甲酰胺塑化热塑性淀粉的性能研究

用甲酰胺作为塑化剂制备了热塑性淀粉 (TPS) ,扫描电镜显示甲酰胺可以使淀粉塑化 ,形成均一的连续相 ;流变性能说明在加工温度范围内 ,甲酰胺塑化淀粉 (FPTPS)的剪切应力对温度变化敏感性要小于甘油塑化淀粉 (GPTPS) ;用热重和DSC研究了热稳定性和玻璃化转变 ;FPTPS在 13%～ 2 3%的水含量时有较好的力学性能 ,水含量为 13%时 ,FPTPS有最大的断裂强度 3 9MPa ;水含量为 17%时 ,FPTPS最大的伸长率为 95 % ;与GPTPS相比 ,在RH(Relativehumidity) =0 5 0 %and 10 0 %环境下 ,FPTPS有良好的耐回生性能 ,这主要是因为甲酰胺可以和淀粉羟基形成更稳定的氢键     

Effect of hydrocolloids on starch thermal transitions,as measured by DSC

Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (T _g) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T _g) was also studied.T _g onset values ranged between –4.5 and –5.5C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at –4C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule.     

Impact of Thermal Treatment on the Starch-Protein Interplay in Red Lentils: Connecting Molecular Features and Rheological Properties

Thermal treatments are widely applied to gluten-free (GF) flours to change their functionality. Despite the interest in using pulses in GF formulations, the effects of thermal treatment at the molecular level and their relationship with dough rheology have not been fully addressed. Raw and heat-treated red lentils were tested for starch and protein features. Interactions with water were assessed by thermogravimetric analysis and water-holding capacity. Finally, mixing properties were investigated. The thermal treatment of red lentils induced a structural modification of both starch and proteins. In the case of starch, such changes consequently affected the kinetics of gelatinization. Flour treatment increased the temperature required for gelatinization, and led to an increased viscosity during both gelatinization and retrogradation. Regarding proteins, heat treatment promoted the formation of aggregates, mainly stabilized by hydrophobic interactions between (partially) unfolded proteins. Overall, the structural modifications of starch and proteins enhanced the hydration properties of the dough, resulting in increased consistency during mixing.     

Isothermal microcalorimetric studies on starch retrogradation

In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After 10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.The authors thank Eva Qvarnström at the Dept. of Thermochemistry and Eva Tjerneld at the Dept. of Food Technology for valuable practical assistance. Financial support was obtained from the Swedish Council for Forestry and Agricultural Research (SJFR) and the Swedish Farmer's Foundation for Agricultural Research (Stiftelsen Lantbruksforskning).     

Role of liquid polymorphism during the crystallization of silicon

Using molecular simulation, we establish the pivotal role played by liquid polymorphs during the crystallization of silicon. When undercooled at a temperature 20% below the melting point, a silicon melt is under the form of the highly coordinated, high-density liquid (HDL) polymorph. We find that crystallization starts with the formation, within the HDL liquid, of a nanosized droplet of the least stable liquid polymorph, known as the almost tetracoordinated low-density liquid (LDL) polymorph. We then show that the crystalline embryo forms within the LDL droplet, close to the interface with the surrounding HDL liquid, thereby following a pathway associated with a much lower free energy barrier than the direct formation of the crystalline embryo from the HDL liquid would have required. This implies that, for substances exhibiting liquid polymorphs, theories, like the classical nucleation theory, and empirical rules, like Ostwald's rule, should be modified to account for the role of liquid polymorphs in the nucleation process.     

尿素和甲酰胺塑化热塑性淀粉

用甲酰胺和尿素作为塑化剂制备了热塑性淀粉 (TPS) .扫描电镜显示甲酰胺和尿素混合物可以使淀粉塑化 ,形成均一的连续相 ;根据FT IR谱图可以确定 ,与甘油相比 ,甲酰胺可以使热塑性淀粉体系在保存时更稳定 ,各基团的化学环境变化更小 ,这是由于甲酰胺可以和淀粉羟基形成更稳定的氢键 .X ray衍射说明甲酰胺和尿素 (重量比为 10 % 2 0 % )作为混合塑化剂可以有效抑制淀粉的回生 ,同时防止尿素结晶析出 .在RH=33%的湿度环境保存 1周 ,这种热塑性淀粉有良好的拉伸强度、伸长率和断裂能 ,分别达到 4 83MPa ,10 4 6 %和 2 17N·m .水含量对热塑性淀粉的力学性能的影响也被研究 .另外 ,热失重实验和吸水实验说明这种热塑性淀粉的热稳定性和耐水性也要优于常用的甘油塑化热塑性淀粉     

