Enzymatic hydrolysis of organic phosphates adsorbed on mineral surfaces

Esters of phosphoric acid constitute a sizable fraction of the total phosphorus supply in the environment and thus play an important role in the global phosphorus cycle. Enzymatic hydrolysis of these esters to produce orthophosphate is often a required reaction preceding phosphorus uptake by plants and microorganisms. Generally, adsorption to environmental particles is assumed to limit this process. Here we show, however, that the rate of enzymatic hydrolysis of glucose-1-phosphate (G1P) adsorbed on goethite by acid phosphatase (AcPase) can be of the same order of magnitude as in aqueous solution. The surface process releases carbon to the solution whereas orthophosphate remains adsorbed on goethite. This hydrolysis reaction is strictly an interfacial process governed by the properties of the interface. A high surface concentration of substrate mediates the formation of a catalytically active layer of AcPase, and although adsorption likely reduces the catalytic efficiency of the enzyme, this reduction is almost balanced by the fact that enzyme and substrate are concentrated at the mineral surfaces. Our results suggest that mineral surfaces with appropriate surface properties can be very effective in concentrating substrates and enzymes thereby creating microchemical environments of high enzymatic activity. Hence, also strongly adsorbed molecules in soils and aquatic environments may be subjected to biodegradation by extracellular enzymes.     

Arsenate adsorption structures on aluminum oxide and phyllosilicate mineral surfaces in smelter-impacted soils

A clearer understanding of arsenic (As) retention and transport in forest soils impacted by copper smelter emissions may reduce risks to human health and provide insight into As behavior in the vadose zone. On Vashon-Maury Island in Puget Sound, As is predominantly associated with the fine (< 63 microm) fraction of surficial soils. X-ray diffraction of oriented samples from the < 2 microm size fraction indicate that clinochlore isthe dominant phyllosilicate. X-ray absorption spectroscopy (XAS) was employed to examine As oxidation state and local coordination environment in impacted soil samples. Arsenic is present as As(V) in tetrahedral coordination with oxygen, associated with aluminum (Al) octahedra in bidentate binuclear (bridging) structures with As-Al distances of 3.15 - 3.16 angstroms. Including multiple scattering (MS) paths derived from the arsenate tetrahedron in esperanzaite significantly improved the match between XAS fine structure (EXAFS) data and models generated from theoretical phase and amplitude functions. The data are interpreted to indicate arsenate adsorption onto poorly crystalline aluminum oxyhydroxides and/or the edges of clinochlore interlayer hydroxyl sheets with constrained geometries causing MS to be important This implies that As initially released from the smelter as particulate As(III) and As(V) oxides was oxidized, dissolved, and adsorbed onto soil minerals and colloids; no evidence for relic arsenic oxide was observed. Physical transport of arsenic oxide particles and As adsorbed on soil colloids may account for limited downward migration of As within the soil column. The oxidizing and mildly acidic pH conditions in the upper vadose zone promote stable sorption complexes; barring substantial changes in soil chemistry, As is not expected to experience significant mobilization.     

Association of micro-organisms with the inner surfaces of bottles of non-carbonated mineral waters

Three brands of non-carbonated mineral water were tested using rinsing techniques and electron microscopy for attachment of bacteria to the inner surface of the bottle. Rinse solutions used were distilled water (DW), DW+0.1% Tween 80, DW+0.1% salt, DW+0.1% SDS. The microbial population attached to the inner surface of the bottles varied between 5-;44% depending upon the brand and the batch of water examined. Most of the attached bacteria (80-;90%) were removed during the first two rinses. Species (Burkholderia cepacia, Methylobacterium mesophilicum, Acidovorax delafieldii, Brevundimonas vesicularis, Xanthomonas campestris) attached to the bottle surface were found to be the same as those in the mineral water. Measurement of the cell surface hydrophobicity of these species failed to prove this as the only factor for attachment to bottle surfaces. Scanning electron micrographs of inner surfaces of bottles showed bacterial attachment of densities of 10⁷cells cm^-;2, with evidence of microcolony but no visible biofilm formation.     

