沙棘渣制备微晶纤维素的酶解条件优化

沙棘浆加工过程中产生酚酸含量高的果渣,因其苦涩无法被饲料工业大量转化,利用其进行微晶纤维素制备是潜在可行的解决途径。以粗提沙棘渣纤维素为处理对象,使用S10041纤维素酶水解,选取液料比、酶添加量、酶解时间、酶解温度、缓冲液p H值、离心转速、烘干温度及纤维素粉碎度8个因素,通过单因素试验和PlackettBurman因素筛选,并经过最陡爬坡试验和Box-Behnken试验优化了酶解条件,随后对制得的微晶纤维进行结构分析。结果表明:在液料比49∶1(m L/g)、酶添加量68 U/m L、酶解时间1.3 h、离心转速3 640 r/min时制得的沙棘微晶纤维素聚合度为355±1.02,与棉微晶纤维素聚合度最为接近。方差分析表明4个选定因素对指标均产生独立影响,因素交互作用对指标影响不显著(P=0.10)。微观结构显示沙棘微晶纤维表面结构更疏松,红外图谱对比沙棘和棉花两种微晶纤维官能团结构相似。     

纳米甘薯渣纤维素对糖尿病大鼠血糖及血脂水平的影响

目的：探讨纳米甘薯渣纤维素对糖尿病大鼠血糖及血脂的影响。方法：选用40 只雄性Sprague-Dawley（SD）大鼠随机分组为5 组,其中1 组大鼠喂食基础饲料作为空白组,另外4 组采用链脲佐菌素（streptozotocin,STZ）诱导大鼠建立糖尿病模型,分为模型对照组（MC组）、普通甘薯渣纤维素组（OC组）、微晶甘薯渣纤维素组（MCC组）和纳米甘薯渣纤维素组（CNC组）,实验期28 d,测定大鼠体质量、采食量、空腹血糖、糖化血清蛋白、血清胰岛素、肝糖原及血脂水平等指标。结果：模型对照组大鼠的采食量,空腹血糖、糖化血清蛋白、血脂水平均显著高于空白组（P＜0.05）,体质量、胰岛素和肝糖原含量明显下降（P＜0.05）,说明造模成功,糖尿病大鼠表现出相应的症状。喂食不同粒度甘薯渣纤维素的糖尿病大鼠,其体质量、血清胰岛素和肝糖原水平有所增加,而空腹血糖、糖化血清蛋白、血脂水平等都有所下降,其中喂食纳米甘薯纤维素的糖尿病大鼠指标变化具有显著性差异（P＜0.05）。结论：从甘薯渣纤维素粒度分析,可以看出随着甘薯渣纤维素粒度的减小,其对糖尿病大鼠血糖血脂的调节作用愈加明显,其中纳米甘薯渣纤维素具有较好的调节血糖血脂水平的作用。     

磁性纤维素微晶稳定O/W型Pickering乳液特性分析

将磁性纤维素微晶复合物作为乳化剂稳定O/W型Pickering乳液,考察磁性纤维素微晶复合物添加量、油水比及均质次数对Pickering乳液的影响。结果表明：Fe3O4粒子的平均粒径约为10 nm,纤维素微晶经过Fe3O4修饰后平均长度约为14.2 μm,表面形态由光滑棒状转变为粗糙形态;纤维素微晶的傅里叶变换红外光谱表明在565 cm－1处出现Fe—O键的吸收峰;Fe3O4、纤维素微晶和磁性纤维素微晶复合物的接触角（θ）分别为46.67°、42.48°、69.58°;稳定Pickering乳液的最佳条件：磁性微晶复合物的添加量1.5 g/100 mL,油水比3∶7,均质次数2 次;磁性微晶复合物初始磁化强度值为56.8 emu/g,经5 次重复使用后磁化强度值降为4.2 emu/g。     

Functional Properties of Chitin and Chitosan

Chitin (poly-β (1?4)-N-acetyl-D-glucosamine), chitosan (deacetylated chitin) and microcrystalline chitin (redispersible chitin powder) were compared with microcrystalline cellulose to examine the use of those cellulose-like biopolymers as functional additives for potential application in food formulations. Water binding, fat binding and emulsifying properties were studied. Baking tests were performed with 0.5–2.0% (flour basis) of microcrystalline chitin added to wheat flour bread or to potato protein fortified (8% potato protein concentrate) white bread. Water-binding capacity and fat binding capacity of chitin, chitosan and microcrystalline chitin ranged from 230–440s (w/w) and from 170–315% (w/w). Chitosan and chitin did not produce emulsions but microcrystalline chitin showed good emulsifying properties and was superior to microcrystalline cellulose. Increasing concentration of microcrystalline chitin (0.12–0.8 g/100 ml water) had a positive effect on emulsion stability. Addition of microcrystalline chitin increased specific loaf volume of white bread and protein fortified breads. Water addition of 65% (flour basis) was found to be optimum for “chitin breads.”     

