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1.
A laboratory procedure for the analysis of the oxygen-18/oxygen-16 isotope ratios of ethanol derived from sugars and fruit juices by pyrolysis-isotope ratio mass spectrometry (IRMS) has been applied to the study of isotopic fractionation induced by the isotope effects of fermentation and distillation. For both processes, an experimental model has been established to describe and explain the observed fractionation phenomena. It is shown that reproducible results can be obtained when appropriate analytical conditions are used. Moreover, the ability of ethanol to act as a reliable indicator of the (18)O/(16)O ratio of sugars in orange juice (and therefore to be used as an internal reference for detecting water addition) is demonstrated both in theory and in practice.  相似文献   

2.
Despite the robustness of isotopic methods applied in the field of wine control, isotopic values can be slightly influenced by enological practices. For this reason, must concentration technique effects on wine isotopic parameters were studied. The two studied concentration techniques were reverse osmosis (RO) and high-vacuum evaporation (HVE). Samples (must and extracted water) have been collected in various French vineyards. Musts were microfermented at the laboratory, and isotope parameters were determined on the obtained wine. Deuterium and carbon-13 isotope ratios were studied on distilled ethanol by nuclear magnetic resonance (NMR) and isotope ratio mass spectrometry (IRMS), respectively. The oxygen-18 ratio was determined on extracted and wine water using IRMS apparatus. The study showed that the RO technique has a very low effect on isotopic parameters, indicating that this concentration technique does not create any isotopic fractionation, neither at sugar level nor at water level. The effect is notable for must submitted to HVE concentration: water evaporation leads to a modification of the oxygen-18 ratio of the must and, as a consequence, ethanol deuterium concentration is also modified.  相似文献   

3.
Until now, no analytical method, not even isotopic ones, had been able to differentiate between sugars coming from C4-metabolism plants (cane, maize, etc.) and some crassulacean acid metabolism plants (e.g., pineapple, agave) because in both cases the isotope distributions of the overall carbon-13/carbon-12 and site-specific deuterium/hydrogen isotope ratios are very similar. Following recent advances in the field of quantitative isotopic carbon-13 NMR measurements, a procedure for the analysis of the positional carbon-13/carbon-12 isotope ratios of ethanol derived from the sugars of pineapples and agave using the site-specific natural isotopic fractionation-nuclear magnetic resonance (SNIF-NMR) method is presented. It is shown that reproducible results can be obtained when appropriate analytical conditions are used. When applied to pineapple juice, this new method demonstrates a unique ability to detect cane and maize sugar, which are major potential adulterants, with a detection limit in the order of 15% of the total sugars, which provides an efficient mean of controlling the authenticity of juices made from this specific fruit. When applied to tequila products, this new method demonstrates a unique ability to unambiguously differentiate authentic 100% agave tequila, as well as misto tequila (made from at least 51% agave), from products made from a larger proportion of cane or maize sugar and therefore not complying with the legal definition of tequila.  相似文献   

4.
The isotopic investigation of vanillin has been extended to the new sources of natural precursors of vanillin recently introduced with a view of obtaining natural vanillin by biotechnological processes. To check the consistency of the isotopic composition of vanillin with that of the corresponding aromatic fragment, a selective degradation reaction into guaiacol was carried out. The reaction was shown to proceed without significant isotopic fractionation at the sites of interest, and an optimized procedure was defined from the results of an experimental design involving the quantity of reagent and the temperature and duration of the experiment. Guaiacol, which can be easily obtained in a reasonable time, is an interesting isotopic probe for carbon- and oxygen-isotope ratio mass spectrometry (IRMS) determinations. It provides (13)C information specific to the aromatic fragment and, combined with delta(13)C values measured on vanillin itself, it improves the authentication potential of carbon-IRMS. Thus, the natural status of ferulic acid may be characterized by significant (13)C depletion at the formyl site. Similarly, the oxygen-18 content of guaiacol is a better authentication tool than delta(18)O of vanillin because it does not suffer the drawback of being altered by chemical exchange of the sp(2) oxygen atom with water in industrial or laboratory procedures. Although collaborative studies are still necessary to improve the interlaboratory reproducibility of the delta(18)O parameters, consistent results can be obtained in an intralaboratory context. It is shown in particular that chemical oxidation of ferulic acid is characterized by a relative enrichment of the aromatic moiety of vanillin.  相似文献   

