丙烯腈水合酶催化动力学及失活动力学研究

对丙烯腈水合酶在丙烯酰胺生产中的一些动力学参数做了探讨.研究表明:ρ(丙烯腈)>30 g/L时将引起底物抑制;底物不加限制的情况下,反应速率与菌悬液的加入量成正比关系;温度升高使反应速度明显加快,在28℃时的反应速率为在16℃时的反应速率的2.3倍;同时,温度的升高又使酶的失活加快,用阿累尼乌斯方程对温度与反应速率进行拟合可以得出催化反应的表观活化能50.6 kJ/mol,失活反应的表观活化能为12.65 kJ/mol.     

Developmental changes in the kinetics of glucose and urea in Holstein calves

Because weaning is the point when the nutrient composition of feed changes for the neonatal ruminant, the present experiment was conducted to assess the developmental changes in the kinetics of glucose and urea over this period, using stable isotopes of glucose and urea, at 4, 13, and 24 wk in calves. Plasma concentrations of nonesterified fatty acids, amino-N, urea-N, and insulin-like growth factor-I increased, but that of growth hormone decreased with age. The plasma glucose concentration increased at 13 wk of age and thereafter decreased at 24 wk of age. The glucose irreversible loss and recycling rates were significantly higher at 4 wk of age than at 13 and 24 wk of age. On the other hand, the irreversible loss and recycling rates of urea, as well as the urea pool size, were higher at 24 wk of age than at 4 and 13 wk. It is concluded that weaning at 6 wk is the pivotal time for the alteration of glucose kinetics. However, the aging process, but not weaning, is important for changes in the kinetics of urea in calves.     

蜂蜜酒发酵动力学研究

在前期工艺优化的基础上,探讨蜂蜜酒发酵过程中主要物质的变化规律,并基于Logistic方程与Luedeking R经验方程,对蜂蜜酒发酵过程中酵母生长动力学、酒精生成动力学、基质消耗动力学模型进行模拟。实验结果显示:模型预测值和实测值的拟合度分别为0.994、0.984、0.996,模型拟合良好,较好的反映了蜂蜜酒发酵过程的动力学特征。      

Inactivation Kinetics of Foodborne Spoilage and Pathogenic Bacteria by Ozone

Ozone was tested against Pseudomonas fluorescens, Escherichia coli O157:H7, Leuconostoc mesenteroides , and Listeria monocytogenes. When kinetic data from a batch reactor were fitted to a dose-response model, a 2-phased linear relationship was observed. A continuous ozone reactor was developed to ensure a uniform exposure of bacterial cells to ozone and a constant concentration of ozone during the treatment. Survivors plots in the continuous system were linear initially, followed by a concave downward pattern. Exposure of bacteria to ozone at 2.5 ppm for 40 s caused 5 to 6 log decrease in count. Resistance of tested bacteria to ozone followed this descending order: E. coli O157:H7, P. fluorescens, L. mesenteroides , and L. monocytogenes.     

高效内循环生物反应器处理脱墨废水动力学特性初步研究

研究了脱墨废水用高效内循环生物反应器处理时的生物降解和生物增长动力学特征,求出了脱墨废水经两种不同预处理后的降解动力学方程及稳态条件下活性污泥的产率系数.与传统活性污泥法相比,其污泥的产率系数只有1/3～1/2.     

丙酮缩甘油的制备及其动力学研究

将生产生物柴油产生的副产物甘油加工成高附加值的丙酮缩甘油可以提高生物柴油的经济效益。采用干燥剂原位除水法,在无溶剂体系中,丙酮与甘油通过原位除水、酸催化缩合反应制备丙酮缩甘油。通过正交实验考察了丙酮与甘油摩尔比、催化剂用量、反应温度、反应时间对丙酮与甘油缩合反应的综合影响,并探讨了缩合反应动力学。在催化剂用量为每摩尔丙酮3 g、反应温度80℃、反应时间1.0 h、丙酮与甘油摩尔比1∶1.4的条件下,丙酮转化率达到87.80%。该缩合反应为准二级反应,活化能Ea为35.58 k J/mol,频率因子为5.657×106。     

单宁酶的制备及其澄清茶饮料的动力学研究

研究了微生物发酵法制备单宁酶及其对茶提取液澄清化的催化动力学。结果表明：以10％浓度的茶提取液，加入3％的单宁酶液，在35℃、pH6．0的条件下反应速率最佳，其催化动力学方程为：     