Retrogradation characteristics of high hydrostatic pressure processed corn and wheat starch

High hydrostatic pressure (HHP) has been investigated as an alternative to thermal processing for food preservation. HHP has been known to affect high molecular weight polymers causing phase change. Starch is gelatinized at a pressure on the order of 600–700 MPa, at 25 °C. Gelatinized starch recrystallizes during storage affecting the texture and shelf life of food products. The effect of HHP processing on the crystallization of starches from different botanical origins during storage at 4 and 23 °C was investigated. Crystallization kinetics of HHP treated wheat and corn starch gels were compared using DSC. The effect of crystallization on structure was evaluated in terms of storage modulus. The rate of retrogradation depended on the storage temperature (23 °C and 4 °C) and the botanical origin of the starch. The least crystallization was observed in HHP treated wheat starch stored at 23 °C. The storage modulus increased with crystallization of starch.     

Effect of Single and Dual Hydrothermal Treatments on the Resistant Starch Content and Physicochemical Properties of Lotus Rhizome Starches

Heat-moisture treatment (HMT) changed the morphology and the degree of molecular ordering in lotus rhizome (Nelumbo nucifera Gaertn.) starch granules slightly, leading to some detectable cavities or holes near hilum, weaker birefringence and granule agglomeration, accompanied with modified XRD pattern from C- to A-type starch and lower relative crystallinity, particularly for high moisture HMT modification. In contrast, annealing (ANN) showed less impact on granule morphology, XRD pattern and relative crystallinity. All hydrothermal treatment decreased the resistant starch (from about 27.7–35.4% to 2.7–20%), increased the damage starch (from about 0.5–1.6% to 2.4–23.6%) and modified the functional and pasting properties of lotus rhizome starch pronouncedly. An increase in gelatinization temperature but a decrease in transition enthalpy occurred after hydrothermal modification, particularly for hydrothermal modification involved with HMT. HMT-modified starch also showed higher pasting temperature, less pronounced peak viscosity, leading to less significant thixotropic behavior and retrogradation during pasting-gelation process. However, single ANN treatment imparts a higher tendency of retrogradation as compared to native starch. For dual hydrothermally modified samples, the functional properties generally resembled to the behavior of single HMT-modified samples, indicating the pre- or post-ANN modification had less impact on the properties HMT modified lotus rhizome starch.     

Intermolecular interactions in polymorphs of trinuclear gold(I) complexes: insight into the solvoluminescence of Au(I)3(MeN=COMe)3

The trinuclear complex, Au(I)3(MeN=COMe)3, which displays a number of remarkable properties including solvoluminescence, has been found to crystallize as three polymorphs. The new triclinic and monoclinic polymorphs crystallized as colorless blocks, whereas the original hexagonal polymorph formed colorless needles. These polymorphs differ in the manner in which the nearly planar molecules pack and in the nature of the aurophilic interactions between them. Each of the three polymorphs of Au(I)3(MeN=COMe)3 shows a distinctive emission spectrum, but only the original hexagonal polymorph shows the low-energy emission that is responsible for its solvoluminescence. Colorless Au(I)3(n-PentN=COMe)3 crystallized from diethyl ether as needles of an orthorhombic polymorph and blocks of a triclinic polymorph. These polymorphs differ in the orientation of the n-Pent substituents, in the orientation of the trimers with respect to one another, and in the nature of the aurophilic interactions between the molecules. Only the triclinic polymorph of Au(I)3(n-PentN=COMe)3 shows luminescence at room temperature, but it is not solvoluminescent. Colorless Au(I)3(i-PrN=COMe)3 has also been prepared and crystallographically characterized. The isopropyl groups protrude out of the plane of the nine-membered ring and prevent self-association. The closest Au...Au contact between molecules is 6.417 A. Crystalline Au(I)3(i-PrN=COMe)3 is not luminescent at room temperature.     

DSC and adiabatic calorimetry study of the polymorphs of paracetamol

Monoclinic (I) and orthorhombic (II) polymorphs of paracetamol were studied by DSC and adiabatic calorimetry in the temperature range 5 - 450 K. At all the stages of the study, the samples (single crystals and powders) were characterized using X-ray diffraction. A single crystal → polycrystal II→ I transformation was observed on heating polymorph II, after which polymorph I melted at 442 K. The previously reported fact that the two polymorphs melt at different temperatures could not be confirmed. The temperature of the II→I transformation varied from crystal to crystal. On cooling the crystals of paracetamol II from ambient temperature to 5 K, a II→ I transformation was also observed, if the 'cooling-heating' cycles were repeated several times. Inclusions of solvent (water) into the starting crystals were shown to be important for this transformation. The values of the low-temperature heat-capacity of the I and II polymorphs of paracetamol were compared, and the thermodynamic functions calculated for the two polymorphs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of High Pressure on the Polymorphs of Paracetamol