5.
The site-specific natural hydrogen isotope ratios of plant metabolites determined by 2H nuclear magnetic resonance (SNIF-NMR method) can provide powerful criteria for inferring mechanistic and environmental effects on biosynthetic pathways. This work examines the potential of isotopic profiles for the main constituents of carbohydrates, glucose and fructose, to distinguish different photosynthetic pathways. An appropriate analytical strategy, involving three suitable isotopic probes, has been elaborated with a view to measuring simultaneously, in conditions devoid of isotopic perturbations, all (or nearly all) of the carbon-bound hydrogen isotope ratios. It is shown that the type of photosynthetic metabolism, either C3 (sugar beet, orange, and grape), C4 (maize and sugar cane), or CAM (pineapple), and the physiological status of the precursor plant exert strong influences on the deuterium distribution in the sugar molecules. Consequently, this isotopic fingerprint may be a rich source of information for the comparison of mechanisms in metabolic pathways. In addition, it can provide complementary criteria to ethanol as a probe for the origin of sugars.  相似文献   

6.
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7.
Isotope ratio mass spectrometry and site-specific natural isotope fractionation-nuclear magnetic resonance were applied to determine the overall carbon isotope ratio (delta13C) and the hydrogen isotope ratios [(D/H)I and (D/H)II] of ethanol, respectively. Ethanol was obtained by distillation of fermented cherry mash from a pot still commonly used in fruit brandy production. Analyses of distillate fractions revealed that the distillation proceeds with a fractionation of ethanol isotopologues. The inverse vapor pressure isotope effect (VPIE) observed for the carbon isotopologues is in accordance with the data reported for distillation of ethanol in spinning band columns. In contrast, the inverse VPIE for hydrogen isotopologues of ethanol observed in spinning band columns could not be confirmed. To investigate whether the observed isotope fractionations might influence the applicability of stable isotope analysis for quality and authenticity assessment of fruit brandies, the collected distillate fractions were recombined to cuts, as is common practice in commercial fruit brandy production. Taking into consideration the limits of repeatability of the method, it could be demonstrated that the isotope fractionations observed do not impair the applicability of stable isotope analysis of the carbon and hydrogen isotopes of ethanol for the authenticity assessment of cherry brandies if the cuts are placed in accordance with common distillers' practice.  相似文献   

8.
灌溉农田水汽氢氧同位素组成特征研究初探   总被引：1，自引：0，他引：1  
灌溉农田生态系统水汽变化能够直接反映其耗水状况。本研究应用基于高频实时气态稳定同位素分析仪的箱式法测定水汽氢氧同位素特征, 结合涡度相关技术所测定的农田水汽通量结果, 探讨不同高度大气水汽在不同时段的稳定同位素组成特征。研究结果表明: 对于不同的时间尺度, 生态系统边界层水汽稳定同位素组成在连续几天内的变化有波动, 日变化比较稳定, 小时尺度波动很小; 水汽稳定同位素的大气背景组成特征表现为日尺度上的组成变化呈稳步富集趋势, 小时尺度上几乎无变化。蒸散水汽重同位素特征随时间推移富集明显, 午夜蒸发和蒸腾水汽同位素组成特征相似, 清晨蒸腾水汽比蒸发水汽轻, 午间蒸腾水汽比蒸发水汽重。对于不同高度的水汽来说, 玻璃箱内蒸散水汽稳定同位素组成要比生态系统边界层2 m 处水汽高。建立了土壤蒸发和植物蒸腾稳定同位素变化特征与蒸散过程的线性关系, 相关系数达到0.87。  相似文献   

