Purification and identification of gamma-glutamyl transpeptidase of milk membranes

Recent evidence suggests that gamma-glutamyl transpeptidase may be involved in the transport of amino acids into the lactating mammary gland. The enzyme also is secreted in milk and is associated mainly with milk membranes. The objective of this study was to purify and characterize gamma-glutamyl transpeptidase from milk membranes. The enzyme has been purified from milk membranes by solubilization with Lubrol WX; treatment with acetone, deoxylcholate, and bromelain; and chromatography on ion exchange and molecular-sieving resins. gamma-Glutamyl transpeptidase was purified over 11,000-fold from milk. Electrophoresis on sodium dodecyl sulfate polyacrylamide gels indicates that the enzyme is composed of two subunits with molecular weights of 57,000 and 25,500. Both subunits are glycoproteins and have been identified in the sodium dodecyl sulfate polyacrylamide gel electrophoresis patterns of whole milk membrane. Kinetic characteristics of the purified enzyme are similar to those determined for intact milk membranes and lactating mammary tissue indicating that the purified enzyme has not been modified functionally by the purification procedure.     

魔芋葡甘聚糖基活性纳米复合膜的构建及性能研究

目的 对魔芋葡甘聚糖(konjac glucomannan, KGM)薄膜进行改良。方法 以KGM为基质, 棉花纤维素纳米晶须(cellulose nanocrystals, CNC)作为增强剂, 马尾藻多酚(phlorotannins from Sargassum, PS)为抗菌抗氧化剂, 通过物理性能、自由基清除能力和抗菌性检测, 筛选KGM/CNC/PS活性纳米复合膜包装材料。该包装材料运用在鲜猪肉保鲜上时, 以菌落总数(total bacterial count, TBC)、总挥发性盐基氮(total volatile base nitrogen, TVB-N)、硫代巴比妥酸反应物(thiobarbituric acid reactive substances, TBARS)、pH等指标判断鲜猪肉腐败变质程度。结果 当质量比KGM:CNC:PS=100:9:9.81 (KCP-9)时, KGM/CNC/PS活性纳米复合膜的热稳定性、力学性能、水蒸气阻隔性能相对其他比例的复合膜显著提高, KGM:CNC:PS=100:9:18.53 (KCP-17)时, 抗氧化和抗菌性能最佳, 后者运用在鲜猪肉上时, TBC、TVB-N、TBARS、pH等指标明显优于对照组中不使用任何保鲜剂的猪肉, 可延缓鲜猪肉腐败变质速度, 延长其货架期。结论 当KGM:CNC:PS=100:9:18.53 (KCP-17)时, KGM/CNC/PS活性纳米复合膜包装材料具有良好的抗氧化和抗菌性, 在食品保鲜领域具有潜在的应用前景, 本研究可为提高食品包装材料机械性能、抗菌性和抗氧化能力研究提供参考。     

角蛋白异质和同质复合膜的破坏行为探讨

为了选择适合于角蛋白基复合膜的短纤维状增强体,本文分别对纯膜,和以无机晶须与羊毛原纤增强的异质和同质复合膜的损伤和破坏行为进行分析,并探讨了头端分叉状的原纤对复合膜的增强与增韧作用。结合显微镜照片,对其拉伸曲线进行了分阶段讨论,结果表明：增强体的力学性质和形态特征对复合膜的破坏过程产生了一定的影响,但复合膜仍以基体的力学性能为主,加入增强体的同时也引入了大量启裂点,对复合膜性能起到劣化作用,但合适性能和形态特征的增强体仍可改善复合膜的性能。     

Fouling of microfiltration and ultrafiltration membranes by natural waters

Membrane filtration (microfiltration and ultrafiltration) has become an accepted process for drinking water treatment, but membrane fouling remains a significant problem. The objective of this study was to systematically investigate the mechanisms and components in natural waters that contribute to fouling. Natural waters from five sources were filtered in a benchtop filtration system. A sequential filtration process was used in most experiments. The first filtration steps removed specific components from the water, and the latter filtration steps investigated membrane fouling by the remaining components. Particulate matter (larger than 0.45 microm) was relatively unimportant in fouling as compared to dissolved matter. Very small colloids, ranging from about 3-20 nm in diameter, appeared to be important membrane foulants based on this experimental protocol. The colloidal foulants included both inorganic and organic matter, but the greatest fraction of material was organic. When the colloidal fraction of material was removed, the remaining dissolved organic matter (DOM), which was smaller than about 3 nm and included about 85-90% of the total DOM, caused very little fouling. Thus, although other studies have identified DOM as a major foulant during filtration of natural waters, this work shows that a small fraction of DOM may be responsible for fouling. Adsorption was demonstrated to be an important mechanism for fouling by colloids.     