微波加热稳定米糠研究

本文探讨影响微波加热稳定米糠的有关因素，对微波加热后米糠温度，水分蒸发和过氧化物酶残余活力进行测定，结果表明，米糠水分含量在微波加热稳定过程中起着重要作用，适当提高米糠含水率和微波功率有利于米糠稳定处理，经微波稳定处理的米糠于25℃储藏8周，酸值上升幅度远低于未处理米糠。     

Experimental study of the adsorption of an ionic liquid onto bacterial and mineral surfaces

Ionic liquids are being developed as a replacement for volatile organic solvents in a range of industrial applications. These liquids have a vanishingly small vapor pressure, making them an attractive alternative to the volatile organic solvents. However, a thorough assessment of the environmental impact of the use of ionic liquids requires a more complete understanding of their fate and transport in environmental systems. Toward this end, we measured the adsorption of the ionic liquid 1-butyl, 3-methylimidazolium chloride (Bmim CI) onto a range of surfaces meant to represent those commonly found in the near-surface environment. We measured adsorption onto the Gram-positive soil bacterial species Bacillus subtilis, onto gibbsite, onto quartz, and onto Na-montmorillonite. We conducted experiments as a function of pH, solid:solute ratio, time, and ionic strength. The experimental results reveal that Bmim CI is unstable in water below pH 6 and above pH 10 and that it exhibits pH independent and ionic strength dependent adsorption onto Na-montmorillonite with 0.4, 0.8, 1.0, 1.2, and 2.0 g/L of clay. We observed no adsorption of the Bmim CI onto B. subtilis (3.95 or 7.91 g (dry weight) bacteria/L) at pH 5.5-8.5 or onto gibbsite (500 or 1285 g/L) or quartz (1000 and 2000 g/L) over the pH range 6-10. Calculated distribution coefficient (KD) values for Bmim CI onto the Na-montmorillonite change as a function of ionic strength; the 10(-4) M ionic strength KD value is 1735 +/- 269 L/Kg, and the 10(-1) M ionic strength KD is 1133 +/- 291 L/Kg. Our results suggest that the geologic retardation of this class of ionic liquid, if present as a dissolved contaminant in the subsurface, would be significant when a significant fraction of interlayer clays are present. However, adsorption onto other common geologic and biological surfaces is likely to be minimal, and the ionic liquids may travel unimpeded in groundwater systems in which these types of surfaces dominate.     

流化床涂布法制备稳定化酶

采用流化床涂布法制备稳定化木聚糖酶,以提高其耐热机械性能。以0.2%海藻酸钠(SA)作为包被剂,木聚糖酶酶粉作为芯材,酶活能得到100%回收。随着包被剂用量的提高,木聚糖酶的耐热性基本不变,但其耐受高温水蒸汽的能力与对照组相比提高了一至两个数量级,其综合耐热机械性能也从1.6倍提高至3.7倍。对比不同包被剂对木聚糖酶的稳定化效果,发现羧甲基纤维素钠(CMC)对酶粉的包被效果略好于SA,多糖包被剂中复配蔗糖或硫酸铵能显著提高酶的耐热机械性能。     

紫外照射对留胚米稳定性的影响

为了提高留胚米的稳定性,采用紫外照射对留胚米进行稳定化处理。采用单因素实验及响应面分析研究紫外照射对留胚米脂肪酶灭活率的影响,同时考察留胚米水分损失率、碎米率和爆腰率的变化。结果表明:紫外照射最佳条件是照射时间11.50 min,照射距离为4.5 cm,初始含水量13%,此时脂肪酶灭活率66.73%、且碎米率增加0.12%、爆腰率增加1.63%、水分散失率增加0.38%,处于可以接受范围内,因此可以选为紫外照射稳定留胚米的工艺参数。     

