超声处理大豆分离蛋白与肌原纤维蛋白共混体系乳化性及凝胶性研究

建立了经过不同程度超声改性（200/400 W、10/20min）的大豆分离蛋白（SPI）与肌原纤维蛋白（MP）的复合体系（W/W=1∶4）,对复合体系的乳化性、凝胶性（流变性、持水性、质构性）及微观结构进行观察。然后确定凝胶形成过程中主要交互作用（疏水交互作用、氢键、二硫键）与凝胶性之间的关系,结果表明,SPI经过10/20min、200/400 W超声处理后会影响MP-SPI复合体系的乳化性、凝胶性。其中MP-USPI（400 W、20min）复合体系乳化性及凝胶性最好,EAI和ESI分别为18.25m2/g和78.88%,持水性提高了28.05%,硬度提高了21.5%,弹性为0.88mm。凝胶结构变得致密、均匀,不规则孔洞变小。随着SPI变性程度的升高,氢键都有下降趋势,疏水交互作用增加,二硫键变化不显著。     

湿热预处理对刺芹侧耳蛋白质理化性质、结构和功能特性的影响

以刺芹侧耳Pleurotus eryngii蛋白为研究对象,分别将其在50℃、60℃和70℃下热处理0至30min,探讨了湿热处理对刺芹侧耳蛋白理化性质、结构和功能特性的影响。结果表明,湿热处理后刺芹侧耳蛋白的疏水性先升高后降低（P<0.05）,总巯基含量先降低后升高（P<0.05）,此外,刺芹侧耳蛋白二级结构受到影响,在50℃和60℃下进行湿热处理后,其α螺旋含量降低,而在70℃下则升高,β-折叠含量减少,β-转角和不规则卷曲增加;功能特性方面,刺芹侧耳蛋白在50℃、60℃和70℃湿热处理的20min内,其乳化和发泡性能分别提高（P<0.05）。因此,湿热处理可以增强刺芹侧耳蛋白的功能特性,并改善其在食品加工中的应用。     

荧光探针在大鼠胃粘膜表面疏水性研究中的应用

采用１－萘胺－８－磺酸（ＡＮＳ）为疏水探针,对大鼠胃粘膜表面疏水性作了研究,结果表明：以ＡＮＳ（２５μｍｏｌ／Ｌ）与胃粘膜表面刮取物（胃粘液凝胶层）混合后的萤光强度（正常为１．２３±０．１９ＲＦＵ／胃）可代表该粘液层的疏水性;以不同浓度ＡＮＳ与胃粘液混合后的萤光强度呈饱和趋势,可用Ｓｃａｔｃｈａｒｄ作图法求得粘液中ＡＮＳ的最大萤光强度（２．４６７±０．６３８ＲＦＵ／胃）和相对亲和系数（０．０３２±０．０１６）,它们可分别代表胃粘液中疏水基团的总量和单个基团的疏水性,从而可阐明胃粘膜被盐酸损伤后凝胶层粘液的ＡＮＳ萤光减弱,系其疏水基团总量减少,而非单个基团的疏水性改变所致。     

酸法脱酰胺修饰对刺芹侧耳蛋白质消化性和功能特性的影响

为研究酸法脱酰胺修饰对刺芹侧耳蛋白质的功能特性和消化性的影响,本研究以刺芹侧耳粉为原料,通过碱提酸沉法提取刺芹侧耳蛋白质,并采用0.175mol/L盐酸、57.5℃改性,改性时间为121min 5s,制备出脱酰胺修饰蛋白质,探索脱酰胺改性对蛋白质的消化性及功能特性的影响。结果表明：脱酰胺修饰可提高刺芹侧耳蛋白质的溶解性、持油性、起泡性和乳化性,但对其持水性的改善作用不明显;同时脱酰胺修饰蛋白质表面疏水性和荧光强度增大,蛋白质巯基和二硫键含量变化不明显;体外消化率提高,消化产物的多肽含量降低,游离氨基酸含量增大。酸法脱酰胺修饰可在一定程度上有效改善蛋白质的功能特性和提高蛋白质的体外消化水平。     

