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The use of two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy as applied to studies of starch, starch products and glycogen is reported. The use of both homonuclear correlation (COSY, relay-COSY and HOHAHA) and heteronuclear correlation (HMQC, HETCOR) experiments is discussed. This approach makes it possible to obtain complete assignments of the proton NMR spectra of these polysaccharides. This is not possible from 1-D spectra due to excessive overlap of the non-anomeric proton signals. The resulting assignments are useful in obtaining structural information regarding starch and related products. Moreover, the greater inherent resolution of the two-dimensional spectra can reveal the presence of low molecular weight carbohydrates (glucose, maltose etc.) in dextrin samples, thus providing information about carbohydrate composition. 相似文献
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One- and two-dimensional 1H and 13C NMR spectra were obtained for a variety of homopolysaccharides, including the glucans dextran and pullulan, and the fructans levan and inulin. The NMR results provided information about the primary structure of these polysaccharides. Our results are in agreement with those determined previously by methylation analysis and other classical methods. The number of α(1 → 44) and α(1 → 6) linkages could be quantitated for pullulan. The presence of a single nonreducing glucose residue in the polyfructose inulin could also be demonstrated. In the case of the branched polysaccharides dextran and levan, it was possible to determine the degree of branching. In addition for lower molecular weight polysaccharides such as inulin and partially hydrolyzed dextran, it was possible to detect signals arising from reducing and non-reducing end groups. Their approximate molecular weight could be determined by quantitation of these signals. 相似文献
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The molecular mobility of water in corn starch powders (71 to 96% solids) was determined by deuterium (2H) and oxygen-17 (17O) high-field Nuclear Magnetic Resonance (NMR) spectroscopy, in deuterium (D2O) and oxygen-17 enriched water (H217O), respectively. The NMR transverse relaxation rate (R2) was related to both the concentration and activity of water (aw). The concentration plot showed two regions of water mobility; trapped and monolayer water. The water activity plot showed two linear regions of water mobility; Region A, from 0.99 to 0.23 aw, and Region B, from 0.23 to 0.11 aw. The linear relationship in Region A between water mobility, as measured by R2 and water activity is hypothesized to be due to the hydrophobic nature of the starch granules which results in diffusion limited water motion. Relaxation rates for 2H and 17O at high aw were compared with one another and literature data. 相似文献
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Nuclear Magnetic Resonance (NMR) spectroscopy was used to probe the primary structure of the glucan pullulan. Carbon-13, proton and phosphorus-31 NMR spectra in aqueous solution of the intact poly-saccharide obtained from three different sources indicate that significant structural differences can occur among these samples. In particular, two samples consist solely of α(1 → 6) linked maltotriose units, in accord with the generally accepted structure. However a third sample has fewer α(1 → 6) linkages and appears to consist of higher α(1 → 6) linked maltooligosaccharides in addition to maltotriose. Unlike the other samples, this sample was also phosphorylated. Enzymatic digestion of pullulan followed by NMR spectroscopy using pullulanase confirmed these results, as did HPLC analysis of the resulting digest, which showed the presence of maltooligosaccharides consisting of ten and more glucose units. However, HPLC analysis of acid hydrolysed pullulan indicated that no sugars other than glucose were present in any of the samples examined. 相似文献
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The mobility of water in corn starch suspensions and high-moisture powders (10 to 70% corn starch) was investigated by Nuclear Magnetic Resonance (NMR) spectroscopy, in water and deuterium oxide. Both oxygen-17 (17O) and deuterium (2H) nuclei were probed with a single pulse. The standard isotropic two-state model with fast exchange was used to interpret these data by means of a physical model (I) and a chemical activity model (II). According to I plots of relaxation rate against concentration indicated three regions of decreasing water mobility. According to II, the relaxation rate was linear with chemical activity over the entire concentration range. The correlation time calculated for the bound water showed high mobility. 相似文献