活性嫩黄K-6G的水解及醇解动力学研究

 针对活性染料在纤维上染色的动力学性能,研究不同条件下一氯均三嗪型活性染料活性嫩黄K-6G(C.I.Reactive Yellow 2)在甲醇碱性水溶液中的醇解和水解反应动力学,并确定了pH值为10时,不同温度下该染料的醇解与水解反应速率常数。研究表明,在80℃,pH值为9～12之间,醇解效率随时间延长逐渐变少,且pH值越高,醇解效率减少的越快, pH值的升高不利于醇解反应进行,即染料的醇解反应优先性下降;在50～70℃,甲醇化反应占相对优势,其速率为水解速率的2～3倍;80～95℃,甲醇化反应速率常数和水解速率常数基本相等。同时实验中还发现染料的醇解和水解反应都是准一级反应。     

复合酶水解鲢鱼蛋白体系动力学模型探讨

在单因素试验确定最佳酶解条件前提下,通过测定不同反应过程中水解度的变化规律来验证复合酶水解鲢鱼体系水解动力学模型。结果表明,复合酶水解鲢鱼蛋白体系水解度与时间关系符合模型:DH=1/b×In(1+abt)。通过几组试验以及数据拟合可以求出该动力学模型的参数a=1.134e/s-0.337 9,b=0.235 1。     

牡蛎微波干燥特性及动力学研究

测定不同微波强度下牡蛎干燥水分曲线及失水速率曲线,考察不同微波强度对牡蛎干制品的复水增重率、收缩率、色差等品质方面的影响。结果表明：增大微波干燥强度可提高干燥速率,缩短干燥时间。在实验条件下,采用中等强度的微波干燥(如5、8W/g),牡蛎微波干燥时间在3.5～30min范围内。牡蛎品质较好。用Page方程建立的牡蛎微波干燥模型,与实验测定值的拟合度较高。     

Hyperketonemia impairs glucose metabolism in pregnant and nonpregnant ewes

The present study was undertaken to test the hypothesis that high ketone body concentrations suppress endogenous production of glucose and in pregnant sheep facilitate development of pregnancy toxemia. Rates of endogenous glucose production [mmol.min(-1)], and rate constants of glucose turnover [min(-1)] were measured in seven 12-h fasted sheep in the presence of normo- and hyperketonemia by use of D-2-[(3)H]-glucose. The measurements were carried out in the same sheep during the nonpregnant nonlactating state, during late pregnancy (10 +/- 7 d antepartum) and during lactation (19 +/- 6 d postpartum). Hyperketonemia (5 to 7 mmol.L(-1)), similar to that present in spontaneous ovine pregnancy toxemia, was induced by continuous intravenous 4-h infusions of DL-beta-hydroxybutyrate (DL-BHB). Glucose turnover [mmol.min(-1)] in the same 7 nonpregnant nonlactating, late pregnant, and lactating sheep was significantly greater during normoketonemia (0.80, 1.16, 1.76) than during hyperketonemia (0.66, 0.92, 1.16, respectively). The rate constants of glucose turnover were not altered by elevation of the BHB concentration. The results demonstrated that high BHB concentrations significantly suppressed endogenous glucose production but showed no effect on glucose utilization. The suppressive effect of hyperketonemia on hepatic glucose production resulted in a significant reduction of plasma glucose concentration and was qualitatively the same in all three reproductive states. The results indicate that hyperketonemia, which is regularly present in late twin pregnant hypoglycemic sheep contributes significantly to the reduction of available glucose. This effect of hyperketonemia may invoke sustained hypoglycemia and may render the ewe into a vicious cycle that probably makes the animal refractory to treatment in most cases.     

不同温度、pH、光照条件下毛蕊花苷的降解动力学

为了研究毛蕊花苷的稳定性,本文采用高效液相色谱法研究毛蕊花苷在不同温度(37、50、60、80、100 ℃)、不同pH(2、6、7、8)、光照/避光条件下的降解动力学。结果表明,毛蕊花苷在不同温度、pH和光照/避光条件下的降解反应均属于一级反应。对毛蕊花苷半衰期的计算结果表明,高温(60 ℃以上)、近中性环境(pH6~8)、光照均不利于毛蕊花苷的保存;毛蕊花苷在中低温(37、50 ℃)、低pH(2)及避光条件下更稳定,半衰期明显延长。本文分析了影响毛蕊花苷稳定性的主要因素,可为毛蕊花苷提取、纯化和活性分析等相关研究提供重要的参考。

     

Shelf-life prediction of fresh blood orange juice

Fresh blood orange juice is successful on the market because of its taste and nutritional value. Yet, it requires accurate control of the cold chain during storage and distribution. A kinetic study was carried out both on growth of spoilage microorganisms (i.e. yeasts) and on decrease of nutritional value (i.e. ascorbic acid and anthocyanin contents) of pasteurised fresh blood orange juice. Kinetic equations were used to set up mathematical models to predict shelf-life of pasteurised fresh blood orange juice under isothermal and non-isothermal conditions. The mathematical model was also able to predict yeast growth in unpasteurised fresh blood orange juice during shelf-life.     