9.
为考察不同加工方式和样本制备目数对茶叶同位素分馏与测定的影响,建立茶叶中4种同位素δ13C、δ15N、δ2H、δ18O的元素分析-稳定同位素比率质谱(EA-IRMS)分析测试方法,研究红茶和绿茶加工过程中同位素分馏及不同目数样本制备的测试影响。结果表明,通过两点法或三点法构建的校准曲线具有很好的相关性,能够满足测试精度要求;相同原料所加工红茶和绿茶中4种同位素比率无显著差异,未发现同位素分馏效应;红茶和绿茶通过研磨后过80目、100目和120目筛与未过筛4种茶叶样品之间同位素比率无显著差异(P<0.05)。因此,相同原料的非发酵(绿茶)和发酵(红茶)加工以及不同目数样本制备对4种稳定同位素测定均无显著影响。本研究结果为茶叶稳定同位素数据库构建以及样品制备提供了方法基础。  相似文献   

10.
A new method has been developed for measuring the D/H ratio of the nonexchangeable sites of citric acid by isotope ratio mass spectrometry (IRMS). Pure citric acid is transformed into its calcium salt and subsequently analyzed by pyrolysis-IRMS. The citric acid isolated from authentic fruit juices (citrus, pineapple, and red fruits) systematically shows higher D/H values than its nonfruit counterpart produced by fermentation of various sugar sources. The discrimination obtained with this simplified method is similar to that obtained previously by applying site specific isotopic fractionation-nuclear magnetic resonance (SNIF-NMR) to an ester derivative of citric acid. The combination of carbon 13 and deuterium measurements of extracted citric acid is proposed as a routine method for an optimum detection of exogenous citric acid in all kinds of fruit juices.  相似文献   

11.
The authenticity and geographical origin of wines produced in Slovenia were investigated by a combination of IRMS and SNIF-NMR methods. A total of 102 grape samples of selected wines were carefully collected in three different wine-growing regions of Slovenia in 1996, 1997, and 1998. The stable isotope data were evaluated using principal component analysis (PCA) and linear discriminant analysis (LDA). The isotopic ratios to discriminate between coastal and continental regions are the deuterium/hydrogen isotopic ratio of the methylene site in the ethanol molecule (D/H)(II) and delta(13)C values; including also delta(18)O values in the PCA and LDA made possible separation between the two continental regions Drava and Sava. It was found that delta(18)O values are modified by the meteorological events during grape ripening and harvest. The usefulness of isotopic parameters for detecting adulteration or watering and to assess the geographical origin of wines is improved only when they are used concurrently.  相似文献   

12.
Stable carbon isotope ratio mass spectrometry (delta13C IRMS) was used to detect maple syrup adulteration by exogenous sugar addition (beet and cane sugar). Malic acid present in maple syrup is proposed as an isotopic internal standard to improve actual adulteration detection levels. A lead precipitation method has been modified to isolate quantitatively malic acid from maple syrup using preparative reversed-phase liquid chromatography. The stable carbon isotopic ratio of malic acid isolated from this procedure shows an excellent accuracy and repeatability of 0.01 and 0.1 per thousand respectively, confirming that the modified lead precipitation method is an isotopic fractionation-free process. A new approach is proposed to detect adulteration based on the correlation existing between the delta13Cmalic acid and the delta13Csugars-delta13Cmalic acid (r = 0.704). This technique has been tested on a set of 56 authentic maple syrup samples. Additionally, authentic samples were spiked with exogeneous sugars. The mean theoretical detection level was statistically lowered using this technique in comparison with the usual two-standard deviation approach, especially when maple syrup is adulterated with beet sugar : 24 +/- 12% of adulteration detection versus 48 +/- 20% (t-test, p = 7.3 x 10-15). The method was also applied to published data for pineapple juices and honey with the same improvement.  相似文献   

13.
蒸发与降水入渗过程中不同水体氢氧同位素变化规律   总被引：4，自引：2，他引：2  
为了研究土壤水蒸发与降水入渗非饱和带过程中不同水体氢氧同位素的变化规律,该文选用2种不同性质的土壤-砂土和黄土,设计了土壤水蒸发和降水入渗室内试验。结果表明:对于砂土,土壤水蒸发过程中剩余水体氢氧同位素分馏遵从瑞利模式;对于黄土,随着蒸发时间的延长,剩余土壤水氢氧同位素值越来越远离瑞利分馏关系线;在降水入渗非饱和带的初期,相对于风干砂土,风干的黄土颗粒对土柱出流水的氢氧同位素值产生了影响,并且出流水的氢氧同位素亦受到土壤原水同位素值的影响,只有入渗的降水达到了一定数量,土柱出流水才能与降水的同位素值相同。该研究可为运用氢氧同位素研究降水能否通过非饱和带补给地下水提供数据分析的依据。  相似文献   