蒸汽-滚筒干燥对稳定化白糠的影响

通过蒸汽-滚筒干燥方法对白糠的稳定化效果进行研究,白糠在加水量15%、平铺厚度4cm、蒸汽压力0.15MPa条件下处理时间15 min,然后利用滚筒干燥方法进行干燥,同时强化灭酶,在滚筒蒸汽压力0.70 MPa条件下干燥30 s取得了理想稳定化效果,脂肪酶灭活率达87.3%,产品水分含量6.5%。稳定化白糠在40℃,相对湿度60%条件下储藏12周,与稳定化处理前相比,稳定化白糠的脂肪酸值、过氧化值和羰基值分别是白糠原料的8.0%、17.1%和18.7%。白糠经蒸汽-滚筒干燥方法稳定化处理后总酚酸含量增加了5.2%,膳食纤维含量降低了0.39%,γ-谷维素、γ-氨基丁酸和α-生育酚含量分别降低了3.33%、3.87%和4.62%,维生素B1、B2和B6含量分别降低了5.08%、4.48%和5.21%,整体损失在5.0%左右,与挤压膨化稳定化方法相对比,白糠的营养功能性成分保留率提高了22.57%～40.13%,该方法稳定化处理白糠,可以有效保留白糠营养功能性成分,延长货架期。     

糙米微波稳定化技术研究

对微波处理糙米的稳定效果进行研究。以米糠作为对照组,探讨比较二者过氧化物酶、脂肪酶的酶灭活情况,同时考察大米品质的变化。结果表明：微波对糙米稳定化效果非常显著,而大米品质也受到影响,因此为获得大米品质损失最小、灭酶效果最好的工艺条件,通过三因素三水平响应面分析,对糙米微波稳定进行优化得最佳工艺参数为微波功率700W、微波时间100s、水分含量21%,理论脂肪酶活、碎米率分别为15.66μmol/(g ·h)、18.92%,实际脂肪酶活、碎米率分别为16.25μmol/(g ·h)、17.33%,强化储藏4周后的游离脂肪酸值较未处理糙米减少13.7%,说明所得的糙米微波稳定工艺可用于糙米稳定的实践。     

微波加热对麦胚品质稳定性研究

探讨了微波处理时间、麦胚原始水分含量及35℃条件下储藏时间对微波加热处理的麦胚稳定性的影响和麦胚蛋白质溶解特性及乳化性影响.结果表明,微波加热原始水分麦胚能够部分抑制脂肪水解酶活性,微波处理时间90 s最佳,120 s麦胚发生焦糊;微波处理麦胚90 s,麦胚中水分由11.83%降到4%,贮藏4周内游离脂肪酸(FFA)由14.82%增加到19.34%,增加1.3倍,而对照组则增加到28.76%,增加1.9倍.麦胚蛋白质在pH 4.0时溶解性最低,pH 6.0时溶解性达到最大值,大于pH 6.0后溶解特性处于稳定状态.微波处理麦胚90 s,麦胚蛋白质的乳化性最大(pH 5～9),pH 5～9范围内,蛋白质的乳化活性影响不大.     

Stabilization of gelatin gels by sugars and polyols

Gelatin gels are known to be stabilized by sugars and polyols. We have made a quantitative study of this effect with the aim of determining the molecular mechanisms involved. The sugars and polyols added were sucrose, glucose, fructose, sorbitol, glycerol and ethylene glycol, at concentrations within the range 0 – 500 g/kg. With the exception of ethylene glycol, their effects were almost identical — at 400 g/kg of additive the shear modulus of the gels increased by a factor of 2.5 and the rate of gelation increased by a factor of 2. Ethylene glycol produced smaller changes. Sucrose at 500 g/kg increased the melting temperature by 3.9°C. The increased rate of gelation could be simply explained as due to increased melting temperature. The junction zones in gelatin gels are regions of collagen triple helix structure and added sugar or polyol increased the proportion of protein reverting to this conformation. The contribution per amino acid residue to the free energy of formation of junction zones changed from –0.34 kJ/mol in water to –3.44 kJ/mol with sucrose at 500 g/kg. The junction zones became smaller (averaging 15 turns of triple helix in water and 0.8 turns in sucrose at 500 g/kg) but at the same time more numerous. This results in a more extensive gel network and consequently greater rigidity. Stabilization appears to be due to preferential hydration of the unfolded polypeptide in the presence of sugar or polyol — rather than a direct effect of the additive on the intermolecular forces stabilizing the collagen triple helix.     

