Synthesis and characterization of amphoteric xylan-type hemicelluloses by microwave irradiation

In this study, a novel amphoteric macromolecule was synthesized by sequential incorporation of carboxymethyl and quaternary ammonium groups into the backbone of xylan-type hemicelluloses under microwave irradiation. The reaction parameters such as the molar ratio of reagent (NaOH or 3-epoxypropyltrimethylammonium chloride)/anhydroxylose unit in hemicelluloses, the temperature, and the reaction time were investigated to optimize the reaction condition. The maximum degrees of substitution (DS) of carboxymethyl and quaternary ammonium groups under the optimum reaction condition were 0.90 and 0.52, respectively, exhibiting a higher efficiency as compared to the conventional heating method. Moreover, the thermal stability and weight-average molecular weight of amphoteric hemicellulosic derivatives decreased as compared to the native hemicelluloses. The viscosity, elastic modulus, and loss modulus of the amphoteric biomacromolecules increased with the increasing DS of quaternary ammonium groups in aqueous solution due to stronger electrostatic attraction. This study provides an efficient and rapid method to prepare amphoteric biomacromolecules.     

Studies of the lauroylation of wheat straw hemicelluloses under heating

Lauroylation of wheat straw hemicelluloses in the N, N-dimethylformamide/lithium chloride system under microwave irradiation was studied. The parameters optimized included lauroyl chloride concentration as the molar ratio of xylose unit in hemicelluloses/lauroyl chloride (1:1-1:4), 4-dimethylaminopyridine concentration (2-10%), reaction time (1-8 min), molar ratio of xylose unit in hemicelluloses/triethylamine (1:2), and reaction temperature (78 degrees C). The reaction efficiency was measured by the yield and degree of substitution (DS). Under an optimum reaction condition (molar ratio of xylose unit in hemicelluloses/lauroyl chloride 1:3, molar ratio of xylose unit in hemicelluloses/triethylamine 1:2, 5% 4-dimethylaminopyridine, 78 degrees C, 5 min), a DS of 1.63 was obtained. Changes in the structure of hemicelluloses were verified by FT-IR and 1H and 13C NMR spectroscopy. The results showed that the lauroylation occurred preferentially at the C-3 position of the xylose unit in hemicelluloses. The behavior of the lauroylated hemicelluloses was monitored by means of thermogravimetric (TG) and differential thermogravimetric (DTG) analysis. It was found that the product with low DS had a lower thermal stability than the native hemicelluloses, whereas the lauroylated polymers with high DS showed a higher thermal stability than the unmodified hemicelluloses.     

超声波辅助碱分离毛竹半纤维素

该文以高效分离毛竹半纤维素为出发点,采用超声辅助碱分离法分离毛竹半纤维素。在固定固液比1∶20g/mL、总浸提时间120min的条件下,分析了KOH溶液质量分数,浸提温度及超声时间对毛竹半纤维素得率的影响。在单因素试验的基础上,采用Box-Behnken试验设计和通过响应面分析对分离工艺进行了优化。结果表明,超声辅助碱分离毛竹半纤维素的最佳分离工艺参数为KOH溶液质量分数3.1%、浸提温度54℃、超声时间56min,此时半纤维素实际总得率为19.28%。浸提温度和KOH溶液质量分数对半纤维素总得率影响显著,超声波作用时间对总得率影响不显著。在相同条件下超声辅助碱分离时半纤维素提取率比无超声辅助时提高4.06%。结果可为毛竹半纤维素分离的工业化提供参考。     