气候变化对不同水分条件下柿幼树光合作用的影响

以两年生柿树为试材,研究了高浓度CO₂处理（700 μmol·mol^-1）、高温处理（日平均温度高于正常日平均温度约5 ℃）、高温和高浓度CO₂复合处理及对照（温度为外界环境温度,CO₂浓度380 μmol·mol^-1）对不同水分条件下柿树净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、水分利用效率(WUE)、叶绿素含量和叶绿素荧光参数F_v/F_m、F_v/F_o的影响.结果表明:高温和高浓度CO₂复合处理使处于各水分条件下的柿树T_r、G_s减小,WUE增大;在高、中水分条件(分别为田间持水量的75%～85%和55%～65%)下高温和高浓度CO₂复合处理使柿树P_n增大,在低水分条件(为田间持水量的35%～45%)下使柿树P_n减小.高浓度CO₂处理使处于各水分条件下的柿树P_n、WUE增大,G_s、T减小.高温及高温和高浓度CO₂复合处理下WUE均受土壤水分状况的影响,并随土壤含水量的升高而升高.与对照相比,高浓度CO₂处理还提高了各水分条件下植株叶片水平的水分利用效率、叶绿素a、叶绿素b、叶绿素（a+b）、类胡萝卜素含量及F_v/F_m和F_v/F_o,缓解了水分胁迫,提高了柿树的抗逆能力.     

可注射更昔洛韦温敏型原位凝胶剂的研究

目的：构建温敏型三嵌段共聚物,研究其理化性质以及用其制备的可注射更昔洛韦温敏型原位凝胶剂的制剂特性。方法：以聚乙二醇（PEG）作为亲水嵌段,丙交酯（LA）和β- 丁内酯（β-BL）的无规共聚物PBLA 作为疏水嵌段,采用开环聚合法合成温敏型三嵌段共聚物PBLA-PEG-PBLA,并对其理化性质进行表征,考察其溶液的胶凝温度/ 临界凝胶浓度、流变学性质、通针性和溶蚀行为以及以更昔洛韦作为模型药物、用其制得的可注射载药温敏型原位凝胶剂的体外释放特性。结果：合成的PBLA-PEG-PBLA 嵌段共聚物重均分子质量在6 000 左右,多分散系数为1.5 左右;其溶液临界凝胶浓度（g?mL-1）为5%~10%,质量浓度（g?mL-1）在10%~25% 时胶凝温度为31~35 ℃,接近并略低于体温;其凝胶在低温下储能模量与黏度较小,当温度接近相转变温度后两者迅速增大;其载药凝胶剂累计释放量经拟合显示遵循一级动力学方程,并呈扩散释药机制。结论：较低质量浓度[10%~15%（g?mL-1）] 的PBLA-PEG-PBLA 更符合玻璃体注射要求,更适用于制备可注射载药温敏型原位凝胶剂。     

飞虱虫疠霉液培菌丝的凝胶化及其杀蚜活性*

用丙烯酰胺淀粉凝胶包埋飞虱虫疠霉(Pandora delphacis)液培菌丝,制成含营养和不含营养的虫霉凝胶,并测试其产孢能力及对桃蚜(Myzus persicae)的侵染力。经持续9 d产孢观察,相同菌丝量条件下,含营养的虫霉凝胶的累计产孢量(1910.9 个/mm2）为不含营养的虫霉凝胶的3.14倍（608.5个/mm2）和对照（纯液培菌丝）的4.69倍（387.5个/mm2）。用虫霉凝胶的“孢子浴”接种桃蚜居群（成蚜与不同龄期若蚜的混合）,在2.23个/mm2的剂量下,接种后第7 d的死亡率达82.3%。结果表明,丙烯酰胺淀粉凝胶作为载体材料,与飞虱虫疠霉的基本生物学特性相容,对虫霉的剂型化具有重要意义     

罗望子胶的流变学性质及凝胶特性研究

罗望子胶的流变学性质和凝胶性能与常见胶种有较大差别。升高温度、提高浓度会增大其表观粘度,这与其单糖组成和多糖结构的特殊性有关。在低浓度下(2%,w/v)罗望子多糖胶水溶液为牛顿流体,而当浓度升高到2.5%(w/v)后呈现非牛顿流体的特性。罗望子多糖胶属于必须有糖存在下才能形成凝胶的氢键结合法。除此之外,罗望子胶粉也可与乙醇通过氢键作用形成高强度凝胶,这种性质是其他多糖胶所不具备的。实验发现,在乙醇体积分数为15%,胶粉浓度1%,85℃恒温搅拌10 min条件下形成的凝胶强度近1 000 Bloom g。在该凝胶体系中适当添加葡萄糖或蔗糖可提高其持水能力。     

