钙析法和酸析法所产褐藻胶质量比较的研究

分别采用酸析法和钙析法提取褐藻酸钠，对所得褐藻胶的质量和得率，以及两种方法的耗费成本进行了比较。实验结果显示：酸析法与钙析法所得褐藻胶在灰分含量、透明度、含钙量和纯度指标上没有显著差异，但是酸析法所得褐藻胶的水不溶物含量较钙析法所得样品低，粘度及凝胶强度均高于钙析法所得样品，两者差异显著，这表明酸析法所得褐藻胶的质量优于钙析法所得褐藻胶：另经分析表明酸析法较钙析法消耗原料少、耗能少、省时省水，且褐藻胶得率无显著性差异，可达到节能减排的目的。     

三氯乙酸沉淀法与硫酸铜沉淀法在液态奶蛋白质检测中适用性研究

分别利用三氯乙酸沉淀蛋白法和硫酸铜沉淀蛋白法与凯氏定氮法相结合,时液态奶蛋白质进行测定.比较研究了亚硝酸钠、硝酸铵、尿素、甘氨酸、水解蛋白等几种非蛋白氮对这两种蛋白沉淀法的影响,并对这两种方法进行比较.结果表明,对于液态奶蛋白氮的测定,三氯乙酸沉淀法与硫酸铜沉淀法在数值上存在着显著性差异,三氟乙酸沉淀法能更有效地排除非蛋白氮对液态奶蛋白氮测定的影响.     

Simultaneous application of dissolution/precipitation and surface complexation/surface precipitation modeling to contaminant leaching

This paper discusses the modeling of anion and cation leaching from complex matrixes such as weathered steel slag. The novelty of the method is its simultaneous application of the theoretical models for solubility, competitive sorption, and surface precipitation phenomena to a complex system. Selective chemical extractions, pH dependent leaching experiments, and geochemical modeling were used to investigate the thermodynamic equilibrium of 12 ions (As, Ca, Cr, Ba, SO4, Mg, Cd, Cu, Mo, Pb, V, and Zn) with aqueous complexes, soluble solids, and sorptive surfaces in the presence of 12 background analytes (Al, Cl, Co, Fe, K, Mn, Na, Ni, Hg, NO3, CO3, and Ba). Modeling results show that surface complexation and surface precipitation reactions limit the aqueous concentrations of Cd, Zn, and Pb in an environment where Ca, Mg, Si, and CO3 dissolve from soluble solids and compete for sorption sites. The leaching of SO4, Cr, As, Si, Ca, and Mg appears to be controlled by corresponding soluble solids.     

Galactosyl oligosaccharide purification by ethanol precipitation

Galactosyl oligosaccharides (GOS) are prebiotics commonly manufactured by β-galactosidase conversion of lactose, producing a mixture containing GOS, lactose, glucose and galactose. Enrichment of GOS in this mixture adds value to the product. This study aimed to determine whether the addition of ethanol to aqueous saccharide solutions could be used to selectively precipitate and enrich GOS from a reaction mixture. High concentrations of ethanol (>70% v/v) were required to induce precipitation. The total saccharide concentration was a significant variable, with higher GOS enrichment occurring at lower total saccharide concentrations. Varying the temperature between 10 and 40 °C had less impact than had changes in the concentration of saccharide or ethanol. GOS was enriched 2.3 (±0.1) fold in the precipitate formed in a solution of 90% (v/v) ethanol with 28 g/L of total saccharide at 40 °C. Performing two such precipitations sequentially reduced the monosaccharides from 48% (w/w) of the total saccharides to 4% (w/w). GOS precipitation has potential for industrial application as it is simple in operation and offers levels of purification similar to those by other techniques.     

沉淀法纯化茶皂素的工艺研究

采用沉淀的方法纯化茶皂素,考察了溶解试剂、溶解试剂体积分数、料液比、沉淀试剂、沉淀试剂用量对产品纯度和回收率的影响。试验得出较理想的纯化工艺条件为:溶解试剂为80%的乙醇,料液比1∶20,沉淀试剂为丙酮,80%乙醇与丙酮体积比1∶2。此条件下得到的茶皂素产品纯度为87.20%,回收率为71.17%。     

醇沉法纯化大豆异黄酮

大豆粕经70%乙醇提取后,提取液回收乙醇后得到浓缩液.以浓缩液为原料,采用醇沉法纯化大豆异黄酮,通过单因素和正交实验确定最佳工艺参数为:浓缩液质量分数为30%,加5倍量95%乙醇搅拌10 min进行醇沉,上清液回收乙醇后调其质量分数为5%,30℃下静置4 h,再以2 000 r/min离心10 min,对沉淀进行水洗,弃去水洗液,沉淀物于60℃干燥.在此条件下,所得产品大豆异黄酮含量达60%以上,得率为0.072 2%.     