14.
Abstract

The isotopic composition of water extracted from various parts of alfalfa (Medicago saliva) plants was compared with that transpired by the plants to validate water extraction procedures, and to define the degree of alteration of the isotopic composition of water that occurred in different plant parts. The mean δ2H and δ18O values of water extracted from the upper tap root and lower crown regions were < 1‰ and 0.3‰ different from that of water transpired, respectively, with an analytical precision similar to that found in previous studies on soils and trees. Water from other plant parts closer to the leaves was enriched in 2H (up to 12.6 in upper stems) and 18O (4.2‰) with respect to that transpired. The enrichment was associated with a greater variability in δ2H values between replicate plants. δ2H‐δ18O data indicated that the isotopic enrichment was due to evaporation during transpiration. The study showed that azeotropic distillation is an accurate means of extracting water from alfalfa, although care is required when obtaining plant samples for comparison with water from the root‐zone.  相似文献   

15.
A postcolumn derivatization method is described for determination of reducing sugars and phosphorylated reducing sugars from chicken meat and other foods using high-performance liquid chromatography (HPLC). Reducing sugars are extracted with ethanol/water, separated on a Kromasil amine-bonded column by isocratic analysis using acetonitrile/water as the mobile phase, and, after postcolumn reaction with tetrazolium blue, are determined by the resulting absorbance at 550 nm. Phosphorylated sugars are first dephosphorylated using alkaline phosphatase and then determined by the same method.  相似文献   

16.
It is well known from earlier work that water stress and salinity results in depressed plant growth and high fruit quality of tomato (e.g. increased sugar and acid levels), but generally is associated with a low marketable fruit yield. In the present work we investigated whether even a small reduction in water supply (without visible symptoms of water stress) also results in a high fruit quality together with high marketable fruit proportions. To characterize fruit quality sugars (glucose and fructose), titratable acids, odour-active aroma volatiles and vitamin C were investigated. Tomato plants (Lycopersicon esculentum Mill. cv Vanessa) were grown in soil and with the onset of fruit development water supply was varied (70% and 50% water capacity). In the treatment with lower water supply plant growth, and in particular the number of fruit settings were depressed and the sugar and vitamin C concentrations in the fruits were significantly increased, especially during fruit ripening. Furthermore, with lower water supply the concentrations of titratable acids and of C6 aldehydes (hexanal, (Z)-3-hexenal and (E)-2-hexenal) were significantly increased in the red fruits. Fruit growth was identical in both treatments. The higher levels of sugars, titratable acids, aroma volatiles and vitamin C are responsible for the higher fruit quality under conditions of lower water supply. Since not all fruits of the well watered plants became mature, the marketable yield in both treatments was rather similar and hence, together with a higher fruit quality in the treatment with lower water supply, high proportions of marketable fruits can be harvested.  相似文献   

17.
基于氧同位素的玉米农田蒸散发估算和区分   总被引：2，自引：1，他引：1  
农田蒸散发(evapotranspiration,ET)的估算和区分是土壤-植物-大气连续体中的重要研究内容,是农业水资源高效利用的重要基础。该研究分析了土壤水、蒸发水汽、蒸腾水汽和大气背景混合水汽氧同位素组成分布特征,并采用2种同位素的方法对玉米农田蒸散发进行估算和区分:1)结合Keeling plot和Craig-Gordon模型的同位素方法(Iso-CG);2)基于土壤水同位素守恒和水量平衡的方法(Iso-WB)。结果表明,在玉米生育期内Iso-WB方法与Iso-CG方法所计算的玉米蒸腾比例分别为0.64~0.91和0.52~0.91,平均值分别为0.80和0.78。玉米蒸散发总量在前期、中期和后期均值分别为3.95、5.30和4.98 mm/d。通过比较参数并与前人研究结果对比分析,表明采用Iso-CG方法估算区分ET相对精确,采用Iso-WB方法计算蒸散发要求的测量精度相对较高,计算误差较大。该研究成果不仅为玉米农田制定灌溉制度及提高用水效率提供了理论依据,而且对深入探索氧同位素水文学领域具有重要意义。  相似文献   

