Volatile compounds from three cultivars of Olea europaea from Italy.

The chemical compositions of the volatile fractions from three Olea europaea L. cultivars (Leccino, Frantoio, and Cipressino) were examined by GC and GC-MS. The results showed that the cultivars can be distinguished on the basis of the volatile fraction compositions.     

Volatile compounds from potato-like model systems

The volatile reaction products of aqueous mixtures comprising combinations of methionine, glucose, linoleic acid, and starch heated in a modified Likens-Nickerson apparatus were extracted and analyzed by gas chromatography-mass spectrometry (GC-MS). The majority of volatile compounds were formed from linoleic acid degradation, hexanal, 2,4-decadienal, and 2-pentylfuran being identified in the greatest amounts. Dimethyl disulfide and dimethyl trisulfide were detected in every system containing methionine. 3-(Methylthio)propanal (methional) and other sulfur compounds were detected when methionine was heated with another precursor. No binding of volatile compounds to starch was observed; rather, starch appeared to act as an additional source of reactive carbohydrate. Almost all the components identified have been identified among the aroma components of cooked potato. No pyrazines, pyridines, or thiazoles were identified, probably due to the relatively low temperature/high moisture conditions.     

Volatile constituents of Chinese chive (Allium tuberosum Rottl. ex Sprengel) and rakkyo (Allium chinense G. Don)

Volatile components were isolated from Chinese chive and rakkyo by simultaneous steam distillation-solvent extraction and analyzed by GC and GC-MS. Sulfur compounds account for 88 and 94% of the total volatiles in the isolated extract of Chinese chive and rakkyo, respectively. In addition to the sulfur compounds commonly reported in the genus Allium, 27 novel volatile sulfur-containing components were found in the isolated extracts of both species. Among them were a sulfide, disulfides, trisulfides, and tetrasulfides with ethyl, butyl, and pentyl groups.     

Odorants generated by thermally induced degradation of phospholipids

The qualitative and quantitative aroma composition of heated aqueous dispersions of egg phosphatidylcholine (PC) and egg phosphatidylethanolamine (PE) were characterized by aroma extract dilution analysis and isotope dilution assay. On the basis of FD-factors and odor activity values, trans-4,5-epoxy-(E)-2-decenal was found to be the most potent odorant followed by (E,E)-2,4-decadienal, 1-octen-3-one, and hexanal. The amount of (E,E)-2,4-decadienal in PC was about 20-fold higher compared to PE, while hexanal was the major odor-active compound in the PE sample. (E,Z,Z)-2,4,7-Tridecatrienal was identified for the first time as an odor-active volatile constituent of heated phospholipids exhibiting a characteristic egg white-like note. Further odorants first reported in thermally treated phospholipids were (Z)-2-decenal, (E)-2-decenal, and (E)-2-undecenal. Differences in the fatty acid composition of PC and PE can only partially explain the quantitative results found in this study, thus suggesting that further parameters may influence the formation of carbonyls from heated aqueous dispersions of phospholipids.     

Detection and structural characterization of thermally generated isoflavone malonylglucoside derivatives

Malonylglucoside isomers were identified by high-performance liquid chromatography with ultraviolet/mass spectrometric detection and nuclear magnetic resonance (NMR). The formation and interconversions of the isomers were monitored in heated buffer and soymilk systems. Two positional or steroisomers of malonylgenistin and malonydaidzin, showing similar UV spectra and molecular weights yet different fragmentation patterns, were detected. NMR characterization of the malonylgenistin isomer revealed its structure to be 4'-O-malonylgenistin, suggesting a malonyl migration from the glucose-6 position to the glucose-4 position. Interconversions of malonylgenistin and its isomer were observed in both buffered and soymilk systems. While malonylgenistin partially converted to the isomer upon thermal treatment, conversion of the isomer to malonylgenistin was more spontaneous. The malonylgenistin isomer represented 6-9% of the total calculated genistein content in soymilk heated at 100 °C for various periods of time. Consequently, disregarding the content of malonylglucoside isomers in processed soy matrices can lead to isoflavone underestimation and misinterpretation of the biological contributions.     

Allium discoloration: precursors involved in onion pinking and garlic greening

Precursors involved in the formation of pink and green-blue pigments generated during onion and garlic processing, respectively, have been studied. It has been confirmed that the formations of both pigments are of very similar natures, with (E)-S-(1-propenyl)cysteine sulfoxide (isoalliin) serving as the primary precursor. Upon disruption of the tissue, isoalliin and other S-alk(en)ylcysteine sulfoxides are enzymatically cleaved, yielding 1-propenyl-containing thiosulfinates [CH3CH=CHS(O)SR; R = methyl, allyl, propyl, 1-propenyl] among others. The latter compounds have been shown to subsequently react with amino acids to produce the pigments. Whereas the propyl, 1-propenyl, and methyl derivatives form pink, pink-red, and magenta compounds, those containing the allyl group give rise to blue products after reacting with glycine at pH 5.0. The role of other thiosulfinates [RS(O)SR'] (R, R' = methyl, allyl, propyl) and (Z)-thiopropanal S-oxide (the onion lachrymatory principle) in the formation of the pigments is also discussed.     