Characterization of casein micelle precipitation by chitosans

We have found that the addition of chitosan, a cationic polymer, on whole or skim milk produces destabilization and coagulation of casein micelles that takes place without changes in the milk pH or the stability of most whey proteins. The amount of lipids recovered in the chitosan-casein aggregates was similar or higher than that obtained with rennet or acid precipitation. Approximately 70% of milk Ca2+ (approximately 750 mg/L) was found in the chitosan-induced aggregates, which is 10 and 50% higher than the amounts observed with acid or rennet coagulations, respectively. Purified alpha, beta-, and kappa-caseins were extensively precipitated by different molecular weight chitosans at pH 6.8. The phosphate groups of caseins seem not to be relevant in this interaction because dephosphorylated alpha- and beta-caseins were equally precipitated with chitosans. Analysis by optical microscopy of the chitosan-casein complex reveals that the size of the aggregates increase as the molecular weight of chitosans increase. Hydrophobic and electrostatic interactions particpate in the association and coagulation of casein micelles with chitosans of different molecular weights. The phenomenon is observed over a broad range of temperature (4 to 70 degrees C) with a reduction in the concentration of chitosan needed to precipitate the caseins that parallels a reduction in the viscosity of the chitosan solutions. Taken together, the results indicate that the electrostatic interactions may contribute energetically to the association between the two biopolymers, but the hydrophobicity of the complex would be the key determinant in the overall energetics of the reaction.     

沉淀分离技术在食品工业中的应用

介绍了沉淀分离技术的基本概念、基本原理、应用以及常用的沉淀分离方法,提供了一些常见的应用实例的基本流程.     

沉淀pH值对烟草Rubisco结晶的影响

烟草Ｒｕｂｉｓｃｏ可以通过控制离子强度与ｐＨ形成六角形、十二面体结晶。晶体的形成受Ｒｕｂｉｓｃｏ沉淀过程中的ｐＨ值的影响。对Ｒｕｂｉｓｃｏ等电点ｐＨ的研究发现，ｐＨ５．０、ｐＨ５．１、ｐＨ５．２、ｐＨ５．３、ｐＨ５．４对Ｒｕｂｉｓｃｏ结晶的影响有明显的规律性；ｐＨ低，Ｒｕｂｉｓｃｏ沉淀速率与沉淀率高，沉淀物不规则，沉淀物复溶率低，结晶速率与结晶率低，对结晶时ｐＨ与离子强度选择范围窄，不利于晶体制备；ｐＨ高，Ｒｕｂｉｓｃｏ缓慢沉淀并形成晶体，沉淀速率与沉淀率虽低，但沉淀物复溶率高，结晶速率与结晶率高，对结晶时ｐＨ与离子强度的选择范围宽，有利于晶体制备。沉淀过程中，ｐＨ５．４是Ｒｕｂｉｓｃｏ结晶制备的最佳ｐＨ值     

西峰区降水特征及变化规律--测试文章

利用1960—2010年的逐月降水资料分析了西峰区降水的变化趋势以及突变情况,采用M-K检验法和滑动t检验法分析了西峰区降水量的突变情况。结果表明：降水量总体上呈下降趋势,下降趋势主要由秋季降水量减少引起;年降水、春季降水以及秋季降水分别在1984、1993、1976年发生了一个由多到少的突变,冬季降水在1970年和2000年发生由少到多的转变,汛期降水分别在1986年和1988年出现了由多到少和由少到多的突变。     

Dynamics of precipitation of casein with carbon dioxide

Carbon dioxide is a green alternative for mineral acids (e.g., sulphuric acid) in protein precipitation. The precipitation using a gaseous precipitant differs from the conventional precipitation in the way and the rate at which the precipitant can be applied to the aqueous solution. In this paper, the consequences of using carbon dioxide were investigated for the precipitation of the milk protein casein. Product properties, such as particle size, solids content and calcium release were investigated in a batch system at various mixing conditions and gas addition rates. In addition, mass transfer coefficients were determined from pH response data.The experiments revealed a strong influence of stirring rate and gas flow rate on the particle size. The main effect of varying the gas flow was through the change of acidification rate, much alike precipitation with sulphuric acid. At high acidification rates, the particle size of casein precipitated with carbon dioxide was smaller than with sulphuric acid.     

