Concentration of proteins as a result of the phase separation of water-protein-polysaccharide systems Part 1. Phase equilibria in water-milk proteins-polysaccharide systems

A thermodynamic compatibility of skimmed milk proteins and polysaccharides (high-methylated apple pectin, gum arabic and arabinogalactan) with various molecular characteristics in aqueous media has been studied. At a certain composition and pH values all the systems studied can be two-phase. one of the phases representing a concentrated solution or a gel of skimmed milk proteins. The lowest compatibility is exhibited by the water-skimmed milk proteins-polysaccharide systems and the highest one by the water-skimmed milk proteins-arabinogalactan systems. Bodies of separation of the waterskimmed milk proteins-polysaccharide systems in the composition-pH coordinates have been obtained and discussed.     

明胶应用性能的研究

文章综述了皮革废弃物明胶的一系列优异物性,如胶体保护性、成膜性、表面活性、凝胶态和溶胶态的可逆转变性、两性聚电解质特性、侧基的高化学反应活性等。及其在感光工业、食品、医药、化妆品、纺织、造纸、防腐抗蚀、化工等行业应用的情况以及所产生的技术经济效益,并对其应用前景作了展望。     

Strand-like phase separation in mixtures of xanthan gum with anionic polyelectrolytes

Binary aqueous mixtures of xanthan gum with anionic polyelectrolytes (alginate, polyacrylate, carboxymethylcellulose, λ-carrageenan, and low methoxyl pectin) exhibited phase separation above threshold concentrations of added polyelectrolyte. Dynamic oscillatory rheology showed that separation was associated with a large decrease in storage modulus, and when viewed under plane-polarised light, the dispersed phase exhibited a birefringent, strand-like morphology indicative of a liquid crystalline phase. At constant xanthan concentration, the strand thickness was inversely related to the viscosity of the added polyelectrolyte solution. Phase diagrams obtained for xanthan:alginate, and xanthan:carboxymethylcellulose mixtures showed that whilst the strands contained both xanthan and polyelectrolyte, the continuous phase was xanthan-free. Mixtures of xanthan gum with neutral polysaccharides (maltodextrin, methylcellulose) did not show phase separation, and separation was not observed when xanthan was replaced by scleroglucan a neutral polysaccharide which, like xanthan, adopts a stiff, helical structure in solution. The alginate concentration required to initiate phase separation was inversely related to alginate molecular weight, and was independent of the alginate mannuronate/guluronate ratio. Higher concentrations of alginate were required to elicit phase separation when the salt content of the mixture was increased. The results suggest that segregative phase separation, driven by repulsive interactions between polyelectrolytes, promotes the formation of liquid crystalline structures in the xanthan-rich domain. The consequence is that the decreased viscosity reported when xanthan solutions undergo liquid crystal formation, occurs at much lower xanthan concentrations, when in the presence of an anionic polyelectrolyte.     

Concentration of proteins as a result of the phase separation of water-protein-polysaccharide systems Part 2. Concentration of milk proteins

The process of concentration of skimmed milk proteins as a result of the phase separation of the waterskimmed milk proteins-polysaccharide systems has been studied. The two-phase systems were obtained by mixing and laying-up skimmed milk and polysaccharide solutions. Used as polysaccharides were pectin, gum arabic and arabinogalactan. The establishment of the phase equilibrium in all the systems under study involves the concentration of the skimmed milk proteins and dilution of the polysaccharide solution. For the water-skimmed milk proteins-pectin system one can observe a transition of the lactose and calcium ions from the milk to the pectin solution. Depending on the concentration conditions, the concentration of the skimmed milk proteins in the protein phase increases by a factor of 5-12 as compared with that in milk. The dispersed phases of the water-skimmed milk proteins-gum arabic and water-skimmed milk proteinsarabinogalactan systems are represented by gel-like particles with skimmed milk concentrations of 30 and 45 wt %, respectively. A value of 30 wt % for the skimmed milk concentration seems to correspond to the critical concentration of the lyotropic gelation of the skimmed milk proteins. The largest involvement of the skimmed milk proteins in the protein phase (91%) of the water-skimmed milk proteins-polysaccharide system was observed to take place at 10°C. α-Lactalbumin is the major protein component of the polysaccharide phase. This concentration process can be defined as a membraneless osmosis. The rate of the process was studied and the time of the establishment of equilibrium in the two-phase systems obtained by mixing and laying-up the solutions was estimated. The greater effectiveness of the membraneless osmosis was shown to be mainly ensured by a fairly large size of the interphase surface of the systems under study.     

明胶应用性能的研究

文章综述了皮革废弃物明胶的一系列优异物性,如胶体保护性、成膜性、表面活性、凝胶态和溶胶态的可逆转变性、两性聚电解质特性、侧基的高化学反应活性等.及其在感光工业、食品、医药、化妆品、纺织、造纸、防腐抗蚀、化工等行业应用的情况以及所产生的技术经济效益,并对其应用前景作出了展望.     