静电纺聚酰胺6纳米纤维膜的制备及其性能

为制备功能性的聚酰胺6(PA6)纳米纤维膜,采用静电纺丝技术制备PA6/聚乙烯吡咯烷酮(PVP)共混纳米纤维膜,并对纤维膜的表面形貌、力学性能和亲水性能进行表征。结果表明,当PA6纺丝液质量分数为28%,PVP的加入量为0.5 g时,纤维膜的微观形貌较好,制备出的纤维直径为132 nm,断裂强度为9.68 MPa,断裂伸长率为31.89%,亲水角为(32.4±1.2)°。研究了不同纺丝时间对纤维膜空气过滤性能的影响,当纺丝时间为0.5 h时,纤维膜具有较好的过滤性能,过滤效率为99.5%,过滤压降为476 Pa。红外分析结果表明,在PA6中加入PVP,在搅拌的过程中二者均匀融合,PVP小分子填充在PA6大分子中,可使纤维膜的亲水性提高。制得的PA6纳米纤维膜可作为加湿器中的湿膜材料得到应用。     

分离用无机膜及其在食品中的应用

概述了无机膜的种类、特点,同时介绍了无机膜在食品分离中的研究应用情况及今后的发展前景。     

Kaempferol and quercetin interactions with model lipid membranes

In the present study, the membrane interactions of the flavonoids kaempferol and quercetin at different temperatures with two different model lipid membranes (without cholesterol) were investigated. A combination of fluorescence spectroscopy, electron paramagnetic resonance spectroscopy, and differential scanning calorimetry were used to detect changes in membrane fluidity. Two fluorophores and two spin probes were used to monitor the membrane characteristics at different depths in the membrane. The dependence of the lipid order on the molar ratio of flavonoid to membranes of phosphatidylcholine:sphingomyelin (2.4:1) and of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine showed that flavonoids increase the lipid order. As with fluorescence spectroscopy, for phosphatidylcholine:sphingomyelin liposomes, the fluidity decrease detected with the spin probes of the electron paramagnetic resonance spectroscopy was less with kaempferol than quercetin, and was higher in the middle of the membrane than close to the water–lipid interface. Below the phase-transition temperature, the polarity surrounding the nitroxide group of the spin probes in the most-ordered membrane domains increases in the presence of kaempferol and quercetin, which indicates that these flavonoids facilitate the penetration of water molecules into the membranes. Kaempferol and quercetin caused a small thermal destabilisation of DPPC transition which shows that the molecules interacted mainly with the polar headgroup regions of the bilayer. With the kaempferol and quercetin, which differ only in their number of –OH groups, their effect on the lipid membranes was more pronounced in the absence of cholesterol and confirmed that even a difference of one –OH group is enough to promote different membrane effects.     

防护服用聚四氟乙烯复合膜的结构和性能

为增强防护服用聚四氟乙烯(PTFE)复合膜的防护性和弹性,提出了PTFE与热塑性聚氨酯(TPU)共同拉伸制备PTFE/TPU复合膜的方法。这种方法还避免了PU涂层PTFE制备复合膜中PU溶剂污染环境等不足。采用扫描电镜、万能强力仪和透湿试验装置分别测试了共同拉伸和涂层复合膜的结构、弹性和透湿性。结果表明,与涂层复合膜相比,共同拉伸复合膜中的聚氨酯膜上完全没有微孔,这增强了薄膜制品的防护性和弹性;共同拉伸膜的透湿量也达到服装舒适性要求。     

Degradation of polyamide nanofiltration and reverse osmosis membranes by hypochlorite

The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)-N). FTIR data indicated the disappearance of the amide II band (1541 cm(-1)) and aromatic amide peak (1609 cm(-1)) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that N-chlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.     

