单分子膜研究的方法及现状

单分子膜一般是将两亲性物质溶解在铺展溶剂中制成铺展溶液，然后铺展在底液上而得的。在其性质的研究中，测定表面压－面积关系曲线是最基本、也是最重要的一种研究手段。但是，仅有表面压－面积曲线所能了解的信息是远远不够的，因此必须结合另一些手段进行研究，测定表面粘度就是其中很重要的一种。而随着现代光谱仪器的更新、发展，光学方法已日益成为单分子膜研究的一个重要途径。     

C16OH／AEO-3混合分子膜抑制水分蒸发的研究

探讨了C16OH／AEO-3复配比例、温度、时间、环境因素等对分子膜抑制水分蒸发效果的影响。研究结果表明,当温度为25℃,膜表面浓度为8．0×10^2g／m^2时,C16OH的抑制率最高仅为35％,引入AEO-3后,当C16OH／AEO-3的复配比例为7：3时,抑制率最高可达60％以上。室外实验表明,混合膜在膜表面浓度为4．0×10^-1g／m^-2时,15d后仍有一定的抑制效果,抑制率依旧保持在30％以上。此外,在15℃-40℃的温度范围内,混合膜的抑制率高于C16OH,显示出更好的抑制水分蒸发能力。透气性测试结果表明,C16OH和混合膜均不妨碍气水界面的氧气交换。分子膜的AFM图像显示,混合膜能形成比C16OH更为凝聚的分子膜,产生更为理想的抑制水分蒸发效果。     

C_(16)OH/AEO-3混合分子膜抑制水分蒸发的研究

探讨了C16OH/AEO-3复配比例、温度、时间、环境因素等对分子膜抑制水分蒸发效果的影响.研究结果表明,当温度为25 ℃,膜表面浓度为8.0×10-2 g/m2时,C16OH的抑制率最高仅为35%,引入AEO-3后,当C16OH/AEO-3的复配比例为7 ∶ 3时,抑制率最高可达60%以上.室外实验表明,混合膜在膜表面浓度为4.0×10-1 g/m2时,15 d后仍有一定的抑制效果,抑制率依旧保持在30%以上.此外,在15 ℃～40 ℃的温度范围内,混合膜的抑制率高于C16OH,显示出更好的抑制水分蒸发能力.透气性测试结果表明,C16OH和混合膜均不妨碍气水界面的氧气交换.分子膜的AFM图像显示,混合膜能形成比C16OH更为凝聚的分子膜,产生更为理想的抑制水分蒸发效果.     

铺展溶剂对气／水界面上C16OH不溶膜的影响

文章探讨了不同铺展溶剂对十六醇（C16OH）不溶膜在空气／水界面上的性能的影响。测试了铺展系数和成膜功,π-t等温线和r-t等温线,并用AFM观察了不同溶剂下的C16OH不溶膜形貌。结果表明以石油醚（30℃～60℃）为铺展溶剂的不溶膜铺展效果最好,铺展15min后,π就达到25mN／m以上,30min以后,π趋于稳定。且石油醚（30℃-60℃）在不溶膜中的残留最少,抑制水分蒸发的效果最好。不溶膜的AFM图像显示,以石油醚（30℃～60℃）作为铺展溶剂的不溶膜结构更紧密,凝聚性更好,膜的缺陷更少,因此抑制水份蒸发的效果更好。     

铺展溶剂对气/水界面上C_(16)OH不溶膜的影响

文章探讨了不同铺展溶剂对十六醇(C16OH)不溶膜在空气/水界面上的性能的影响.测试了铺展系数和成膜功,π-t等温线和r-t等温线,并用AFM观察了不同溶剂下的C16OH不溶膜形貌.结果表明以石油醚(30℃～60℃)为铺展溶剂的不溶膜铺展效果最好,铺展15 min后,π就达到25 mN/m以上,30 min以后,π趋于稳定.且石油醚(30℃～60℃)在不溶膜中的残留最少,抑制水分蒸发的效果最好.不溶膜的AFM图像显示,以石油醚(30℃～60℃)作为铺展溶剂的不溶膜结构更紧密,凝聚性更好,膜的缺陷更少,因此抑制水份蒸发的效果更好.     