Stabilization of ascorbic acid by microencapsulation in liposomes

Ascorbic acid was encapsulated with high efficiency inside liposomes. In this form, its stability was enhanced compared to that in free aqueous solution, and particularly in the presence of a number of factors widespread in foods, which normally lead to its rapid degradation. Possible mechanisms for these stabilizing effects are discussed. Amongst other potential applications, these findings are relevant to the preservation of nutritional supplements of vitamin C in solution and to the development of naturally derived antioxidant systems for food protection.     

PAN纤维的接触式预氧化工艺

环境保护和可持续性发展对社会发展越来越重要,节能技术的使用已是经济成功的关键。随着这一趋势的发展,越来越多有前景的轻质材料(如碳纤维)得以应用。探讨了亚琛工业大学纺织技术研究中心(ITA)在碳纤维技术领域的研究,介绍了作为i Carbon项目一部分的聚丙烯腈纤维接触式预氧化工艺。     

Influence of pH on plutonium desorption/solubilization from sediment

Aqueous Pu concentrations and oxidation state transformations as a function of pH were quantified and compared between sorption/desorption studies and literature solubility values. When Pu(V) was added to a red subsurface sandy-clay-loam sediment collected near Aiken, South Carolina, 99% of the Pu sorbed to the sediment within 48 h. Throughout the study, > or = 94% of the Puaq remained as Pu(V), whereas < or = 6% was Pu(VI) and < or = 1% was Pu(IV). This is in stark contrast to the sorbed Pu which was almost exclusively in the +4 oxidation state. The fraction of aqueous Pu (Puaq/Pusolid) decreased by >2 orders-of-magnitude when the contact time was increased from 1- to 33-days, presumably the result of Pu(V) reduction to Pu(IV). The desorption studies were conducted with a sediment that had been in contact with Pu (originally as PuIV(NO3)4) for 24 years. At near neutral pH, a decrease of 1-pH unit resulted in almost an order-of-magnitude increase in the concentration of Puaq (7.5 x 10(-10) M at pH 7 and 3.6 x 10(-9) M at pH 6). Similar to the sorption experiment, > or = 96% of the Puaq was Pu(V/VI). The Puaq concentrations from the desorption experiment were similar to those of the Pu(V) amended sorption studies that were permitted to equilibrate for 33 days, suggesting that the latter had reached steady state. The Puaq concentrations as a function of pH followed near identical trends with literature solubility values for PuO2(am), except that the desorption values were lower by a fixed amount, suggesting either Pu sorption was occurring in this sediment system or that a more crystalline, less soluble form of Pu existed in the sediment than in the literature water-PuO2(am) system. Based on Pu sorption experiments and measured sediment surface charge properties as a function of pH, the latter explanation appears more likely. pH had a more pronounced effect on solubility and Puaq concentrations than on sediment charge density (or Puaq oxidation state distribution). Slight changes in system pH can have a large impact on Pu solubility and the tendency of Pu to sorb to sediment, thereby influencing Pu subsurface mobility.     

水分调节对原料米糠微波稳定化的增效作用

食品物料中大都有水分存在,而水分子作为极性分子在微波场中有着极强的响应,本研究从优化微波稳定米糠工艺的角度出发,以米糠脂肪酶残余活力和酸价为主要指标值,着重考察米糠水分含量对微波稳定米糠效果的影响。研究发现,提高米糠水分含量对微波有明显的增效作用,通过单因素和正交试验得出微波稳定米糠影响因素大小依次为:米糠含水率>微波功率>微波处理时间;微波稳定优化水平组合为米糠含水率23%、微波功率800 W、微波处理时间105 s,该优化条件下米糠脂肪酶残余活力为20.24%,显示出高抑酶率且对米糠无热损伤。同时,以原始米糠为对照,将按上述最优条件处理的米糠和仅以功率800 W、时间105 s处理的米糠进行储存对比实验,定期测定米糠酸价以验证协同水分调节的最优微波稳定方案的稳定效果,实验证明,水分调节和微波协同作用处理后的米糠储存时间最长,分别为原始米糠储存时间的3.4倍和仅微波处理米糠的1.5倍,证实基于水分调节的微波处理对米糠稳定有显著效果。