小麦秸秆纤维素均相醚化制备羧甲基纤维素工艺优化

为了利用小麦秸秆通过均相反应制备羧甲基纤维素(CMC,carboxymethyl cellulose),采用氢氧化钠和过氧化氢回流加热法制备小麦秸秆纤维素。以加入氧化锌的氢氧化钠/尿素/硫脲体系为溶剂,采用冻融循环法溶解小麦秸秆纤维素,利用正交试验获得了该溶解体系的最佳组成。在溶解了小麦秸秆纤维素的氢氧化钠/尿素/硫脲/氧化锌的体系中,以氯乙酸钠为醚化剂制备CMC,并对其进行红外光谱分析和取代度(degree of substitution,DS)测定。结果表明:在固液比为1∶20 g/mL,质量分数为10%NaOH,反应温度为85℃,回流3.5 h和固液比为1∶30 g/m L,质量分数为3%H_2O_2,反应温度为85℃,回流3 h处理小麦秸秆,纤维素提取率最高为84.61%,同时能较好的脱除半纤维素和木质素;最佳溶解体系为:质量分数为7%NaOH,11%硫脲,5%尿素,0.05%氧化锌,0℃时,最大溶解度为2.880 1 g。红外光谱试验表明小麦秸秆纤维素与微晶纤维素特征吸收峰基本一致,醚化反应生成的CMC与商品CMC的特征吸收峰基本一致。CMC的取代度受纤维素用量、温度和氯乙酸钠与纤维素葡萄糖单元(AGU,anhydroglucose unit)的摩尔比影响,随纤维素用量和氯乙酸钠与纤维素AGU的摩尔比增大而提高,随醚化温度的增加先增大(55℃)后降低。研究结果为以小麦秸秆为原料,经NaOH和H_2O_2处理获得纤维素,溶解在加入氧化锌的氢氧化钠/尿素/硫脲体系中,与氯乙酸钠经过均相醚化反应合成取代度较高的CMC提供参考。     

Relative quantification of N(epsilon)-(Carboxymethyl)lysine,imidazolone A,and the Amadori product in glycated lysozyme by MALDI-TOF mass spectrometry

The nonenzymatic glycation of proteins by reducing sugars, also known as the Maillard reaction, has received increasing recognition from nutritional science and medical research. In this study, we applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to perform relative and simultaneous quantification of the Amadori product, which is an early glycation product, and of N(epsilon)-(carboxymethyl)lysine and imidazolone A, two important advanced glycation end products. Therefore, native lysozyme was incubated with d-glucose for increasing periods of time (1, 4, 8, and 16 weeks) in phosphate-buffered saline pH 7.8 at 50 degrees C. After enzymatic digestion with endoproteinase Glu-C, the N-terminal peptide fragment (m/z 838; amino acid sequence KVFGRCE) and the C-terminal peptide fragment (m/z 1202; amino acid sequence VQAWIRGCRL) were used for relative quantification of the three Maillard products. Amadori product, N(epsilon)-(carboxymethyl)lysine, and imidazolone A were the main glycation products formed under these conditions. Their formation was dependent on glucose concentration and reaction time. The kinetics were similar to those obtained by competitive ELISA, an established method for quantification of N(epsilon)-(carboxymethyl)lysine and imidazolone A. Inhibition experiments showed that coincubation with N(alpha)-acetylargine suppressed formation of imidazolone A but not of the Amadori product or N(epsilon)-(carboxymethyl)lysine. The presence of N(alpha)-acetyllysine resulted in the inhibition of lysine modifications but in higher concentrations of imidazolone A. o-Phenylenediamine decreased the yield of the Amadori product and completely inhibited the formation of N(epsilon)-(carboxymethyl)lysine and imidazolone A. MALDI-TOF-MS proved to be a new analytical tool for the simultaneous, relative quantification of specific products of the Maillard reaction. For the first time, kinetic data of defined products on specific sites of glycated protein could be measured. This characterizes MALDI-TOF-MS as a valuable method for monitoring the Maillard reaction in the course of food processing.     

施加PAM与CMC对土壤水分入渗与蒸发特征的影响

施加化学改良剂是改良土壤和提高农田水分有效性的重要途径,深入了解化学改良剂对土壤水分运动过程的影响是合理利用化学方法改良土壤的基础。通过开展室内土柱试验研究表施聚丙烯酰胺(PAM)和羧甲基纤维素钠(CMC)2种化学改良剂,分析不同施量的化学改良剂(PAM和CMC)对土壤水分入渗和蒸发特征的影响。结果表明:随着PAM和CMC施加量的增加,不同化学改良剂均降低了土壤水分入渗过程,抑制了土面蒸发过程。综合考虑不同化学改良剂的保水、抑蒸性能,施加CMC的减渗、抑蒸作用高于施用PAM,且CMC施量为0.08%的效果最佳。同等减渗、抑蒸效果下,CMC的施用量相对PAM的施用量更少。     