The precipitation of proteins by carboxymethyl cellulose.

Carboxymethyl cellulose (CMC) formed insoluble complexes with beta-lactoglobulin, bovine serum albumin and Na caseinate. Maximum precipitation of the beta-lactoglobulin-CMC complex occurred at pH 3-2, whereas maximum precipitation of the bovine serum albumin. The percentage of protein precipitated by CMC decreased with increasing ionic strength of the solution, the rate of decrease being least for bovine serum albumin. At a given ionic strength, more protein was precipitated by CMC of high degree of substitution than by CMC of low degree of substitution. The change in pH (delta pH) occurring on mixing CMC and unbuffered protein solutions, each initially at the same pH, was measured. delta pH was negative for beta-lactoglobulin-CMC mixtures over the pH range 7--2 (minimum at pH 5-5). For bovine serum albumin--Cmc and Na caseinate--CMC mixtures, delta pH was positive between pH 7 and 3-2 (maximum at pH 4-5), zero at pH 3-2 and negative between pH 3-2 and 2-0 (minimum at pH 2-8).     

Poly and perfluorinated carboxylates in North American precipitation

Although perfluorocarboxylates (PFCAs) have been detected in a number of environmental matrices, there are very few reports on concentrations in precipitation. In this study PFCAs, fluorotelomercarboxylates (FTCAs), and fluorotelomer-unsaturated carboxylates (FTUCAs), were determined in wet only precipitation samples from nine sites in North America. The analytical method involved derivatization of the carboxylates and measurement of the 2,4-difluoroanilide by GC-MS. Samples from three remote sites in Canada had low concentrations of perfluorooctanoate (PFOA) (<0.1-6.1 ng/L). Significantly higher concentrations of PFOA were found at 4 northeastern United States and 2 southern urban Canadian sites, with Delaware having the highest levels (85 ng/L PFOA, with a range of 0.6-89 ng/L) and a maximum flux of 13 000 ng/m2. 8:2- and 10:2 FTCAs and FTUCAs were detected at all 4 U.S. sites and 2 urban Canadian sites (<0.07-8.6 ng/L), most frequently at the Delaware site. Longer chained PFCAs (deca-, undeca-, and dodeca-perfluorocarboxylates) were detected (<0.07-5.2 ng/L) at 2 urban Ontario sites but not determined in other samples. Air mass back trajectory results for 3 U.S. sites indicate highly populated urban areas in the New York to Washington corridor as the main sources of PFOA, although low PFOA levels associated with air masses coming off the Atlantic Ocean imply multiple sources.     

沉淀分离技术在蛋白质处理方面的应用

概述了蛋白质处理方面的几种常用沉淀分离技术的基本原理、特点、所用试剂及影响因素等.     

Evidence for surface precipitation of phosphate on goethite

Recent studies have suggested that the interaction between phosphate and goethite includes ternary adsorption/ surface precipitation as well as surface complexformation. The ternary adsorption/surface precipitation process envisioned involves the dissolution of the goethite crystal and subsequent adsorption of iron on the surface-bound phosphate. Further evidence to support the suggested process is needed. The process was investigated using two approaches. First, the sorption of iron spiked into a slurry of phosphated goethite and the effect of the iron sorption on phosphate uptake kinetics were investigated to determine whether iron would be adsorbed on the phosphated surface and whether it would enhance phosphate adsorption. Lead was also spiked into solution for comparison. Second, changes in the xi-potential of phosphated goethite were monitored with time. Adsorption of iron on the surface of phosphated goethite should increase the xi-potential of the goethite. Iron spiked into a phosphated goethite slurry was adsorbed on the solid with a concurrent adsorption of phosphate. The iron adsorption did not change the slow phosphate adsorption kinetics. Lead spiked into the solution was also sorbed but to a lesser extent than iron and with a lower apparent P:Pb mole ratio. Lead addition also changed the phosphate adsorption kinetics. With time, the xi-potential of phosphated goethite became more positive, returning almost to the potential of unphosphated goethite at low surface coverages. The slow increase in xi-potential over time indicates that long-term reactions are occurring on the goethite surface, most likely involving the dissolution of goethite to release iron and the subsequent reaction between the iron and surface-bound phosphate. These results provide strong support for the surface precipitation model, and are inconsistent with models envisioning the reaction between phosphate and the goethite surface as involving only monolayer surface complex formation.