Growth kinetics of Listeria monocytogenes in broth and beef frankfurters--determination of lag phase duration and exponential growth rate under isothermal conditions

ABSTRACT:  The objective of this study was to develop a new kinetic model to describe the isothermal growth of microorganisms. The new model was tested with Listeria monocytogenes in tryptic soy broth and frankfurters, and compared with 2 commonly used models—Baranyi and modified Gompertz models. Bias factor (BF), accuracy factor (AF), and root mean square errors (RMSE) were used to evaluate the 3 models. Either in broth or in frankfurter samples, there were no significant differences in BF (approximately 1.0) and AF (1.02 to 1.04) among the 3 models. In broth, the mean RMSE of the new model was very close to that of the Baranyi model, but significantly lower than that of the modified Gompertz model. However, in frankfurters, there were no significant differences in the mean RMSE values among the 3 models. These results suggest that these models are equally capable of describing isothermal bacterial growth curves. Almost identical to the Baranyi model in the exponential and stationary phases, the new model has a more identifiable lag phase and also suggests that the bacteria population would increase exponentially until the population approaches to within 1 to 2 logs from the stationary phase. In general, there is no significant difference in the means of the lag phase duration and specific growth rate between the new and Baranyi models, but both are significantly lower than those determined from the modified Gompertz models. The model developed in this study is directly derived from the isothermal growth characteristics and is more accurate in describing the kinetics of bacterial growth in foods.     

Thermal Degradation of Partially Purified Paralytic Shellfish Poison Toxins at Different Times, Temperatures, and pH

ABSTRACT: Mixtures of purified and partially purified paralytic shellfish poisoning (PSP) toxins including C1/2 and B1 toxins, gonyautoxins 1-4 (GTX), neosaxitoxin (NEO), and saxitoxin (STX) were heated at different temperatures (90 to 130 °C), heating times (10 to 120 min), and pH (3 to 7) and analyzed by HPLC. C toxins declined rapidly at low pH, and GTX 1/4 toxins decreased at high temperatures and at high pH. GTX 2/3 increased initially at low pH and then declined with subsequent heating, whereas STX increased consistently at pH 3 to 4. The integrated total specific toxicity declined at high pH (6 to 7). The kinetics of thermal destruction were 1^st order, and the efficacy of thermal destruction was highly dependent on pH, with rapid thermal destruction of carbamate compounds at higher pH. D values of carbamate toxins decreased with increasing temperature at high pH. Heating at low pH resulted in conversion of least toxic compounds to highly toxic compounds.     

马铃薯膳食纤维对胆固醇的吸附性能及动力学研究

研究了用马铃薯渣制备的新型膳食纤维(PDF)对胆固醇的吸附。实验结果表明PDF对胆固醇具有一定的吸附作用,可做为人体较好的营养纤维,吸附的最佳条件为:PDF用量0.5～1.0g,胆固醇的浓度为60～100μg/ml,吸附达平衡的时间约为30min,低温有利于吸附。PDF对胆固醇的吸附机理是物理吸附。动力学研究表明PDF对胆固醇的吸附符合Freundlich模式。     

PAM的分散聚合法制备及其应用研究进展

介绍了分散聚合法制备聚丙烯酰胺的研究进展,对聚丙烯酰胺分散聚合的成核与稳定机理、聚合过程的动力学、反应参数对聚合反应的影响以及运用分散聚合法制备聚丙烯酰胺的应用进行了概述。     

阿拉伯糖的稀酸水解法制备与动力学分析

目的:优选生物质水解制备阿拉伯糖工艺,并对其水解过程进行动力学分析。方法:利用单因素试验和响应面试验优化稀酸水解阿拉伯胶制备阿拉伯糖的工艺条件,并进行水解过程的动力学研究。结果:最佳水解工艺条件为：反应时间237 min,硫酸浓度0.16 mol/L,反应温度91℃,在此条件下进行3次平行验证实验,水解液中L-阿拉伯糖浓度的平均值为35.45 g/L。利用Saeman模型拟合,得到阿拉伯糖生成与降解的动力学参数。阿拉伯胶的水解为内扩散控制反应过程。结论:阿拉伯胶的水解过程为连续的拟均相一阶反应过程,Saeman模型能较好地描述阿拉伯胶水解制备阿拉伯糖的过程。