菊粉在乙醇溶液中成胶行为规律的研究

为探索菊粉在乙醇溶液中成胶行为及凝胶质构变化规律,采用加热/冷藏的方法制配制菊粉凝胶,考察质量分数35%、45%和55%的菊粉溶液在体积分数0-40%乙醇溶液中的成胶行为,利用质构仪分析不同条件下凝胶的质构特性。试验发现随菊粉质量分数的增加其在乙醇溶液中的成胶能力增强;乙醇体积分数对菊粉成胶能力影响显著,当乙醇体积分数低于30%时,随着其体积分数的增加菊粉的成胶能力和持水性显著提高;当乙醇体积分数高于30%时,随着其体积分数的提高菊粉的成胶能力和持水性呈下降的趋势。质构仪分析表明,增加菊粉含量可显著提高凝胶的质构特性,而乙醇对凝胶质构有双向作用,随乙醇体积分数的增加,凝胶质构特性呈现先增大后减少的趋势,对硬度、强度、黏附力及黏着性的影响拐点为20%,而对凝聚性和咀嚼性的影响拐点为10%。     

Modeling Gelation of Egg Albumen and Ovalbumin

The Flory gelation theory and a new protein gelation model were used to investigate the aggregation reactions of egg albumen and ovalbumin. Results showed that 178 to 267 ovalbumin monomers were required to establish the initial ovalbumin gel at the gel point temperature, 81°C. The gel point temperature for egg albumen was 72°C by the Instron and 60°C by protein solubility. The values of the activation energy rate constants for the formation of the different aggregates in the pre-gel stage suggested that the larger ovalbumin aggregates were more reactive than the smaller ones.     

Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

凝胶剂性能与凝胶软糖(2)

1.3生产工艺根据配方中水的用量,预先将部分水与淀粉调成淀粉乳,其余的水与淀粉乳一起加入砂糖和淀粉糖浆中,加热溶化,不断搅拌,煮沸熬至所需的浓度时,加入着色剂和香味料,然后以粉模成型法(Mogul Type Process)将熬好的糖浆浇注到粉模中,送入烘房干燥达到所需的产品水分含量要求,再进行脱模包     

Protease-Induced Aggregation and Gelation of Whey Proteins

Aggregation and gelation of whey proteins induced by a specific protease from Bacillus licheniformis was revealed by turbidimetry, size exclusion chromatography, dynamic light scattering and rheology. The microstructure of the gel was examined by transmission electron microscopy. During incubation of 12% whey protein isolate solutions at 40°C and pH 7, the major whey proteins were partly hydrolyzed and the solution gradually became turbid due to formation of aggregates of increasing size. The viscosity of the hydrolysate simultaneously increased and eventually a gel formed. The gel had a particulate type of microstructure. We hypothesized that the aggregates forming the gel were held together by noncovalent interactions.     

Some Studies on Starch Gelation

The mechanical behaviour of starch gels at small static deformations was investigated. In the concentration range 6 - 30% w/w starch gels behave as Hookean solids with a linear dependence between shear modulus and concentration. At a fixed concentration the shear modulus of starch gel increases in the order potato <maize <pea. The starch gel was considered to be a composite in which swollen gelatinized starch granules reinforce an interpenetrating amylose gel matrix. The factors which influence the mechanical behaviour of this composite are discussed.     

魔芋葡甘露聚糖的凝胶化特性

用测定动态粘弹性的方法探讨了碱存在下天然及乙酰化魔芋葡甘露聚糖(KGM)的凝胶化动力学特性。通过固有粘度和光散射的测定决定了KGM样品的分子量和其他分子参数。研究使用的KGM样品经乙酰化处理后发现其已被降解,但经乙酰化后的KGM的分子量与乙酰化度几乎不相关, 约为天然KGM分子量的1/2。当碱凝固剂(Na2CO3)的浓度为固定值时,观察到了凝胶化时间随KGM浓度的增大和温度的升高而缩短,但随乙酰化度的增加而变长的倾向。乙酰化处理后的KGM的脱乙酰基反应和后续的凝胶化过程比天然KGM缓慢,但能形成更有弹性的凝胶。以上现象表明,乙酰基团的存在对KGM的凝胶化过程起着极其重要的作用。在较为缓慢的凝胶化过程中,能够形成数量更多且分布均匀的凝胶网络结点,从而得到更具弹性的凝胶。     

Gelation of casein-whey protein mixtures

Heated milk consists of a mixture of whey protein-coated casein micelles and soluble whey protein aggregates. The acid-induced gelation properties of heated milk are consistently different from those of unheated milk—i.e., a shift in gelation pH, stronger gels, and a different microstructure of the gels. In this study we investigated the role of the different fractions of denatured whey proteins on the acid-induced gelation, the gel hardness, and the microstructure. Both whey protein fractions contribute to the observed shift in gelation pH, although by a different mechanism. Obtaining gels with high gel hardness occurs most effectively when all denatured whey proteins are present as whey protein aggregates. It was observed that disulfide bridge exchange reactions during the acid-induced gelation at ambient temperature play an important role for both whey protein fractions. Additionally, disulfide interactions seem to occur between the aggregates and the casein micelles during the gel state. In this study, we show the development of a new approach for confocal scanning laser microscopy measurements—i.e., separate staining of the proteins in milk. By using this method, we were able to determine that, although whey protein aggregates are not linked to the casein micelles, they nevertheless gel at the same moment. This work adds to a better understanding of the role of denatured whey proteins during acid-induced gelation and could improve the effective use of whey proteins.     

