Competitive binding of aroma compounds by beta-cyclodextrin.

Retention of six aroma compounds has been studied after dehydration of ternary mixtures of aroma water and beta-cyclodextrin. A maximal retention of a mole of aroma per mole of beta-cyclodextrin has been observed for five of the aroma compounds, whereas retention of benzyl alcohol can be twice as high. Retention of a mixture of aroma compounds has also been studied. It has been noted that when volatile compounds compete for the same binding sites on beta-cyclodextrin, ethyl hexanoate, 2-methylbutyric acid, and benzyl alcohol are, respectively, better retained than ethyl propionate, hexanoic acid, and hexanol. Preferential retention observed with esters can be simply explained by their difference of physicochemical properties, but for the acids and alcohols a study at the molecular scale has been necessary. The better retention of 2-methylbutyric acid can be explained by differences in the nature of interaction between the acids and their carrier. At least selectivity of retention noted for the alcohol could be due to a difference in the location of the guest and also a difference in the number of aroma molecules that can be bound per polysaccharide molecule.

Evolution of the taste of a bitter Camembert cheese during ripening: characterization of a matrix effect.

The objective of this study was to characterize the effect of ripening on the taste of a typically bitter Camembert cheese. The first step was to select a typically bitter cheese among several products obtained by different processes supposed to enhance this taste defect. Second, the evolution of cheese taste during ripening was characterized from a sensory point of view. Finally, the relative impact of fat, proteins, and water-soluble molecules on cheese taste was determined by using omission tests performed on a reconstituted cheese. These omission tests showed that cheese taste resulted mainly from the gustatory properties of water-soluble molecules but was modulated by a matrix effect due to fat, proteins, and cheese structure. The evolution of this matrix effect during ripening was discussed for each taste characteristic.

Evolution of the composition of a selected bitter Camembert cheese during ripening: release and migration of taste-active compounds.

The aim of this study was to add to the understanding of changes in taste that occur during the ripening of a bitter Camembert cheese by the evolution of its composition. Physicochemical analyses were performed on rind, under-rind, and center portions of a Camembert cheese selected for its intense bitterness. At each of the six steps of ripening studied organic acids, sugars, total nitrogen, soluble nitrogen, phosphotungstic acid soluble nitrogen, non-protein nitrogen, Na, K, Ca, Mg, Pi, Cl, and biogenic amines were quantified in each portion. Changes in cheese composition seemed to mainly result from the development of Penicillium camemberti on the cheese outer layer. Migration phenomena and the release of potentially taste-active compounds allowed for the evolution of saltiness, sourness, and bitterness throughout ripening to be better understood. Apart from taste-active compounds, the impact of the cheese matrix on its taste development is discussed.

Isolation of oligopeptides from the water-soluble extract of goat cheese and their identification by mass spectrometry.

A procedure for the separation and identification of small peptides from the water-soluble fraction of a goat cheese was developed. The water-soluble extract was ultrafiltered (1000 Da membrane cutoff), and peptides were isolated by sequential chromatography: size exclusion chromatography (HPLC-grade water), anion exchange chromatography (phosphate buffer gradient), and semipreparative reverse-phase high-performance liquid chromatography (water/acetonitrile gradient). The fractions obtained were analyzed by combined mass spectrometry methods including electrospray ionization, liquid secondary ionization, and tandem mass spectrometry to identify and to confirm the sequences of 28 tri- to octapeptides naturally appearing in goat cheese during ripening. Among these peptides, 26 are produced by degradation of caseins but do not correspond to the known specific cleavages due to chymosin. Only low correlation was found between hydrophobicity of peptides and HPLC elution time with acetonitrile gradient.

Determination of taste-active compounds of a bitter Camembert cheese by omission tests.

The taste-active compounds of a Camembert cheese selected for its intense bitterness defect were investigated. The water-soluble fraction (WSE) was extracted with pure water and fractionated by successive tangential ultrafiltrations and nanofiltration. The physicochemical assessment of these fractions led to the construction of a model WSE which was compared by sensory evaluation to the crude water-soluble extract, using a panel of 16 trained tasters. As no significant difference was perceived, this model WSE was then used directly or mixed with other cheese components for omission tests. Among the main taste characteristics of the WSE (salty, sour, umami and bitter), bitterness was found to be due to small peptides whose mass distribution was obtained by RPHPLC-MS (400-3000 Da) and whose taste properties are discussed.

Taste active compounds in a goat cheese water-soluble extract. 1. Development and sensory validation of a model water-soluble extract.

