Analysis of strigolactones,germination stimulants for striga and orobanche,by high-performance liquid chromatography/tandem mass spectrometry

A simple and rapid analytical method for strigolactones, germination stimulants for the root parasitic weeds witchweed (Striga spp.) and broomrape (Orobanche spp.), has been developed using high-performance liquid chromatography connected to tandem mass spectrometry (LC/MS/MS). The natural strigolactones (strigol, sorgolactone, orobanchol, and alectrol) were clearly separated and identified by LC/MS/MS. As low as 0.1 pg/microL of strigol and 0.5 pg/microL of sorgolactone could be quantified, whereas 1 pg/microL was needed for the quantification of orobanchol (S/N > 10). Using this method, it was found that red clover produces orobanchol and alectrol but not strigol. The roots of red clover seedlings were found to produce 13, 70, 58, and 65 pg of orobanchol/plant 1, 2, 3, and 4 weeks after germination, respectively.     

A critical account on the inception of Striga seed germination

The seeds of the parasitic weed Striga germinate in response to stimulants exuded by the roots of host plants and some nonhost plants. Literature data are summarized that support the view that strigolactones induce germination of parasitic weed seeds via a receptor-mediated mechanism. The suggestion by Lynn et al. that the strigol D-ring is solely responsible for germinating Striga seeds via a redox reaction was based on hypothesized structural similarities between the natural compound dihydrosorgoleone (SXSg) and the strigol D-ring. Experiments have shown that the mechanistic connection between SXSg and the strigol D-ring is not valid, and therefore the proposed redox mechanism for the induction of Striga seed germination by strigolactones does not hold.     

从山豆根组培根中提取、分离独脚金属杂草发牙、芽刺激物质的研究

试验研究了从山豆根(Menispermum dauricum DC.)组培根中提取、分离独脚金属杂草[Striga hermonthica(Del)Benth]发芽刺激物质,其提纯、分离过程是首先将发芽剌激物质吸附在XAD-4树脂表面后采用甲醇脱洗,通过乙酸乙脂:水分配提取,活性物质在Sephadex LH20开口型人工填充柱上进行柱层析,活性组分合并后进一步采用商业提供的C18 Sep-Pak(10g)柱进行柱层析,之后采用分取和分析高效液相色谱提纯、分离,每一步提纯过程中均采用Striga种子发芽实验鉴定活性物质的存在。高效液相色谱分析表明有3种活性物质,其中主要活性物质与Strigol有十分相似的色谱特性,最后经质谱鉴定为Strigol或Strigol类似物质,并首次报道Strigol是植物的代谢产物。     

Structural identification of nonvolatile dimerization products of glucosamine by gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and nuclear magnetic resonance analysis

The degradation profile of glucosamine bulk form stressed at 100 degrees C for 2 h in an aqueous solution was studied. Column chromatography of acetylated product mixture led to isolation of two pure compounds (1b and 2b) and a mixture of at least three isomers (3b). 1a and 2a were identified as 5-(hydroxymethyl)-2-furaldehyde (5-HMF) and 2-(tetrahydroxybutyl)-5-(3',4'-dihydroxy-1'-trans-butenyl)pyrazine, respectively, by utilizing a variety of analytical techniques, such as GC-MS, LC-MS, on-line UV spectrum, (1)H and (13)C NMR, and DEPT, as well as (1)H-(1)H COSY. 3a was identified as 2-(tetrahydroxybutyl)-5-(2',3',4'-trihydroxybutyl)pyrazine, commonly known as deoxyfructosazine. In addition, glucosamine solid dosage form was exposed to 40 degrees C/75% relative humility for 10 weeks. Methanol extract of glucosamine solid dosage form was analyzed after acetylation by LC-MS, resulting in degradants 3b and 4b. 3a and 4a were, therefore, determined as deoxyfructosazine and 2,5-bis(tetrahydroxybutyl)pyrazine (fructosazine), respectively. Furthermore, the mechanisms of formation of identified degradation products are proposed and briefly discussed.     