不同流体界面上大豆11S球蛋白吸附膜膨胀黏弹性的比较研究

采用轴对称滴形分析法(ADSA)检测了空气/水、正十二烷/水和大豆油/水界面上不同浓度(0.001%~0.1%)的大豆11S球蛋白吸附膜的表面膨胀黏弹性随吸附时间的变化。研究表明,在体相蛋白溶液pH8.0和离子强度0.05mol/L的恒定条件下,随着吸附时间的延长,表面膨胀弹性增大,膨胀弹性明显大于膨胀黏性。从表面流变学的角度分析,空气/水和大豆油/水界面上大豆11S球蛋白吸附膜实际上是弹性的,膨胀弹性随液滴体相蛋白浓度的增加而增大,受界面类型的影响很大。空气/水界面上吸附膜的膨胀黏弹性最大,而大豆油/水界面上吸附膜的膨胀黏弹性最小。     

分子蒸馏单月桂酸甘油脂的研制

纯度在90%以上的单月桂酸甘油脂(GML)具有优良的乳化和防腐功效。由于GML是热敏性难分离物质,所以需要采用分子蒸馏(MolecularDistillation)提取高纯度的GML产品。本文从空气残压、蒸馏温度、冷凝面温度、料液流速等几个方面着手,结合分子平均自由程理论,确定了GML粗产品的分子蒸馏工艺。      

分子蒸馏单月桂酸甘油脂的研制

纯度在90%以上的单月桂酸甘油脂(GML)具有优良的乳化和防腐功效。由于GML是热敏性难分离物质,所以需要采用分子蒸馏(MolecularDistillation)提取高纯度的GML产品。本文从空气残压、蒸馏温度、冷凝面温度、料液流速等几个方面着手,结合分子平均自由程理论,确定了GML粗产品的分子蒸馏工艺。     

基于分子交联的蛋白膜性能改良技术的研究进展

蛋白膜由于具有无毒害、可降解、绿色环保、可延长食品保质期、提供营养等优点,在可食膜研究领域具有重要地位。如何改善其相对较弱的机械强度以及某些不足的阻隔性能,是研究者长期以来一直关注并将持续关注的问题。本文首先阐述了蛋白膜的成膜机制、性能指标,接着重点对基于分子交联的蛋白膜性能改良技术,包括物理交联、化学交联、酶法交联以及物理能交联等进行综述,最后对蛋白膜交联的意义和发展趋势进行了展望。     

基于分子印迹膜用于检测组胺的电化学传感器

利用电化学传感技术,对水样中的组胺进行检测,为研发相应的食品快检技术与设备提供技术基础。在金电极上制备分子印迹膜,应用电化学进行表征,建立电化学检测组胺的方法。该方法检出限:0.5ng/mL,检测范围:0.5ng/mL~50 ng/mL,检测时间30 min。所建立的方法对于检测水样的组胺具有灵敏度高、准确度好和精密度高。     

Diffusion coefficient of antimony leaching from polyethylene terephthalate bottles into beverages

A variety of polyethylene terephthalate (PET) bottles commercially available as soft drink containers from 80 different brands was collected in Japan and subsequently examined to determine the amount of Sb in both the PET plastic and drink. The concentration of Sb in the plastic material ranged from 0.1 to 216.5 mg/kg, while this value ranged from 0.3 to 1.6 μg/L in bottled solutions. The diffusion coefficients of Sb in PET samples were determined at 25, 40, 55, and 70 °C. The migrated-Sb in all simulated food solutions (e.g., ultra pure water, 4% acetic acid, and 50% ethanol) increased with storage time and temperature. The temperature-dependent diffusion coefficients were derived from the Arrhenius equation. The predicted model for Sb migration suggested that storage conditions of all PET drink products should be below 70 °C for a maximum of 72 d to avoid Sb levels above the recommended value of 5 μg/L, which is based on the European standards.     