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Pulsed nuclear magnetic resonance was used to monitor the thermophysical transition of aqueous egg albumin dispersion. Gelling, which was manifested by an increase in force required to penetrate the surface of the dispersion, was accompanied by a decrease in T1, the spin-lattice relaxation time of water protons in the dispersion. There was a high, negative correlation coefficient between gel strength and T1. Apparent rate kinetics of the transition was fist order for changes in T1 and zero order for changes in gel strength, with activation energies for the rate constants of 42.62 and 43.68 kcal/mole, respectively. 相似文献
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运用单边全开放式核磁共振技术对常见掺假牛乳进行快速检测,并对室温条件下贮藏的市售盒装酸奶进行跟踪监测。在非均匀磁场下采用SGSE-CPMG(static gradient spin echo carr-purcell-meiboom-gill)序列测量各个样品的横向弛豫时间(记为T2CPMG),经弛豫校正可得到测试样品的横向弛豫时间T2。研究表明,在恒定梯度磁场中不同掺假比例样品随掺假质量浓度的升高其T2CPMG逐渐增大,经弛豫矫正后盒装酸奶样品T2峰位的变化可间接反映其新鲜度。运用单边核磁共振技术可实现乳制品品质的快速无损检测,被测样品无需复杂预处理,其系统硬件结构简单可便携(或安装)至现场进行实时检测。 相似文献
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Unique Hydration Behavior of Potato Starch as Determined by Deuterium Nuclear Magnetic Resonance 总被引:1,自引:0,他引:1
Deuterium Nuclear Magentic Resonance (NMR) measurements at 4.7 Tesla revealed a unique hydration behavior of potato starch that involved the presence of a tightly bound water population with anisotropic motions within the potato starch granule, even in the presence of excess, bulk water in potato starch slurries. Well-defined powder patterns with residual deuterium quadrupole splittings of about 1 kHz were also observed at 20°C for raw potato tubers. Three other water populations, a weakly bound, a surface-trapped, and a bulk water population, were also present up to 60% starch and were in fast exchange with each other at room temperature, resulting in a broadened, single Lorentzian 2H NMR peak. These three water populations were absent below 35% moisture content in potato starch, but not in corn starch. The unique hydration properties of potato starch might be important for novel processing methodology. 相似文献
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SHELLY J. RICHARDSON 《Journal of food science》1988,53(4):1175-1180
The molecular mobility of both the water component and the starch component of three instant starches was determined by proton decoupled oxygen-17 (17O) and proton decoupled carbon-13 (13C) Nuclear Magnetic Resonance (NMR) spectroscopy. The effect of starch concentration and various storage conditions were studied. The molecular mobility of the water associated with each of the instant starches over all concentrations studied as measured by 17O NMR transverse relaxation rates was not much slower than that of free or bulk water. The effect of storage conditions on the molecular mobility and conformation of the starches, as monitored by proton decoupled 17O and 13C NMR, was in most cases small, despite the observed differences in retrogradation among the starches. 相似文献
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Comparative studies of the hydration of maltodextrins were undertaken by proton, deuterium and oxygen-17 NMR. The 1H and 2H-NMR transverse relaxation rates of hydrated maltodextrins were sensitive to both chemical exchange with the solvent and hydrogen bonding involving hydroxyl groups. The short average correlation time of water “bound” to maltodextrins (~ 47 ps) derived from our 17O-NMR data shows that water is highly mobile and that maltodextrins–at high moisture contents–contribute little to the stability of food products. The onset of aggregation is monitored by all three nuclei. The mechanism of this aggregation process involves hydrogen bonding in un-heated polysaccharide mixtures and waxy maize starch samples, and is markedly affected by heating to 60°C. 相似文献
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Rapid Determination of Total and Solid Fat Contents in Chocolate Products by Pulsed Nuclear Magnetic Resonance 总被引:1,自引:0,他引:1
A rapid pulsed NMR method of fat analysis in chocolate without prior solvent extraction was developed. Total fat content of 43 chocolate products was determined at 60°C using sucrose-oil mixtures as standards. Solid fat content (SFC) was calculated from the liquid oil content at different temperatures. Total fat content agreed to 0.90% standard error of prediction as compared with the Soxhlet method. SFC as determined by NMR correlated well with the dilatometry (r = 0.98) and the DSC (r = 0.96) results. This technique is suitable for quality control of chocolate and other lowmoisture, high-fat products. 相似文献
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