Metabolism of the insecticide metofluthrin in cabbage (Brassica oleracea)

The metabolic fate of metofluthrin [2,3,5,6-tetrafluoro-4-(methoxymethyl)benzyl (E,Z)-(1R,3R)-2,2-dimethyl-3-(prop-1-enyl)cyclopropanecarboxylate] separately labeled with (14)C at the carbonyl carbon and the α-position of the 4-methoxymethylbenzyl ring was studied in cabbage ( Brassica oleracea ). An acetonitrile solution of (14)C-metofluthrin at 431 g ai ha(-1) was once applied topically to cabbage leaves at head-forming stage, and the plants were grown for up to 14 days. Each isomer of metofluthrin applied onto the leaf surface rapidly volatilized into the air and was scarcely translocated to the untreated portion. On the leaf surface, metofluthrin was primarily degraded through ozonolysis of the propenyl side chain to produce the secondary ozonide, which further decomposed to the corresponding aldehyde and carboxylic acid derivatives. In the leaf tissues, the 1R-trans-Z isomer was mainly metabolized to its dihydrodiol derivative probably via an epoxy intermediate followed by saccharide conjugation in parallel with the ester cleavage, whereas no specific metabolite was dominant for the 1R-trans-E isomer. Isomerization of metofluthrin at the cyclopropyl ring was negligible for both isomers. In this study, the chemical structure of each secondary ozonide derivative was fully elucidated by the various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy together with cochromatography with the synthetic standard, and their cis/trans configuration was examined by the nuclear Overhauser effect (NOE) difference NMR spectrum.     

Ent-2'-epi-Orobanchol and its acetate, as germination stimulants for Striga gesnerioides seeds isolated from cowpea and red clover

Striga gesnerioides is a root parasitic weed of economic significance to cowpea (Vigna unguiculata) crops in Western Africa. Seeds of the parasite germinate in response to cowpea root exudates. Germination stimulants for the seeds were isolated from the hydroponic culture filtrate of cowpea, and their structures were unambiguously determined as (-)-(3aR,4R,8bR,2'R)-ent-2'-epi-orobanchol and (+)-(3aR,4R,8bR,2'R)-ent-2'-epi-orobanchyl acetate, on the basis of mass, CD, and (1)H NMR spectra; optical rotatory power; and chromatographic behavior on HPLC. The alcohol was first isolated and identified from the cowpea root exudates, and the acetate may be the same compound that had been previously isolated from the exudates and designated as alectrol. Identity of the stimulants produced by cowpea to those produced by red clover (Trifolium pratense) was confirmed.     

Identification, quantitative determination, and antioxidative activities of chlorogenic acid isomers in prune (Prunus domestica L. )

Neochlorogenic acid (3-CQA) and cryptochlorogenic acid (4-CQA), isolated from prune (Prunus domestica L.), were identified by NMR and MS analyses. In addition, the quantity of chlorogenic acid isomers in prune were measured by HPLC. These isomers, 3-CQA, 4-CQA, and chlorogenic acid (5-CQA), were contained in the ratio 78.7:18. 4:3.9, respectively. 4-CQA was identified and quantified in prune for the first time, and relatively high amounts of this isomer were characteristic. Antioxidative activities of the chlorogenic acid isomers, such as scavenging activity on superoxide anion radicals and inhibitory effect against oxidation of methyl linoleate, were also evaluated. Each isomer showed antioxidative activities which were almost the same.     

Glycosidic conjugates of C13 norisoprenoids, monoterpenoids, and cucurbates in Boronia megastigma (Nees)

Analysis of a methanolic extract of marc from Boronia megastigma (Nees) using LC-MS (APCI, nominal mass) provided strong evidence for the presence of both glycosides and malonyl glycosides of methyl cucurbates, C13 norisoprenoids including megastigmanes, and monoterpene alcohols. Subsequent fractionation of an extract from the marc using XAD-2 and LH 20 chromatography followed by LC-UV/MS-SPE-NMR and accurate mass LC-MS resulted in the isolation and identification of (1R,4R,5R)-3,3,5-trimethyl-4-[(1E)-3-oxobut-1-en-1-yl]cyclohexyl β-D-glucopyranoside (3-hydroxy-5,6-dihydro-β-ionone-β-D-glucopyranoside); 3,7-dimethylocta-1,5-diene-3,7-diol-3-O-β-D-glucopyranoside; and a methyl {(1R)-3-(β-D-glucopyranosyloxy)-2-[(2Z)-pent-2-en-1-yl]cyclopentyl}acetate stereoisomer (a methyl cucurbate-β-D-glucopyranoside); and provided evidence for 3,7-dimethylocta-1,5-diene-3,7-diol-3-O-(6'-O-malonyl)-β-D-glucopyranoside in boronia flowers.     