新型氟乙烯乙烯基醚树脂增强膜材料的制备及其力学性能

针对聚四氟乙烯（PTFE）膜材料烧结成型温度高,能量消耗大,安全生产要求高等难题,研发了可兼顾PTFE 膜各方面性能的低温成型氟乙烯乙烯基醚树脂（FEVE）膜。研究了以涤纶织物为基材,FEVE 树脂为基体的实验室手工刮涂和200 ℃以内的低温固化成型工艺,并将研制的FEVE/ 涤纶膜材料与广泛使用的PTFE/ 玻璃纤维膜材料在力学性能和自洁性方面进行了对比。结果表明：FEVE 膜材料的拉伸强度可达到PTFE 建筑膜材料的99.6%,撕裂强度可通过浸渍涂层法达到PTFE 膜材料的1.3 倍,表征抗沾污性的接触角为100.4°,满足了膜材料疏水接触角大于或等于90°的要求,从而印证了FEVE 膜材料低温成型技术的可行性。     

Migration measurement and modelling from poly(ethylene terephthalate) (PET) into soft drinks and fruit juices in comparison with food simulants

Poly(ethylene terephthalate) (PET) bottles are widely used for beverages. Knowledge about the migration of organic compounds from the PET bottle wall into contact media is of interest especially when post-consumer recyclates are introduced into new PET bottles. Using migration theory, the migration of a compound can be calculated if the concentration in the bottle wall is known. On the other hand, for any given specific migration limit or maximum target concentration for organic chemical compounds in the bottled foodstuffs, the maximum allowable concentrations in the polymer C _P,0 can be calculated. Since a food simulant cannot exactly simulate the real migration into the foodstuff or beverages, a worse-case simulation behaviour is the intention. However, if the migration calculation should not be too overestimative, the polymer-specific kinetic parameter for migration modelling, the so-called A _P value, should be established appropriately. One objective of the study was the kinetic determination of the specific migration behaviour of low molecular weight compounds such as solvents with relatively high diffusion rates and, therefore, with high migration potential from the PET bottle wall into food simulants in comparison with real beverages. For this purpose, model contaminants were introduced into the bottle wall during pre-form production. The volatile compounds toluene and chlorobenzene were established at concentrations from about 20–30 mg kg^?1 to 300–350 mg kg^?1. Phenyl cyclohexane was present at concentrations of 35, 262 and 782 mg kg^?1, respectively. The low volatile compounds benzophenone and methyl stearate have bottle wall concentrations of about 100 mg kg^?1 in the low spiking level up to about 1000 mg kg^?1 in the highly spiked test bottle. From these experimental data, the polymer specific parameters (A _P values) from mathematical migration modelling were derived. The experimental determined diffusing coefficients were determined, calculated and compared with literature data and an A _P′ value of 1.0 was derived thereof for non-swelling food simulants like 3% acetic acid, 10% ethanol or iso-octane. For more swelling condition, e.g. 95% ethanol as food simulant, an A _P′ value of 3.1 seems to be suitable for migration calculation. In relation to PET recycling safety aspects, maximum concentrations in the bottle wall were established for migrants/contaminants with different molecular weights, which correspond with a migration limit of 10 μg kg^?1. From the experimental data obtained using food simulants and in comparison with beverages, the most appropriate food simulant for PET packed foods with a sufficient but not too overestimative worse-case character was found to be 50% ethanol. In addition, it can be shown that mass transport from PET is generally controlled by the very low diffusion in the polymer and, as a consequence, partitioning coefficients (K _P/F values) of migrants between the polymer material and the foodstuff do not influence the migration levels significantly. An important consequence is that migration levels from PET food-contact materials are largely independent from the nature of the packed food, which on the other hand simplifies exposure estimations from PET.     

AB-8大孔树脂对中华补血草根多酚的吸附洗脱特性

从S-8、NKA-9、AB-8、NKA和D4020大孔树脂中筛选出AB-8树脂,研究了AB-8树脂对中华补血草根多酚的吸附洗脱特性。结果表明:AB-8树脂对中华补血草根多酚的饱和吸附时间为5h,吸附等温线符合Lang-muir模型,饱和吸附量为55.30mg/g,提取液pH值对吸附过程影响不显著;以质量浓度1.99mg/mL的提取液上柱,流速为1mL/min时,吸附泄漏点为10BV(柱床体积,1BV=30mL),饱和点为32BV,因此,采用串柱法有利于AB-8树脂吸附能力的发挥;用体积分数70%乙醇作为洗脱剂,以流速1mL/min洗脱,获得的多酚纯度为58.29%。     

Determination of Bisphenol A diglycidyl ether (BADGE) and its hydrolysis products in canned oily foods from the Austrian market