18.
A new procedure to determine individual sugar (sucrose, glucose, and fructose) 13C isotope ratios, using liquid chromatography-isotope ratio mass spectrometry (HPLC-IRMS), has been developed to improve isotopic methods devoted to the study of honey authenticity. For this purpose 79 commercial honey samples from various origins were analyzed. Values of delta13Choney ranged from -14.2 to -27.2", and delta13Cprotein ranged from -23.6 to -26.9". A very strong correlation is observed between the individual sugar 13C ratios, which are altered in the event of sugar addition, even at low levels. The use of Deltadelta13C [fruct-glu], Deltadelta13C [fruct-suc], and Deltadelta13C [gluc-suc] systematic differences as an authenticity criterion permits the sugar addition [C3, beet sugar; or C4, cane sugar, cane syrup, isoglucose syrup, and high-fructose corn syrup (HFCS)] to be reliably detected (DL = 1-10%). The new procedure has advantages over existing methods in terms of analysis time and sensitivity. In addition, it is the first isotopic method developed that allows beet sugar addition detection.  相似文献   

19.
植物叶片、茎秆和土壤水δ18O和δD是研究土壤植被大气系统生态水文循环过程的重要示踪剂。与传统的稳定同位素质谱(IRMS)技术相比,稳定同位素红外光谱(IRIS)技术具有测量速度快、运行成本低等优势,将促进稳定同位素生态学的发展。但是利用低温真空蒸馏抽提技术获得的植物叶片和茎秆水中含有甲醇和乙醇类有机污染物,造成δ18O和δD的IRIS测量值偏离IRMS测量值(2.64±0.43)‰和(3.6±0.8)‰,超过了仪器精度。本研究利用纯水混入不同浓度的色谱纯甲醇或乙醇,结合Los Gatos公司的光谱分析软件确定甲醇(NB)和乙醇(BB)类物质污染程度的光谱度量值,建立了δ18O和δD的光谱污染校正方法。研究表明,同一台分析仪建立的校正曲线无明显的时间漂移;不同分析仪建立的校正曲线存在显著差异;IRIS校正值与IRMS测量值的交叉验证表明,IRIS测定冬小麦和夏玉米叶片和茎秆水的δ18O和δD可以被准确地校正,与IRMS的差值分别为(0.11±0.12)‰和(0.7±0.4)‰。  相似文献   

20.
Soil respiration and photosynthesis are the two largest carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere and, therefore, the dominant processes influencing the oxygen isotopic composition of atmospheric CO2. The characterization of temporal and spatial variations of plant and soil‐related fluxes of different oxygen isotopologues of CO2 (12C16O2; 12C16O18O) is relevant to constraining the global carbon budget. The oxygen isotopic composition of soil‐respired CO2 is controlled by its release rate, the degree of isotopic equilibrium with soil water and the diffusional transport of CO2. The hypothesis of this study was that, as well as soil moisture, the soil particle size, the presence of an organic litter layer and the enzyme carbonic anhydrase (CA) would have a significant impact on the oxygen isotopic composition of soil‐released CO2. We tested this hypothesis with soil microcosm experiments on columns of medium and fine sand. Soil water content and soil texture influenced the isotopic composition of soil‐released CO2 significantly. A litter layer had a significant effect on the isotopic composition of water vapour but not on CO2 released from soil. In the absence of CA, oxygen isotope equilibration between the CO2 invasion flux and soil water was insignificant, whereas in the presence of CA about 55% of the CO2 invading the soil exchanged oxygen isotopes with soil water. Our findings highlight the importance of small‐scale variability of soil attributes for the oxygen isotopic composition of soil‐released CO2 as well as the strong impact of CA activity in soils.  相似文献   

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