高剪切乳化技术辅助提取荷叶水不溶性膳食纤维工艺优化及其物性分析

为扩大荷叶在食品加工中的开发应用性,研究采用高剪切乳化技术辅助提取荷叶水不溶性膳食纤维(insoluble dietary fiber,IDF),优化提取工艺;测定其基本物性,并与常规粉碎、球磨式粉碎处理进行对比。结果表明,在剪切转速8000 rpm剪切时间4 min,酸液浓度0.25 mol/L,酸解温度45℃条件下荷叶IDF得率最高,为83.84%。此荷叶IDF水溶性13.81%,持水性5.65 g/g,持油性1.97 g/g,膨胀性1.93 mL/g。与球磨式粉碎相比,处理时间短,荷叶纤维呈束状、层次分明,荷叶纤维内质未被完全破坏;产品水溶性较低,持水性和膨胀性较高。高剪切乳化技术在食品纤维组分的加工中具有较好的应用潜力。     

飞虱虫疠霉液培菌丝的凝胶化及其杀蚜活性

用丙烯酰胺淀粉凝胶包埋飞虱虫疠霉（Pandora delphacis)液培菌丝,制成含营养和不含营养的虫霉凝胶,并测试其产孢能力及对桃蚜（Myzus persicae)的侵染力。经持续9d产孢观察。相同菌丝量条件下,含营养的虫霉凝胶的累计产了解量（1910.9个/mm^2)为不含营养的虫霉凝胶的3.14倍（608.5个/mm^2)和对照（纯液培菌丝）的4.69倍（387.5个/mm^2)。用虫霉凝胶的“孢子浴”接种桃蚜居群（成蚜与不同龄期若蚜的混合）,在2.23个/mm^2的剂量下,接种后第7d的死亡率达82.3%。结果表明,丙烯酰胺淀粉凝胶作为载体材料,与飞虱虫疠霉的基本生物学特性相容,对虫霉的剂型化具有重要意义。     

Impact of the structure of arabinoxylan gels on their rheological and protein transport properties

Water-extractable arabinoxylan (WEAX) gels exhibiting different structural, rheological and protein transport properties were obtained upon laccase treatment of WEAX solutions, by modifying (i) the initial ferulic acid (FA) content of WEAX from 2.3 to 1.6 μg/mg AX or (ii) the AX concentration of the WEAX solution from 0.5 to 2.0% (w/v). WEAX gels with di and tri-ferulic acid (di-FA, tri-FA) contents varying from 6.2 to 3.2 μg/ml gel and from 0.61 to 0.27 μg/ml gel, respectively, were obtained. In parallel, increases in gel mesh sizes from 201 to 331 nm and reduction of G′ of gels from 160 to 12 Pa were observed. The differences in structural and rheological characteristics of WEAX gels were reflected in their capacity to load and release proteins of M_w ranging from 43 to 669 kDa. The possibility of modulating protein release from WEAX gels makes these gels potential candidates for the controlled delivery of proteins.     

Rheology and fracture of mixed ι- and κ-carrageenan gels: Two-step gelation

It is shown that under certain circumstances, on cooling mixed ι- and κ-carrageenan solutions, the two forms gel separately at different temperatures, with the ι form gelling first. This ‘two-step gelation’ was only observed when both sodium and potassium ions were present, with a sodium/potassium mole ratio of between 1 and 100. For such mixed gels, a κ fraction as low as 2·5% of the total carrageenan has significant effects on their rheology, both at low deformation and fracture. In these systems, the κ form, gelling in the presence of an existing ι gel, produces measurable rheological effects at much lower concentrations than if it were alone. This behaviour can be used as a sensitive test of the ‘rheological purity’ of samples of ι-carrageenan.     