响应面试验优化苹果渣微晶纤维素制备工艺

研究利用苹果渣纤维素制备微晶纤维素的方法过程。在水解时间50min、水解温度100℃条件下,采用响应曲面设计法设计、分析,研究酸水解纤维素制备微晶纤维素时,各因素料液比、盐酸质量分数和次氯酸钠添加量及3因素间两两交互作用对微晶纤维素得率的影响。结果表明,各因素对得率影响的显著性表现为盐酸质量分数＞料液比＞次氯酸钠添加量。分析等高线和响应面,得出各因素两两之间的交互作用对得率都显著。通过求解回归方程得出最佳工艺条件为料液比1:25(g/mL)、盐酸质量分数6%、次氯酸钠添加量2.5mL/100mL,此条件下微晶纤维素制备得率达到69.5%。     

Optimization of enzymatic oligomerization reaction conditions for three milk protein products via ceteris-paribus approach

Via a ceteris-paribus approach, optimum reaction conditions for an oxidoreductase- (lactoperoxidase; laccase; glucose oxidase) induced oligomerization of milk proteins were assessed for three different milk protein products (sodium caseinate; whey protein isolate; skim milk powder).Optimum protein monomer modification conditions were enzyme- and substrate-specifically identified, yielding protein monomer modification levels of, e.g., 58% in case of lactoperoxidase-induced (w/w = 5% protein; 1.8 μmol hydrogen peroxide/mg protein; 4.8 U lactoperoxidase/mg protein; 50 °C; 1 h; pH 7.0), 92% in case of laccase-induced (w/w = 5% protein; 0.02 μmol chlorogenic acid/mg protein; 0.01 U laccase/mg protein; 40 °C; 1 h; pH 7.0) and 86% in case of glucose oxidase-induced (w/w = 1% protein; 0.5 U glucose oxidase/mg protein; 40 °C; 16 h; pH 7.0) modification of total milk proteins from skim milk powder.The study for the first time provides a comprehensive overview over reaction conditions facilitating high degrees of milk protein monomer modification upon oxidoreductase-induced oligomerization in regard to food protein tailoring via application of less substrate- and reaction-specific enzymes than transglutaminase.     

Mineral Binding Characteristics of Lignin, Guar Gum, Cellulose, Pectin and Neutral Detergent Fiber under Simulated Duodenal pH Conditions

Effective stability constants (K_cff) and amount of Fe bound by lignin, cellulose, guar gum, low and high methoxy pectin and NDF were determined under simulated duodenal pH conditions. Guar gum bound 8.4 μmol Fe per g fiber with the greatest affinity (K_cff= 6.27 × 10⁶) of any of the fibers studied; NDF, high methoxy pectin, and one of the binding sites of lignin bound 5.0. 5.0, and 19.5 μmol Fe, respectively. per g fiber, with a K_cff > 10⁵, and cellulose bound Fe so weakly that an effective stability constant could not be calculated. Lignin had two distinct binding sites for Fe, Zn, and Cu with the high affinity sites binding in the following order: Fe > Cu > Zn, but with twice as much Cu bound as either Fe or Zn.     

Rheological properties of aqueous blends of high purity barley β-glucan with high purity commercial food gums

Rheological properties such as flow behaviour, viscosity, viscoelasticity, and thixotropy of solutions of β-glucan purified from barley fibre concentrate and twelve commonly used food gums, alone and in combinations, were characterised using an oscillatory rheometer. Pure gums and gum combinations were evaluated at 0.5% and 0.75% (w/w) total gum concentration in aqueous medium, whereas the β-glucan/gum ratios were kept at 90/10 or 80/20 (w/w). Viscosity synergism was observed for β-glucan solutions in combination with xanthan, iota-carageenan, and carboxymethyl cellulose. However, barley β-glucan blends with lambda-carageenan, Konjac, high- and low-methoxyl pectin, microcrystalline cellulose, alginate, and gum arabic showed marked lowering of the viscosity compared to β-glucan alone. In addition, β-glucan/xanthan gum blends demonstrated improved shear tolerance compared to xanthan dispersions alone, and soft gel transformation. Non-thixotropic behaviour was observed for 0.5 and 0.75% (w/w) β-glucan dispersions and its gum combinations. None of the gum combinations studied demonstrated thixotropy.     

