Enzymic production of feruloyl xylo-oligosaccharides from corn cobs by a family 10 xylanase from Thermoascus aurantiacus

Feruloyl xylo-oligosaccharides (FeXOSs) were obtained from corn cobs (CCs) by treatment with a Thermoascus aurantiacus family 10-β-d-endoxylanase. CCs subjected to a sonication (ST-CC) or an autoclave treatment in order to enhance enzymic access and FeXOS production. Enzymic FeXOS production was increased by CCs thermal treatment up to 3.5 times. The kinetic parameters K_E and V_max, describing enzyme-dependent production rates of FeXOSs from CCs, were estimated at 130±20 nM and 290±10 nM h⁻¹, respectively. The reaction parameters affecting the FeXOS production, such as substrate concentration, enzyme loading and reaction time, have been investigated. The maximum FeXOS production was observed after 24 h incubation of 100 g L⁻¹ AT-CC with 570 nM xylanase. The obtained yield was 12 μmol of FeXOSs per gram of CC.     

A152G突变对GH43家族麦氏交替单胞菌木聚糖酶XynZT-2的影响

前期研究发现GH43家族近缘物种相同位点存在天然突变.为了探究保守位点区域的基因突变对酶催化性能的影响,对来源于麦氏交替单胞菌(Alteromonas macleodii)的木聚糖酶XynZT-2利用软件计算、随机突变及天然存在的突变进行分子改造,定点突变第152位丙氨酸为甘氨酸(A152G),将原酶与突变酶基因转化到...     

An investigation of two xylan‐degrading enzymes and a novel xylanase inhibitor in malted barley

Two enzymes with activity on xylan and xylan‐based substrates were isolated from malted barley. One appears to be relatively anionic and the other more cationic. Both are endo‐acting enzymes. The first of these was studied in more detail and shown to be of molecular weight ca. 59,000 and capable of acting through the pH range 5–7.5. It is relatively heat tolerant, with 30% of its activity surviving for 30 min at 70 °C. A low‐molecular‐weight (ca. 1300) inhibitor of xylanase that developed during germination was investigated. Its potency was not lowered by treatment with proteolytic enzymes, but treatment with polyvinylpolypyrrolidone did reduce its impact. Ultraviolet spectrophotometry and Fourier transform infrared spectroscopy, as well as staining with Folin–Ciocalteu reagent, indicated the presence of phenolic species, while mass spectroscopy studies suggested the presence of arabinose and possibly poly‐hexose. The presence of material that stained with aniline phthalate would be consistent with the presence of reducing sugar in the inhibitor. Copyright © 2013 The Institute of Brewing & Distilling     

An exopolysaccharide from a probiotic: Biosynthesis dynamics,composition and emulsifying activity

An exopolysaccharide (EPS) was isolated from Bacillus coagulans RK-02. Time course accumulation of EPS was studied with respect to biomass growth. The probiotic bacterium produces an EPS during exponential and stationary growth phases. Growth kinetics of the producer organism was characterized. The probiotic bacterium exhibited high affinity for the growth limiting substrate and hence grows at a higher specific growth rate. Based on HPLC and FTIR analyses, the EPS was found to be heteropolymer composed of galactose, mannose, fucose, glucose and glucosamine. The EPS showed significant emulsifying activities in different vegetable oils/hydrocarbon substrates. To the best of our knowledge, this is the first report on a bacterial EPS with fucose as a constituent sugar and also the first report on an EPS from B. coagulans.     

Chlorinated aromatics from combustion: influence of chlorine,combustion conditions,and catalytic activity

Research on the formation of chlorinated aromatics in combustion processes has mainly taken place in the laboratory. Previous attempts to correlate observation data from commercial plants have been inconclusive. This study reports on the outcome of an industrial experiment in a full-scale afterburner. The influence of chlorine input, combustion temperature, and catalytic activity was investigated in a factorial design with two blocks. Polychlorinated benzenes, dibenzo-p-dioxins, and dibenzofurans were formed both at combustion temperatures and below 400 degrees C. The results show that all three experimental factors have statistically significant impact on the formation and release of these toxic byproducts. The quantitative dependence between chlorine input and the occurrence of chlorinated aromatics is of particular interest due to previous controversy. The purpose with this study was to ensure that the installation of a boiler for energy recovery would not cause elevated emissions of chlorinated aromatics. The experiment demonstrated that this risk is probably low, since the presence of catalytic material or an increase in chlorine input is required for this to happen. A general conclusion was that industrial experimentation employing the principles of statistical design could improve the validity in recommendations regarding commercial plant operation.     