Effect of hydrostatic pressure on the two (I – monoclinic and II – orthorhombic) polymorphs of paracetamol was studied by X-ray diffraction in the diamond anvil cell at pressures up to 4.5 GPa (for the monoclinic form) and up to 5.5 GPa (for the orthorhombic form). The two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph, (ii) transitions between the polymorphs induced by pressure. The anisotropy of structural distortion of polymorphs I and II was well reproducible from sample to sample, also from powder samples to single crystals. The bulk compressibility of the two forms was shown to be practically the same. However, a noticeable qualitative difference in the anisotropy of structural distortion was observed: with increasing pressure the structure of polymorph II contracted in all the directions showing isotropic compression in the planes of hydrogen-bonded molecular layers, whereas the layers in the structure of the polymorph I expanded in some directions. Maximum compression in both polymorphs I and II was observed in the directions normal to the molecular layers. The transitions between the polymorphs induced by pressure were poorly reproducible and depended strongly on the sample and on the procedure of increasing/decreasing pressure. No phase transitions were induced in the single crystals of the monoclinic polymorph at pressures at least up to 4GPa, although a partial transformation of polymorph I into polymorph II was observed at increased pressure in powder samples. Polymorph II transformed partly into the polymorph I during grinding. The transformation could be hindered if grinding was carried out in CCl₄. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of gluten-free bread crumb baked at atmospheric and reduced pressures using TD-NMR

This research aimed to study the effects of using a partial vacuum for bread baking on macromolecules and water distribution in gluten-free bread. Bread baking under partial vacuum results in greater oven rise and a larger gas fraction in the crumb. Because water's boiling point decreases under reduced pressure, it was expected that its distribution within the dough and its interactions with the others dough's constituents (mainly starch) would differ from those in bread baked under atmospheric pressure. Time-domain nuclear magnetic resonance was used, as it has the rare capacity to quantify both gelatinization and retrogradation of starch. Complementary rheological measurements made it possible to show that crumb Young's modulus was mostly influenced by the gas fraction whereas there was little change in starch gelatinization and retrogradation when dough was baked under partial vacuum. When insufficiently hydrated (48%), the volume of breads was practically the same whatever the baking process. Meanwhile, the nuclear magnetic resonance results suggested that amylose short-term crystallization (on cooling) is dependent on water content. In addition, crumb Young's modulus during storage at room temperature correlated with an increase in free induction decay signal intensity.     

Evaluation of black tea polyphenol extract against the retrogradation of starches from various plant sources

The effects of black tea polyphenol extract (BTPE) on the retrogradation of starches from different plant sources were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). DSC analysis shows that the gelatinization temperature of maize starch and starches from different rice varieties increased with increasing BTPE level. After storage at 4 °C, BTPE at a concentration of 15% markedly retarded the retrogradation of maize starch and starches from different rice varieties. Native maize starch and starches from different rice varieties showed typical A-type X-ray diffraction patterns, while native potato starch showed a typical B-type X-ray diffraction pattern. Adding BTPE significantly affected the crystalline region and intensities of X-ray diffraction peaks of maize and rice starch granules. It is concluded that adding BTPE markedly inhibits the retrogradation of maize starch and starches from different rice varieties, but has no significant influence on the gelatinization and retrogradation characteristics of potato starch.     

微晶淀粉

综述了微晶淀粉的用途和制备方法。微晶淀粉的制备方法按上生成微量的主要步骤可划分为回生法、水解法和结晶法三类。在以晶型（如A、B、C和V型）对微晶淀粉进行分类的基础上，本文按制备方法的不同将微晶淀粉分为回生微晶淀粉、原微晶淀粉和结晶微晶淀粉。文章对微晶淀粉的含义进行了界定，认为微晶淀粉是具有较高结晶度的淀粉微束、片晶或其它晶形的聚集体，并对微晶淀粉的晶型及晶型之间的转化进行了详细论述。     

Polymorphism of dinitro[tris(2‐aminoethyl)amine]cobalt(III) chloride

Three polymorphs of bis(nitrito‐κN)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) chloride, [Co(NO₂)₂(C₆H₁₈N₄)]Cl, have been structurally characterized in the 100–300 K temperature range. Two orthorhombic polymorphs are related by a solid‐state enantiotropic order–disorder k2 phase transition at ca 152 K. The third, monoclinic, polymorph crystallizes as a nonmerohedral twin. In the structure of the high‐temperature (300 K) orthorhombic polymorph, the Co^III complex cation resides on a crystallographic mirror plane, whereas the Cl⁻ anion occupies a crystallographic twofold axis. In the unit cell of the monoclinic polymorph, the cationic Co^III complex is in a general position, whose charge is balanced by two halves of two Cl⁻ anions, each residing on a crystallographic twofold axis.     