The aim of this study was to evaluate the impact of the components of a goat cheese water-soluble extract (WSE) on its flavor by both physicochemical and sensory techniques with special emphasis on taste. After characterization of the organoleptic properties of the cheese, the WSE was extracted with pure water and submitted to successive tangential ultrafiltrations and nanofiltration. The physicochemical assessment of these fractions led to the constitution of a model mixture (MWSE) compared by sensory evaluation to the crude WSE, using a panel of 16 trained members. The results of both sensory profile and triangular tests indicate no significant difference, therefore proving that the reconstitution of the WSE was correct, thereby showing the sensory neutrality of lipids and peptides smaller than 500 Da, which had not been included in the MWSE. Moreover, the cheese gustatory characteristics are comparable to those of the WSE despite weaker levels of sharpness and astringency in the extract, the respective origins of which are discussed.

Taste active compounds in a goat cheese water-soluble extract. 2. Determination of the relative impact of water-soluble extract components on its taste using omission tests.

The aim of this work was to determine the relative impact of water-soluble compounds on the gustatory properties of a goat cheese water-soluble extract (WSE). Using a semisynthetic model mixture (MWSE) previously elaborated in physicochemical and gustatory accordance with the cheese WSE (see part 1, Engel et al. J. Agric. Food Chem. 2000, 48, 4252-4259), omission tests were performed. Among the main taste characteristics of the WSE (salty, sour, and bitter), saltiness was explained by an additive contribution of sodium, potassium, calcium, and magnesium cations, whereas sourness was mainly due to a synergistic effect involving sodium chloride, phosphates, and lactic acid and bitterness was found to result from calcium and magnesium chlorides, the impact of which was partially masked by sodium chloride. In contrast, amino acids, lactose, and peptides did not have any significant impact on WSE taste properties. To quantify the contribution of the taste active compounds to bitterness and saltiness, stepwise multiple linear regressions were performed. Those contributions were expressed as a percentage of the considered taste characteristic intensity in the WSE. The model obtained allowed up to 97.4% of the perceived saltiness to be described and approximately 85% of the bitterness.

Metabolism of ricinoleic acid into gamma-decalactone: beta-oxidation and long chain acyl intermediates of ricinoleic acid in the genus Sporidiobolus sp.

In order to study differences in gamma-decalactone production in yeast, four species of Sporidiobolus were cultivated with 5% of methyl ricinoleate as the lactone substrate. In vivo studies showed different time courses of intermediates of ricinoleic acid breakdown between the four species. In vitro studies of the beta-oxidation system were conducted with crude cell extracts of Sporidiobolus spp. and with ricinoleyl-CoA (RCoA) as substrate. The beta-oxidation was detected by measuring acyl-CoA oxidase, 3-hydroxyacyl-CoA dehydrogenase activities, and acetyl-CoA production. The time courses of the CoA esters resulting from RCoA breakdown by crude extract of Sporidiobolus spp. permit the proposal of different metabolic models in the yeast. These models explained the differences observed during in vivo studies.

Novel scheme for biosynthesis of aryl metabolites from L-phenylalanine in the fungus Bjerkandera adusta.

Aryl metabolite biosynthesis was studied in the white rot fungus Bjerkandera adusta cultivated in a liquid medium supplemented with L-phenylalanine. Aromatic compounds were analyzed by gas chromatography-mass spectrometry following addition of labelled precursors ((14)C- and (13)C-labelled L-phenylalanine), which did not interfere with fungal metabolism. The major aromatic compounds identified were benzyl alcohol, benzaldehyde (bitter almond aroma), and benzoic acid. Hydroxy- and methoxybenzylic compounds (alcohols, aldehydes, and acids) were also found in fungal cultures. Intracellular enzymatic activities (phenylalanine ammonia lyase, aryl-alcohol oxidase, aryl-alcohol dehydrogenase, aryl-aldehyde dehydrogenase, lignin peroxidase) and extracellular enzymatic activities (aryl-alcohol oxidase, lignin peroxidase), as well as aromatic compounds, were detected in B. adusta cultures. Metabolite formation required de novo protein biosynthesis. Our results show that L-phenylalanine was deaminated to trans-cinnamic acid by a phenylalanine ammonia lyase and trans-cinnamic acid was in turn converted to aromatic acids (phenylpyruvic, phenylacetic, mandelic, and benzoylformic acids); benzaldehyde was a metabolic intermediate. These acids were transformed into benzaldehyde, benzyl alcohol, and benzoic acid. Our findings support the hypothesis that all of these compounds are intermediates in the biosynthetic pathway from L-phenylalanine to aryl metabolites. Additionally, trans-cinnamic acid can also be transformed via beta-oxidation to benzoic acid. This was confirmed by the presence of acetophenone as a beta-oxidation degradation intermediate. To our knowledge, this is the first time that a beta-oxidation sequence leading to benzoic acid synthesis has been found in a white rot fungus. A novel metabolic scheme for biosynthesis of aryl metabolites from L-phenylalanine is proposed.

