壳聚糖/卡拉胶聚电解质复合物的制备及其性能的基础研究

用天然多糖壳聚糖和卡拉胶合成壳聚糖/卡拉胶聚电解质复合物(PEC),探讨了PEC合成过程中的反应机理,考察PEC聚电解质在不同pH缓冲溶液中的稳定性和做药物释放载体的可能性。      

壳聚糖/果胶复合作用研究

研究了壳聚糖与果胶形成聚电介质复合物的作用.红外光谱IR图谱显示,壳聚糖和果胶形成的物质出现-NH3+ -OOC一次价键,表明发生了-NH2和-COOH的次价键反应,说明壳聚糖和果胶分子之间发生了聚电解质反应.胶体滴定、浊度滴定实验结果表明,壳聚糖和果胶在pH5.0～6.0范围内按一定比例、通过静电相互作用形成聚电解质复合物(PEC).壳聚糖与果胶形成PEC的最佳复合比例以及PEC临界转变pH(pHω)与壳聚糖的分子量、脱乙酰度密切相关.当壳聚糖的分子量由5万增至50万时,壳聚糖和果胶的最佳复合比例γψ8:2逐渐降低为3:7,pHω由5.0升为6.0;壳聚糖脱乙酰度由80%升至95%时,γψ由8:2逐渐降低为4:6,pHω由6.5降为5.0.     

壳聚糖/果胶复合作用研究

研究了壳聚糖与果胶形成聚电介质复合物的作用。红外光谱IR图谱显示,壳聚糖和果胶形成的物质出现-NH3+-OOC-次价键,表明发生了-NH2和-COOH的次价键反应,说明壳聚糖和果胶分子之间发生了聚电解质反应。胶体滴定、浊度滴定实验结果表明,壳聚糖和果胶在pH5·0～6·0范围内按一定比例、通过静电相互作用形成聚电解质复合物（PEC）。壳聚糖与果胶形成PEC的最佳复合比例以及PEC临界转变pH（pHω）与壳聚糖的分子量、脱乙酰度密切相关。当壳聚糖的分子量由5万增至50万时,壳聚糖和果胶的最佳复合比例γφ由8∶2逐渐降低为3∶7,pHω由5·0升为6·0;壳聚糖脱乙酰度由80%升至95%时,γφ由8∶2逐渐降低为4∶6,pHω由6·5降为5·0。      

三种离子物质对壳聚糖/果胶聚电解质复合物牛血清蛋白释放特性的影响

分别添加氯化钠、硫酸钠、氯化铁制备壳聚糖/果胶聚电解质复合物(PEC),研究其对牛血清蛋白(BSA)的负载能力及模拟释放行为,以探讨三种离子物质对壳聚糖/果胶PEC在蛋白缓释方面的影响。氯化铁PEC对BSA的包埋率最大,其次为硫酸钠、氯化钠,载药率为氯化钠PEC最大、其次为硫酸钠、氯化铁。在单一模拟环境中,各PEC在模拟胃液中的BSA累积释放率最小,在模拟结肠液中最大;氯化钠会使PEC的BSA释放率降低,而硫酸钠与氯化铁则可增大蛋白释放率;各PEC的蛋白释放行为属于Fick扩散。在连续模拟环境中,模拟胃液中BSA累积释放率较低,在模拟肠道环境中BSA大量释放,含有氯化钠的PEC累积释放率最低;在模拟结肠液中含有果胶酶时,各PEC的BSA累积释放率可达98%以上;各PEC的蛋白释放动力学属于非Fick扩散。含有三种离子物质的壳聚糖/果胶PEC均具有良好的p H敏感性和定点释放特性。     

离子对壳聚糖/果胶/阿拉伯胶 PEC 膜性质的影响

本文研究了添加Na Cl、CaCl_2及FeCl_3对壳聚糖/果胶/阿拉伯胶聚电解质复合物(PEC)溶液的浊度、膜的溶胀度、接触角和机械性能等的影响,并通过红外光谱分析和扫描电镜观察,探讨了离子对PEC静电复合及膜结构的影响。结果表明:在0~60 mmol/L浓度范围内,PEC溶液浊度随离子浓度的增大呈现先升高后降低的趋势;离子种类及浓度对PEC膜的溶胀度影响趋势不同,添加50 mmol/L FeCl_3的PEC膜溶胀度显著提高;离子种类及浓度对PEC膜接触角的影响趋势不同;离子添加可以显著提高PEC膜的拉伸强度,降低断裂伸长率,添加40 mmol/L FeCl_3的PEC膜具有最高的拉伸强度;红外光谱分析发现,离子添加不影响壳聚糖和果胶、阿拉伯胶之间的静电复合方式;扫描电镜观察发现添加NaCl、CaCl_2的PEC膜表面相对光滑,而添加FeCl_3形成的膜表面凹凸不平,较粗糙。     

