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1.
A technique was established to remove impurities (e.g., salts) from starch dissolved in strong alkali and neutralized with acid to accommodate starch structural analysis via intermediate-pressure size-exclusion chromatography (IPSEC). Starch (corn and wheat) subjected to an alkaline-microwave dissolution scheme (35 s microwave heating in a mixture of 6 M urea and 1 M KOH) was either treated with ion-exchange resin or passed through a desalting column to remove salt/urea contaminants. Control (untreated) starch solution analyzed by IPSEC displayed a significant interfering peak (attributable to salt/urea), which coeluted with the starch amylose peak. The interfering peak was most efficiently eliminated by first passing the starch solution through a desalting column, which process effectively removed impurities (e.g., salts/urea) without appearing to adversely impact the starch structural analysis. This simple technique coupled with the rapid alkaline-microwave starch dissolution procedure greatly expedites structural investigation of starch by facilitating analysis by IPSEC.  相似文献   

2.
Molecular characteristics based on absolute weight‐average molecular weight (Mw) and z‐average radius of gyration (Rg) of normal corn starch were analyzed by high‐performance size‐exclusion chromatography (HPSEC) attached to multiangle laser‐light scattering (MALLS) and refractive index (RI) detectors under different starch dissolution and analytical conditions. Autoclaving (121°C, 20 min) or microwave heating (35 sec) provided better HPSEC recovery and higher Mw for starch molecules than simple dissolution in hot water. The Mw for the autoclaved corn amylopectin and amylose fractions separated with a TSK G5,000 column at 60°C were 201 × 106 and 3.3 × 106, respectively. The specific volume for gyration (SVg) calculated from Mw and Rg could be used for the comparison of molecular compactness which was inversely related to the degree of branching. The SVg values of amylopectin and amylose fractions in the chromatogram (TSK G5,000, autoclaved for 20 min) were 0.092 and 0.529, respectively. But a portion (20–30%) of large amylopectin molecules did not pass the injection membrane filter (3.0 μm) and the SEC column, resulting in incomplete recovery. The unfiltered portion varied according to the dissolution treatment. Homogenization (7,000 rpm, 5 or 10 min) of the starch solution improved the recovery of the amylopectin fraction, but significantly increased the Mw of the amylose fraction (17 × 106). Sonication for 5 min degraded starch molecules. For accurate analysis of a native starch using an aqueous SEC, the starch should be fully dissolved with proper treatment such as autoclaving or microwaving, and the column should be improved for full recovery of large amylopectin molecules.  相似文献   

3.
Structural characteristics of starches have been important to determine their physicochemical and functional properties. Solubilization procedures were tested to find a higher solubilization percentage and thereafter to study the structural characteristics of amylose and amylopectin. Size‐exclusion chromatography with refractive index (SEC‐RI) system using a pullulan standard curve was tested to study the amylose molar mass. Also, a microbatch system using a MALLS detector was used to determine the molar mass and gyration radius of starch and amylopectin. Microwave heating produced higher solubility percentages than autoclaving, and there was a difference between both starches. The sample solubilized with microwave heating presented higher molar mass and gyration radius values than autoclave samples, showing that this process for structural studies provided information representative of the initial starch sample. When starch components were separated, amylose showed lower purity than amylopectin. Lower purity was obtained for amylose separated from barley starch, but no difference was obtained for purity of amylopectin separated from both starches. Barley amylopectin had a higher solubility percentage than maize amylopectin. Molar mass of barley amylose was 1.03 × 105 g/mol and for maize of 2.25 × 105 g/mol. Molar mass values of amylopectin separated from both starches were lower than the starch counterparts, although the same solubilization procedure (microwave heating) was used. The difference might be due to depolymerization during separation of starch components.  相似文献   

4.
Microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) was developed as a simple and effective method for fast sampling of volatile organic compounds (VOCs) from Eucalyptus citriodora Hook (E. citriodora) leaves. During microwave heating, a simple shielding device made of aluminum foil was used to protect the SPME fiber from microwave irradiation while allowing the sample to be heated. A room temperature water bath was also used to allow microwave heating to be conducted in a more controlled manner. The inner heating caused by microwave irradiation dramatically accelerated the emission of VOCs from the sample, but no marked change in headspace temperature in the sample vial was found. Under optimum conditions, the extraction efficiencies obtained with microwave heating were much higher than those obtained without microwave heating for all fibers used, namely, 7-microm polydimethylsiloxane (PDMS), 100-microm polydimethylsiloxane (PDMS), 65-microm polydimethylsiloxane/divinylbenzene (PDMS/DVB), and 75-microm carboxen/polydimethylsiloxane (CAR/PDMS). The improvement of extraction efficiency using MA-HS-SPME allowed more VOC events to be detected, with more balanced extraction of VOCs of lower and higher molecular masses. Moreover, a good linear relationship was found between sample size and GC-FID response (total peak area of VOCs), indicating the usefulness of MA-HS-SPME for quantitative analysis of individual volatile compounds in E. citriodora leaves.  相似文献   