Male sex pheromone of cockroachEurycotis floridana (walker) (Blattidae, Polyzosteriinae): Role and composition of tergites 2 and 8 secretions.

InEurycotis floridana, the male calling behavior is associated with the exposition of epidermal glands located under tergites 2, 7, and 8. 4-Hydroxy-5-methyl-3(2H)-furanone and 4-hydroxy-2,5-dimethyl-3(2H)-furanone were recently identified as the specific components of tergite 7 secretion. Methylene chloride extracts of tergite 7 and its major compound 4-hydroxy-5-methyl-3(2H)-furanone attract the conspecific females at a distance. Methylene chloride extracts of tergite 8 are also attractive at a distance to the females, whereas extracts of tergite 2 had no effect on males and females. Our GC investigations showed the absence of specific compounds in tergite 2 secretions. The GC-MS analyses revealed that the male secretion of the gland under tergite 8 is mainly a mixture of (2R*, 3R*)-butanediol, 1-dodecanol and benzyl 2-hydroxybenzoate. These compounds were tested at different concentrations on their own, or as a mixture. Only (2R*, 3R*)-butanediol and 1-dodecanol were attractive for the females. Their functions, as components of the male sex pheromone, in addition with the two derivatives of the furanone are discussed.

Sesquiterpenes in the frontal gland secretions of nasute soldier termites from New Guinea.

In five New GuineaNasutitermes (N. gracilirostris, N. novarumhebridarum, N. torresi, N. triodiae, and an undescribed speciesN. sp.F), we have detected and identified 10 sesquiterpenes. Eight of these compounds (ß)-elemene,ß-caryophyllene,α-humulene,α-muurolene,γ-selinene,ß-selinene, germacrene-A, and γ2-cadinene) were identified by GC and GC-MS (EI). Two uncommon sesquiterpenes, (5R(*), 7R(*), 10S(*))-selina-4(14),11-diene and (5R(*), 7R(*), 10S(*))-selina-3,11-diene, were identified by GC, GC-MS (EI, CI), GC-FTIR, and mono- and bidimensional NMR. Whereas in most species sesquiterpenes are present in low or trace amounts, inN. novarumhebridarum the sesquiterpenic fraction of soldier frontal gland secretion is equal to that of the monoterpenes.

Chemistry of pheromonal and defensive secretions in the nymphs and the adults ofDysdercus cingulatus Fabr. (Heteroptera, Pyrrhocoridae).

The exocrine secretions from the nymphs and the adults of both sexes inD. cingulatus were chemically investigated. Seven compounds were identified in the anterior glands, and eleven in the median dorsoabdominal glands of nymphs and adults of both sexes. Fifty-five compounds were identified in the defensive glands (34 in posterior dorsoabdominal glands ofnymphs and 21 in metathoracic glands of adults), and six in the sternal glandular epithelium of the males. The biological function of the glandular secretions and of their identified compounds were investigated and are discussed.

Chemistry of defensive secretions in nymphs and adults of fire bug,Pyrrhocoris apterus L. (Heteroptera, Pyrrhocoridae).

The defensive secretions from the nymphs and the adults of both sexes inP. apterus were chemically investigated. Forty components were identified from the nymphal posterior dorsoabdominal glands and 35 from the adult metathoracic glands of both sexes. Within the 43 identified chemicals, we found 23 aldehydes, five saturated hydrocarbons, five alcohols, three ketones, three lactones, two terpenes, one phenol and one ester. Thirteen of these compounds had never been reported within the Heteroptera. Whereas eight components are specific to the nymphs, methyl pentenal, (E)-2-hexenol, and heptadecanal are the only adult-specific components. The biological role of all the identified chemicals is almost unknown inP. apterus and is discussed comparatively with regard to other Heteroptera.

2-Methylthiazolidine and 4-ethylguaiacol, male sex pheromone components of the cockroachNauphoeta cinerea (dictyoptera, blaberidae): A reinvestigation.

InNauphoeta cinerea, male calling behavior is associated with sex pheromone release by the sternal glands. The male pheromone that attracts females from a distance is a mixture of 2-methylthiazolidine and 4-ethylguaiacol. It is active at very low concentrations, 0.05 and 0.01 ng, respectively. Two other compounds, 3-hydroxy-2-butanone and 2-methyl-2thiazoline, act at close range, keeping the female in the vicinity of the male. The function of the volatile pheromone and those of previously described contact pheromones are discussed in regard to their possible involvement in the establishment of male dominant-subordinate relationships.

Gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry of cyclic fatty acid monomers isolated from heated fats.

The analysis of hydrogenated cyclic fatty acid monomers isolated from heated linseed and sunflower oils is achieved by gas chromatography-tandem mass spectrometry of their pentafluorobenzyl esters. Collisionally activated dissociation of the carboxylate anions produced by electron-capture ionization shows remote charge-site fragmentation that allows location of cyclopentane and cyclohexane rings by examining the resulting mass-analysed ion kinetic energy spectra. Oxidative ozonolysis of the methyl esters of the unsaturated cyclic fatty acid monomers allows location of some double bonds. However, preliminary results obtained with remote charge fragmentation of synthetic unsaturated models make this approach an alternative for double bond location in the cyclic fatty acid monomers isolated from heated fats.

(3Z,6Z,8E)-3,6,8-Dodecatrien-1-ol: Sex pheromone in a higher fungus-growing termite,Pseudacanthotermes spiniger (Isoptera, macrotermitinae).

The female sex pheromone of the fungus-growing termitePseudacanthotermes spiniger (Termitidae, Macrotermitinae) was isolated from sternal glands of alates. The compound inducing attraction and excitation in males was identified as the (3Z,6Z,8E)-3,6,8-dodecatrien-1-ol by GC-MS, microhydrogenation, GC-FTIR, and NMR. This unsaturated alcohol is present in both sexes but in much higher quantities in females than in males (about 10 times). The hypothesis is suggested that this alcohol, which is detected at extremely low concentrations by the workers ofP. spiniger, may be used either as a trail-following pheromone or a sex pheromone according to concentrations and to target castes. The presence of this alcohol in Macrotermitinae reinforces the idea of a phylogenetic proximity between this subfamily of higher termites and the lower termites Rhinotermitidae, where the unsaturated alcohol was previously found. The sternal glands of alates ofP. spiniger also contain a geometric isomer of (3Z,6Z,8E)-3,6,8-dodecatrien-1-ol.

Isolation and identification of 4,6,8-trimethyl-7,9-undecadien-5-ol, a female-specific compound, in tergal gland secretion ofCryptocercus punctulatus scudder (Dictyoptera: Cryptocercidae).

The secretion of the tergal glands ofCryptocercus punctulatus consists of a complex mixture of 27 compounds. Of this mixture, only one compound (compound B) is specific for females. By dissecting 200 tergal glands, 50 µg of pure compound B was collected by preparative GC; it was identified as (Z, E-4,6,8-trimethyl-7,9-undecadien-5-oI. Its functions as well as its absolute configuration still have to be determined.

Tergal glands of male and femaleCryptocercus punctulatus scudder (Dictyoptera: Cryptocercidae): Composition, sexual dimorphism, and geographic variation of secretion.

Males and females ofCryptocercus punctulatus possess tergal glands, but they differ in position, size, morphology, and secretion chemistry. Compound A (linalyl acetate) is the most abundant of the 21 compounds found only in the secretion of these glands. Compound B, 4,6,8-trimethyl-7,9-undecadien-5-ol, is specific to the tergal secretion of females.C. punctulatus lives only in the United States; its distribution is disjunct. Compound A is found in samples from the eastern population but is absent in samples from the western population. The amount of compound B per gland in samples from the western population is at least twice as high as in the samples from the eastern populations.

Occurrence of geometrical isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids of rats fed heated linseed oil.

Mono trans geometrical isomers of 20:5 n-3 and 22:6 n-3 were detected in liver lipids of rats fed heated linseed oil. The isomers were identified as being 20:5 delta 5c,8c,11c,14c,17t and 22:6 delta 4c,7c,10c,13c,16c,19t. These fatty acids were isolated as methyl esters by preparative high-performance liquid chromatography (HPLC) on reversed phase columns followed by silver nitrate thin layer chromatography (AgNO3-TLC). The structures were identified using partial hydrazine reduction, AgNO3-TLC of the resulting monoenes, oxidative ozonolysis of each monoene band, and gas-liquid chromatography (GLC) of the resulting dimethyl esters and monomethyl esters. Fourier-transform-infrared spectrometry confirmed the trans geometry in isolated 20:5 and 22:6 isomers. The isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids probably resulted from desaturation and elongation of 18:3 delta 9c,12c,15t, a geometrical isomer of linolenic acid present in the heated dietary oil.