中空聚四氟乙烯纤维膜制备与结构特征

为制备管式中空聚四氟乙烯纤维膜,探究了管式多层膜的结构特征。采用宽16.0 mm、厚0.2 mm的聚四氟乙烯纤维膜原膜进行包缠烧结,制备了管式中空聚四氟乙烯纤维膜。通过红外光谱和3D激光显微镜,测试了原膜宽度(16.0~64.0 mm)、包缠层数(6~12层)及添加剂(封闭型异氰酸酯)等不同因素对所制备的管式中空聚四氟乙烯纤维膜的影响。结果表明:通过包缠烧结制备的管式中空聚四氟乙烯纤维膜孔隙率高、整体均匀性好、孔隙相通性好,具有较好的过滤性能。     

聚丙烯腈抗菌复合纳米纤维膜的制备及其抗菌性能

为研究分析不同抗菌剂对聚丙烯腈(PAN)抗菌纳米纤维的影响,进一步开发功能性纳米纤维纺织品,通过静电纺丝方法制备PAN/三氯生(TCS)、PAN/TiO₂抗菌复合纳米纤维膜,借助扫描电子显微镜、傅里叶红外光谱仪等对纳米纤维膜的微观结构和性能进行表征。结果表明:相对于纯 PAN纳米纤维膜,PAN/TCS 和PAN/TiO₂抗菌纳米纤维膜的纤维直径减少了39% ~ 71%,拉伸强度增加了12% ~ 88%; PAN/TCS 复合纳米纤维膜对金黄色葡萄球菌和大肠杆菌的抑菌圈都大于1 mm;由于TiO₂为非溶出型菌剂,PAN/TiO₂复合纳米纤维未发现抑菌圈;PAN/TCS 和PAN/TiO₂纳米纤维对金黄色葡萄球菌和大肠杆菌的抑菌率都达到了91.98%以上,且抑菌率随着TCS和TiO₂质量分数的增加而增加。     

Research Watch: Charged membranes

Wastewater.     

静电纺锡/聚丙烯腈纳米纤维膜制备与表征

将纳米锡(Sn)与聚丙烯腈(PAN)共混,采用静电纺丝法制备Sn/PAN纳米纤维膜并进行炭化处理。使用扫描电子显微镜、透射电子显微镜和X射线衍射法对纤维平均直径、直径分布、Sn在纤维上的存在情况以及Sn加入到PAN中静电纺丝后的结晶程度进行表征,将炭化后的纤维膜直接制成锂离子电池负极,测试其电化学性能。结果表明:随着纺丝电压升高或固化距离增大,纤维直径减小;当静电纺丝电压为14 kV,固化距离为14 cm时,纤维平均直径较小,分布最均匀;炭化后纤维变细;Sn加入到PAN中静电纺丝后发生团聚,结晶程度明显下降;Sn/PAN作为锂离子电池负极材料,具有良好的储能性能。     

聚乙烯-分子筛复合膜用于樱桃的保鲜包装研究

以低密度聚乙烯、线性低密度聚乙烯、乙烯/乙酸乙烯酯共聚物、Hβ分子筛及硬脂酸为原料,吹制获得新型聚乙烯复合膜。以新采鲜樱桃为保鲜对象,探讨了复合膜的保鲜效果及分子筛含量的影响。实验考察了樱桃贮藏后的外观变化、呼吸强度、失重率、折光率和硬度等指标。结果表明,室温下M3膜对新摘樱桃的保鲜效果最好,其保鲜时间达10d以上。     

转谷氨酰胺酶的膜固定化研究

以臭氧活化后的聚丙烯微孔膜为载体,并以丙烯酸为单体、戊二醛为交联剂固定转谷氨酰胺酶。研究了臭氧活化时间、接枝反应时间、温度、单体浓度、莫尔盐浓度对接枝率的影响,并对固定化条件进行研究。确定了最佳固定化条件为：己二胺浓度15%,胺烷基化温度50℃、时间120min,戊二醛浓度3%,交联温度30℃、45min,酶浓度10mg/mL,固定化时间20h。此条件下载酶量为30.23mg/g膜,酶活力可达16.9U/g膜。     