5.
The objective of this study was to compare gelatinization properties and molecular composition of starches extracted from locally grown organic and conventional spelt using thermal, rheological, and SEC analyses, along with Concanavalin A method. Organic and conventional spelt was planted in six replicated plots, and the extracted starch was analyzed for their gelatinization properties. DSC showed that the gelatinization temperature ranged from 56.7 to 68.8 °C with an average peak of 62.4 °C, with no evidence for statistical difference in gelatinization properties between treatments. Rheological behavior variation among samples was more pronounced than that between the two growing conditions. The amylose content ranged from 23.0% to 29.8%. There was no significant difference in the molecular weight of amylose and amylopectin irrespective of the plot locations, although a significant difference was found between the amylopectin molecular weight of organic and conventional spelt starches when analyzed collectively. The organic spelt starch studied may substitute the conventional starch when gelatinization behavior is considered.  相似文献   

6.
Dimethyl sulfoxide (DMSO), with either 50 mM LiBr, 10% water, or both, was used as solvent for multi-angle laser-light scattering (MALLS) batch mode analysis of rice starch, and amylopectin and amylose weight-average molecular weight (Mw). DMSO/50 mM LiBr was a better solvent for these measurements than was DMSO/10% water, based on this solvent's ability to dissolve starch and to reduce the size of starch aggregates. Starch concentration decreased and amylose:amylopectin ratio increased when starch suspended in DMSO was centrifuged or filtered prior to size-exclusion chromatography (SEC)-MALLS analysis. A higher amylose:amylopectin ratio made starch more soluble, and the higher this ratio, the lower the Mw of eluted amylopectin. For SEC analysis of Mw, fractions of starch amylopectin and amylose dispersed in DMSO-based solvents yielded better results than starch dispersed directly into the solvents, because dispersion of these fractions decreased starch aggregation. When these two starch components were fractionated and then dissolved separately in DMSO/50 mM LiBr, the Mw of dispersed amylopectin ranged from 40 to 50 million, and that of amylose was ca. 3 million, whereas starch from three rice varieties of varying amylose content ranged from 60 to 130 million. We recommend that SEC evaluation of amylopectin and amylose be accomplished with fractionated samples as in this study; such evaluations were superior to evaluations of natural mixtures of amylopectin and amylose.  相似文献   

7.
Abstract

Application of a microwave dissolution technique to soil materials aided by acid digestion procedures has many advantages, but the incomplete dissolution of sandy soils has been noted. The objectives of this study were to modify a microwave oven digestion technique to facilitate the determination of the total elemental content of soils and geologic materials containing greater than 45% sand and apply these data to determine natural separations in parent materials. A microwave dissolution technique using aqua regia (HNO3 and HCl) and hydrofluoric acid (HF) was modified such that the HF is added to the solid 16 hours prior to aqua‐regia addition and subsequent microwave heating. Elemental recoveries were validated using a NBS coal fly ash standard. This procedure was applied to soil core samples representing a wide range of geological and pedological weathering sequences and soil textural classes. Separations in the parent material were determined by observing natural breaks in the elemental concentrations and comparing them to soil morphology data.  相似文献   

8.
Mechanism of crumb toughening in bread-like products by microwave reheating   总被引：1，自引：0，他引：1  
Comparing breads reheated in conventional and microwave ovens revealed that the latter considerably toughens the crumb texture when internal boiling is induced. Moisture loss in itself has a relatively minor toughening effect. The major changes, caused by boiling, occur only in systems with starch concentration in excess of a threshold level of about 37% (wet basis). Substantially greater amounts of amylose are leached out of the granules in the case of sustained boiling during microwave heating, as compared to conventional oven heating. The free amylose solution is being "pushed" by the generated steam pressure toward the air-cell wall interface. A rich amylose phase is accumulated at that interface and over the granules. Upon cooling, the amylose undergoes rapid phase changes; thus, toughening is apparent in a relatively short time after heating. Minimizing the textural deleterious effects in microwave reheating of bread-like products should entail (a) preventing or minimizing internal boiling, (b) diluting of the starch concentration below the threshold level, (c) interfering with the amylose phase change by using complex forming agents.  相似文献   