Gel properties and molecular forces of lamb myofibrillar protein during heat induction at different pH values

The gel properties and molecular forces of the Aohan Merino lamb myofibrillar protein (MP) were investigated during heat induction at different pH levels. The effects of pH values (from 5.0 to 8.5) on the lamb MP gel textures and water-holding capacities were analyzed. The protein gels had the lowest water-holding capacity and a disordered microstructure at pH 5.5 (P < 0.05) and had the lowest level of hardness at pH 6.5 (P < 0.05). The hardness and water-holding capacity were found to be the highest at pH 8.0 (P < 0.05), which coincided with a compact and ordered microstructure. At these three representative pH values, hydrophobic interactions were the main forces that were observed during gel formation, but the pH level also influenced the formation of ionic and hydrogen bonds. Different mechanisms of gel formation were therefore observed at different pH values. In conclusion, the formation of heat-induced gels with different properties was a result of the dominant molecular forces that are regulated by pH. These findings provide a theoretical basis for the innovation of heat-induced gel lamb products.     

Mixed gels made from protein and κ-carrageenan

The rheological behavior of mixed gels made from soy or pea protein concentrates with the addition of κ-carrageenan was investigated using uniaxial compression and dynamic measurements. Pea protein concentrate (PPC) exhibited greater synergy with κ-carrageenan than soy protein concentrate (SPC) in relation to gel strength, gel stiffness and pH stability. A modified Takanayagi treatment of dynamic measurements indicated a shift in the continuous phase from protein to κ-carrageenan at concentrations of 4–8% κ-carrageenan in the total solids. This shift occurred at lower concentrations when PPC was used compared to SPC.     

Thermally induced protein gelation: gelation and rheological characterization of highly concentrated ovalbumin and soybean protein gels

In order to optimize the use of proteins as functional ingredients in foods, one needs more insight into the effects of environmental conditions (pH, ionic strength, and temperature) on the functional properties of protein. This paper summarizes the results of an extensive study on heat-induced gelation of ovalbumin (egg-white protein) and soybean protein in the concentration range from 10 to 35 g/100 g. It was the aim of the study to relate the rheological properties of thermally induced protein gels to the microstructure of the gel and the physicochemical properties of the constituent protein. The gelling behavior of the protein was quantified with rheological techniques, and the physical properties of the gels were determined, at small and large deformations. From the swelling/dissolving behavior of the gels in various media, the nature of the crosslinks was determined qualitatively. The microstructure of the gels was determined with electron microscopy. Nmr-spectroscopy was applied in order to elucidate changes in conformation during heating. It was found that the formation of a continuous covalently crosslinked network is not a prerequisite for thermally-induced protein gelation. The properties of a gel strongly depend on the pH at which the gel is formed. When heat-set at high pH(pH～10), a homogeneous, strong, and almost transparent gel is formed, consisting of flexible crosslinked protein gels. Heat-setting at low pH (pH 5) leads to the formation of a heterogeneous and weak gel, which easily exudes water. This gel consists of crosslinked aggregated protein. The ionic strength of the solvent in which the protein is dissolved and heat-set has a much lower effect on gel properties.     

The Effectiveness of Cryoprotectants in Inhibiting Multiple Freeze-Thaw-Induced Functional and Rheological Changes in the Myofibrillar Proteins of Common Carp (Cyprinus carpio) Surimi

The purpose of the present study was to investigate the effects of cryoprotectants (4 % sucrose?+?4 % sorbitol) on functional and rheological changes, including thermal stability, dynamic rheological and emulsifying properties, gel texture profile, gel whiteness, gel water-binding capacity, and gel microstructure, in the myofibrillar proteins (MP) of common carp (Cyprinus carpio) surimi subjected to multiple freeze-thaw cycles (FT, 0, 1, 3 and 5 times). Increased numbers of FT cycles were accompanied by reduced thermal transition temperature (T _max), reduced enthalpy of denaturation (ΔH) (P?<?0.05), and enhanced susceptibility to thermal aggregation. The observation of the gel microstructure indicated that the FT processes produced empty spaces and changed the aggregate gel structure into a coarser-stranded network. The addition of cryoprotectants significantly prevented the reduction of MP thermal stability (P?<?0.05). The protective effect on protein functionality was demonstrated by the cryoprotectant’s efficacy in maintaining the three-dimensional gel network by small-strain oscillatory rheological testing and increasing the emulsifying capacity and emulsion stability of the MP. The FT process caused a decrease (P?<?0.05) in whiteness, water-binding capacity, and texture (hardness, springiness, and gumminess) of the MP gels, which were reduced by the addition of cryoprotectants. Overall, the FT-induced loss of the abovementioned functional and rheological properties was significantly reduced by the presence of cryoprotectants.     

