Accurate and reproducible determination of lignin molar mass by acetobromination

The accurate and reproducible determination of lignin molar mass by using size exclusion chromatography (SEC) is challenging. The lignin association effects, known to dominate underivatized lignins, have been thoroughly addressed by reaction with acetyl bromide in an excess of glacial acetic acid. The combination of a concerted acetylation with the introduction of bromine within the lignin alkyl side chains is thought to be responsible for the observed excellent solubilization characteristics acetobromination imparts to a variety of lignin samples. The proposed methodology was compared and contrasted to traditional lignin derivatization methods. In addition, side reactions that could possibly be induced under the acetobromination conditions were explored with native softwood (milled wood lignin, MWL) and technical (kraft) lignin. These efforts lend support toward the use of room temperature acetobromination being a facile, effective, and universal lignin derivatization medium proposed to be employed prior to SEC measurements.     

Variation in the flavonol glycoside composition of almond seedcoats as determined by maldi-tof mass spectrometry

Seedcoats of 16 almond varieties were screened for flavonol glycosides by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Flavonol glycosides were extracted by a simple methanolic extraction followed by a quick cleanup procedure with a Sep-Pak C(18) cartridge. Each of the 16 seedcoat samples exhibited a unique composition. Four flavonol glycosides, isorhamnetin rutinoside, isorhamnetin glucoside, kaempferol rutinoside, and kaempferol glucoside, were detected and quantified with use of rutin as an internal standard. Individual peak ratios were very consistent across triplicate analyses of all samples; the average standard deviation was 9%. In all almond varieties, isorhamnetin rutinoside was the most abundant flavonol glycoside, and the total content ranged from 75 to 250 microg/g.     

Study of thermal aggregation of oat globulin by laser light scattering

The heat-induced aggregation of oat globulin was studied using size-exclusion chromatography (SEC) combined with on-line multiangle laser light scattering (MALLS) and quasi-elastic light scattering (QELS). The unheated oat globulin exists as a mixture of hexamer (>95%), trimer, and dimer forms of hexamer. The molecular weight of the hexamer was estimated by MALLS to be 330 000, close to that deduced from the genomic cloned data of the acidic and basic polypeptides of oat globulin. From QELS measurements, it can be predicted that the hexamer exists as two annular trimeric rings, with a diameter of 11.8 nm, placed on top of each other, forming an oblate cylinder with a height of about 8.5 nm. Upon heating at 100 degrees C, the oat globulin hexamers and trimers were dissociated into monomers. The heat-denatured monomers, probably assuming an extended structure, were associated to form small aggregates, which were further aggregated to high molecular weight complexes. Upon further heating (60 min), the soluble aggregates were associated to form insoluble aggregates. Aggregation of oat globulin occurred at a much faster rate at 110 degrees C. The results indicate that the SEC-MALLS-QELS system is suitable for studying thermal aggregation of food proteins.     

Determination of the absolute molecular weight averages and molecular weight distributions of alginates used as ice cream stabilizers by using multiangle laser light scattering measurements

High-performance size exclusion chromatography with multiangle laser light scattering detection (HPSEC-MALLS) was used for characterizing complete molecular weight distributions for a range of commercial alginates used as ice cream stabilizers. For the samples investigated, molecular weight averages were found to vary between 115 000 and 321 700 g/mol and polydispersity indexes varied from 1. 53 to 3.25. These samples displayed a high content of low molecular weights. Thus, the weight percentage of material below 100 000 g/mol ranged between 6.9 and 54.4%.     

Daily variations in oligosaccharides of human milk determined by microfluidic chips and mass spectrometry

Human milk is a complex biological fluid that provides not only primary nourishment for infants but also protection against pathogens and influences their metabolic, immunologic, and even cognitive development. The presence of oligosaccharides in remarkable abundance in human milk has been associated to provide diverse biological functions including directing the development of an infant's intestinal microflora and immune system. Recent advances in analytical tools offer invaluable insights in understanding the specific functions and health benefits these biomolecules impart to infants. Oligosaccharides in human milk samples obtained from five different individual donors over the course of a 3 month lactation period were isolated and analyzed using HPLC-Chip/TOF-MS technology. The levels and compositions of oligosaccharides in human milk were investigated from five individual donors. Comparison of HPLC-Chip/TOF-MS oligosaccharides profiles revealed heterogeneity among multiple individuals with no significant variations at different stages of lactation within individual donors.     