Preferred Formation of Minority Concomitant Polymorphs in 2D Self‐Assembly under Lateral Nanoconfinement

Control over polymorph formation in the crystallization of organic molecules remains a huge scientific challenge. Now, preferential formation is presented of one polymorph, formed by chiral molecules, in controlled two‐dimensional (2D) nanoconfinement conditions at a liquid–solid interface. So‐called nanocorrals to control concomitant polymorph formation were created in situ via a nanoshaving protocol at the interface between 1‐phenyloctane and covalently modified highly‐oriented pyrolytic graphite (HOPG). The preferentially formed polymorphs, which were less stable in the large‐scale monolayers, could be selected simply by varying the orientation of the square nanocorrals with respect to the HOPG lattice.     

丙烯酸-2-乙基己酯改性玉米淀粉

接枝共聚合;丙烯酸-2-乙基己酯改性玉米淀粉     

Synthesis, thermal properties, and biodegradability of propyl-etherified starch

High amylose corn starch (HACS) was etherified with 1-bromopropane in dimethyl sulfoxide. The structure of the products was characterized by infra-red and ¹H-NMR spectroscopy. The degree of substitution (DS) on glucose unit calculated from ¹H-NMR spectrum was varied from 0.9 to 2.7 by changing feed ratio of 1-bromopropane to HACS. Thermogravimetric analysis reveals that the etherified HACS has a higher decomposition temperature than unmodified HACS. Differential scanning calorimetry analysis reveals that the etherified starch has a clear glass transition temperature which decreased with increasing DS, and that no melting point is observed. This result demonstrates that the etherified HACS mainly consists of amorphous region. The biodegradation rate decreases with increasing degree of etherification.     

A comparative study of two polymorphs of bis(1‐hydroxy‐2‐methylpropan‐2‐aminium) carbonate

Alkanolamines have been known for their high CO₂ absorption for over 60 years and are used widely in the natural gas industry for reversible CO₂ capture. In an attempt to crystallize a salt of (RS)‐2‐(3‐benzoylphenyl)propionic acid with 2‐amino‐2‐methylpropan‐1‐ol, we obtained instead a polymorph (denoted polymorph II) of bis(1‐hydroxy‐2‐methylpropan‐2‐aminium) carbonate, 2C₄H₁₂NO⁺·CO₃²⁻, (I), suggesting that the amine group of the former compound captured CO₂ from the atmosphere forming the aminium carbonate salt. This new polymorph was characterized by single‐crystal X‐ray diffraction analysis at low temperature (100 K). The salt crystallizes in the monoclinic system (space group C2/c, Z = 4), while a previously reported form of the same salt (denoted polymorph I) crystallizes in the triclinic system (space group P, Z = 2) [Barzagli et al. (2012). ChemSusChem, 5 , 1724–1731]. The asymmetric unit of polymorph II contains one 1‐hydroxy‐2‐methylpropan‐2‐aminium cation and half a carbonate anion, located on a twofold axis, while the asymmetric unit of polymorph I contains two cations and one anion. These polymorphs exhibit similar structural features in their three‐dimensional packing. Indeed, similar layers of an alternating cation–anion–cation neutral structure are observed in their molecular arrangements. Within each layer, carbonate anions and 1‐hydroxy‐2‐methylpropan‐2‐aminium cations form planes bound to each other through N—H…O and O—H…O hydrogen bonds. In both polymorphs, the layers are linked to each other via van der Waals interactions and C—H…O contacts. In polymorph II, a highly directional C—H…O contact (C—H…O = 156°) shows as a hydrogen‐bonding interaction. Periodic theoretical density functional theory (DFT) calculations indicate that both polymorphs present very similar stabilities.     

The use of polymer heteronuclei for crystalline polymorph selection

A method for the production of crystalline polymorphs from solution is described which utilizes a diverse set of polymer heteronuclei. Application to crystalline polymorph selection for the important pharmaceuticals acetaminophen and carbamazepine is demonstrated. This method provides a new paradigm for polymorph selection, where solvent and temperature conditions can be chosen on the basis of process considerations and the polymer heteronucleus can be varied for specific polymorph production.