9.
微波提取法对樱桃、猕猴桃和枸杞多糖特性的影响   总被引：2，自引：1，他引：1  
微波提取是近年来发展迅速的天然产物提取技术之一。为考察微波提取对多糖得率、结构及生物学功能的影响,论文采用微波功率1 000 W和提取温度140℃,以不同提取时间5,10 和20 min分别对樱桃、猕猴桃和枸杞中多糖进行提取。结果表明,微波提取多糖的得率、相对分子质量和抗氧化性低于传统提取方法,随着微波提取时间延长,多糖相对分子质量逐步降低,但多糖得率与抗氧化性无显著变化;微波提取得到的多糖在单糖组成上与传统提取方法有一定的差异。该研究结果对应用微波提取水果多糖条件的选择及多糖品质控制有一定的参考价值。  相似文献   

10.
The rheological behavior of concentrated starch preparations from various origins was studied by dynamic mechanical thermal analysis (DMTA). Four types of starch were used: wheat, potato, normal, and waxy corn adjusted to moisture contents in the 42–49% (w/w) range. The thermal treatments of the starch-water mixtures consisted of heating to 85°C and cooling to room temperature, both at a rate of 1°C/min. During heating, the storage modulus (E′) appearance was first characterized by an increase with a maximum at ≈70°C (or potato starch at 63°C) followed by a decrease to 85°C. During cooling, storage modulus increased steadily down to room temperature. The magnitude of these variations depended on the starch type. Despite some differences, all the loss tangent curves showed a decrease during heating from 60–70°C to 85°C, followed by a plateau during cooling. To propose an interpretation for the DMTA results, we measured, by laser-light diffraction, the influence of heating (up to the maximum E′ peak) on the distribution of the granule sizes of the different starches. Moreover, differential scanning calorimetry (DSC) was used to measure the temperature range where the melting of starches ordered regions occurred. Partial melting enthalpies were plotted against temperature. The hypothesis of a relationship between swelling and an increase in rigidity during heating seemed to be confirmed by laser-light diffraction, whereas DSC indicated the decrease in rigidity was caused predominantly by order-disorder transitions. During cooling, amylose gelation plays a major role in the rigidity increase, but a contribution of amylopectin is not excluded.  相似文献   

11.
Corn starch amylopectin (AP) fine structure and gel textural properties of dry‐milled grit and flour fractions were investigated in 10 corn cultivars. Amylopectin was isolated by fractionating the starch derived from these two milled fractions using size‐exclusion chromatography (SEC). Fine structure was characterized by SEC after thorough debranching with pullulanase. SEC revealed three major fractions of debranched AP from the grit and flour portion. Amylopectin in the grit portion had a significantly higher proportion of long chains (DPn 70–75) and a postulated lower extent of chain branching than its flour counterpart. Texture profile analysis showed that flour gels from the grit fraction had significantly higher values for hardness, gumminess, and springiness compared with gels from the floury fraction. Trends were similar for starch gels of the two dry‐milled fractions, though only springiness was significantly different. The finding that differences in AP fine structure in dry‐milled fractions relate to gel textural differences suggests that dry millers may be able to produce flours of different functionalities that would be suited for different end uses. Additionally, mixing the dry‐milled flour fraction with a grit‐derived flour would result in different product properties.  相似文献   

12.
为了研究农作物秸秆在微波辐照下的热解特性,采用定制的微波加热装置,进行了整包秸秆的微波热解试验,并对秸秆微波热解的产物和能耗进行了考察。结果表明,微波加热过程中料包内部温度分布均匀,升温迅速。微波输入功率是影响加热过程的关键因素, 同时料包内部的传热传质对温度分布也有重要影响。微波加热会引发秸秆的热解反应,气体产物主要由氢气、一氧化碳、甲烷和二氧化碳等组成,通过氮吸附方法和扫描电镜分析,得到了固体产物的比表面积、孔容和孔径。微波热解电耗较大,应该合理选择微波功率和物料处理量,以提高经济性。该文结果可为农作物秸秆的资源化利用提供基础性资料。  相似文献   