Process Parameters and Technological Quality of French Rolls Produced with Dry Sourdough to Reduce Sodium

The search for alternatives for salt reduction in bread is a challenge. This study aimed to evaluate the use of dry sourdough (DS) for the reduction of sodium in French rolls, using a 2² central composite rotatable design. Sodium chloride (NaCl) (0–2.5%) and DS (0–10%, flour basis) were added to the formulations. The reduction of NaCl decreased high‐speed mixing time, proofing time, oven spring, cut opening, and cut height. The addition of DS increased high‐speed mixing time and proofing time and, at higher concentrations, decreased oven spring, cut opening, and cut height. Color parameters also showed effect of DS. Specific volume, shape, and texture of the rolls were not affected by the variables. Thus, the use of DS was shown to be viable for the reduction of sodium in French rolls, because we reached up to 45% salt reduction at concentrations below 5% DS, with desirable technological characteristics.     

Effects of domestication on structural polysaccharides and dietary fiber in nopalitos (Opuntia spp.)

Domestication is an evolutionary process that modifies morphological, physiological, chemical and genetic features of wild plants, and is a product of artificial selection. A gradient of domestication can be appreciated in species of the Opuntia genus. There are wild species like O. streptacantha, others semi-domesticated like O. hyptiacantha O. megacantha and O. albicarpa, or other like O. ficus-indica with the highest degree of domestication. At the same time, some structural polysaccharides have been associated with plant drought and freeze resistance. This study aimed at quantify five groups of structural polysaccharides in 14 variants of nopalitos (edible young cladodes of flat-stemmed spiny cacti consumed as vegetables) of Opuntia spp. in a domestication gradient. Given that extreme environment is less frequent under cultivation than in the wild, we hypothesized that structural polysaccharides in nopalitos are reduced throughout the domestication process. The experiment was conducted as a completely randomized design with a 5?×?14 two-factor factorial treatment structure, with four replications. Mucilages, pectins, hemicelluloses and cellulose were extracted and dietary fiber content was calculated. ANOVA of data was performed, pair wise comparisons of species and variants were conducted by Tukey test and principal components analysis was carried out. Mucilages were higher in O. ficus-indica (12% of total dry mass) and pectins, loosely and tightly bound hemicelluloses in O. streptacantha (2.5, 9 and 3%, respectively). All five species had similar content of cellulose (5.1% dry mass); but, O. streptacantha presented more dietary fiber. Higher pectins and both loosely and tightly bound hemicelluloses content in wild species can be related to genotype and the persistence of reaction to a wild environment. Mucilages which are one of the main characteristics of consumer preference and loosely bound hemicelluloses could have impact for selection during Opuntia domestication.     

寒旱环境植物护坡力学效应与根系化学成分响应

该项研究以试验区两种生长期为6a的灌木植物柠条锦鸡儿、霸王为例,分析了根系中所含半纤维素、木质素、纤维素和果胶质4种主要化学成分及其含量,并探讨了根系力学强度与其化学成分及其含量变化之间的关系。结果表明:柠条锦鸡儿根系平均抗拉强度为28.36～34.75MPa,霸王为4.53～6.61MPa,即柠条锦鸡儿根系平均抗拉强度显著大于霸王,且这两种灌木根系所含的4种化学成分由多至少依次为半纤维素、木质素、纤维素、果胶质,其中柠条锦鸡儿根系半纤维素含量为17.8%～29.03%,木质素为3.41%～5.36%,纤维素为2.3%～2.79%,果胶质为1.45%～2.15%;霸王根系半纤维素含量为15.6%～23.04%,木质素为3.69%～4.89%,纤维素为2.1%～3.06%,果胶质为1.92%～2.37%。两种灌木根系纤维素含量与根径、根系抗拉强度之间均表现出一定相关性;霸王根系半纤维素含量与其根系根径、抗拉强度之间呈相关性;柠条锦鸡儿根系果胶质含量与其根径、根系抗拉强度间均呈相关关系。本项研究可为进一步分析植物根系力学强度及其效应与根系组成特性之间的变化关系提供理论依据。     

