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21.
Biochemical characteristics and thermal inhibition kinetics of polyphenol oxidase extracted from Thompson seedless grape 总被引:2,自引:0,他引:2
Polyphenol oxidase (PPO) was isolated from Thompson seedless grape (Vitis vinifera ‘Thompson Seedless’), and its biochemical characteristics were studied. The PPO showed activity to catechol and D, L-DOPA, but not towards monophenol
l-Tyrosine, diphenols guaiacol and caffeic acid, and triphenols pyrogallic acid and gallic acid. Apparent Michaelis–Menten
constant (K
m) and maximum velocity of the reaction (V
max) values were 45.0 ± 0.05 mM and 500.0 ± 15.3 OD400 nm/min for catechol, and 34.6 ± 0.03 mM and 384.6 ± 11.7 OD478 nm/min for D, L-DOPA, respectively. The obtained similar specificity values of V
max/K
m ratio of catechol and D, L-DOPA indicated their similar affinity to Thompson seedless PPO. The most effective inhibitor was
l-cysteine, followed in decreasing order by ascorbic acid, sodium metabisulfite, EDTA, NaCl, and citric acid. It was discovered
that metal ions of Mg2+ and Cu2+ increased, while Zn2+ and K+ reduced the PPO activity. Sugars showed inhibition on the PPO activity, with higher effect by sucrose and lower effect by
fructose and glucose. Optimum pH and temperature for grape PPO activity were 6.0 and 25 °C with 10 mM catechol as substrate.
The enzyme was heat stable between 10 and 25 °C, but showed significant activity loss at temperatures higher than 40 °C and
completely inactivation at 70 °C for 10 min. Thermal inactivation of PPO showed a first-order kinetic with an activation energy
(E
a) of 146.1 ± 10.8 kJ/mol at pH 6.0. 相似文献
22.
为研究枯草芽孢杆菌对烟叶化学成分和吸味品质的影响,从初烤后烟叶中筛选出一株微生物(H11),结合菌株形态和16S rDNA序列分析,初步鉴定为枯草芽孢杆菌枯草亚种(Bacillus subtilis subsp. subtilis);用H11对20 kg河南平顶山低等级烟叶(2017 DCFB)发酵30 h,对比分析发酵前后烟叶感官质量、常规化学成分、中性香味成分的变化,并采用宏基因组测序技术,分析了发酵前后烟叶表面微生物群落变化,探讨了酶在烟叶发酵中的作用。与发酵前相比,烟气透发性好、甜感增强、香气质提升、香气量增加;水溶性总糖和还原糖含量(质量分数)分别增加了2.52%和1.92%;(E)-β-大马酮、二氢猕猴桃内酯和巨豆三烯酮C等香味成分含量(质量分数)分别增加了25.92%、10.57%和12.15%;烟叶表面微生物数量明显减少,芽孢杆菌属(Bacillus)微生物丰度增加至微生物总量的76%。枯草芽孢杆菌(Bacillus subtilis)对烟叶化学成分和吸味品质有重要影响,且具有发酵时间短和处理量大等特点,可为微生物发酵低等级烟叶提供参考。 相似文献
23.
24.
结构二次防御能力分析的荷载效应组合方法 总被引:4,自引:0,他引:4
利用概率论和结构可靠度的基本概念,根据建筑结构上永久荷载和可变荷载的分布特性以及偶然事件的发生特点,提出对结构进行结构二次防御能力分析时应当采用的荷载效应组合方法。可供结构工程师对结构进行偶然荷载工况下的建模和分析时参考。 相似文献
25.
Al对原位自生Ti基复合材料中TiB晶须增强相生成的作用 总被引:5,自引:0,他引:5
借助于X射线衍射(XRD),差示量热分析(DSC)以及扫描电镜(SEM)研究了A1对Ti基复合材料中TiB晶须增强相生成的作用。研究结果表明:无论在Ti—B体系,还是在Ti—B—A1体系中,生成的增强相均为TiB,A1的加入并没有导致新相的产生;Ti—B体系中加入A1后,促进了TiB的生成反应,使TiB的初始生成温度从1262℃降低到856℃;并且TiB增强相得以细化,分布均匀。 相似文献
26.
27.
基于VOF法,分别选取标准k-ε紊流模型、RNG k-ε紊流模型和Realizable k-ε紊流模型,对某一超高水头、大泄量竖井旋流泄洪洞的水力特性进行数值模拟,并将紊流模型计算结果与模型实验数据进行了对比分析。结果表明:3种紊流模型模拟计算所得的空腔直径、竖井壁面压强、旋流角等参数变化趋势与模型试验测试结果基本相同,但量值有所差别。相比较而言,Realizable k-ε紊流模型计算所得旋转水流的空腔直径、压坡底板与部分竖井壁面压强、旋流角在量值上更接近试验测量值。因此,Realizable k-ε紊流模型能够更好地模拟这种具有超高水头、大泄量、强旋转并带有自由液面旋转水流的水力特性。 相似文献
28.
A wastewater desalination system based on a low‐temperature air source heat pump was developed and studied in this paper. The system consists of 2 main parts: the wastewater flow process and the heat pump cycle. A series of experiments were conducted on the system under different conditions, and the effect of the evaporation temperature was investigated. This system can reach equilibrium at any evaporation temperature using the combination of the compressor and vacuum pump. To treat wastewater with low boiling point organic matter, the system was operated at a low evaporation temperature of 48°C. The organic matter remained in the concentrated wastewater, and the organic removal was approximately 97%. Three kilograms of treated water was produced in 1 hour with an energy consumption of 250 W. The performance ratio (PR) obtained from the experiments ranged from 4.6 to 7.3. The cost for treating 1 kg of water was 0.038 yuan CNY assuming 0.5 yuan CNY per kWh at the compressor frequency of 50 Hz. 相似文献
29.
Ning Han Junling Cheng Dezhi Han Guoliang Chen Shuguang Zhang Guangjian Wang Naitao Yang Shaomin Liu 《国际能源研究杂志》2019,43(14):8890-8897
Recently, the reported Perovskite/Ruddlesden‐Popper composite with significant improvement of oxygen surface kinetics has been adopted into gas separation process. Here, we report a novel La0.7Sr0.3FeO3 ? δ/(La0.5Sr0.5)2CoO4 + δ (LSF‐LSC) composite hollow fiber membrane (HFM), which was characterized by X‐ray diffraction (XRD), scanning electron microscope (SEM), and thermal expansion test, etc. The O2 permeation test results indicated that, under sweeping gas of pure He (100 mL min?1), the composite HFM exhibited the superior O2 permeability (0.72 mL min?1 cm?2) at the temperature of 950°C with respect to the single La0.7Sr0.3FeO3 ? δ (LSF) membrane, acid‐etched membrane, and (La0.5Sr0.5)2CoO4 + δ (LSC)‐coated membrane. Moreover, the composite membrane exhibited high CO2 tolerance as well as phase stability. The generation of hetero‐interface between Ruddlesden‐Popper phase and perovskite phase could be responsible for the improvement of the oxygen transportation over the fabricated composite membrane. 相似文献
30.
针对罗茨鼓风机故障情况,根据各部件工作原理及使用要求,制定相应的修复工艺,并成功实施,对修复前后的数据作了对比。总结出了部分罗茨鼓风机的修理经验。 相似文献