 Bisphenol A diglycidyl ether (BADGE) is determined in canned oily foods from Austria using a new simplified HPLC method. Samples are extracted with pentane, back extracted with methanol, and finally dissolved in the mobile phase (cyclohexane/tert–butyl methyl ether). Separation is performed on a normal-phase HPLC column using fluorescence detection. Verification of the BADGE-containing peak is carried out by using off-line GC-MS. Additionally, the synthesis and determination of BADGE hydrolysis products, Bisphenol A bis(2,3-dihydroxypropyl) ether (BADGE.2H₂O) and Bisphenol A glycidyl (2,3-dihydroxypropyl) ether (BADGE.H₂O) are presented. From 67 analyzed cans, containing various fatty meat or fish products, 16% were above the maximum quantity of 1 mg/kg tolerated by the European Community, 45% were in the range between 0.1–1 mg/kg, 24% between 0.02 and 0.1 mg/kg, and in 15% the BADGE concentrations were below the detection limit of 0.02 mg/kg. The hydrolysis product BADGE.H₂O was not detected in any sample, whereas BADGE.2H₂O was found in some samples up to a concentration of 0.5 mg/kg. Received: 11 May 1998 / Revised version: 1 July 1998     

Highly regenerable and storageable all-chemical based PEG-immunosensor chip for SPR detection of ppt levels of fragrant compounds from beverage samples

Simple, automated and cost-effective sensor systems intended for detection of low-molecular-weight (LMW) fragrant compounds are indispensable at automated, bottle-filling production lines of food and beverage industries. Here, we report our investigations on the development of a highly regenerable and storageable surface plasmon resonance (SPR)-based biosensor for detection of trace amounts of benzaldehyde (BZ), a characteristic fragrant compound of peach products. The sensing surface was fabricated by self-assembling of long-chain polyethyleneglycol(PEG)-dialkanethiols on thin Au-films and by followed covalent-binding of a BZ analog on the self-assembly of PEG-dialkanethiols. The all-chemical based BZ-bound PEG-monolayer chip shows specific binding affinity toward anti-BZ antibody (BZ-Ab). The principle of indirect competitive immunoassay, promising highly sensitive and consistent detection of small molecular analytes, has been applied, wherein immunospecific binding of BZ-Ab onto the BZ-bound sensor surface is inhibited by analyte BZ present in test sample. The immunosensor exhibited excellent sensitivity for BZ detection over a wide concentration range of 0.1–80 ng/ml (ppb). The BZ-bound monolayer surface was highly regenerable and storageable for repeated use of a same sensor chip. The assay reproducibility was proved through sequential multiple analysis of the same sensor chip for more than 50 regeneration cycles. Sensitivity was enhanced further by an add-on strategy involving anti-(rabbit IgG)-functionalized Au nanoparticles (nAu-Ab), with which the sensor-signal is enhanced by about 15–18 times and the amount of BZ-Ab antibody required for an analysis could be reduced to one-tenth. With the enhancement technique, detection of as low as 7 pg/ml (ppt) BZ directly from beverage samples has been demonstrated.     

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94 kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195 mM) and physiological efficiency (K_cat/K_m of 144.5 mM s). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45 °C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65 °C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54 kJ mol⁻¹, 24.89 kJ mol⁻¹, −82.34 kJ mol⁻¹ and 337.20 J mol⁻¹ K⁻¹.     

Optimised methodology for carboxymethylation of (1→3)‐β‐d‐glucan from Yeast (Saccharomyces cerevisiae) and promotion of mechanical activation

With a view to utilise yeast (1→3)‐β‐d ‐glucan as biological response modifiers with better water solubility, carboxymethylation was carried out by a two‐step alkalisation and etherification with monochloroacetic acid. Four technological parameters of carboxymethylation were investigated by orthogonal experiments for obtaining the maximum degree of substitution (DS), apparent viscosity (η) and solubility of carboxymethyl derivatives. In view of the orthogonal analysis, the optimal technological parameters were reaction temperature 50 °C, total reaction time 5 h, 3 mL of 50% sodium hydroxide as the second alkali dosage and 15 mL of 4 m chloroacetic acid. In addition, it was found that ball milling pretreatment for original (1→3)‐β‐d ‐glucan can be an advantage for carboxymethylation. By contrast, DS, η and solubility of carboxymethyl product increased 24%, 6% and 22%, respectively, suggesting the effect of ball milling pretreatment could not be neglected on improvement of DS, η and solubility for carboxymethyl products.