离子对壳聚糖/果胶/阿拉伯胶 PEC 膜性质的影响

本文研究了添加Na Cl、CaCl₂及FeCl₃对壳聚糖/果胶/阿拉伯胶聚电解质复合物（PEC）溶液的浊度、膜的溶胀度、接触角和机械性能等的影响,并通过红外光谱分析和扫描电镜观察,探讨了离子对PEC静电复合及膜结构的影响。结果表明:在0⁶0 mmol/L浓度范围内,PEC溶液浊度随离子浓度的增大呈现先升高后降低的趋势;离子种类及浓度对PEC膜的溶胀度影响趋势不同,添加50 mmol/L FeCl₃的PEC膜溶胀度显著提高;离子种类及浓度对PEC膜接触角的影响趋势不同;离子添加可以显著提高PEC膜的拉伸强度,降低断裂伸长率,添加40 mmol/L FeCl₃的PEC膜具有最高的拉伸强度;红外光谱分析发现,离子添加不影响壳聚糖和果胶、阿拉伯胶之间的静电复合方式;扫描电镜观察发现添加NaCl、CaCl₂的PEC膜表面相对光滑,而添加FeCl₃形成的膜表面凹凸不平,较粗糙。      

离子对壳聚糖/果胶聚电解质复合物溶胀性及微观结构的影响研究

本文将壳聚糖、果胶在含有六种不同离子的溶液环境中复合,考察离子种类及浓度对壳聚糖/果胶聚电解质复合物（PEC）得率、溶胀度（水及模拟环境中）、红外光谱及微观结构的影响。离子价态对PEC得率的影响为：三价离子〉二价离子〉一价离子;离子浓度低时,离子浓度促进PEC得率增加,离子浓度高时,离子浓度抑制PEC得率增加。离子种类不同,PEC的溶胀过程不同,复合环境中含有FeCl3和Fe2（SO4）3的PEC在水中具有最大、最小溶胀度,分别为56.87±0.63和9.21±0.13;含有MgSO4和Fe2（SO4）3的PEC在胃肠模拟液中具有最大、最小溶胀度,分别为361.74±6.21和28.01±0.66。红外光谱结果表明添加离子并未影响PEC中NH3＋/COO-键的形成。扫描电镜结果显示PEC呈海绵多孔状,添加离子后PEC孔壁厚度增加9.76±1.03%至334.19±5.12%不等,表面更加光滑,而孔隙状态因离子种类不同而不同。研究表明PEC得率、溶胀度及微观结构受到离子影响,但其交联方式不变。     

固定化载体对苹果酒发酵的影响

本试验采用三种不同载体壳聚糖、卡拉胶及壳聚糖与卡拉胶的混合物对苹果酒发酵酵母固定化技术进行改进。以浓缩苹果汁为原料,加入茶多酚作为抗氧化剂,通过测定发酵过程中的残糖、酒精度、透光率等理化指标的变化情况,考察不同固定化载体对发酵速度和发酵效果的影响。结果表明,用壳聚糖与卡拉胶的混合体改良后固定化时,发酵效果最好。     

卡拉胶的交互作用特性及其在食品工业中的应用

对卡拉胶与电解质、食品胶和蛋白质等之间的交互作用特性进行了研究，同时对卡拉胶在食品工业中的研究进展进行了综述。     

壳聚糖食品微胶囊的制备及其控制释放

壳聚糖是天然的生物材料,具有独特的阳离子性质和优良的成膜性,可单独作为微胶囊化壁材,也可与小分子表面活性剂或大分子聚电解质发生静电相互作用,形成双层界面保护膜。综述了壳聚糖食品微胶囊的制备方法、影响因素及其对物质的控制释放作用,为壳聚糖在食品微胶囊化中的研究和应用提供理论基础。     

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3-7). The SPI formed very large (> 50 ??m) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ??-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.     