Sensitive determination of sulfate in drinks and vegetables digests by Rayleigh light scattering technique

In this paper, a novel and sensitive method based on Rayleigh light scattering technique (RLS) was proposed for the determination of sulfate using a conventional spectrofluorometer. Sulfate was transformed to BaSO4 particles, which displayed intense light scattering in aqueous solutions. The effects of factors such as wavelength, acidity, stabilizers and interferents were studied in detail. The RLS intensity of the BaSO4 suspension was obtained in 0.1 mol L(-1) of [H+] and the addition of 2 mL of cationic polyacrylamide (CPAM) with 7.05 x 10(-3) mmol mL(-1) charged cations and 1.0 mL of BaCl2.2H2O (5.0%) at 510 nm. In the range of 8-400 microg mL(-1), RLS intensity was linear to the concentration of BaSO4, and the detection limit was 0.3 microg mL(-1). To determine the feasibility of the proposed method, some samples of water, drinks, and vegetables digests were analyzed, and the results were in agreement with the standard turbidimetric method. Good recovery results were also obtained in the range of 94-105%. Although this method was limited in stability, it was characterized with simplicity, sensitivity, reliability, and little interference.     

Stability constants of Mn(II)-complexes in soils as determined by a voltammetric method

A voltammetric method was used for the determination of stability constants (log K) of Mn(II)-complexes in soils. Log K values were of the order of 2–5, being largest at the stage of intensive decomposition of organic matter. The complexing agents were primarily negative in electric charge, and could be retained by soils containing free iron oxides.     

Plant availability of phosphorus in dead herbage ingested by surface-casting earthworms

A combined field and glasshouse technique was developed to evaluate the plant-availability of phosphorus from two sources. The first source was ryegrass which had been ingested by earthworms and excreted in surface casts, and the second was untreated ryegrass. Surface casts labelled with ³²P were obtained in the field from earthworms fed with ³²P-labelled ryegrass. In a glasshouse study, labelled casts or labelled herbage were placed on the surface of soil in which ryegrass was growing. Ryegrass recovered proportionately more ³²P from cast material than from dead herbage. The results suggest that earthworms increase the short-term plant availability of P derived from plant litter by two to three fold. The effect of surface-casting earthworms on the rate of cycling of P in soils of different P status is discussed.     

不同前处理条件对动态光散射检测酪蛋白胶束粒径的影响

为了准确评价乳的稳定性和加工性能,探讨不同前处理条件对动态光散射检测酪蛋白胶束粒径的影响,研究了稀释液的种类(超纯水、钙咪唑缓冲液、模拟牛乳超滤液和牛乳超滤液)、稀释液温(4和25℃)和稀释液的放置时间(0~48 h)对脱脂乳中酪蛋白胶束粒径的动态光散射测试结果的影响,并将酪蛋白胶束粒径的动态光散射测试结果与冷冻透射电镜图像中测得的真实结果进行比较。研究发现以超纯水和钙咪唑缓冲液作为脱脂乳稀释液时,部分胶束发生解离,影响测试结果;采用牛乳超滤液及模拟牛乳超滤液作为稀释液时,胶束的微环境没有改变,反映了胶束的真实粒径及分布;放置24 h后,牛乳超滤液及模拟牛乳超滤液将产生颗粒;温度对测试有显著的影响(P0.05):4℃的样品用25℃的稀释液进行稀释后,动态光散射的计数率和粒径分别增大了16.6%和11.4%;25℃的样品用4℃的稀释液进行稀释后,计数率和粒径分别降低了16.1%和9.8%。结果表明酪蛋白胶束粒径的测试前处理较适宜的条件为:在与样品的温度相同条件下,以配置好后24 h内的模拟牛乳超滤液或牛乳超滤液(10 k Da超滤膜)作为脱脂乳的稀释液进行稀释。通过与冷冻电镜条件下测得的酪蛋白胶束粒径的真值比较,发现该前处理条件下酪蛋白胶束粒径的动态光散射测试结果的相对误差为-5.7%~1.8%,表明该样品前处理方法可用于动态光散射方法快速检测酪蛋白胶束粒径。研究结果为快速、准确地获取酪蛋白胶束的粒径信息,进而准确分析乳的稳定性及加工性能提供参考。     