Preparation and Structure Characterization of Carboxymethyl Corn Starch Under Ultrasonic Irradiation

To discover new synthesis technology and increase the degree of substitution (DS) of carboxymethyl starch (CMS), ultrasound‐modified CMS (U‐CMS) was successfully prepared under ultrasonic irradiation in the alkali condition with corn starch (CS) as the raw material, ethyl alcohol as the solvent, and monochloroacetic acid as the carboxymethylated reagent. The effects of ultrasound conditions (ultrasonic action sequence, ultrasonic radiation time, and ultrasonic power) and etherification time after ultrasonic irradiation on DS of U‐CMS were studied separately through single‐factor experiments. Meanwhile, the granule morphology, crystal type, and molecular structure of U‐CMS were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT‐IR). The results showed that DS of U‐CMS prepared under certain conditions (ultrasonic radiation time before alkalization, 40 min; ultrasonic radiation temperature, 35°C; ultrasonic power, 170 W; and etherification time, 180 min) improved 38.7% compared with that without ultrasonic radiation. The SEM, XRD, and FT‐IR results illustrated that crystal‐type change of the starch granule after ultrasonic irradiation was not obvious. However, the number of sunken points and holes on the granule surface increased, so that the specific surface expanded, which improved the carboxymethylation.     

江苏省大型沼气工程沼液理化特性分析

集约化畜禽养殖场沼气工程是一项提供清洁能源、减轻环境污染、潜力巨大的生物质能源工程。该研究采集了江苏省21个规模化养猪场和奶牛场内大型沼气工程的沼液样本,进行了氮磷钾等理化特性分析。结果表明,由厌氧反应罐排出的沼液呈中性至微碱性,还原能力较强。猪场和奶牛场沼液中总氮分别集中在400～900 mg/L和200～400 mg/L范围内,其中铵态氮占总氮量的70%以上;总磷分别集中在30～100 mg/L和300 mg/L以上,可溶性磷含量变异较大;总钾分别集中在100～500 mg/L和500 mg/L以上。沼气工程运行时间对沼液理化性状影响显著,运行时间越长系统稳定性越好。氧化塘对沼液中颗粒物、氮素和磷素有显著的削减作用,多级氧化塘处理效果更明显。     

低浓度甘蔗渣化学浆流变特性的研究

该文对不同浓度、打浆度、剪切速率对低浓度甘蔗渣化学浆流变特性的影响进行了实验研究,对不同因素引起浆料表观黏度变化的机理进行了分析,结果表明：随浆料浓度增加,纸浆表观黏度呈指数式增加;打浆度影响浆料的微观结构,随打浆度升高,纸浆表观黏度呈下降趋势;低浓度纸浆的表观黏度随剪切速率提高而递减。在实验测量范围内,甘蔗渣低浓度纸浆为满足幂律关系的非牛顿流体,拟合的本构方程的流变特性指数n<1,因此其在测量范围内为拟塑性流体。另外,随着纸浆浓度的降低,流变特性指数n增加,表明随低浓度纸浆逐渐变稀,所表现出的流变特性向着牛顿流体的方向趋近。低浓度纸浆流变特性的研究为纸浆模塑生产线流送系统提供了设计基础。     

Extraction and characterization of original lignin and hemicelluloses from wheat straw

Original lignin and hemicelluloses were sequentially extracted with high yield/purity, using acidic dioxane/water solution and dimethyl sulfoxide, from ball-milled wheat straw. The acidic dioxane lignin fraction is distinguished by high beta-O-4' structures and by low amounts of condensed units (beta-5', 5-5', and beta-1'). Hemicelluloses contain arabinoxylans as the major polysaccharides, which are substituted by alpha-l-arabinofuranose, 4-O-methylglucuronic acid, acetyl group (DS = 0.1), and xylose at O-3 and/or O-2 of xylans. It was found that arabinoxylans form cross-links with lignins through ferulates via ether bonds, glucuronic acid via ester bonds, and arbinose/xylose via both ether and glycosidic bonds, respectively, in the cell walls of wheat straw. Diferulates are also incorporated into cross-links between lignin and hemicelluloses as well as lignification of wheat straw cell walls. The guaiacyl unit is considered to be a significant condensed structural constructor in extracted lignin and a connector between lignin and carbohydrates.     

