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1.
在质量浓度为20 g/L大豆分离蛋白(SPI)中分别加入终质量浓度分别为1、3 g/L的L-精氨酸(L-Arg)和L-赖氨酸(L-Lys),以不加氨基酸、仅调节与上述溶液对应相同pH的样品为处理对照,制备水包油型(O/W)乳状液。通过物化手段及光谱技术表征SPI结构、溶液的物化性质和乳化性能以及乳状液的微观结构。结果表明,L-Arg、L-Lys可提升SPI溶液的pH,显著提高蛋白溶解度(从77.1%到最大91.3%)、降低浊度,促进蛋白分子疏水性基团折叠而降低蛋白疏水性,有效降低SPI在溶液中的粒径大小并提高蛋白带电量,降低蛋白所成乳状液的乳滴大小且提高其均匀性;改性后的SPI比对照组的乳化活性和乳化稳定性分别提高了31.4%和78.9%;相比之下,L-Arg比L-Lys更能有效地改性SPI结构而获得更高的乳化活性,且乳化活性随着两种氨基酸浓度的增加而增强。  相似文献   

2.
在质量浓度为20 g/L大豆分离蛋白(SPI)中分别加入终质量浓度均为1、3 g/L的L-精氨酸(L-Arg)和L-赖氨酸(L-Lys),以不加氨基酸、仅调节与上述溶液对应相同pH的样品为处理对照,制备水包油型(O/W)乳状液。通过物化手段及光谱技术表征SPI结构、溶液的物化性质和乳化性能以及乳状液的微观结构。结果表明,L-Arg、L-Lys可提升SPI溶液的pH,显著提高蛋白溶解度(从77.1%到最大91.3%)、降低浊度,促进蛋白分子疏水性基团折叠而降低蛋白疏水性,有效降低SPI在溶液中的粒径大小并提高蛋白带电量,降低蛋白所成乳状液的乳滴大小且提高其均匀性;改性后的SPI比对照组的乳化性和乳化稳定性分别提高了31.4%和78.9%;相比之下,L-Arg比L-Lys更能有效地改性SPI结构而获得更高的乳化性,且乳化性随着这两种氨基酸浓度增加而增强。  相似文献   

3.
将CaCl2加入质量浓度分别为120 g/L银杏果分离蛋白及5.0 g/L果胶(两种酯化度,分别为38%和76%)的复合溶液中,使钙离子最终质量浓度分别0.05 g/L、0.11 g/L和0.22 g/L,基于此复合溶液制备热诱导复合凝胶。采用粒径和ζ-电位法、流变学及质构学、蛋白凝胶电泳技术、红外光谱和扫描电镜技术表征成胶分子物化性质、成胶性过程及复合凝胶功能性和微观结构,以探讨Ca2+对蛋白/果胶复合物胶凝性影响及其潜在的机制。结果表明,Ca2+降低成胶复合物大小但不改变复合物的带电量;降低热诱导凝胶流变学特性,形成结构松散的复合凝胶;进而弱化凝胶质构特性但对其持水性无显著影响。Ca2+破坏蛋白与果胶间的作用,竞争性地与果胶结合。随着Ca2+浓度增加,以上效应越为显著。相比之下,高酯化度果胶比低酯化度果胶对Ca2+更为敏感。  相似文献   

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以白果分离蛋白(GSPI)为成胶基质材料,制成溶液向其中分别加入γ-氨基丁酸(GABA)和L-瓜氨酸(L-Cit),均质后再将溶液pH分别调至5.0,6.0和7.0,制备热诱导凝胶。采用物化分析法、机械力学、蛋白凝胶电泳,SEM及FTIR表征GSPI/氨基酸溶胶的物性、凝胶性和微观结构,并探讨他们对GSPI凝胶性能的影响及其机理。结果表明,以上两种氨基酸对GSPI溶解度无提升作用,但能显著降低蛋白疏水性;GABA促进溶胶聚集并降低其ζ-电位,而L-Cit在pH 7.0时则促进解聚和提高ζ-电位;两者均能促进蛋白分子疏水基团向内折叠。在pH 5.0和pH 7.0时,以上两种氨基酸特别是L-Cit显著提高蛋白凝胶性能,而在pH 6.0时则弱化凝胶性能。其影响机制可能是氨基酸与GSPI之间的静电作用,而这种效应依赖于所在体系的pH。  相似文献   

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为减少乳清蛋白用量,用马铃薯蛋白替代乳清蛋白质量的一半制备热诱导凝胶。通过色度、质构、水分分布、流变等考察了总蛋白浓度(40~80 g/L)对于复合凝胶物理性质的影响。结果表明,复合凝胶的最低成胶浓度为50 g/L,与乳清蛋白80 g/L的最低成胶浓度相比,乳清蛋白用量减少了2.2倍。总蛋白浓度从50 g/L提高到80 g/L时,复合凝胶偏黄,硬度和弹性分别增加了5.28倍和5.90%,但束缚水含量降低了3.63%。储能模量(G'')显示较弱的频率依赖性。CLSM和SEM观察表明,蛋白浓度80 g/L的复合凝胶孔隙尺寸小,具有由颗粒聚集体组成的均一致密网络结构,因而具有较高G''。红外光谱表征结果表明,复合凝胶中β-折叠和β-转角约占蛋白二级结构的70%。溶解度测试结果表明,维持复合凝胶结构的作用力中氢键和疏水相互作用的贡献高于二硫键。  相似文献   