Volatile compounds produced from monosodium glutamate in common food cooking

A mixture of soybean oil and/or water, sugar and/or monosodium glutamate (MSG) was water-boiled or oil-heated at 100, 120, 140, 160, or 170 degrees C, respectively, and volatile compounds produced were isolated by solid-phase microextraction and then identified by GC and GC/MS. Oxidative thermal degradation products of fatty acids (OTDPFA) were the major volatile compounds detected for all water-boiled samples. When MSG and sugar were heated together, 2, 5-dimethyl pyrazine and methyl pyrazine were also detected at or after 160 min heating. Water added in soybean oil increased OTDPFA production. In oil-heated samples of soybean oil alone, soybean oil with MSG, and soybean oil with sugar, OTDPFA were also the major compounds found. The samples containing MSG also produced 2-pyrrolidone, and the samples containing sugar also produced furfural and 5-hydroxy methyl furfural. The samples containing soybean oil, sugar, and MSG produced 23 pyrazines, OTDPFA, and gamma-butyrolactone as the major volatile compounds. The contents of OTDPFA were lower in MSG plus sugar and MSG-added samples, and it is postulated that antioxidant activities were produced in cooking.     

Isolation and identification of organosulfur compounds oxidizing canine erythrocytes from garlic (Allium sativum)

Five compounds oxidizing canine erythrocytes were isolated from an aqueous ethanol garlic extract by silica gel column chromatography and preparative thin-layer chromatography. On the basis of nuclear magnetic resonance, infrared spectroscopy, and mass spectrometry, they were identified as three known compounds: bis-2-propenyl trisulfide (1), bis-2-propenyl tetrasulfide (2), and bis-2-propenyl pentasulfide (3) as well as two novel compounds, bis-2-propenyl thiosulfonate (4) and trans-sulfuric acid allyl ester 3-allylsulfanyl-allyl ester (5). A mixture of compounds 1-3 and compounds 4 and 5 induced methemoglobin formation in canine erythrocyte suspension in vitro resulting in the oxidation of canine erythrocytes. These groups of characteristic organosulfur compounds contained in garlic probably contribute to oxidations in blood. The constituents of garlic have the potential to oxidize erythrocytes and hemoglobin, suggesting that foods containing quantities of garlic should be avoided for feeding dogs.     

In vitro antiproliferative activity of isothiocyanates and nitriles generated by myrosinase-mediated hydrolysis of glucosinolates from seeds of cruciferous vegetables

A comparison of the effect of isothiocyanates and nitriles derived from some glucosinolates, namely, epi-progoitrin, sinalbin, glucotropaeolin, glucocheirolin, and glucoraphenin, on human erythroleukemic in vitro cultured cells was studied. Many studies have in fact evidenced that a consumption of vegetable containing glucosinolates could reduce the development of colorectal cancer. In the experimental conditions used, the production of isothiocyanates and nitriles from glucosinolates is almost quantitative as confirmed by HPLC or GC-MS analysis. The obtained results demonstrated that in general nitriles are considerably less potent than the corresponding isothiocyanates in inhibiting cancer cell growth. Particularly, the isothiocyanates inhibitory activity on K562 cells growth is higher in the case of products derived from epi-progoitrin, glucotropaeolin, glucoraphenin, and glucocheirolin; while for nitriles the higher activity in inhibiting K562 cells growth is showed by sinalbin-derived product. Considering the antiproliferative activity found for isothiocyanates and nitriles, further studies will be aimed to the possible application of glucosinolate-derived products as chemopreventive cancer agents for the reduction of colorectal cancer.     

Characterization of some Allium hybrids by aroma precursors, aroma profiles, and alliinase activity