13.
《Cereal Chemistry》2017,94(6):928-933
Japonica and indica rice starches (10% w/w) were pregelatinized in a boiling water bath for 5 or 10 min and subsequently heat‐treated in a dry state for 0, 1, 2, or 3 h at 130°C to examine the effects of dry heating on pasting viscosity, paste clarity, thermal properties, X‐ray diffraction pattern, and gel strength of pregelatinized starches. Heat treatment obviously changed the physicochemical properties of pregelatinized rice starch. The pregelatinized rice starches had higher peak viscosity and final viscosity than the corresponding native rice starches. Heat treatment of pregelatinized rice starch for 1 h increased the peak viscosity, but treatment for 2 or 3 h decreased the peak viscosity compared with the unheated pregelatinized rice starch. The indica rice starch exhibited more substantial changes in pasting viscosity than did japonica rice starch during heat treatment. The melting enthalpy of the endothermic peak occurred at 90–110°C, and the intensity of the X‐ray diffraction peak at 20° was increased by dry heating, possibly owing to the enhanced amylose‐lipid complexes. The dry heat treatment of pregelatinized starch caused an increase in paste clarity and a decrease in gel strength.  相似文献   

14.
Differential scanning calorimetric analysis was performed on the admixture of 4% hsian-tsao leaf gum and 8% wheat starch as a function of salt types and concentrations. The salt concentrations (C(s)) studied were 5-100 mM for sodium and potassium chloride, and 3.4-34 mM for calcium and magnesium chloride. It was found that hsian-tsao leaf gum or starch alone did not present a readily recognizable exothermic peak or endothermic peak during cooling or heating in DSC. However, mixing these two polymers promoted the intermolecular binding and subsequent gelation of the mixtures as evidenced by the DSC exothermic and endothermic peaks during cooling and heating, respectively. The setting and melting temperatures of such a mixed system shifted progressively to higher temperatures with increasing concentrations of added salts. It was considered that the aggregated mixed polymers formed thermally stable junction zones with higher binding energies. The thermal behavior change was more remarkable by the addition of K(+) than by Na(+), and by Ca(2+) than by Mg(2+). For monovalent cations, the DSC heating and cooling curves showed a single endothermic and exothermic peak. For divalent cations at low concentration, the DSC curves showed a single peak. However, with sufficient divalent cations, the DSC curves eventually developed a bimodal character. A mixed system with sufficient Ca(2+) could form firm gel that was difficult to remelt completely upon heating to 130 degrees C, indicating the possibility of the formation of ionic bonds through cross-links with the carboxyl groups in hsian-tsao leaf gum.  相似文献   

15.
Extruded pellets were prepared from normal corn starch using a corotating twin‐screw extruder (25:1 L/D ratio, 31 mm diameter screw), and then expanded by heating in a conventional microwave oven for 70 sec. The effects of gelatinization level and moisture content of the extruded pellets on the morphology and physical properties of the microwave‐expanded products such as puffing efficiency, expansion bulk volume, and bulk density were investigated. The expanded shape and air cell structure differed according to the degree of gelatinization of the pellets. Maximum puffing efficiency and expansion volume with the pellets containing 11% moisture were achieved at 52% gelatinization. For this level of gelatinization, starch was extruded at 90°C barrel temperature. In addition, the moisture content of the pellets critically affected the expansion behavior. The maximum puffing efficiency and expansion volume were achieved in a moisture range of 10~13%. For optimum product shape and uniform air cell distribution, the pellets should undergo sudden release of the superheated vapor during the microwave‐heating. The expansion by microwave‐heating was optimized at ≈50% gelatinization.  相似文献   

16.
Thermal properties of corn starch extraction intermediates from four types of corn were studied using differential scanning calorimetry. Starch at four different stages of extraction, including a standard single-kernel starch isolation procedure and three starch extraction intermediates, was isolated from mature corn kernels of B73 and Oh43 inbreds and the mutants of waxy (wx) and amylose extender (ae) in an Oh43 background. Differences in thermal properties and moisture and protein contents of starch from the extraction stages were statistically analyzed. Most thermal properties (gelatinization and retrogradation onset temperatures, gelatinization and retrogradation ranges, gelatinization and retrogradation peak temperatures, gelatinization and retrogradation enthalpies, peak height index, and percentage of retrogradation) of starches extracted at stage 3 intermediate (a procedure that did not include a final washing step) were similar to those of starch extracted by the standard single-kernel isolation procedure. Values for gelatinization peak temperature, gelatinization enthalpy, and peak height index were different between the standard and the stage 3 intermediate. The values obtained from starches extracted at stage 3, however, were consistent and predictable, suggesting that this extraction intermediate might be used in screening programs in which many starch samples are evaluated. By using the stage 3 extraction, samples could be evaluated in three rather than four days and the procedure saved ≈0.5 hr of labor time. The other two starch extraction intermediates, which excluded filtering and washing or filtering, washing, and steeping, produced starch with thermal properties generally significantly different from starch extracted by the standard single-kernel isolation procedure.  相似文献   