SAR studies of sesquiterpene lactones as Orobanche cumana seed germination stimulants

Studies of the structure-activity relationship (SAR) directed to evaluate the effect of several sesquiterpene lactones (SL) as germination stimulants of three Orobanche spp. (O. cumana, O. crenata, and O. ramosa) have been achieved. Results are compared with those obtained in the same bioassay with an internal standard, the synthetic analogue of strigol GR-24. A high specificity in the germination activity of SL on the sunflower parasite O. cumana has been observed, and a relationship between such activity and the high sunflower SL content is postulated. Molecular properties of the natural and synthetic germination stimulants (GR-24, GR-7, and Nijmegen-1) and SL have been studied using MMX and PM3 calculations. Consequently, comparative studies among all of them and their activities have been made. SL tested present similarities in molecular properties such as the volume of the molecule and the spatial disposition of the carbon backbone to the natural germination stimulant orobanchol. These properties could be related to their biological activity.     

Susceptibility of the tomato mutant high pigment-2dg (hp-2dg) to Orobanche spp. infection

The consumption of natural products with potential health benefits has been continuously growing, and enhanced pigmentation is of major economic importance in fruits and vegetables. The tomato hp-2 ( dg ) is an important mutant line that has been introgressed into commercial tomato cultivars marketed as lycopene rich tomatoes (LRT) because of their enhanced fruit pigmentation, attributed to higher levels of carotenoids, including lycopene. Strigolactones are signaling compounds that mediate host finding in root parasitic plants and are biosynthetically derived from carotenoids. Considering the high carotenoid content of the hp-2 ( dg ) mutant, we studied its susceptibility to the root parasite Orobanche. In a field experiment, the average number of Orobanche aegyptiaca plants growing on hp-2 ( dg ) was surprisingly significantly reduced compared with its isogenic wild-type counterpart. In vitro assays and LC-MS/MS analysis showed that this reduction was associated with a lower production of strigolactones, which apparently renders the high-carotenoid hp-2 ( dg ) mutant less susceptible to Orobanche.     

Structural analogues of homoeriodictyol as flavor modifiers. Part III: short chain gingerdione derivatives

In order to find new flavor modifiers, various short chain gingerdione derivatives were synthesized as structural analogues of the known bitter masker homoeriodictyol and evaluated by a sensory panel for masking and sweetness enhancing activities. 1-(4-Hydroxy-3-methoxyphenyl)hexa-3,5-dione ([2]-gingerdione) and the homologue 1-(4-hydroxy-3-methoxyphenyl)hepta-3,5-dione ([3]-gingerdione) at concentration ranges 50-500 mg kg (-1) showed the most promising masking activity of 20-30% against bitterness of a 500 mg kg (-1) aqueous caffeine solution. Additionally, both compounds were able to reduce the bitterness of a 5 mg kg (-1) quinine solution by about 20%; however, the bitter tastes of salicine, the model peptide H-Leu-Trp-OH, and KCl solutions were not reduced. Whereas for bitter masking activity a vanillyl moiety seems to be important, some of the tested isovanillyl isomers showed an interesting sweet enhancing effect without exhibiting a significant intrinsic sweetness. The isomer 1-(3-hydroxy-4-methoxyphenyl)hexa-3,5-dione ([2]-isogingerdione) at 100 mg kg (-1) caused a significant and synergistic increase of 27% of sweet taste of a 5% sucrose solution.     