Development of an E-H2O2/TiO2 photoelectrocatalytic oxidation system for water and wastewater treatment

In this study, an innovative E-H2O2/TiO2 (E-H2O2 = electrogenerated hydrogen peroxide) photoelectrocatalytic (PEC) oxidation system was successfully developed for water and wastewater treatment. A TiO2/Ti mesh electrode was applied in this photoreactor as the anode to conduct PEC oxidation, and a reticulated vitreous carbon (RVC) electrode was used as the cathode to electrogenerate hydrogen peroxide simultaneously. The TiO2/Ti mesh electrode was prepared with a modified anodic oxidation process in a quadrielectrolyte (H2SO4-H3PO4-H2O2-HF) solution. The crystal structure, surface morphology, and film thickness of the TiO2/Ti mesh electrode were characterized by X-ray diffraction and scanning electron microscopy. The analytical results showed that a honeycomb-type anatase film with a thickness of 5 microm was formed. Photocatalytic oxidation (PC) and PEC oxidation of 2,4,6-trichlorophenol (TCP) in an aqueous solution were performed under various experimental conditions. Experimental results showed that the TiO2/Ti electrode, anodized in the H2SO4-H3PO4-H2O2-HF solution, had higher photocatalytic activity than the TiO2/Ti electrode anodized in the H2SO4 solution. It was found that the maximum applied potential would be around 2.5 V, corresponding to an optimum applied current density of 50 microA cm(-2) under UV-A illumination. The experiments confirmed that the E-H2O2 on the RVC electrode can significantly enhance the PEC oxidation of TCP in aqueous solution. The rate of TCP degradation in such an E-H2O2-assisted TiO2 PEC reaction was 5.0 times that of the TiO2 PC reaction and 2.3 times that of the TiO2 PEC reaction. The variation of pH during the E-H2O2-assisted TiO2 PEC reaction, affected by individual reactions, was also investigated. It was found that pH was well maintained during the TCP degradation in such an E-H2O2/TiO2 reaction system. This is beneficial to TCP degradation in an aqueous solution.     

Uncertainties in charring correction in the analysis of elemental and organic carbon in atmospheric particles by thermal/optical methods

Thermal/optical methods are widely used in the determination of aerosol organic carbon (OC) and elemental carbon (EC) collected on quartz filters. A fraction of OC undergoes charring to form pyrolytically generated EC (PEC) during thermal analysis. The correct speciation of OC and EC in thermaVoptical methods depends on one of the following two assumptions: (1) PEC evolves before native EC evolves in the analysis or (2) PEC and native EC have the same apparent light absorption coefficient (sigma) at the monitoring light wavelength. Neither of these assumptions has actually ever been checked or tested. The first assumption is invalidated by the observation that the combustion of PEC overlaps that of native EC despite multiple stepwise combustion at temperatures ranging from 575 to 910 degrees C. An examination of sigma versus EC evolution indicates that the sigma values of PEC and EC are not the same in most cases and the a value of PEC is not constant during a single thermal analysis. The second assumption is thus invalid as well. The measured EC concentrations can either overestimate or underestimate the true native EC concentrations depending on the relative magnitude of the a values of the PEC and native EC at the point where the instrument sets the EC/OC split line. Both over- and underestimation have been observed in real aerosol samples. The unequal a values of PEC and EC also explain that different temperature programs, when employed to analyze the same filter samples, systematically yield different EC and OC concentrations. Our findings imply that minimizing charring improves the accuracy of the EC/OC split in thermal/optical methods.     

Evaluation of the MPN, Anderson-Baird-Parker, Petrifilm E. coli and Fluorocult ECD method for enumeration of Escherichia coli in foods of animal origin.

Commercially available beta-D-glucuronidase (GUR) based methods, Petrifilm E. coli (PEC) and Fluorocult ECD (FECD), and ISO standard MPN and Anderson-Baird-Parker (ABP) procedures were evaluated for routine enumeration of E. coli in naturally contaminated foods of animal origin. The methods concerned were classifiable in a sequence of best qualities for: production, MPN > ABP = PEC = FECD; costs, FECD > ABP = PEC > MPN; time per measurement, ABP = PEC = FECD > MPN; practical use, PEC > FECD > ABP > MPN; detection at low contamination, MPN > ABP = PEC > FECD. The ABP and PEC method appeared useful for routine counting of E. coli in raw meat, poultry and meat products, whereas the MPN procedure turned out to be more sensitive, however, impractical and considerably more expensive. The FECD method was inexpensive although suitable for the enumeration of E. coli at higher contamination level (> 50 cfu/g). The indole and MUG indicators both applied to demonstrate E. coli with the ABP or FECD method proved to be equal in specificity.     