Carrot pectin methylesterase and its inhibitor from kiwi fruit: Study of activity, stability and inhibition

Carrot pectin methylesterase (PME) and its inhibitor (PMEI) from kiwi fruit were successfully purified by affinity chromatography. Enzyme and inhibitor activity and stability and PME–PMEI complex formation, as influenced by intrinsic product factors (pH and NaCl) and extrinsic process factors (temperature and pressure), were studied. The effect of temperature- or pressure-induced denaturation of PME and PMEI on their respective activities was assessed by estimating inactivation kinetic parameters. PME inactivation obeyed first-order kinetics. The enzyme was rather heat-labile but pressure-stable. PMEI inactivation was best described by a model taking into account a processing-stable PMEI intermediate. The behavior of PME and the PME–PMEI complex at elevated temperature or pressure in the presence of pectin was explored by following methanol formation as a function of treatment time. PME catalytic activity was stimulated up to a certain temperature or pressure level before declining. No conclusive evidence was obtained for a temperature-induced dissociation of the PME–PMEI complex, whereas high pressure exposure caused the complex to separate.

Industrial relevance

PME activity control is a major point of interest in the quest of obtaining high quality plant-derived food products. The current study demonstrates that both traditional thermal processing and novel high hydrostatic pressure processing allow stimulation as well as inactivation of PME and, hence, directing the PME-catalyzed pectin hydrolysis. An alternative or additional approach to control endogenous PME activity (e.g. to obtain cloud-stable juices) is through enzyme inhibition using kiwi PMEI. In this context, pH and NaCl boundaries for application were established, the existence of a temperature- and pressure-stable PMEI intermediate was shown and the PME–PMEI complex was proven not to be dissociated at mild temperature and pressure levels. These observations endorse the possibility of inhibiting undesirable PME activity remaining after mild processing.     

An investigation into the supramolecular structure,solubility, stability and antioxidant activity of rutin/cyclodextrin inclusion complex

The formation of supramolecular inclusion complexes between rutin and four cyclodextrins, namely β-cyclodextrin (β-CD), (2-hydroxypropyl)-α-cyclodextrin (HP-α-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD), and the effects of the complexation on the stability and antioxidant activity of rutin were investigated. Results from phase-solubility studies showed that rutin formed 1:1 stoichiometric inclusion complexes with HP-α-CD, β-CD, HP-β-CD and HP-γ-CD; the complexes formed with HP-γ-CD and HP-β-CD had the greatest stability constants, followed by β-CD and HP-α-CD. Thermodynamic studies demonstrate that the inclusion of rutin into HP-β-CD was an exothermic process which occurred spontaneously. Two-dimensional rotating-frame nuclear Overhauser effect spectroscopy (2D ROESY) ¹H NMR analyses show that the A ring of rutin was the part of the molecule that most likely inserted into the cavity of HP-β-CD, thus forming a supramolecular inclusion complex. Formation of such an inclusion complex conferred moderate degrees of protection to rutin from degradation by heat and UV radiation during storage, and significantly enhanced its antioxidant capacity as determined by three different procedures.     

黑曲霉木聚糖酶（xynZF-2）基因克隆、表达及酶学性质分析

利用RT-PCR技术从黑曲霉（Aspergillusniger）XZ-3S中成功克隆出木聚糖酶基因（xynZF-2）的cDNA序列（Genbank登录号为：JQ700382）。该基因核苷酸序列阅读框全长678bp,编码225个氨基酸,其中成熟肽为107个氨基酸。以重组质粒pUCm-T—xynZF-2为模板,扩增得到编码xynZF－2成熟肽的cDNA片段（624bp）。将其与表达载体pET－28a连接,构建重组表达载体pET－28a—xynZF－2,并转化大肠杆菌（Escherichiacoh）BL21（DE3）,获得重组工程菌BL21／xynZF-2。经IPTG诱导表达,木聚糖酶的的比酶活最高可达42．33U／mg。重组表达的木聚糖酶最适反应温度为40℃,最适反应pH为5．0,在碱性条件下具有良好的稳定性。Fe^3＋对酶的激活作用最为明显。     