烟草根系分泌物酚酸类物质的鉴定及其对根际微生物的影响

【目的】烟草连作已导致土传病害发生、 烟株生长受抑制、 产量下降和品质恶化等问题。烟株对自身及土壤微生物产生的化感作用,是烟草产生连作障碍的一个重要原因,其中化感物质中的根系分泌物是烟株与土壤微生物间相互作用的重要物质,探索烟草根系分泌物对根际微生物生长的影响是生物防控烟草青枯病的理论依据。【方法】本文利用超高效液相色谱串联四级杆飞行时间质谱(UPLC-Q-TOF/MS)技术,分离、 鉴定烟草根系分泌物中主要酚酸类物质的种类和含量; 通过添加外源酚酸类物质,研究在液体培养基中烟草根系分泌物中的主要酚酸类物质对病原菌及拮抗菌的影响,并在土壤中添加鉴定出的主要酚酸类物质; 通过土壤培育试验,研究其对土壤微生物多样性和数量变化,特别是对烟草青枯病菌及其拮抗菌生长的影响。【结果】1)烟草根系分泌物粗提物对病原菌(茄科劳尔氏菌)生长的促进率为16.8％,对拮抗菌(短短芽孢杆菌)的生长抑制率达到29.4％; 2)UPLC-Q-TOF/MS检测根系分泌物中主要酚酸类物质为苯甲酸和3-苯丙酸,含量分别为0.25 μg/g干根重和1.15 μg/g干根重; 3)液体培养外源添加低浓度的苯甲酸(≤ 2 μg/L)和3-苯丙酸(≤ 3 μg/L)促进病原菌和拮抗菌的生长; 4 μg/L的苯甲酸对病原菌生长抑制作用不显著,对拮抗菌生长的抑制率达到90.2％,6 μg/L的 3-苯丙酸对病原菌的生长具有促进作用,对拮抗菌的生长抑制率达到81.1％,外源高浓度苯甲酸(≥4 μg/L)和3-苯丙酸(≥ 7 μg/L)抑制病原菌与拮抗菌的成长; 4)土壤中添加3 μg/kg土的苯甲酸时,土壤中病原菌的数量增加12.3％,而拮抗菌的数量减少21.0％,土壤细菌、 放线菌和真菌的数量分别降低37.5％,41.9％和55.6％; 3-苯丙酸浓度达到8 μg/kg土时,拮抗菌生长量减少14.5％,对病原菌没有显著影响,土壤细菌、 放线菌和真菌的数量分别降低69.9％,57.2％和80.7％; 5)土壤添加4 μg/kg的苯甲酸和7 μg/kg的3-苯丙酸后,土壤微生物Shannon指数、 Simpson指数、 McIntosh指数显著下降,分别仅为对照的57.7％、 94.1％、 88.1％和97.6％ 73.3％、 80.0％。【结论】烟草根系分泌物粗提物促进病原菌生长抑制拮抗菌生长,根系分泌物中酚酸类物质主要为苯甲酸和3-苯丙酸,液体培养中4 μg/L的苯甲酸或6 μg/L的 3-苯丙酸浓度是对病原菌生长抑制不明显但显著抑制拮抗菌生长的分界点,土壤外源添加3 μg/kg的苯甲酸或8 μg/kg的3-苯丙酸时,是土壤增加病原菌减少拮抗菌数量的分界点,同时土壤微生物功能多样性显著下降,病原菌对根系分泌物中苯甲酸和3-苯丙酸的利用优于拮抗菌,这也是烟草长期连作引起青枯病暴发流行的机理之一。     

Effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system

The effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system were studied. All-trans beta-carotene, 9-cis beta-carotene, beta-cryptoxanthin, and lycopene were adsorbed onto a C(18) solid phase and exposed to a continuous flow of water saturated with oxygen or ozone at 30 degrees C. Carotenoids were analyzed using HPLC with a C(30) column and a photodiode array detector. Approximately 90% of all-trans beta-carotene, 9-cis beta-carotene, and beta-cryptoxanthin were lost after exposure to ozone for 7 h. A similar loss of lycopene occurred in only 1 h. When exposed to oxygen, all carotenoids, except beta-cryptoxanthin, degraded at lower rates. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates: lycopene > beta-cryptoxanthin > all-trans beta-carotene > 9-cis beta-carotene. The major degradation products of beta-carotene were tentatively identified on the basis of their elution on the HPLC column, UV-Vis spectra, and electrospray LC-MS. Predominant isomers of beta-carotene were 13-cis, 9-cis, and a di-cis isomer. Products resulting from cleavage of the molecule were beta-apo-13-carotenone and beta-apo-14'-carotenal, whereas epoxidation yielded beta-carotene 5,8-epoxide and beta-carotene 5, 8-endoperoxide.     

Nasunin from eggplant consists of cis-trans isomers of delphinidin 3-[4-(p-coumaroyl)-L-rhamnosyl (1-->6)glucopyranoside]-5-glucopyranoside

Two major anthocyanins were isolated from the acidified methanolic extract of eggplant (Solanum melongena L.) by column chromatography and preparative high-performance liquid chromatography. These anthocyanins were interconvertible under room light illumination condition. By means of tandem time-of-flight mass spectrometry and nuclear magnetic resonance spectroscopy, their structures were identified and elucidated as delphinidin 3-[4-(cis-p-coumaroyl)-l-rhamnosyl(1-->6)glucopyranoside]-5-glucopyranoside (compound 1) and delphinidin 3-[4-(trans-p-coumaroyl)-l-rhamnosyl-(1-->6)glucopyranoside]-5-glucopyranoside (compound 2), respectively. The results indicated that nasunin comprised cis and trans isomers of the p-coumaric acid moiety in its structure.     