Associative phase separation involving canola protein isolate with both sulphated and carboxylated polysaccharides

Associative phase separation within admixtures of canola protein isolate (CPI) and anionic polysaccharides (alginate and ι-carrageenan) was investigated as a function of pH (1.50–7.00) and biopolymer weight mixing ratio (1:1–50:1, w/w) by turbidimetric analysis. Solubility of formed complexes was also studied vs. protein alone as a function of pH. In both CPI–polysaccharide systems, critical pH, associated with the onset of soluble and insoluble complexes, shifted to higher pHs as the mixing ratios increased to a 20:1 CPI–polysaccharide ratio, and then became constant. Complexes formed primarily through electrostatic attractive forces with secondary stabilisation by hydrogen bonding. Solubility of the CPI–alginate system was significantly enhanced relative to CPI alone or CPI–ι-carrageenan.     

盐析分相固相萃取-液相色谱法测定梨汁中苯甲酰脲农药

乙腈作萃取剂,盐析分相提取,弗罗里硅土固相小柱净化,反相高效液相色谱法测定梨汁中的除虫脲和氟苯脲。Diamonsil C18色谱柱,甲醇:水=85:15流动相,流速1.0mL/min,室温,260nm紫外检测。在0.5～100μg/mL范围内2组分线性良好,除虫脲和氟苯脲平均回收率分别为75.11%和83.16%,相对标准偏差为1.03%和1.74%,方法检出限0.0086μg/mL和0.0136μg/mL。     

双水相体系萃取分离L-组氨酸的研究

采用PEG-(NH4)2SO4双水相体系萃取分离L-组氨酸。实验考察了pH、温度、聚乙二醇加入量、L-组氨酸初始浓度、硫酸钠及L-赖氨酸的存在对萃取分离的影响。结果表明:L-组氨酸在该双水相体系的分配系数K随体系pH和聚乙二醇加入量的增大而减小,随着L-组氨酸初始浓度和L-赖氨酸加入量的增大而增大,而温度和Na2SO4的影响不明显;L-组氨酸在该双水相体系的萃取率η随体系pH和聚乙二醇加入量的增大而增大,随着L-组氨酸和L-赖氨酸加入量的增大而减小,而温度和Na2SO4的影响同样不明显。     

肌原纤维蛋白热诱导凝胶特性研究进展

肌原纤维蛋白质是肌肉中一类重要的结构蛋白质群,它对于肉食制品的品质和特性具有非常重要的影响.肌原纤维蛋白的凝胶特性是形成肉制品独特的质构、保水性、乳化性以及感官特性的决定性因素.本文介绍了肌原纤维蛋白凝胶机制、功能特性及其影响因素,为进一步了解肉制品加工特性提供一定理论指导.     

结冷胶的成胶特性及应用研究进展

本文综述了结冷胶的凝胶特性，凝胶机制和流变学特性，对结冷胶的凝胶原理、显微结构也进行了阐述。并介绍了结冷胶复配体系的特点及其应用前景。     

W/O emulsions: solvent phase separation for pH determination

The aim of this investigation was to find a measure for the phase separation by substances capable of rapidly demulsifying emulsions, which is necessary for the correct determination of the pH in cosmetic W/O emulsions. Results are reported for pH determination in the separated water phase of W/O emulsions containing metal soaps, micropigments and thermally unstable active agents. Of the substances investigated – solvents of different polarity and electrolytes – the best were mixtures of the polar butanol, which has a surfactant-like molecular structure and limited oil and water solubility, and the low polar trichloromethane which in particular has strong fat- and wax-dissolving properties. The combination achieved within 10 to 20 min at room temperature complete phase separations. Stable preparations, based on a polymer emulsifier (cetyl dimethicone copolyol), were demulsified as well as metal soap stabilized creams which characteristically contain a high amount of stabilizing waxes. The so-called solvent phase separation method was confirmed by using model preparations of known pH. During the investigation of model emulsions matching those used in practice, it was found, for example, that magnesium and aluminium stearate as well as various types of micronized zinc oxide which are dissolved or dispersed in the oil phase can shift the pH of the aqueous phase during manufacture from an initial acidic value through neutral to pH 8–10. Time-related and temperature-related changes in pH in formulations containing thermally unstable additives such as dihydroxyacetone or urea can be easily monitored.