植物中酪氨酸酶的筛选及不同抑制剂对其活性的影响

以新鲜马铃薯、红富士苹果、红蛇果、秀珍菇和紫茄子为研究对象,从中分别提取酪氨酸酶并测定其酶活力,发现紫茄子中提取的酪氨酸酶具有最大酶活力。因此选紫茄子中提取的酪氨酸酶做进一步研究。选邻苯二酚作为茄子酪氨酸酶底物,进一步研究了有机类、无机类和天然类三大类抑制剂对酪氨酸酶催化活性的影响,并测定了这些抑制剂的IC50值。      

An evaluation of extracts of five traditional medicinal plants from Iran on the inhibition of mushroom tyrosinase activity and scavenging of free radicals

This study aimed to evaluate the free radical scavenging and inhibition properties of five medicinal plants, including Quercus infectoria Olive., Terminalia chebula Retz. , Lavendula stoechas L., Mentha longifolia L., Rheum palmatum L., toward the activity of mushroom tyrosinase using l -tyrosine and l -3,4-dihydroxyphenylalanine ( l -DOPA) as the substrate. The methanol extracts of Q. infectoria and T. chebula showed strong radical scavenging effect in 2,2'-dipheny l -1-picrylhydrazyl (DPPH) assay (IC₅₀ = 15.3 and 82.2 μg mL⁻¹ respectively). These plants also showed inhibitory effects against the activity of mushroom tyrosinase in hydroxylation of l -tyrosine (85.9% and 82.2% inhibition, respectively). These two plants also inhibited the oxidation of l -DOPA similar to kojic acid as positive control (IC₅₀ = 102.8 and 192.6 μg mL⁻¹ respectively). In general Q. infectoria and T. chebula significantly inhibited tyrosinase activity and DPPH radical. Both activities were concentration-dependant but not in linear manner. It is needed to study the cytotoxicity of these plant extracts in pigment cell culture before further evaluation and moving to in vivo conditions.     

固态发酵啤酒糟产木聚糖酶的菌种筛选及其产酶条件研究

从40株保藏菌种中筛选得到1株能发酵啤酒糟高产木聚糖酶的菌株黑曲霉AN27—2—1。通过单因素实验和正交实验对黑曲霉AN27—2—1固态发酵啤酒糟产木聚糖酶的条件进行优化，结果表明：在培养基组分为啤酒糟：玉米芯：麸皮=6：2：2，NH4NO3 2％，吐温800.1％，加水比为1：2，接种量为3．5％，培养温度为30℃，培养周期为2d-3d，产酶活达310．54U／g。     

The influence of xylanase and thermal treatment on the composition and interfacial rheology properties of whole wheat dough liquor

The dough liquor (DL) centrifuged from dough played an important role in determining the gas cell stability during dough making, and the adding of xylanase (XYL) in the dough could efficiently increase the stability of DL foam, especially at 60 °C. In this work, we prepared whole wheat dough added with different dosages of XYL and extract the DL. The components especially proteins in DL and their interaction mechanism and interfacial rheology properties at the air–water interface were studied. The proteins formed protein aggregates (>150 kDa) at 60 °C. After XYL treatment, DL solution exhibited higher protein surface hydrophobicity and surface pressure. And the equilibrium surface pressure of DL varied between 23 and 28 mN m⁻¹. At 25 °C, the interfacial dilatational modulus increased by 26.77% and 14.22% compared with control, respectively. And the XYL can improve the interface shear strength both for the unheated and heated DL solutions. These findings showed that XYL might improve the ability of DL constituents to stabilise the air–water interface to contribute to the stability of gas cells in the dough. The obtained results have provided a theoretical basis for improving the gas cell stability by changing the properties of whole wheat DL with the addition of XYL.     

