In vitro fermentation of cereal dietary fibre carbohydrates by probiotic and intestinal bacteria

A range of probiotic and other intestinal bacteria were examined for their ability to ferment the dietary fibre carbohydrates β‐glucan, xylan, xylo‐oligosaccharides (XOS) and arabinoxylan. β‐Glucan was fermented by Bacteroides spp and Clostridium beijerinckii but was not fermented by lactobacilli, bifidobacteria, enterococci or Escherichia coli. Unsubstituted xylan was not fermented by any of the probiotic bacteria examined. However, many Bifidobacterium species and Lactobacillus brevis were able to grow to high yields using XOS. XOS were also efficiently fermented by some Bacteroides isolates but not by E coli, enterococci, Clostridium difficile, Clostridium perfringens or by the majority of intestinal Lactobacillus species examined. Bifidobacterium longum strains were able to grow well using arabinoxylan as the sole carbon source. These organisms hydrolysed and fermented the arabinosyl residues from arabinoxylan but did not substantially utilise the xylan backbone of the polysaccharide. Arabinoxylan was not fermented by lactobacilli, enterococci, E coli, C perfringens or C difficile and has potential to be an applicable carbohydrate to complement probiotic Bif longum strains in synbiotic combinations. © 2002 Society of Chemical Industry     

利用玉米芯木聚糖酶法制备低聚木糖的研究

该文采用源于Thermotoga maritima的木聚糖酶基因工程菌JMl09(DE3)／pET-20b-xynB制备木聚糖酶液，试验结果表明，工程菌产木聚糖酶的最佳诱导条件：诱导剂乳糖浓度为25mmol／L；诱导时间为6h。酶法制备低聚木糖时，采用3％～5％的底物浓度和11．25U／g的酶用量较为适宜。TLC检测海栖热袍菌木聚糖酶水解玉米芯木聚糖的酶解产物主要为木二糖和木三糖。     

食品防腐剂丙酸钙中微量元素铬的测定

测定用鸡蛋壳制作的食品防腐剂———丙酸钙中痕量铬并对其可信度进行证明。采用化学发光法和石墨炉原子吸收法进行测定并比较其结果。两种方法均可达到快速、简便、干扰小、重现性好,均可达到生产中检测的要求。化学发光法的最低检出限为1.5×10-12g/ml,Cr3+在1×10-10～1×10-6g/ml浓度范围内与发光强度呈较好的线性关系。采用石墨炉原子吸收体系检测,最低检出限为1×10-12g/ml,标准曲线范围为0～1×10-6g/ml。     

自水解预处理对杨木聚木糖分布的影响

采用免疫荧光标记法结合共聚焦显微镜(CLSM)研究了自水解强度对杨木聚木糖分布的影响。结果表明,聚木糖荧光信号较均匀地分布于杨木纤维细胞壁中,随强度因子的增大细胞壁中心部位荧光信号下降逐渐增多,细胞壁边缘荧光信号下降较少,有些部位甚至会稍许增加。采用高效液相色谱(HPLC)检测法测得强度因子增强到3.72时,聚木糖含量从原料的14.64%下降到7.33%;对聚木糖荧光图谱进行区域强度统计,可得出与HPLC检测法结果相同的变化趋势。     

Esterase Activity of Serum Albumin Studied by 1H NMR Spectroscopy and Molecular Modelling

Serum albumin possesses esterase and pseudo-esterase activities towards a number of endogenous and exogenous substrates, but the mechanism of interaction of various esters and other compounds with albumin is still unclear. In the present study, proton nuclear magnetic resonance (¹H NMR) has been applied to the study of true esterase activity of albumin, using the example of bovine serum albumin (BSA) and p-nitrophenyl acetate (NPA). The site of BSA esterase activity was then determined using molecular modelling methods. According to the data obtained, the accumulation of acetate in the presence of BSA in the reaction mixture is much more intense as compared with the spontaneous hydrolysis of NPA, which indicates true esterase activity of albumin towards NPA. Similar results were obtained for p-nitophenyl propionate (NPP) as substrate. The rate of acetate and propionate release confirms the assumption that there is a site of true esterase activity in the albumin molecule, which is different from the site of the pseudo-esterase activity Sudlow II. The results of molecular modelling of BSA and NPA interaction make it possible to postulate that Sudlow site I is the site of true esterase activity of albumin.     