Various Allium hybrids, obtained by the crossbreeding of Allium cepa (onion) as the mother plant and six taxonomically distant wild species obtained by embryo rescue, were investigated with special respect to their individual profiles of cysteine sulfoxides as well as enzymically and nonenzymically formed aroma substances. Alliinase (EC 4.4.1.4) catalyzes the conversion of odorless (+)-S-alk(en)yl-L-cysteine sulfoxides into volatile thiosulfinates. These thiosulfinates were converted to a variety of sulfides by steam distillation. SPME-gas chromatography (GC) and high-performance liquid chromatography (HPLC) used for the analysis of aroma components and their precursors permitted a high sample throughput, so that numerous gene bank accessions and Allium breeding materials were analyzed within a comparatively short time. Cysteine sulfoxides as well as alliinase activity were found in all investigated samples at different levels, but (+)-S-methyl-L-cysteine sulfoxide (methiin) was the most abundant sulfoxide present. (+)-S-(trans-1-Propenyl)-L-cysteine sulfoxide (isoalliin) is typical for onion and was found in all investigated hybrids. The pattern of the other cysteine sulfoxides depended strongly on the parent plants used. The profile of aroma components corresponded with the related pattern of aroma precursors (cysteine sulfoxides). Successful hybridization was proven by randomly amplified polymorphic DNA analysis. Together with these established marker techniques, HPLC and SPME-GC analysis provide support to breeding projects designed to improve the health and aroma properties of Allium hybrids.     

Volatile compounds of Psidium salutare (H.B.K.) Berg. fruit

Volatile compounds were isolated from Psidium salutare fruits by simultaneous steam distillation-solvent extraction according to the Likens-Nickerson procedure. Compounds were identified by capillary GC and GC-MS. One hundred and fifty compounds were identified in the aroma concentrate, from which limonene, myrcene, and alpha-pinene were found to be the major constituents in the fruit.     

Volatile organic compounds in the roots and rhizosphere of Pinus spp.

Plant roots normally release a complex mixture of chemicals which have important effects in the rhizosphere. Among these different root-emitted compounds, volatile isoprenoids have received very little attention, yet they may play important and diverse roles in the rhizosphere, contributing to the regulation of microbial activity and nutrient availability. It is therefore important to estimate their abundance in the rhizosphere, but so far, there is no reliable sampling method that can be used to measure realistic rates of root emissions from plants growing in field conditions, or even in pots. Here, we measured root content of volatile isoprenoids (specifically monoterpenes) for Pinus pinea, and explored the feasibility of using a dynamic bag enclosure method to measure emissions from roots of intact pot-grown plants with different degrees of root cleaning. We also investigated a passive diffusion method for exploring monoterpenes in soil at incremental distances from mature Pinus sylvestris trees growing in field conditions. Total monoterpene content of P. pinea roots was 415±50 μg g⁻¹ fresh wt in an initial screening study, and between 688±103 and 1144±208 μg g⁻¹ dry wt in subsequent investigations. Emissions from shaken-clean roots of intact plants and roots of intact plants washed to remove remaining soil after shaken-clean experiments were 119±14 and 26±5 μg g⁻¹ dry wt h⁻¹, respectively. Emissions from intact roots in soil-balls were an order of magnitude lower than from shaken-clean roots, and probably reflected the amount of emitted compounds taken up by physical, chemical or biological processes in the soil matrix surrounding the roots. Although monoterpene content was not significantly different in droughted roots, emission rates from droughted roots were generally significantly lower than from well-watered roots. Finally, passive sampling of monoterpenes in the soil at different distances from mature P. sylvestris trees in field conditions showed significantly decreasing sampling rates with increasing distance from the trunk. We conclude that it is feasible to measure volatile isoprenoid emissions from roots but the method of root preparation affects magnitude of measured emissions and therefore must be decided according to the application. We also conclude that the rhizosphere of Pinus species is a strong and previously un-characterized source of volatile isoprenoid emissions and these are likely to impact significantly on rhizosphere function.     

Complex coacervates for thermally sensitive controlled release of flavor compounds

To improve the appeal of frozen baked foods upon heating, we have encapsulated flavor oil in complex coacervate microcapsules using gelatin and gum Arabic. Variation of polyion concentrations and homogenization rate affected particle morphology, size distribution, and oil release upon heating. Release of the oil from formulations was determined by a simple spectroscopic method based on separation of oil labeled with a lipophilic dye from unaffected particles. When heated to 100 degrees C or higher, univesicular microcapsules (prepared with a lower homogenization rate) released almost all of the encapsulated oil, while multivesicular microcapsules (produced by high homogenization rates) resulted had lesser degrees of release. The oil remained encapsulated during 4 weeks of storage at 4 and -20 degrees C (freezing and thawing) but was released by exposure to 100 mM NaCl at room temperature. When particles were cooled after releasing their oil content, the oil was re-encapsulated.     

Volatile compounds released by enzymatic hydrolysis of glycoconjugates of leaves and grape berries from Vitis vinifera Muscat of Alexandria and Shiraz cultivars.