土壤调理剂对烤烟根系活力及根际土壤微生物碳代谢特征的影响

为探究土壤调理剂对烤烟根系微生态环境的影响,采用小区试验,研究土壤调理剂在不同施用量(0、1 500、3 000和4 500 kg·hm^-2)水平下烤烟根系活力的动态变化及微生物碳代谢特征。结果表明,添加土壤调理剂3 000 kg·hm^-2对烤烟生长发育中后期时的根系活力提高效应最大,移栽后60、90 d较对照分别提高了115.8%、85.3%。羧酸类、氨基酸类是烤烟根际土壤微生物利用的主要碳源,土壤调理剂作用下,羧酸类碳源在移栽后30 d并无显著变化,移栽后60、90 d,施用土壤调理剂3 000 kg·hm^-2对羧酸类和氨基酸类碳源的利用率提高作用均最显著,且微生物多样性均一性指数也显著增加。在移栽后30 d,影响微生物碳代谢强度及多样性的主要因素是烤烟根系活力,而移栽后60、90 d,主要影响因素是土壤调理剂。综上,施用土壤调理剂能提高烤烟根系活力,改善土壤微生态环境,以3 000 kg·hm^-2施用量为宜。本研究结果为土壤调理剂在烤烟生产上的应用提供了理论参考。     

Development of a magnetic particle-based enzyme immunoassay for the determination of penoxsulam in water

A competitive enzyme-linked immunoassay (ELISA) for the quantitation of Penoxsulam [2-(2,2-difluoroethoxy)-6-(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide] in ground and surface waters was developed. This immunoassay utilizes magnetic particles as the solid phase to which polyclonal rabbit anti-Penoxsulam antibodies are attached. The ELISA has an estimated detection limit of 0.17 ppb (microg/mL) of Penoxsulam in water. Specificity studies indicate that the antibody can distinguish Penoxsulam from its major metabolites and structurally similar pesticides. Interference studies indicate that the ELISA has a wide tolerance of sample pH and salinity and for compounds commonly found in surface and ground waters. The ELISA was shown to compare favorably to LC-MS/MS on ground and surface water samples (r(2) = 0.957). The various studies performed demonstrate the usefulness of the ELISA technique as a rapid and high-throughput analytical method for the cost-effective monitoring of water samples.     

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.     

Isolation, structure determination, synthesis, and sensory activity of N-phenylpropenoyl-L-amino acids from cocoa (Theobroma cacao)

Application of chromatographic separation and taste dilution analyses recently revealed besides procyanidins a series of N-phenylpropenoyl amino acids as the key contributors to the astringent taste of nonfermented cocoa beans as well as roasted cocoa nibs. Because these amides have as yet not been reported as key taste compounds, this paper presents the isolation, structure determination, and sensory activity of these amino acid amides. Besides the previously reported (-)-N-[3',4'-dihydroxy-(E)-cinnamoyl]-3-hydroxy-L-tyrosine (clovamide), (-)-N-[4'-hydroxy-(E)-cinnamoyl]-L-tyrosine (deoxyclovamide), and (-)-N-[3',4'-dihydroxy-(E)-cinnamoyl]-L-tyrosine, seven additional amides, namely, (+)-N-[3',4'-dihydroxy-(E)-cinnamoyl]-L-aspartic acid, (+)-N-[4'-hydroxy-(E)-cinnamoyl]-L-aspartic acid, (-)-N-[3',4'-dihydroxy-(E)-cinnamoyl]-L-glutamic acid, (-)-N-[4'-hydroxy-(E)-cinnamoyl]-L-glutamic acid, (-)-N-[4'-hydroxy-(E)-cinnamoyl]-3-hydroxy-L-tyrosine, (+)-N-[4'-hydroxy-3'-methoxy-(E)-cinnamoyl]-L-aspartic acid, and (+)-N-[(E)-cinnamoyl]-L-aspartic acid, were identified for the first time in cocoa products by means of LC-MS/MS, 1D/2D-NMR, UV-vis, CD spectroscopy, and polarimetry, as well as independent enantiopure synthesis. Using the recently developed half-tongue test, human recognition thresholds for the astringent and mouth-drying oral sensation were determined to be between 26 and 220 micromol/L (water) depending on the amino acid moiety. In addition, exposure to light rapidly converted these [E]-configured N-phenylpropenoyl amino acids into the corresponding [Z]-isomers, thus indicating that analysis of these compounds in food and plant materials needs to be performed very carefully in the absence of light to prevent artifact formation.     