Characterization of commercial and experimental sodium caseinates by multiangle laser light scattering and size-exclusion chromatography

A range of sodium caseinate samples were characterized by a multiangle laser light scattering (MALLS) system or by the use of MALLS as an on-line detector with size-exclusion chromatography (SEC). Sodium caseinate solutions, analyzed using a MALLS system alone, gave weight-average molar mass (M(w)) values in the range 1200-4700 kDa and z-average root-mean-square radius (R(g)) values ranged from approximately 50 to 120 nm. When these solutions were ultracentrifuged at 90000g for 1 h, a cloudy top layer was formed; the subnatant was carefully removed and analyzed by SEC-MALLS. The M(w) values were found to be in the range approximately 30-575 kDa, and R(g) values ranged from approximately 22 to 49 nm. During SEC, the MALLS system detected some very large-sized material that eluted close to the void volume; this material was hardly detected by the concentration detectors, i.e., ultra-violet (UV) and differential refractive index (DRI). The intensity of the light scattering (LS) signal from this very large sized material was greatly reduced in the subnatant. SEC of sodium caseinate samples revealed two main peaks with M(w) of approximately 420-750 kDa and 39-69 kDa, respectively. The R(g) values were very large for a protein molecule, and initial calculations suggested that the shape of caseinate molecules was likely to be highly elongated.     

不同pH条件下黄壤胶体凝聚的动态光散射研究

土壤胶体的凝聚或分散紧密地联系着许多环境问题,并受胶体表面电荷性质的调控.以黄壤为实验材料,利用动态光散射技术研究pH作用下该可变电荷胶体颗粒的凝聚动力学.结果发现:土壤胶体的凝聚与否强烈依赖于pH.不同浓度HNO3和KOH诱发的土壤胶体凝聚均表现出慢速和快速凝聚特征,在快速凝聚中,HNO3作用较KOH作用的黄壤胶体平均凝聚速率更高、变化更快,表明表面电荷中和诱发的凝聚远大于压缩双电层诱发的凝聚.通过快速平均凝聚速率变化的反转点对应的pH,估计电荷零点(Zero pointof charge,ZPC),提供了一个实验测定ZPC的新方法.     

利用3D模型模拟天空与叶面散射对玉米冠层截光率的影响

该文利用并行蒙特卡罗光线跟踪模型定量分析了天空散射与叶片散射对玉米冠层截光率的影响.模拟试验表明:相同辐射强度时,冠层截获的光强与受剑照射的叶片在天空散射时都比直接辐射时多;当太阳高度角小于60°时,冠层在阴大截获的总光强小于晴大,但至少60%的叶片在阴大截获的光强大于晴大时截获的光强;叶片散射对冠层光分布的影响与波长...     

光散射技术在土壤胶体颗粒相互作用研究中的应用

由于测试手段的限制,目前对土壤中粒径为0·001～1μm的"超微粒子"之间相互作用的微观效应研究还未引起足够的重视。本文从散射角和悬液颗粒密度两个方面讨论了光散射技术在土壤胶体研究中的应用条件,探讨了土壤胶体颗粒凝聚动力学机制及形成的聚合体结构特征。结果表明:(1)对于本实验所用黄壤悬液,应用光散射准确测定的散射角范围为90°～135°,初始颗粒密度范围为1·90×10-3～0·119gL-1。(2)在自相关曲线平滑地衰减至基线且散射光强保持不变的条件下,可以用光散射技术准确测定土壤胶体颗粒凝聚过程中有效直径、最可几粒径及粒径分布的变化,反映凝聚动力学规律。(3)在298K、90mmolL-1KNO3体系中用动态光散射测得黄壤胶体颗粒凝聚动力学为扩散控制团簇聚集机制,用静态光散射测得形成的聚合体分形维数为1·56±0·02。     

The effects of sulfate and non-sulfate particles on light scattering at the Mauna Loa Observatory