海藻酸钠/微晶纤维素复合壁材的性能及对精油微胶囊缓释性的影响

将微晶纤维素与海藻酸钠混合,形成复合壁材用于制备精油微胶囊。通过探讨微晶纤维素的添加对壁材溶液流变性以及壁材膜机械性能、透油性、吸湿性和透水性的影响,研究海藻酸钠/微晶纤维素复合壁材对柠檬精油微胶囊包埋效率及精油释放速率的影响。结果表明,复合溶液表观黏度随微晶纤维素含量的增加而增加,随温度的升高而逐渐下降,且都比海藻酸钠的表观黏度高。红外光谱结果表明海藻酸钠和微晶纤维素相容性很好,通过氢键形成复合体系。微晶纤维素较大程度增强壁材复合膜的机械性能,膜的透油性、吸湿性和透水性随微晶纤维素的增加而降低。4%微晶纤维素含量的复合壁材对柠檬精油微胶囊包埋效率比未添加的效率提高了9.2%,并且微晶纤维素的添加能有效延缓微胶囊精油在高温和高湿环境下的释放。     

微晶纤维素的现状及其前景

微晶纤维素是可自由流动的纤维素晶体组成的天然聚合物,它是天然纤维素经稀酸水解并经一系列处理后得到的极限聚合度的产物。微晶纤维素作为天然植物纤维原料已经进入全面应用阶段。本文论述了微晶纤维素的特性、理化性质、制备方法及其应用,较全面地介绍了微晶纤维素。     

木质纤维素酸水解利用现状

介绍了木质纤维素酸水解的应用现状,对纤维素酸水解制备微晶纤维素及微晶纤维素的应用、纤维素酸水解制备燃料乙醇作了简要概述。     

Batch Fractionation of Bovine Caseins with Diethylaminoethyl Cellulose,

To obtain gram amounts of the various casein fractions, whole casein dispersed in 3.3 M urea (pH 7.4) containing 77 mg/L dithiothreitol was fractionated at 5°C by ion-exchange adsorption on diethylaminoethyl cellulose, Whatman DE 52, with stepwise salt extraction. Fractions were obtained by successive extraction with .00, .035, .085, .12, and .175 M sodium chloride, which upon further purification by appropriate recycling, yielded the minor β-casein (previously named γ-caseins), κ-caseins, major β-casein, α_s2-caseins, and α_s1-caseins, respectively.     

微晶纤维素染色工艺研究

用黑色活性染料对微晶纤维素进行染色，考察染液的pH值、盐（硫酸钠、碳酸钠）加入量、皂洗剂用量、皂洗时间对微晶纤维素上染率的影响，得到了较佳的染色工艺条件。     

麦草秸秆微晶纤维素的制备工艺

研究以麦草秸秆为原料制取微晶纤维素的制备工艺。运用添加乙酸的乙醇法低污染制浆技术,溶出麦草秸秆中的木素、半纤维素等杂质,采用全无氯的臭氧及过氧化氢漂白工艺对粗纤维素进行漂白,然后通过盐酸水解和稀碱处理制备得到微晶纤维素。结果表明,试验制取的微晶纤维素符合合成革用微晶纤维素的标准。在提取粗纤维素过程中催化剂乙酸的最佳用量是2%。水解时间对微晶纤维素产品聚合度的影响较大。麦草秸秆制取微晶纤维素的最佳工艺条件为:液比1:15,水解温度70℃,水解时间90min。碱处理的工艺条件为:碱浓5%,温度80℃,处理时间30min。     

响应面法优化油茶粕培养里氏木霉酶系活力条件及发酵工艺研究

以油茶粕为底物,对里氏木霉发酵进行培养,研究了油茶粕比例、微晶纤维素添加量、接种量和pH对里氏木霉纤维素酶活力的影响。在单因素实验的基础上,采用响应面分析,优化发酵条件为:油茶粕比例为8. 6%,微晶纤维素添加量为0. 93%,接种量为12. 48%,pH值为4. 9。在该条件下,羧甲基纤维素酶活力为8. 47 U/mL,微晶纤维素酶活力为9. 28 U/mL,纤维二糖酶活力为5. 05 U/mL,滤纸酶活力为5. 44 U/mL。     

