction systems. 2-Ethenyl- and (Z)-2-propenyl-3,5-dimethylpyrazine, both having an intense roast potato smell were, however, selectively formed in the presence of ribose or rhamnose, respectively. Based on quantitative data, pathways generating the latter two pyrazines via their 1-desoxyosones as key intermediates are discussed. Received: 11 March 1998     

Characterisation of the most odour-active compounds in a peel oil extract from Pontianak oranges (<Emphasis Type="Italic">Citrus nobilis</Emphasis> var. Lour. <Emphasis Type="Italic">microcarpa</Emphasis> Hassk.)

Isolation of the volatile fraction from the peel of Pontianak orange (Citrus nobilis var. Lour. microcarpa Hassk.) by a careful solvent extraction/vacuum distillation process followed by application of an aroma extract dilution analysis (AEDA) revealed 32 odour-active compounds in the flavour dilution (FD)-factor range of 4–2048, 26 of which could be identified. On the basis of high FD-factors, (R)/(S)-linalool, myrcene, (R)-limonene, and 1,8-cineole were characterised as the most potent odorants, followed by octanal, (E,E)-2,4-decadienal, nerol, (E)-2-dodecenal, geraniol, and (E,E)-2,4-nonadienal. In addition, one odorant resembling the characteristic sulphurous, resinous aroma of the Pontianak peel oil was detected with a quite high FD-factor of 128. By mass spectrometry followed by synthesis, 1-phenylethanethiol exhibiting an intense sulphurous, resinous smell at the very low odour threshold of 0.005 ng/L in air, was found to be responsible for the odour impression detected in the extract. 1-Phenylethanethiol occurring as a mixture of the (R)-(76%) and the (S)-enantiomer (24%) has previously not been reported as odorant in foods. Application of static headspace aroma dilution analysis (SHA) on Pontianak peel revealed the green, grassy smelling odour-active compounds hexanal and (Z)-3-hexenal as further important odorants in the headspace above the peels.     

Characterisation of the key aroma compounds in the peel oil of Pontianak oranges (<Emphasis Type="Italic">Citrus nobilis</Emphasis> Lour. var. <Emphasis Type="Italic">microcarpa</Emphasis> Hassk.) by aroma reconstitution experiments

Nineteen odour-active compounds previously identified with high Flavour Dilution factors in an extract from the peel oil of Pontianak oranges (Citrus nobilis Lour. var. microcarpa Hassk.) were quantified using stable isotope dilution assays (SIDA). For this purpose, four new SIDA were developed, i.e. for the quantification of (E)-2-dodecenal, geraniol, nerol, and 1-phenylethanethiol. The results showed that (R)-limonene, myrcene, and (R)-α-pinene were the predominant compounds present in concentrations between 0.4 and 60 mg/g peel. An aroma recombinate containing the nineteen aroma compounds in the concentrations naturally occurring in the peel oil elicited the overall aroma of the peel oil itself, thus confirming the identification experiments. Furthermore, omission experiments showed that the unique odour quality of the peel is significantly influenced by the resinous, sulphurous-smelling 1-phenylethanethiol, although its concentration was only 38 ng/g peel.     

Visualization of a recombinant gene protein in the baculovirus expression vector system using confocal scanning laser microscopy

Expression of the recombinant protein beta-galactosidase in the Spodoptera frugiperda Sf-9 insect cell line infected by the Autographa californica nuclear polyhedrosis virus expressing beta-galactosidase (AcNPV-betagal) was visualized using confocal scanning laser microscopy with fluorescent staining of both the recombinant protein and the cell nucleus. The average size of the insect cells and the intracellular DNA concentration both increased markedly, respectively reading 3.8- and 2.3-fold the values before infection. The average beta-galactosidase activity began to increase at 20-24 h post infection and finally reached 1.9 x 10(4) units/ml. As the post infection time increased, the stained nucleus images expanded and spread broadly. Beta-galactosidase was first identified by fluorescent staining at 12 h post-infection, filled the cell at 27 h, began to be released at 36 h, and finally spread out of the cell. The locations of the nucleus and expressed beta-galactosidase were identified from computerized tomograms and 3-dimensional images.     

Identification and quantification by LC–MS/MS of a new precursor of 3-mercaptohexan-1-ol (3MH) using stable isotope dilution assay: Elements for understanding the 3MH production in wine

The isotopically labelled S-3-(hexan-1-ol)-glutathione d₂/d₃ (G3MHd₂/d₃) was synthesized with a strategy based on acid-labile protecting groups. The natural analogue of this compound could be a precursor of 3-mercaptohexanol, a varietal thiol reminiscent of grape fruit, released during alcoholic fermentation. In a first time, deuterated glutathione conjugate was used to perform identification and quantification by stable isotope dilution assay of G3MH in musts from several varieties: Sauvignon, Riesling and Gewurztraminer.     

Antioxidant capacity and inhibitory effect of grape seed and rosemary extract in marinades on the formation of heterocyclic amines in fried beef patties

The effect of oil-based marinades containing grape seed extract (Vitis vinifera L.; 0.2, 0.4, 0.6 and 0.8 g/100 g) formulated in a water/oil emulsion or rosemary extract (Rosmarinus officinalis; 0.12, 0.2, 0.6, 1.0 and 1.5 g/100 g) in oil on the formation of heterocyclic amines (HAs) in fried beef patties was examined. After application of marinades and frying, four HAs MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), PhIP (2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine), Norharman, and Harman were found at low levels in all fried patties, MeIQx (0.3–1.0 ng/g), and PhIP (0.02–0.3 ng/g). The content of MeIQx and PhIP were significantly reduced by approx. 57% and 90% (p < 0.05), respectively, after use of marinades containing the highest extract concentration. The antioxidant capacity of grape seed was about two-times greater than that of rosemary extract. A correlation between inhibition of HAs and Trolox-equivalents (MeIQx, R² = 0.85, p < 0.001; PhIP, R² = 0.83, p < 0.001) was found. Sensory tests showed a high acceptance of flavour and colour for controls and samples.