Synthesis and Characterization of Starch Acetates with High Substitution

Acetylation of high‐amylose (70%) maize starch to high degree of substitution (DS) was studied by reacting starch with acetic anhydride using 50% aqueous NaOH as the catalyst. DS increased with increasing reaction times and increasing ratios of acetic anhydride to starch. Reaction efficiency (RE) increased with longer reaction times and decreased with increases in the ratios of acetic anhydride to starch for extended reaction times. Increasing the amount of NaOH increased both DS and RE. A series of starch acetates with DS values of 0.57–2.23 were prepared and their crystalline structures, chemical structures, thermal stability, and morphological properties were investigated. After acetylation, and as DS increased from 0.57 to 2.23, the crystalline structures of starch steadily disappeared. The carbonyl group's peak at 1,740 cm^‐1 appeared in the FTIR spectra. The intensity of this peak increased with a decrease in the peak intensity of the hydroxyl groups at 3,000‐3,600 cm^‐1, indicating that the hydroxyl groups on starch were replaced by the acetyl groups. Thermal stability of starch acetates increased. The smooth surface of the starch granules became rough with acetylation. Further acetylation led to the loss of the starch granules and the formation of beehive‐ and fibrous‐like structures.     

Hemicelluloses prior to aspen chemithermomechanical pulping: pre-extraction, separation, and characterization

A portion of hemicelluloses and acetic acid can be pre-extracted with dilute sulfuric acid prior to the aspen chemithermomechanical pulp process. The streams collected from the second press-impregnation stage after acid pre-extraction contain a significant amount of acid pre-extracted hemicelluloses. Most of the total sugars obtained from the pressate were xylan, in which xylan was further hydrolyzed to sugar monomers under the acid pre-extraction condition. To fully understand the characteristics of hemicelluloses yielded prior to pulping, the pre-extracted hemicelluloses were separated and characterized by FT-IR, (1)H NMR, and thermogravimetric analysis in this study. Most of the FT-IR bonds from the hemicelluloses agreed well with the other two spectra of birch xylan and CA0050 xylan, except a new absorption at 1734 cm(-1) contributed to acetyl groups. The hemicelluloses obtained from acid pre-extraction began to decompose significantly at about 225 °C, slightly lower in comparison with organosolv and alkaline hemicelluloses reported in the literature.     

Plasma-enhanced modification of xanthan gum and its effect on rheological properties

The structure and rheological properties of xanthan gum (XG) modified in a cold plasma environment were investigated. XG was functionalized in a capacitively coupled 13.56-MHz radio frequency dichlorosilane (DS)-plasma conditions and, consecutively, in situ aminated by ethylenediamine. The surface structure of modified XG was evaluated on the basis of survey and high-resolution ESCA, FTIR, and fluorescence labeling techniques. The types of species generated in DS-plasma were reported using residual gas analysis (RGA). The aqueous solutions of modified XG were cross-linked and cured at room temperature to form stable gels. The dynamic rheological characteristics of virgin XG and functionalized and cross-linked XG were compared. It was found that parameters such as plasma treatment time and concentration of solutions can be optimized to form stable gels of XG. Thus, cold plasma technology is a novel, efficient, and nonenzymatic route to modify XG.     