Role of Tryptophan 38 in Loading Substrate Chain into the Active-site Tunnel of Cellobiohydrolase I from Trichoderma reesei

Cellobiohydrolase I from Trichoderma reesei ( Tr Cel7A) is one of the best-studied cellulases, exhibiting high activity towards crystalline cellulose. Tryptophan residues at subsites -7 and -4 (Trp40 and Trp38 respectively) are located at the entrance and middle of the tunnel-like active site of Tr Cel7A, and are conserved among the GH family 7 cellobiohydrolases. Trp40 of Tr Cel7A is important for the recruitment of cellulose chain ends on the substrate surface, but the role of Trp38 is less clear. Comparison of the effects of W38A and W40A mutations on the binding energies of sugar units at the two subsites indicated that the contribution of Trp38 to the binding was greater than that of Trp40. In addition, the smooth gradient of binding energy was broken in W38A mutant. To clarify the importance of Trp38, the activities of Tr Cel7A WT and W38A towards crystalline cellulose and amorphous cellulose were compared. W38A was more active than WT towards amorphous cellulose, whereas its activity towards crystalline cellulose was only one-tenth of that of WT. To quantify the effect of mutation at subsite -4, we measured kinetic parameters of Tr Cel7A WT, W40A and W38A towards cello-oligosaccharides. All combinations of enzymes and substrates showed substrate inhibition, and comparison of the inhibition constants showed that the Trp38 residue increases the velocity of substrate intake ( k _on for forming productive complex) from the minus side of the subsites. These results indicate a key role of Trp38 residue in processively loading the reducing-end of cellulose chain into the catalytic tunnel.     

Effect of fibre size on the quality of fibre-enriched layer cakes

The effects of fibre type (wheat bran, oat bran, cellulose microcrystalline), size (50, 80, 250 μm) and percentage of substitution (0%, 12%, 24%, 36%) on batter and layer cake characteristics were determined. Batter density, and the rheological parameters (G′ and G″) increased with fibre size, but the flow index decreased. Especially with 20% wheat bran, large-sized fibre gave the most firm, chewy and yellow cakes, while providing the most significant sensory differences with the control. Cakes with microcrystalline cellulose were the most similar to the control. All cakes obtained high sensory scores, indicating that they were not disagreeable for consumers. It is possible to obtain high quality cakes when adding up to 20% of fibre, but selection of an adequate fibre is necessary.     

流动分析法测定烟草中的纤维素

建立了测定烟草中纤维素含量的流动分析法。采用纤维素酶酶解烟草中的纤维素,利用流动分析仪测定水解液中的葡萄糖。结果表明:①最优酶解条件为:烟粉0.25 g,缓冲溶液60 mL,酶用量0.25 g,水解温度37℃,水解时间24 h;②方法的相对标准偏差(RSD)为2.40%,回收率为96.7%～103.8%,检测限为0.11 mg/mL。该方法适合于烟草中纤维素含量的测定。     

没食子酸微晶纤维素酯的制备及性能研究

以微晶纤维素、没食子酸为原料,在催化剂的作用下,采用直接酯化法合成没食子酸微晶纤维素酯。在单因素试验的基础上,对合成时间、温度、催化剂用量、没食子酸和微晶纤维素用量比等因素进行正交试验,确定最佳合成条件为：没食子酸和微晶纤维素的反应物配比(GA:MCC)为4:1(m/m)时,以磷钨酸为催化剂,催化剂用量为相对于没食子酸质量的10%,在温度120℃条件下反应10h。产物具有清除烷基自由基、羟自由基、超氧阴离子自由基的能力,其DPPH 自由基清除率达到80% 以上。     

胡萝卜渣微晶纤维素的制备

以胡萝卜渣为原料,采用酸水解法制备微晶纤维素,考察了酸浓度、酸解时间以及酸解温度对微晶纤维素得率的影响。通过单因素和正交试验结果分析确定优化工艺条件,并对制备的微晶纤维素性能进行分析。结果表明:优化的工艺条件是,酸浓度为6%、酸解时间60min、酸解温度80℃,微晶纤维素的得率为33.8%。