1-MCP处理对杏鲍菇采后生理和结构变化的影响

以杏鲍菇为试材,分别研究1-甲基环丙烯（1-methylcyclopropene,1-MCP）的不同剂量及不同处理时间对杏鲍菇采后质量损失率、多酚氧化酶（PPO）活性及菇体断面微细结构的影响。结果表明：当1-MCP的剂量为0.3 μL/L时,质量损失率和PPO活性在贮藏末期分别较对照组下降了5.94%和37.38%,菇体断面微细结构较贮藏初期变化最小;当1-MCP的处理时间为24 h时,质量损失率和PPO活性在贮藏末期分别较对照组下降了5.42%和33.98%,贮藏前后菇体断面微细结构变化最小。实验证明了1-MCP的最适处理剂量为0.3 μL/L、最适处理时间为24 h。最适条件下的1-MCP处理能有效地减缓果实质量损失率和褐变程度,减小菇体断面微细结构变化,有利于延长杏鲍菇的贮藏期,具有明显的保鲜效果。     

Novel silica/poly(2,6-dimethyl-1,4-phenylene oxide) hybrid anion-exchange membranes for alkaline fuel cells: Effect of silica content and the single cell performance

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based organic-inorganic hybrid alkaline membranes with enhanced hydroxyl (OH⁻) conductivity are prepared in response to the relatively low conductivity of previously reported PPO-based systems. The membranes also exhibit higher swelling-resistant properties and the hydroxyl (OH⁻) conductivity values are comparable to previously reported fluoropolymer-containing membranes: 0.012-0.035 S cm⁻¹ in the temperature range 30-90 °C. Other favorable properties for fuel cell application include high tensile strengths up to 25 MPa and large ion-exchange capacities in the range 2.01-2.27 mmol g⁻¹. Beginning-of-life fuel cell testing of a membrane with a thickness of 140 μm yielded an acceptable H₂/O₂ peak power density of 32 mW cm⁻² when incorporated into an alkaline membrane electrode assembly. Therefore, this class of hybrid membrane is suitable for application in alkaline membrane fuel cells.     

高压二氧化碳和超高压对多酚氧化酶和果胶甲酯酶结构的影响

为考察高压二氧化碳(HPCD)和超高压技术钝化多酚氧化酶(PPO)和果胶甲酯酶(PE)活性的机理,采用SDS-PAGE电泳、红外光谱和荧光光谱对处理前后酶蛋白的结构进行比较研究。结果表明：经过不同压强HPCD处理和超高压处理60min后,PPO和PE的活性均随着处理压强的增大而逐渐降低。SDS-PAGE电泳分析显示处理后酶蛋白的肽链不发生断裂,但红外光谱和荧光光谱分析显示酶蛋白的二级和三级结构均发生变化。因此,HPCD和超高压技术通过改变PPO和PE酶蛋白的结构达到钝化酶活性的目的。     

葡萄与葡萄酒中多酚氧化酶研究进展

在葡萄与葡萄酒的加工过程中,多酚氧化酶可以引起葡萄汁和葡萄酒的氧化,尤其是白葡萄酒,严重影响了葡萄酒的品质。本文总结了葡萄中多酚氧化酶的结构和功能及其在葡萄中的分布情况,并且揭示了在葡萄酒酿造工艺中其引起氧化褐变的机制,同时介绍了影响多酚氧化酶活性的因素和多酚氧化酶抑制剂应用等的研究进展,为进一步控制葡萄酒酿造过程中多酚氧化酶引起的氧化褐变提供参考。     

PROFIBUS总线在烟箱输送线上的应用

本文介绍了基予西门子S7-315 PLC的PROFIBUS DP现场总线控制系统,系统基于西门子ET200远程I／O模块实现丹佛斯变频器从站硬件组态,丹佛斯变频器使用PPO协议,着重介绍DP从站诊断以及读写变频器智能从站程序的编写流程。     

Effect of temperature in synthesis of silver nanoparticles in triblock copolymer micellar solution

