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Preston C Richling E Elss S Appel M Heckel F Hartlieb A Schreier P 《Journal of agricultural and food chemistry》2003,51(27):8027-8031
By use of extracts prepared by liquid-liquid separation of the volatiles from self-prepared juices of pineapple fruits (Ananas comosus) (n = 14) as well as commercial pineapple recovery aromas/water phases (n = 3), on-line capillary gas chromatography-isotope ratio mass spectrometry was employed in the combustion (C) and the pyrolysis (P) modes (HRGC-C/P-IRMS) to determine the delta(13)C(VPDB) and delta(2)H(VSMOW) values of selected pineapple flavor constituents. In addition to methyl 2-methylbutanoate 1, ethyl 2-methylbutanoate 2, methyl hexanoate 3, ethyl hexanoate 4, and 2,5-dimethyl-4-methoxy-3[2H]-furanone 5, each originating from the fruit, the delta(13)C(VPDB) and delta(2)H(VSMOW) data of commercial synthetic 1-5 and "natural" (biotechnologically derived) 1-4 were determined. With delta(13)C(VPDB) data of pineapple volatiles 1-4 varying from -12.8 to -24.4 per thousand, the range expected for CAM metabolism was observed. Compound 5 showed higher depletion from -20.9 to -28.6 per thousand. A similar situation was given for the delta(2)H(VSMOW) values of 3-5 from pineapple ranging from -118 to -191 per thousand, whereas 1 and 2 showed higher depleted values from -184 to -263 per thousand. In nearly all cases, analytical differentiation of 1-5 from pineapple and natural as well as synthetic origin was possible. In general, natural and synthetic 1-5 exhibited delta(13)C(VPDB) data ranging from -11.8 to -32.2 per thousand and -22.7 to -35.9 per thousand, respectively. Their delta(2)H(VSMOW) data were in the range from -242 to -323 per thousand and -49 to -163 per thousand, respectively. 相似文献
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Prange A Modrow H Hormes J Krämer J Köhler P 《Journal of agricultural and food chemistry》2005,53(17):6930-6938
Cereals contaminated by Aspergillus spp., Penicillium spp., and Fusarium spp. and their mycotoxins, for example, ochratoxin A (OTA) and deoxynivalenol (DON), are not only a risk to human and animal health but can also show poor technological properties and baking quality. The influence of these genera on the sulfur speciation of low molecular weight (LMW) subunits of glutenin was characterized by investigating suboptimally stored wheat samples in situ by X-ray absorption near edge structure (XANES) spectroscopy and baking tests. Field fungi of the genus Fusarium have hardly any influence on both the sulfur speciation of wheat gluten proteins and the baking properties, whereas storage fungi of the genera Aspergillus and Penicillium have a direct influence. An increased amount of sulfur in sulfonic acid state was found, which is not available for thiol/disulfide exchange reactions in the gluten network, and thus leads to a considerably reduced baking volume. From changes of the composition of the mould flora during suboptimal storage of wheat and from the mycotoxin contents, it can be concluded that microbial competitive interactions play an important role in the development of the mould flora and the mycotoxin concentrations during (suboptimal) storage of wheat. 相似文献
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Michael RichterUeli A. Hartwig Emmanuel FrossardJosef Nösberger Georg Cadisch 《Soil biology & biochemistry》2003,35(10):1325-1335
Plant response to increasing atmospheric CO2 partial pressure (pCO2) depends on several factors, one of which is mineral nitrogen availability facilitated by the mineralisation of organic N. Gross rates of N mineralisation were examined in grassland soils exposed to ambient (36 Pa) and elevated (60 Pa) atmospheric pCO2 for 7 years in the Swiss Free Air Carbon dioxide Enrichment experiment. It was hypothesized that increased below-ground translocation of photoassimilates at elevated pCO2 would lead to an increase in immobilisation of N due to an excess supply of energy to the roots and rhizosphere. Intact soil cores were sampled from Lolium perenne and Trifolium repens swards in May and September, 2000. The rates of gross N mineralisation (m) and NH4+ consumption (c) were determined using 15N isotopic dilution during a 51-h period of incubation. The rates of N immobilisation were