The results of a 1 yr sampling program designed to quantify the effects of sulfate and non-sulfate particles on light scattering measurements routinely made at the Mauna Loa Observatory in Hawaii are described. Aerosol sampling with a cascade impactor was conducted at an altitude of 3400 m above sea level near the summit of a large, gently sloping volcano during nocturnal downslope flow, when particles are believed representative of clean, mid-tropospheric background conditions. A microchemical spot test using a transmission electron microscope was applied to quantitatively identify individual sulfuric acid, ammonium sulfate, and non-sulfate particles. Simultaneous measurements of integrated light scattering with a four-wavelength nephelometer were also made. The results of the study indicate that significant variations in aerosol chemistry and morphology occur at Mauna Loa Observatory over an annual period. Episodes of high particle scattering caused by large non-sulfate particles, presumably soil dust, occur mainly in the spring and are generally associated with strong northwesterly large scale flow. Evidence has been gathered suggesting that dust storms over the Asian continent largely account for the springtime turbidity peak in Hawaii. During other times of the year, the effects of sulfate and non-sulfate particles on light scattering are approximately equal.     

Estimating the three-dimensional structure of canopy foliage based on the light measurements in a Betula ermanii stand

In order to more accurately evaluate the functional activity of forest stands by canopy production and evapotranspiration, we improved the methods for field measurements and statistical modeling to estimate foliage configuration (spatial distribution of leaves) while simultaneously reconstructing the three-dimensional photosynthetically active photon flux density (PPFD) distribution (PPFD pattern) in a forest canopy. By using a sensor (photodiode) array, a PPFD pattern was observed in summer 2002 under the canopy in an even-aged, pure stand of Japanese mountain birch Betula ermanii Cham. (17-years old) in Hokkaido, northern Japan. A Markov chain Monte Carlo (MCMC) sampling technique is developed such that a set of foliage configurations generated by the model referred to as the Gibbs foliage canopy (GFC) approximates the field-measured PPFD pattern. The posterior distribution of the foliage configurations is generated by the parallel tempering MCMC of eight independent series of foliage configurations. The GFC model generated the posterior distribution of the LAI estimates (mean 4.56) that appeared to be appropriate in comparison to other LAI estimates of the B. ermanii stand based on the indirect and nondestructive methods by LAI-2000 (LAI = 3.43) and litterfall traps (LAI = 5.56) because they could be under- and overestimated, respectively. Our evaluations of the canopy production and evapotranspiration rates suggest that the relationship between LAI and canopy functions was not very simple because it depended on the nonlinear functional forms of the leaf responses of photosynthesis and transpiration to PPFD. The current study demonstrates an application of MCMC techniques that can generate a set of possible structures of unobserved/unobservable objects based on the high-resolution dataset obtained by some indirect (or remote-sensing) methods.     

Determination of 1-deoxynojirimycin in mulberry leaves using hydrophilic interaction chromatography with evaporative light scattering detection

A simple and rapid method for determining 1-deoxynojirimycin (DNJ), a potent glucosidase inihibitor present in mulberry leaves (Morus alba and Morus bombysis), by high-performance liquid chromatography coupled to an evaporative light scattering detector (ELSD) has been developed. DNJ was separated from an extract of mulberry leaves on a TSKgel Amide-80 column, which is a representative column for hydrophilic interaction chromatography. During postcolumn detection, DNJ was detected by ELSD and concurrently identified by mass spectrometry. The detection limit was 100 ng. This method is sufficiently sensitive for determining DNJ in mulberry leaves and other related products.     

Study of thermal aggregation of globulin from common buckwheat (Fagopyrum esculentum Moench) by size-exclusion chromatography and laser light scattering

The heat-induced aggregation of common buckwheat (Fagopyrum esculetum Moench) globulin (BWG) was studied using size-exclusion chromatography (SEC) combined with on-line multiangle laser light scattering (MALLS) and quasielastic light scattering (QELS). The unheated BWG was found to exist mainly as a hexamer, with an estimated weight-average molecular weight (M(w)) of 342 000, close to that deduced from the genomic cloned data of 13S buckwheat globulin. The QELS data predicted that the hexamer exists as two annular trimeric rings (diameter approximately 10.8 nm) placed on top of each other, forming an oblate cylinder (height approximately 9.1 nm). Upon heating, hexamers and trimers were dissociated and then associated to form extended small aggregates, finally forming compact, large macroaggregates. N-Ethylmaleimide would favor macroaggregate formation and increased the molar masses and hydrodynamic radii of the soluble aggregates, suggesting a different aggregation process in the presence of the sulfhydryl-blocking agent. A plot of log hydrodynamic radius versus log molar mass showed changes in the slope during heat treatment, suggesting conformational transformation in the heat-denatured and aggregated BWG molecules.