Neuronal protein gene product 9.5 (IEF SSP 6104) is expressed in cultured human MRC-5 fibroblasts of normal origin and is strongly down-regulated in their SV40 transformed counterparts

Neuronal protein gene product 9.5 (PGP 9.5) most likely identical to ubiquitin carboxyl-terminal hydrolase isozyme LI (UCH-LI) has been reported to be expressed almost exclusively in neuronal and neuroendocrine tissues. By two-dimensional (2D) immunoblotting, comigration and microsequencing of proteins recovered from 2D gels we have identified PGP 9.5/UCH-LI as polypeptide IEF SSP 6104 (M_r = 27000, PL = 5.49) in the comprehensive 2D gel cellular protein database of human embryonal lung MRC-5 fibroblasts [(1989) Electrophoresis 10, 76–115; (1990) Electrophoresis 11, 1072–1113]. This protein is expressed at high levels in quiescent and proliferating cultured normal fibroblasts and is strongly down-regulated (about 10 times) in their transformed counterparts.     

Metal ion substitution in phospholipase C (Bacillus cereus) and its effect on enzyme stability

The effect of guanidinium chloride solutions on the circular dichroism of native (ZnZn-) and apophospholipase C (Bacillus cereus) indicated marked protein unfolding at denaturant concentrations of 1.4–1.8 M and 0.1–0.6 M, respectively. With the apoenzyme near u.V. region circular dichroism bands remained even after all ordered structure appeared to have been lost. Apophospholipase C bound two equivalents of Ni²⁺, Cd²⁺, Co²⁺, Mn², Pb²⁺ or Cu²⁻, with only the latter metal causing marked changes either in circular dichroism or protein fluorescence relative to the native enzyme. Stability in guanidinium chloride for the metalloforms of phospholipase C decreased in the order: ZnZn->ZnCo->NiNi->CoCo->PbPb->CdCd->MnMn-apoenzyme.     

The thiol-specific antioxidant protein from human brain: gene cloning and analysis of conserved cysteine regions

The complete cDNA encoding human thiol-specific antioxidant protein (PRP) was isolated from a human brain cDNA library in the λZap expression vector. An open reading frame (ORF) was identified and found to encode a polypeptide of 197 aa with a M_r of 21 729. The cDNA contained 98 bp of 5′-untranslated sequence (UTR) and 259 bp of 3′-UTR containing a poly(A) signal, AATAAA. Expression of the human PRP cDNA in Escherichia coli yielded a functionally active protein. The observed local sequence homologies between human PRP and other homologous proteins whose functions have not yet been defined give important insight into elucidating the biochemical function of a new protein family which has highly conserved regions containing cysteine.     

The effect of hydroxyl radicals on the rheological performance of hylan and hyaluronan

Shear flow, dynamic oscillation and extensional viscosity measurements were used to compare the rheological performance of several hylan samples (M_v 1.6, 3.2, 3.7, 4.7 and 5.6×10⁶) and hyaluronan (M_v 1.4 and 1.8×10⁶) before and after hydroxyl radicals (√OH) induced degradation. It was found that the higher molecular weight cross-linked structure of hylan was more resistant to degradation than hyaluronan and that this superior stability was reflected in various rheological parameters. The √OH degradation of the initial hylan and hyaluronan samples produced a range of polysaccharides based on hylan and hyaluronan with molecular weight covering a range from 0.5–5.6×10⁶. The rheological parameters associated with the polysaccharides could then also be studied. Zero shear values of the complex viscosity (η*), dynamic viscosity (η′) and shear viscosity (η) were calculated using the method of Morris¹ and shown to approach the same value at zero shear or frequency. An adaptation of the method of Gibbs et al.² gave a ‘master curve’ for the storage and loss modulus of hyaluronan and hylan, which encompasses a 10-fold molecular weight and a 5-fold concentration variation. In all instances for hylan, the storage modulus predominates over the loss modulus, whereas for hyaluronan, the reverse is true, demonstrating the greater elasticity of hylan throughout the whole experimental range of molecular weights and concentrations.