Glycoconjugates from Muscat of Alexandria and Shiraz leaves and grape berries were isolated by adsorption on Amberlite XAD-2 resin, and enzymatically released aglycons were analyzed by GC-FID and GC-MS. About 120 aglycons were fully or tentatively identified. Compositional differences were observed between leaves and berries of the two varieties in five aglycon chemical groups: C6 alcohols, aliphatic alcohols, monoterpenes, shikimates, and C(13)-norisoprenoids, which were much more abundant in the leaves than in the berries. The differences observed for C(13)-norisoprenoids were in agreement with their hypothetical independent biosynthesis in leaves and berries. Thus, 3-hydroxy-beta-damascone, an important norisoprenoid aglycon of grape berries, was not detected in leaves, whereas its oxidized derivative, 3-oxo-alpha-damascone, was absent in berries. Compositional differences were also observed between Muscat and Shiraz leaves. 3-Oxo-alpha-ionol was not detected in Shiraz leaves, and its retro derivatives were less abundant than in Muscat of Alexandria leaves. Conversely, in Shiraz leaves the levels of 7,8-dihydroionone derivatives, such as megastigman-3,9-diol and 3-oxo-7,8-dihydro-alpha-ionol, were higher than in Muscat of Alexandria leaves.     

Volatile compounds in the production of liquid beet sugar

Samples from different parts of a beet sugar factory and refinery were analyzed with respect to volatile compounds by means of liquid-liquid extraction followed by gas chromatography-mass spectrometry (GC-MS). A limited number of the samples were analyzed by means of gas phase extraction (headspace) followed by GC-MS. Selected compounds were followed through the sugar manufacturing process. The behavior of different compounds varied greatly throughout the process, with some compounds such as geosmin (trans-1, 10-dimethyl-trans-9-decalol), dimethyl disulfide, and propionic and hexanoic acid present at the beginning of the process but disappearing rapidly after further processing. Other compounds, such as indole, dihydrobenzofuran, and 2-phenylethanol, were not detected at the start of the process but were formed later on and removed in the final product. In the final product, three pyrazines remained at fairly low concentrations, together with 3-methylcyclopentadione, ethylhexanol, and methyl pyrrole ketone.     

Volatile compounds from Escherichia coli O157:H7 and their absorption by strawberry fruit

Volatile compounds emitted by cultures of two strains of the pathogenic bacterium Escherichia coliO157:H7 and a nonpathogenic strain of E. coli were trapped on Super-Q porous polymer and identified by GC-MS. The predominant compound produced by all three strains was indole with lesser amounts of other components including methyl ketones, 2-heptanone, 2-nonanone, 2-undecanone, and 2-tridecanone. The vapor-phase profiles of these strains were similar for most chemicals identified but differed with regard to ketones. Strawberry fruit was shown to be a suitable host for E. coli O157:H7 with the population of the bacterium either increasing or remaining stable after 3 days depending on inoculation level. Headspace analysis of the volatile compounds from inoculated fruit yielded no detectable quantity of indole. Strawberry fruit readily absorbed indole and other volatile compounds produced by the bacteria and in some cases metabolized the compounds to new volatile products. Thus, headspace "marker" compounds indicating possible bacterial contamination of fruit were largely removed from the vapor phase by the strawberries.     

Chemical characterization of interspecific hybrids between Allium cepa L. and Allium kermesinum Rchb

Interspecific hybridization between wild and cultivated species of the genus Allium has been performed to generate plant material possessing biochemical properties of both parental plants. These cross-breeding experiments should lead to Allium plants with higher amounts of valuable constituents. The chemical characterization of interspecific hybrids between A. cepa and A. kermesinum is described on the basis of their sulfur-containing constituents and secondary metabolites. In addition, the hybrid character has been proven by random amplified polymorphic DNA (RAPD) analysis of the progenies obtained from the crosses. It has been shown that the distribution of the cysteine sulfoxides as well as the volatile secondary metabolites in the hybrids is not uniform. The profiles are mainly determined by the paternal wild species A. kermesinum. It has been ascertained that the gas chromatography profiles of the hybrids show increasing amounts of unsymmetrical substituted oligosulfides, which are known to be physiologically active substances. On the basis of statistical calculations, three different types of hybrids can be separated. The chemical analysis of cysteine sulfoxides and volatile sulfur-containing substances is shown to be a useful tool for breeding purposes as it allows an effective selection with regard to optimal distribution and amount of valuable constituents.     

Structure of steroidal saponins from underground parts of Allium nutans L.

Four steroidal glycosides including deltoside and nolinofuroside D and two novel saponins were isolated from underground parts of Allium nutans L. On the basis of the spectral (LSIMS and NMR) analysis, the structures of the new compounds were established as 25R Delta(5)-spirostan 3beta-ol-3-O-?alpha-L-rhamnopyranosyl(1-->2)-[beta-D-glucopyranosyl(1 -->4)]-O-beta-D-galactopyranoside? and 25R Delta(5)-spirostan 1beta, 3beta-diol 1-O-beta-D-galactopyranoside. On the basis of the extraction efficiency, the concentration of saponins was established to be about 4% of dry matter, which makes this species a good source of steroidal saponins for commercial use.