Direct observation of microbial adhesion to membranes

Direct microscopic observation and an interfacial force model were used to better understand and control microbial adhesion to polymeric ultrafiltration membranes. The model was used to predict a "critical flux", below which cells deposited reversibly, and direct observation was used to visually quantify cell deposition and removal. In preliminary direct observation experiments, permeate reversal (backpulsing) was more effective than cross-flow hydrodynamics at removing deposited cells. In experiments conducted below the critical flux, no cell accumulation was observed over repeated forward-reverse filtration cycles; however, a small fraction of cells deposited irreversibly regardless of the flux, membrane, or solution chemistry. The fraction of irreversibly deposited cells was consistent with the equilibrium surface coverage attained without permeation (i.e., due to heterogeneous adsorption). Although steric forces were not invoked to establish a critical flux, when operating above the critical flux, a balance between permeation drag and steric repulsion appeared to determine the strength of adhesion of cells to membranes. Direct observation also confirmed that above the critical flux fouling occurred and pressure losses accumulated over several backpulse cycles, whereas below the critical flux there were no observable pressure losses or fouling.     

丝素共混膜的研究进展

介绍丝素与聚乙烯醇、聚丙烯酰胺、壳聚糖、海藻酸钠和纤维素等聚合物的共混膜,比较分析丝素共混膜的结构、力学性能;综述了丝素共混膜作为细胞培养底物、可控药物释放载体、人工皮肤、人工肌腱、酶固定材料等在生物医学领域的应用研究进展;阐述丝素与聚合物共混制膜在生物医学和药学材料上应用的潜在价值。     

转谷氨酰胺酶在聚丙烯膜上的固定化研究

采用紫外光两次照射接枝的方法在聚丙烯膜表面接枝甲基丙烯酸甲酯,以提高膜表面的生物相容性和固定化酶的生物活性.探究了影响接枝率的光照时间、距离、单体浓度等重要影响因素后,接枝率最高可达38.38%.固定化的条件为己二胺活化温度50℃、浓度15%、120min,戊二醛交联浓度4%、30℃、40min,酶农度15mg/mL时,4℃下固定化24h,膜的酶蛋白承裁量最高为1009.26μg/g膜,固定化酶膜的活力可达到1.87U/g膜.     

Organic fouling and chemical cleaning of nanofiltration membranes: measurements and mechanisms

Fouling and subsequent chemical cleaning of nanofiltration (NF) membranes used in water quality control applications are often inevitable. To unravel the mechanisms of organic fouling and chemical cleaning, it is critical to understand the foulant-membrane, foulant-foulant, and foulant-cleaning agent interactions at the molecular level. In this study, the adhesion forces between the foulant and the membrane surface and between the bulk foulant and the fouling layer were determined by atomic force microscopy (AFM). A carboxylate modified AFM colloid probe was used as a surrogate for humic acid, the major organic foulant in natural waters. The interfacial force data were combined with the NF membrane water flux measurements to elucidate the mechanisms of organic fouling and chemical cleaning. A remarkable correlation was obtained between the measured adhesion forces and the fouling and cleaning behavior of the membrane under various solution chemistries. The AFM measurements further confirmed that divalent calcium ions greatly enhance natural organic matter fouling by complexation and subsequent formation of intermolecular bridges among organic foulant molecules. Efficient chemical cleaning was achieved only when the calcium ion bridging was eliminated as a result of the interaction between the chemical cleaning agent and the fouling layer. The cleaning efficiency was highly dependent on solution pH and the concentration of the chemical cleaning agent.     

Role of zinc in lipid and fatty acid metabolism and in membranes

This review addresses the role of zinc in the metabolism of lipids including cholesterol, phospholipids, triglyceride, fatty acids, lipoproteins, and essential fatty acids and it discusses to a limited extent the role of zinc in membranes as well as zinc's known effects on receptors. The evidence which is compiled demonstrates two main features of the interactions of zinc in lipid and fatty acid metabolism; 1) that zinc intimately affects many aspects of lipid metabolism through established enzymes but also has modulatory effects whose mechanism is not obvious or established, and 2) many of the observations are superficially contradictory and do not lend themselves to ready explanation. These are the features of a field whose time has come and which beckons further research to clarify these issues.