estimated either as the difference between m and the net N mineralisation rate or as the amount of 15N released from the microbial biomass after chloroform fumigation. Soil samples from both swards showed that the rates of gross N mineralisation and NH4+ consumption did not change significantly under elevated pCO2. The lack of a significant effect of elevated pCO2 on organic N turnover was consistent with the similar size of the microbial biomass and similar immobilisation of applied 15N in the microbial N pool under ambient and elevated pCO2. Rates of m and c, and microbial 15N did not differ significantly between the two sward types although a weak (p<0.1) pCO2 by sward interaction occurred. A significantly larger amount of NO3− was recovered at the end of the incubation in soil taken from T. repens swards compared to that from L. perenne swards. Eleven percent of the added 15N were recovered in the roots in the cores sampled under L. perenne, while only 5% were recovered in roots of T. repens. These results demonstrate that roots remained a considerable sink despite the shoots being cut at ground level prior to incubation and suggest that the calculation of N immobilisation from gross and net rates of mineralisation in soils with a high root biomass does not reflect the actual immobilisation of N in the microbial biomass. The results of this study did not support the initial hypothesis and indicate that below-ground turnover of N, as well as N availability, measured in short-term experiments are not strongly affected by long-term exposure to elevated pCO2. It is suggested that differences in plant N demand, rather than major changes in soil N mineralisation/immobilisation, are the long-term driving factors for N dynamics in these grassland systems. 相似文献
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Hartwig Schulz 《Genetic Resources and Crop Evolution》2004,51(7):795-795
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Aguilar-Cisneros BO López MG Richling E Heckel F Schreier P 《Journal of agricultural and food chemistry》2002,50(26):7520-7523
By use of headspace SPME sampling and a PLOT column, on-line capillary gas chromatography-isotope ratio mass spectrometry was employed in the combustion (C) and the pyrolysis (P) modes (HRGC-C/P-IRMS) to determine the delta(13)C(VPDB) and delta(18)O(VSMOW) values of ethanol in authentic (n = 14) and commercial tequila samples (n = 15) as well as a number of other spirits (n = 23). Whereas with delta(13)C(VPDB) values ranging from -12.1 to -13.2 per thousand and from -12.5 to -14.8 per thousand similar variations were found for 100% agave and mixed tequilas, respectively, the delta(18)O(VSMOW) data differed slightly within these categories: ranges from +22.1 to +22.8 per thousand and +20.8 to +21.7 per thousand were determined for both the authentic 100% agave and mixed products, respectively. The data recorded for commercial tequilas were less homogeneous; delta(13)C(VPDB) data from -10.6 to -13.9 per thousand and delta(18)O(VSMOW) values from +15.5 to +22.7 per thousand were determined in tequilas of both categories. Owing to overlapping data, attempts to differentiate between white, rested, and aged tequilas within each of the two categories failed. In addition, discrimination of tequila samples from other spirits by means of delta(13)C(VPDB) and delta(18)O(VSMOW) data of ethanol was restricted to the products originating from C(3) as well as C(4)/CAM raw materials. 相似文献
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Black bindweed seed (Polygonum convolvulus) from the 1987 harvest was tested for possible toxicity in a 38-day range-finding test with Wistar rats which received feed rations on the basis of VDT-1 standard feedstuff and components of 5 or 20%. Histological liver findings as well as parameters recorded from laboratory diagnosis (plasma activities of ALAT, ASAT, and gamma GT as well as total protein and albumin levels in plasma) were indicative of incipient impairment of liver metabolism. More detailed and comprehensive chemico-analytical investigations are recommended, with due consideration of the unity between high-value primary components, on the one hand, and possibly toxic secondary constituent substances, on the other. 相似文献
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