Starch Acetate‐Maleate Mixed Ester Synthesis and Characterization

A new starch acetate‐maleate mixed ester with different degrees of substitution (DS) for each ester group was prepared. High‐amylose (70%) corn starch was first reacted at 123°C with ≈4.5 equivalents of acetic anhydride for different times, and then the intermediate products were further reacted at 80°C with 0.27–1.1 equivalents of maleic anhydride for a fixed time. ¹H NMR and alkaline saponification were used to determine DS values of acetyl and maleate groups. Increasing the reaction time from 60 to 120 min for starch and acetic anhydride increased DS of the acetyl group, while DS of the maleate group increased with increasing amounts of maleic anhydride. There was a good agreement between the two methods for DS determination. The reaction efficiency of acetylation increased from ≈30 to 50% with reaction time, and maleation decreased from ≈30 to 20% with increasing amounts of maleic anhydride. The mixed esters were characterized by ¹H NMR, ¹³C NMR, FTIR, DSC, and TGA. Characteristic peaks in ¹H NMR, ¹³C NMR, and FTIR spectra indicated the presence of acetyl and maleate groups in starch molecules. The exothermic peak in the DSC curve and the increase in thermal stability from the TGA curve were attributed to thermal cross‐linking of the double bond of the maleate group.     

Chemical response of hardwood oligosaccharides as a statistical function of isolation protocol

Hardwoods contain a substantial amount of hemicellulose-type oligosaccharides, the chemical structures of which are typically categorized in the xylan saccharide class. The efficient and selective isolation of these hemicelluloses is regarded as one of the most critical obstacles to overcome for their eventual biomaterial and bioenergy utilization. Therefore, the objective of the current work was to perform a fundamental exploration of the function of extraction pH, temperature, and time on the final chemical properties of the extracted hemicelluloses. The extraction chemistries employed varied pH and showed that acidic conditions provided a higher extractive yield versus alkaline conditions. An alkaline environment gave higher yields than an acidic environment and also resulted in much higher lignin removal from wood, especially at high temperature. In general, control of the pH chemistry leads to a change in the carboxylic acid groups present in the extracts. When the extraction pH changed from acidic to alkaline, the total carboxylic acid group content in the hemicelluloses removed significantly increased due to more acetic acid group hydrolysis and increased lignin degradation.     

Reduction of aflatoxins B1 and B2 with sodium borohydride.

Reduction of aflatoxin B1 and aflatoxin B2 with sodium borohydride quantitatively yielded new fluorescent derivatives, designated as aflatoxin RB1 and aflatoxin RB2. Mass spectrometric data showed that RB1 and RB2 were trihydroxy derivatives of B1 and B2, respectively. Nuclear magnetic resonance analysis revealed that new chemical shifts were present in aflatoxins RB1 and RB2 in addition to those of the parent aflatoxins. The new compounds had lower melting points and different ultraviolet and infrared spectra compared to aflatoxins B1 and B2 and the monohydroxy derivative aflatoxicol. They were lses toxic to chick embryos than the parent toxins. Since the reduction yields were quantitative and since the reduction products could be detected at low levels comparable to those for B1 and B2, the reduction reaction could be used as a confirmatory test for both aflatoxins B1 and B2. Preliminary results obtained from gas-liquid chromatography (GLC) analysis of the trimethylsilyl derivatives of aflatoxins RB1 and RB2 indicated that these compounds could furnish the basis for developing an analytical GLC method for aflatoxins B1 and B2.     

流通加压热水液化木质生物质

在160～280℃温度范围内,10 MPa,10 mL/min条件下,考察了反应温度对木粉溶解百分比、水溶解部分中半纤维素来源糖类、纤维素来源糖类及降解产物生成的影响,研究了流通加压热水液化生物质的过程。随着温度的升高,木粉溶解百分比逐渐增大,280℃条件下,96.5%的木粉可溶解于水中。水溶解部分中,半纤维素来源糖类和纤维素来源糖类均随温度升高而增大,并分别在250℃和280℃时达最大值,降解产物5-羟甲基糠醛产率和糠醛产率也随温度升高而增大。同时,采用X射线衍射分析水不溶性残渣发现,随着处理温度的升高,残渣相对结晶度逐渐升高,但当温度达到280℃时,相对结晶度骤然下降且（002）晶面衍射峰消失,表明纤维素结晶结构被彻底破坏。残渣的傅立叶红外光谱分析表明,半纤维素在250℃即被完全水解;280℃时,半纤维素和纤维素特征峰均消失,残渣特征峰主要为木质素来源芳香环。研究表明,流通加压热水可以用于木质生物质的全水解来获取糖类。