Knowing that poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) in aqueous solution is thermoresponsive, the effect of temperature on formation and stabilisation of silver nanoparticles has been investigated systematically. Synthesis of silver nanoparticles was achieved from silver ammonia complex [Ag(NH₃)₂]⁺ in aqueous solution of hydroxyl terminated PEO–PPO–PEO at four different temperatures. A non-Arrhenius behaviour for the rate of silver reduction with temperature was observed. The hydrodynamic diameter of the composite coils suddenly increased at certain intermediate time indicating sudden agglomeration of individual micelles to form bigger network structures. The size and the distribution of the nanoparticles show a bimodal distribution at the lowest temperature. At intermediate temperature, particles of the smallest size with a narrow distribution was achieved. At the highest temperature, a bunch-like particle morphology was found. Chemical changes in polymer properties were observed at higher temperatures. The results suggest that at a lower temperature, a change in polymer morphology play an important role in controlling the particle size and their distribution, whereas at a higher temperature, this role is shifted to the chemical change of the polymer. At an intermediate temperature, a balance between the two effects provides the optimum condition for formation of silver nanoparticles of small size and narrow distribution.     

HIPS/PPO共混物拉伸和冲击断裂面的电镜观察

研究了高冲击强度聚苯乙烯(HIPS)/聚苯醚(PPO)共混物断面3个特征区的形貌特征及形成机制,分析了它们对材料力学性能的影响。     

西葫芦多酚氧化酶酶学特性研究

以邻苯二酚为底物,采用分光光度法对西葫芦多酚氧化酶(PPO)的酶学特性及不同抑制剂对多酚氧化酶活性的影响进行研究。结果表明,西葫芦多酚氧化酶最适pH为6.6,最适温度为35℃,90℃处理5min可使该酶失活。多酚氧化酶催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.0417mol/L,Vmax=208.33U。四种抑制剂对PPO的抑制效果由强到弱依次为:亚硫酸氢钠>L-半胱氨酸>抗坏血酸>柠檬酸。     

超高压技术在鲜榨桃汁加工中的应用

以鲜榨桃汁为原料,分别研究了热处理对其多酚氧化酶(PPO)、过氧化物酶(POD)的灭酶效果影响和超高压对其微生物的灭菌效果影响。结果显示:PPO、POD相对残存酶活随着热处理温度和时间的增加而减小,PPO对热处理的耐受性明显高于POD,最适灭酶条件为75℃1min;菌落总数、霉酵总数和乳酸菌数均随着超高压处理压力和时间的增加而减少,霉菌和酵母菌对超高压的耐受能力明显差于细菌,最适灭菌条件为600MPa10min;按以上最适条件生产的桃汁在1个月贮藏期内达到商业无菌。     

Silicate-based polymer-nanocomposite membranes for polymer electrolyte membrane fuel cells

Proton-exchange membrane fuel cells have emerged as a promising emission free technology to fulfill the existing power requirements of the 21st century. Nafion^® is the most widely accepted and commercialized membrane to date and possesses excellent electrochemical properties below 80 °C, under highly humidified conditions. However, a decrease in the proton conductivity of Nafion^® above 80 °C and lower humidity along with high membrane cost has prompted the development of new membranes and techniques. Addition of inorganic fillers, especially silicate-based nanomaterials, to the polymer membrane was utilized to partially overcome the aforementioned limitations. This is because of the lower cost, easy availability, high hydrophilicity and higher thermal stability of the inorganic silicates. Addition of silicates to the polymer membrane has also improved the mechanical, thermal and barrier properties, along with water uptake of the composite membranes, resulting in superior performance at higher temperature compared to that of the virgin membrane. However, the degrees of dispersion and interaction between the organic polymer and inorganic silicates play vital roles in improving the key properties of the membranes. Hence, different techniques and solvent media were used to improve the degrees of nanofiller dispersion and the physico-chemical properties of the membranes. This review focuses mainly on the techniques of silicate-based nanocomposite fabrication and the resulting impact on the membrane properties.