Enumeration of coliforms and Escherichia coli in frozen black tiger shrimp Penaeus monodon by conventional and rapid methods

Conventional (most probable number, MPN) and rapid methods-including Chromocult coliform agar (CCA), Fluorocult(R) LMX broth (LMX), and Petrifilm Escherichia coli count plates (PEC) for enumeration of coliforms and E. coli in frozen black tiger shrimp from Thailand were compared in order to assess the possibility of using one of the rapid methods for routine analysis. Enumeration of coliforms and E. coli from 18 samples of regular frozen black tiger shrimp and 156 samples of frozen black tiger shrimp experimentally contaminated with coliforms or E. coli at concentrations of approximately 10, approximately 10(2), and approximately 10(3) CFU g(-1) revealed that at the level of approximately 10 CFU g(-1), coliform numbers ranked as LMX>CCA>MPN=PEC and E. coli as MPN=LMX=PEC=CCA. At the level of approximately 10(2) CFU g(-1), coliform numbers ranked as LMX>MPN=PEC=CCA and E. coli as MPN=LMX>PEC=CCA. At the level of 10(3) CFU g(-1), coliforms ranked as LMX>MPN=CCA>PEC and E. coli as MPN>LMX>CCA>PEC. Agreements with the conventional MPN method for coliforms were LMX 108%, PEC 87.2%, and CCA 91.2% and agreements for E. coli were LMX 101%, PEC 95.7%, and CCA 96.3%. Sensitivities (%) ranked LMX>MPN>CCA=PEC for coliforms and E. coli, whereas equal specificities (100%) of all methods for coliforms and E. coli were demonstrated. Rankings for the other parameters compared were: convenience, PEC>CCA=LMX>MPN; time to detection, MPN>LMX=PEC=CCA; expense, MPN=PEC>CCA>LMX; labor, MPN>LMX=CCA>PEC; accuracy for coliforms, PEC>CCA>MPN>LMX; and accuracy for E. coli, PEC=CCA>LMX>MPN.     

TiO2/Ti rotating disk photoelectrocatalytic (PEC) reactor: a combination of highly effective thin-film PEC and conventional PEC processes on a single electrode

A TiO2/Ti rotating disk photoelectrocatalytic (PEC) reactor has been developed and successfully applied to degrade Rhodamine B (RB) and other dyes in textile effluents. The innovative concept behind the reactor design is to simultaneously perform two processes on one electrode. These two processes are (1) highly effective thin-film PEC, in which the upper half of the round disk photoanode was coated with a thin layer of wastewater and exposed to UV radiation in air; and (2) the conventional PEC, in which the other half of the disk was immersed in bulk wastewater and irradiated by the same light source. The average aqueous film thickness was about 75 microm. The disk electrode was kept rotating at 90 rpm to continuously refresh the thin aqueous film for the upper side of the electrode and to promote the mass transfer of the target pollutants and the degradation products on the lower part of the disk. Using 20-150 mg L(-1) RB solutions as a model system, thin-film PEC removed total color and total organic carbon (TOC) by 27-84% and 7-48%, respectively, within 1 h, much higher than 3-55% and 0-30% removal by conventional PEC under the same treatment conditions. Results also suggest that the thin-film process was especially superior for treating high concentration solutions. Application of the rotating disk PEC reactor in industrial textile effluents showed a satisfactory result. The recycle experiments demonstrated excellent stability and reliability of the rotating disk PEC electrode. This study proposed a new concept for designing a PEC reactor applicable to industrial wastewater treatment.     

Photoelectrocatalytic activity of highly ordered TiO2 nanotube arrays electrode for azo dye degradation

A highly ordered titanium dioxide nanotube arrays (HOTDNA) electrode was prepared in hydrofluoric acid solution by electrochemical anodization technique on a pure titanium sheet. The HOTDNA electrode was characterized by FE-SEM microscopy, X-ray diffraction, and UV-vis spectra. The linear-sweep photovoltammetry response on the HOTDNA electrode is presented in this work. The photogenerated current of 0.3 mA/cm2 was observed significantly upon illumination with applied potential of 0.5 V in the UV regions at the central wavelength of 253.7 nm. Photoelectrocatalytic (PEC) and photocatalytic (PC) activities of the HOTDNA electrode were evaluated in the degradation of methyl orange (MeO) in aqueous solution. A set of optimized conditions such as anodic potential, calcinations temperature, and MeO concentration on the PEC activity was investigated. The PEC and PC activities of HOTDNA electrode were compared. We concluded that the HOTDNA electrode was an effective photoelectrode for achieving an enhanced MeO degradation.