Impact of xylan structure and lignin–xylan association on methane production from C5-sugars

Xylan biopolymers are the dominant hemicelluloses present in agricultural plant materials which have potential use in various biotechnological processes including methane production. Hence, the effect of lignin content and the structural features of xylan on anaerobic digestion were studied by using synthetic assemblies consisting of xylans and lignin models (dehydrogenation polymers). The ramification by arabinose and uronic acid was shown to be a key factor in low methane potential (BMP) from xylans and xylan–lignin assemblies. Indeed, BMP increased when xylose content was increased, and decreased when arabinose and uronic acid contents were increased. Lignin content and molecular weight were found to be the most influential parameters on the anaerobic digestion rate. Digestion rate decreased when the lignin content and molecular mass increased.     

Real-time monitoring of hemicellulose liquefaction in ethylene glycol

Xylan was used as a model material to study the liquefaction of hemicellulose in the presence of ethylene glycol. The ReactIR^TM reaction analysis system was used to monitor the entire liquefaction process online. The results showed that xylan was decomposed and transferred to liquid phase. The gel permeation chromatography results of the liquid products showed that the weight average molecular of xylan decreased signi?cantly to around 1728 g/mol after liquefaction. Gas chromatography-mass spectrometry revealed that the ethylene glycol liquefaction products from xylan include ethylene glycol and its derivatives, alcohols, aldehydes, ketones, some acids and their esters.     

丙二醇单甲醚丙酸酯合成体系的气相色谱分析

自行研制了氰乙基(25%,质量分数)甲基硅橡胶(XE-60)石英毛细管色谱柱。建立了对含游离酸的丙二醇单甲醚丙酸酯的色谱分析方法。该法具有分离效果好,分析速度快的优点。     

壳聚糖硫酸盐催化丙酸丁酯的绿色合成研究

研究了丙酸与丁醇在壳聚糖硫酸盐催化剂作用下的酯化反应,考察了反应时间、催化剂用量、醇酸摩尔比等因素对丙酸丁酯酯化率的影响。实验结果表明反应的最佳条件为:丙酸用量为0.1mol,醇酸摩尔比为1.4,壳聚糖硫酸盐用量为1.2g,反应时间为1.5h,酯化率达97.2%,催化剂重复使用5次仍保持较高活性。无污染产生,具有绿色合成的特点。产品经折光率、红外光谱进行了表征。     

Synthesis of esters: Development of the rate expression for the Dowex 50 Wx8-400 catalyzed esterification of propionic acid with 1-propanol

The kinetics of the esterification reaction of propionic acid with 1-propanol over the ion-exchange resin Dowex 50Wx8-400 has been studied in this investigation. Kinetic experiments were conducted using a 1 L Lab-Max system at a stirrer speed of 900 rpm over a temperature range of 303.15 -333.15 K. The catalyst loading was varied from 10 to 60 g dry cat/L and acid to alcohol molar ratios of 1:1, 1:2, 1:4, 2:1 and 4:1 were employed. The equilibrium constants for this reaction were determined in separate experiments at 303.15, 313.15 and 323.15 K. The values were equal to 33.18, 30.62 and 28.37, respectively, with a standard enthalpy change of reaction of 6.4 kJ/mol. These values show the reaction to be mildly exothermic. It was found that both external and internal diffusion limitations did not affect the overall reaction rate. The conversion of propionic acid increased with increasing temperature and catalyst loading and decreased with increasing initial mole fraction of acid. The increase in chain length of acid or alcohol or branching had a retarding effect on the conversion. Several kinetic models were tested to correlate the kinetic data, the pseudo-homogeneous (P-H) model, the Eley-Rideal (E-R) model, the Langmuir-Hinshelwood (L-H) model, the modified Eley-Rideal (M-E-R) model and the modified Langmuir-Hinshelwood (M-L-H) model. In all models, the activity coefficients were estimated using UNIFAC to account for the non-ideal thermodynamic behavior of reactants and products. A correction factor for the resin affinity for water (α) was used in both M-E-R and M-L-H models. The above models predicted the kinetic behavior of the studied system with an overall error ranging from 1.65% to 13.32%. Water was found to be more strongly adsorbed than other species present in the system. The M-E-R model between adsorbed 1-propanol and non-adsorbed propionic acid which assumes surface reaction as the rate controlling step, with α equal to 2, was found to be the best model with the least overall error (1.65%). The activation energy for the esterification was estimated to be 67.3 kJ/mol by this model.