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转氨酶是苯丙酮酸酶法制备L-苯丙氨酸的关键酶源,为提高转氨酶的发酵产酶密度,文章采用补料分批培养方式对大肠杆菌A5发酵产酶进行了研究。优化的补料培养工艺为:初始葡萄糖质量浓度5 g/L,初始氮源体积分数为玉米浆5 mL/L、蛋白胨质量浓度1.5 g/L,控制发酵过程pH值7.5,当葡萄糖质量浓度下降为2 g/L,开始每隔2 h补加质量浓度为120 g/L的葡萄糖溶液,从8 h起每隔2 h补加20 mL/L玉米浆+6 g/L蛋白胨及0.6 g/L的4种氨基酸溶液(L-甲硫氨酸、L-缬氨酸、L-异亮氨酸和L-谷氨酸)。在此条件下发酵培养24 h,菌体干质量浓度达10.5 g/L,比优化前产酶量提高了126%。  相似文献   

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泡沫分离技术是一种浓缩分离蛋白十分经济有效的方法,然而发酵液中消泡剂的存在限制了该技术直接应用。在以蛋清蛋白为目标蛋白质,聚环氧丙烷环氧乙烷甘油醚(PGE)为消泡剂的模拟溶液中,通过加入表面活性剂来进行泡沫分离。初步探索了溶液pH、表面活性剂甜菜碱,高分子多糖羧甲基纤维素钠(SCMC)、无机盐NaCl对蛋白质泡沫吸附行为的影响。实验表明,当甜菜碱通过静电作用与蛋白质结合形成疏水性更强的复合物时,可有效促进蛋白质在界面的吸附。初始蛋白浓度为0.5g·L-1,消泡剂浓度为0.016g·L-1,甜菜碱浓度0.4g·L-1,溶液pH6.0时,有78%的蛋白质浓缩在泡沫液中,其富集比为3.73。SCMC和NaCl均能促进蛋白质的分离,只是当SCMC浓度超过0.15g·L-1时,其收率的提高是以富集比的降低为代价。  相似文献   

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铀矿石化学浸出与细菌浸出沉淀产物的比较   总被引:1,自引:0,他引:1  
为了研究细菌在铀矿石细菌浸出中的作用及产物,设计了Fe~(2+)浓度分别为2.01和4.63g/L的化学浸出和细菌浸出4种矿粉实验与Fe~(2+)浓度为4.63g/L的化学浸出和细菌浸出2种矿块实验.监测了矿粉浸出体系中pH值、Eh值及铀浓度随时间的变化,并对铀矿石化学浸出和细菌浸出的矿块表面形貌、元素及矿物组成进行了分析.结果表明,在4种矿粉浸出体系中,Fe~(2+)浓度分别为2.01和4.63g/L的化学浸出铀矿石浸出率分别为64.86%和69.13%,细菌浸出浸出率分别为94.35%和92.80%.试块化学浸出后表面主要为硅酸盐类矿物,细菌浸出后表面主要是黄钾铁矾类矿物.细菌浸出体系中含适量铁可有效降低沉淀量,提高浸出率.  相似文献   

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以L.谷氨酸一钠作为浸出剂浸出低品位氧化铜矿的常见铜形态-碱式碳酸铜,根据配位化学理论,研究了Cu(Ⅱ)-Glu2--CO32--H2O体系中Cu(Ⅱ)的配合平衡热力学,并绘制了L-谷氨酸一钠浓度0~3 mol/L和pH 5~14内的热力学平衡图,研究了L-谷氨酸-钠浓度、pH和游离CO32-浓度对L-谷氨酸-钠浸出碱式碳酸铜的影响,并对热力学计算结果进行了实验验证.结果表明,铜离子浓度理论计算值与实验值相对误差的绝对平均值为5.32%,所选数据的准确性较好,同时也说明用谷氨酸一钠浸出低品位氧化铜矿是可行的.  相似文献   

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利用摇瓶实验对纯Fe2(SO4)3溶液浸出高砷金精矿进行了研究,考察了温度及Fe3+浓度的影响,并与细菌直接浸矿进行了对比.同时,在Fe2(SO4)3溶液中加入高密度嗜中温氧化亚铁硫杆菌、嗜中温氧化硫硫杆菌、中度嗜热西伯利亚硫杆菌,考察其对Fe2(SO4)3溶液的辅助浸出作用.结果表明,Fe3+溶液化学浸出可迅速溶解高砷金精矿,随温度升高,浸出率先升后降,80℃时达最大;浸出前期Fe3+浓度的积累对浸出速率影响不大,初始Fe3+浓度越高As的浸出率越高,但当Fe3+浓度高于40g/L,由于沉淀严重,浸出率降低;连续浸出情况下,Fe3+浓度可维持恒定,10g/L的Fe3+可保持较快的矿物浸出速率.对照实验表明,较高的矿浆浓度对浸矿菌生长繁殖有显著影响.高密度浸矿菌可维持Fe2(SO4)3溶液中较高的Fe3+浓度并及时消除反应产生的S层的阻碍,有利于Fe2(SO4)3溶液对矿物的浸出.  相似文献   

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Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.  相似文献   

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In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.  相似文献   

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A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by 1H MAS NMR. For direct comparison purposes, an SiO2 coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N2 absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.  相似文献   

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Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.  相似文献   

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Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.  相似文献   

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