17.
Heating with microwave energy and tannin complexation of kafirin both increase the tensile strength of cast kafirin bioplastic films. The effects of these treatments on the molecular structure of kafirin and of kafirin in the film were investigated. SDS-PAGE of heated wet kafirin showed an increase in kafirin oligomers. Disulfide groups increased in heated kafirin and in films made from the heated kafirin. Fourier transform infrared (FTIR) spectroscopy of heated kafirin and films made from the heated kafirin indicated an increase in beta-sheet conformation. In contrast, kafirin complexation with tannic acid (TA) and sorghum condensed tannin (SCT) resulted in a slight decrease in beta-sheet conformation in the kafirin and a larger decrease in the kafirin in the films. Raman spectroscopy showed that, with TA, there was a shift in peak from 1710 to 1728 cm(-1) for kafirin-tannic acid complexes, indicating kafirin and tannic acid interaction. The protein conformational changes presumably facilitated cross-linking between kafirin molecules and/or between kafirin and the tannins. Thus, although both heating with microwave energy and tannin complexation cause cross-linking of kafirin to increase film tensile strength, their effects on kafirin structure appear to be different.  相似文献   

18.
该文以甲苯为焦油模型化合物,利用生物质焦炭诱导其转化合成气,探讨加热方式和通入CO2对甲苯转化的影响。结果表明:同等工况下,微波加热(microwave heating,MH)下甲苯转化率高于常规加热(electrical heating,EH),甲苯转化率最大差值为15.58%。通入CO2可促进甲苯转化,MH和EH下分别在CO2流量为80和40 m L/min达到最高转化率93.73%和82.13%。引入CO2可调控甲苯定向制备合成气,且对生物质焦炭造成碳损耗。损耗碳可转化合成气,且CO2通入量越高,其贡献越大。MH下合成气最大产率为173.66 m L/min,为裂解反应的5.68倍。甲苯裂解率持续降至49.0%,之后趋于稳定。甲苯重整转化率维持较高水平,140 min后开始减弱,同时合成气收率平缓降低。该文研究结果对高效利用焦油和减排CO2有借鉴意义。  相似文献   

19.
Methylcellulose (MC) is ingested by humans in food and pharmaceutical formulations. The functional properties of MC like those of other linear polymers depend primarily on polymer length or molar mass for largely linear polymers. Although many studies in animals and humans have shown complete excretion of MC, in vitro human fecal fermentation studies indicate that MC can be degraded and presumably lose some of its functionality. In this study, MC polymer distribution in the feces from rats fed a diet containing 8% methylcellulose were compared to the fed MC. The water-soluble polymers in the feces were separated by a size exclusion chromatography (SEC) and the polymer distributions determined by multiple angle laser light scattering (MALLS). Detection of the fluorescent MC-calcofluor complex was used to confirm the identity of the eluting MC peak. All dietary MC was recovered in the feces. There is a small shift (P < 0.06) in the weight-averaged molecular weight of polymer distribution of MC extracted from the feces to 2.71 +/- 0.15 x 10(5) g/mol from 3.15 +/- 0.02 x 10(5) g/mol in the standard. There is also an increase in the polydispersity from 1.21 in the standard to 1.8 in the fecal extract. The distribution of the substituted methoxylated glucose monomers by gas chromatography also confirms the stability of MC fed to rats. The amount of actual hydrolysis is estimated to be about 0.1 glycosidic linkage/molecule. MC is not easily determined by standard dietary fiber methods, and SEC with MALLS and/or fluorescence may be a useful alternative.  相似文献   

20.
微波是波长微小的电磁波,具有很强的介质穿透能力,可实现物料内外的同时升温。在利用微波熟化淀粉类食品时,具有热效率高、可控性强、设备占地小等优点。本文介绍了淀粉升温糊化过程中微波热效应和非热效应;总结了研究微波非热效应的几种新手段;比较了微波处理与热传导处理在淀粉升温糊化过程中,淀粉颗粒表观特征、晶体结构和分子结构的变化以及热学特性的差异;论述了微波处理淀粉乳中水的响应。本文为后续深入研究微波处理对食物中淀粉糊化的影响与微波糊化淀粉特性的开发利用提供了参考。  相似文献   

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