Quantitation of 13 heterocyclic aromatic amines in cooked beef, pork, and chicken by liquid chromatography-electrospray ionization/tandem mass spectrometry

The concentrations of heterocyclic aromatic amines (HAAs) were determined, by liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI-MS/MS), in 26 samples of beef, pork, and chicken cooked to various levels of doneness. The HAAs identified were 2-amino-3-methylimidazo[4,5- f]quinoline, 2-amino-1-methylimidazo[4,5- b]quinoline, 2-amino-1-methylimidazo[4,5- g]quinoxaline (I gQx), 2-amino-3-methylimidazo[4,5- f]quinoxaline, 2-amino-1,7-dimethylimidazo[4,5- g]quinoxaline (7-MeI gQx), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline, 2-amino-1,6-dimethyl-furo[3,2- e]imidazo[4,5- b]pyridine, 2-amino-1,6,7-trimethylimidazo[4,5- g]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline, 2-amino-1,7,9-trimethylimidazo[4,5- g]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-9 H-pyrido[2,3- b]indole, and 2-amino-3-methyl-9 H-pyrido[2,3- b]indole. The concentrations of these compounds ranged from <0.03 to 305 parts per billion (micrograms per kilogram). PhIP was the most abundant HAA formed in very well done barbecued chicken (up to 305 microg/kg), broiled bacon (16 microg/kg), and pan-fried bacon (4.9 microg/kg). 7-MeI gQx was the most abundant HAA formed in very well done pan-fried beef and steak, and in beef gravy, at concentrations up to 30 microg/kg. Several other linear tricyclic ring HAAs containing the I gQx skeleton are formed at concentrations in cooked meats that are relatively high in comparison to the concentrations of their angular tricyclic ring isomers, the latter of which are known experimental animal carcinogens and potential human carcinogens. The toxicological properties of these recently discovered I gQx derivatives warrant further investigation and assessment.     

Hydrolysis kinetic parameters of DP 6, 7, 8, and 9-12 fructooligosaccharides (FOS) of onion bulb tissues. effect of temperature and storage time

The objective of this study was to report on the variation of DP 6 isomers (6b, 6c + 6d1 + 6d2), 7a, 8, and 9-12 fructooligosaccharides (FOS) and their hydrolysis parameters [percent hydrolysis, consumption rate, hydrolysis rate constant (k(obsd)), and half-life time (t(1/2))] in onion bulb tissues stored for 6 months at 10, 15, or 20 degrees C. The hydrolysis of DP 6 isomers, 7a, and 8 ranged from 74 to 85%, whereas that of DP 9-12 averaged 86%. The consumption rate of 6b, 6c + 6d1 + 6d2, 7a, 8, and -12 averaged 25, 58, 38, 26, and 48 microg/g of fresh weight per week, respectively. The k(obsd) showed large variation from 53 x 10(-3) week(-1) (lowest value) to 92 x 10(-3) week(-1) (highest value), whereas the half-life t(1/2) of the different FOS ranged between 7.5 and 13.1 weeks. DP 6b isomers increased during the first month, and then the content decreased sharply during the second month at 20 degrees C but remained stable during the last 4 months, whereas at 10 and 15 degrees C, 6b decreased progressively from the first to the six month. In contrast, DP 6c + 6d1 + 6d2 decreased abruptly within the first 3 months at 10, 15, and 20 degrees C; however, during the last 3 months they remained stable, ranging between 0.32 and 0.39. Variation of DP 7a, 8, and 9-12 FOS was close to that of DP 6 FOS isomers. DP 7a increased slightly during the first month, and afterward 7a started decreasing progressively during the last 5 months. DP 8 FOS showed a similar pattern independent of temperature regime: they increased slightly within the first month, but from the second month, DP 8 began decreasing progressively and continued decreasing to the sixth month. DP 9-12 FOS also varied similarly to DP 6c + 6d1 + 6d2. They decreased sharply within the first 2 months, and during the last 4 months, they continued to decrease slowly. Surprisingly, these variations occurred independently of temperature regimes and were affected only by storage duration. It was concluded that highly polymerized FOS are preferably hydrolyzed rather than low DP FOS isomers because they have a relatively high content of fructosyl end chains.