An apple a day: the influence of memory on consumer judgment of quality

Regular consumers of apples are subjected to a high level of variability in sensory experience. This is due to the biological variation between individual apples, and the deterioration in quality that occurs when fruit are stored for many months. Therefore consumer assessment of quality is likely to be strongly influenced by their capacity to remember past experiences. In this study, we examined the ability of untrained participants to detect differences in apple texture (a primary determinant of quality for many consumers) when presented with fruit at daily and ∼1 min intervals. Each day the participants were given an apple that differed in firmness (measured by an instrumental puncture test) by 0, 5, 10, or 15 N from the fruit tasted on the previous day. They were asked whether the apple was harder, the same or softer than the previous apple, and how sure they were of their answer. The results were analysed using a traditional, bipolar, and weighted bipolar R-index. When comparing apples eaten at daily intervals, the participants were able to detect differences in texture when the instrumental firmness of the fruit differed by as little as 5 N (note that consumers might experience apples between ∼50 and ∼85 N during the year). When the participants tasted apples at ∼1 min intervals, they experienced difficulty detecting any difference in texture even when instrumental firmness of the fruit differed by as much as 15 N. The poorer performance of participants at ∼1 min presentation intervals may be explained by the disruption of a memory trace for texture by other similar but interfering memories (i.e. factors akin to ‘proactive interference’ and ‘suffix’ effects found in research on visual and acoustic memory).     

Extraction optimisation,antioxidant activity and inhibition on α-amylase and pancreatic lipase of polyphenols from the seeds of Syzygium cumini

The objectives of this study were to determine the optimal extraction conditions of polyphenols from Syzygium cumini seeds by response surface methodology and investigate their antioxidant activity and inhibition on α-amylase and pancreatic lipase. As results, the optimal extraction conditions in the ultrasonic extraction process which maximised total polyphenols content, minimised the IC₅₀ values of α-amylase and pancreatic lipase were determined as follows: extraction time 60 min, ethanol concentration 63% and solvent/solid ratio 44 mL g⁻¹. The main phenolic compounds in partially purified fraction of Syzygium cumini seeds were catechin, epicatechin, kaempferol, gallic, 5-caffeoylquinic, caffeic and ferulic acids. In addition, the partially purified fraction inhibited 87.66 ± 5.55 and 86.61 ± 3.15% of α-amylase and pancreatic lipase, respectively. The results suggested that Syzygium cumini seeds could be explored as a natural antioxidant and could be used as a source of highly antidiabetic and anti-obesity bioactive compounds.     

Microwave-assisted organic acid extraction of lignin from bamboo: Structure and antioxidant activity investigation

Microwave-assisted extraction in organic acid aqueous solution (formic acid/acetic acid/water, 3/5/2, v/v/v) was applied to isolate lignin from bamboo. Additionally, the structural features of the extracted lignins were thoroughly investigated in terms of C₉ formula, molecular weight distribution, FT-IR, ¹H NMR and HSQC spectroscopy. It was found that with an increase in the severity of microwave-assisted extraction, there was an increase of phenolic hydroxyl content in the lignin. In addition, an increase of the severity resulted in a decrease of the bound carbohydrate content as well as molecular weight of the lignin. Antioxidant activity investigation indicated that the radical scavenging index of the extracted lignins (0.35–1.15) was higher than that of BHT (0.29) but lower than that of BHA (3.85). The results suggested that microwave-assisted organic acid extraction provides a promising way to prepare lignin from bamboo with good antioxidant activity for potential application in the food industry.     

脱磺对亚硫酸盐法制浆废液中木质素提取的影响

以亚硫酸盐法制浆废液为原料,经脱磺处理后木质素的提取率显著提高,并通过正交试验深入探讨经脱磺处理的黑液中硫酸用量、沉淀时间、沉淀温度等反应条件对木质素提取纯化的影响。结果表明,高纯木质素提取最佳条件为：黑液与15％硫酸比为1：2,沉淀温度90℃,沉淀时间1．5h。     

Effect of subcritical water extraction conditions on the activity of alcohol metabolizing enzymes,ACE inhibition,and tyrosinase inhibition in Protaetia brevitarsis larvae

Food Science and Biotechnology - In order to develop processing methods with high physiological activity for Protaetia brevitarsis larvae (PBL), subcritical water (SCW) extraction was applied. The...