High Performance Liquid Chromatography of 2,5-Dimethyl-4-Hydroxy-3 (2H)-Furanone in Pineapple and Grapefruit Juices

A reversed-phase HPLC method was developed for rapid analysis of 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF), the compound responsible for the “burnt-pineapple” flavor in pineapple juices. A Zorbax ODS column was used with a mobile phase of 0.05M sodium acetate (pH 4.0)/methanol (70:30); detection was by UV at 290 nm. Sample clean up was accomplished by solid-phase extraction with C-18 Sep-Pak cartridges. DMHF contents ranged from 1.6 to 27.3 ppm from 10 fresh pineapple juices. Using this system, the production of DMHF was monitored in canned grapefruit juices during storage at varying temperatures.     

PURIFICATION AND CHARACTERIZATION OF LIPOXYGENASE ISOZYMES FROM CANOLA (Brassica napus cv, WESTAR) SEED

Four isozymes, I', II'a, II'b and III’ of lipoxygenase (EC 1.13.11.12) from Canola (Brassica napus, cv Westar) seed were purified by successive chromatography on ion-exchange and size-exclusion columns using a Fast Protein Liquid Chromatograph (FPLC). The homogeneity of each isozyme was demonstrated by a single protein band on SDS-polyacrylamide gel electrophoresis. The molecular weights of isozymes I', II'a, II'b and III’ were 72, 000, 106, 000, 78, 000 and 62, 000, respectively. The optimum pH for lipoxygenase activity was 6.5 for isozyme I’ and 6.0 for isozymes II'b, II'b and III'. Apparent K_m value for isozymes I', II'a, II'b and III’ were 5.5 × 10^?4 M, 3.4 × 10^?4 M, 4.0 × 10^?4 M and 3.8 × 10^?4 M, respectively. Isozyme I’ displayed preferential activity towards monolinoleate and dilinoleate, while isozyme II'a demonstrated preferential activity towards dilinoleate followed by mono- and trilinoleate. No enzymatic activity was observed with both isozymes I’ and II'a toward free linoleic acid. Isozyme II'b showed activity towards free linoleate as well as mono-, di- and trilinoleate. Isozyme III’ showed preferential activity towards free linoleate. The activity of isozymes I’ and II'a was inhibited completely by the addition of 10 mM and 4 mM KCN, respectively, while the addition of 3 mM and 10 mM KCN to isozymes II'b and III', respectively, increased activity by approximately 20%.     

开闸式异重流前峰行进规律:数值求解

本文首先以数值方法求得开闸式异重流前峰行进规律。数值求解基于重在化群（ＲＮＧ）ｋ－ε湍流应力封闭模式，能合理反映异重流的过渡性局部湍流特征，结果与实验相符，表明开闸式湍动重流的前峰行进有两个阶段，先是坍塌段，峰速不变，后是自相似段，峰这随时间以－１／３次规律递减。     

EFFECT OF GROWTH TEMPERATURE AND MEDIA ON INACTIVATION OF LISTERIA MONOCYTOGENES BY CHLORINE

The objective of this study was to determine the effect of growth environment on the susceptibility of Listeria monocytogenes to inactivation by hypochlorite sanitizer. Cells were grown in tryptic soy broth (TSB) at 35, 21, and 6°C and in 1:15 dilution of TSB (low nutrient medium, LNM) at 35°C. Late exponential phase cells were harvested, washed, and exposed to a 1 ppm sodium hypochlorite solution for periods up to 5 min. After 30 s exposure, cells grown at 35°C in TSB were reduced in number by 2.1 ± .3, at 21°C, 3.1 ± .3 and at 6°C, 3.4 ± .3 log units. After 30 s exposure to 5 ppm free chlorine cells grown at 35°C in TSB were reduced in number by 5.2 ± .2 and in LNM by 3.1 ± .1 log units. These data demonstrate that growth environment has a significant effect on chlorine inactivation of L. monocytogenes.     

Assessment of Cheddar Cheese Quality by Chromatographic Analysis of Free Amino Acids and Biogenic Amines

The free amino acids and biogenic amines extracted from normal and late-gassing Cheddar cheeses were derivatized with heptafluorobutyric anhydride and trifluoroacetic anhydride, respectively, before quantification by gas-liquid chromatography. On a microgram scale, twenty amino acids were positively identified in both types of cheese, but only high levels of γ-amino acid butyrate (0.3 to 19.4 mg/g) and small quantities of arginate were found to be associated with “poorly aged” Cheddar cheeses. Histamine (1.54 and 1.22 mg/g) and tyramine (0.32 and 0.43 mg/g) were the bioamines present in highest concentrations in both cheeses.     

深层搅拌水泥土基底加固层的三维随机有限元分析

在软土基坑开挖过程中,围护结构的最大侧向位移往往出现在开挖面以下。常用的防范方法是采用深层搅拌法对设计深度以下2~3 m的软土层进行水泥加固处理,形成水泥土加固层以减少围护结构的侧向位移。由于水泥土的强度具有显著的空间变异性,工程设计中通常采用较为保守的整体强度设计值。考虑深层搅拌桩形成过程中的两种主要不确定性因素:桩身位置不确定性和桩身内部水泥土强度不均匀性,将水泥土加固层的强度模拟为随机场,且将其作为材料变量结合有限元仿真模拟进行受力分析。分析结果表明水泥土加固层的设计强度可表示为钻心取样强度平均值减去t倍标准差,对系数t进行了详细探讨,所得结果可为今后类似工程设计提供参考依据。     

关于住居能源碳排放量影响因素的研究——基于中国省际面板数据的实证分析

以中国省级行政单位为研究对象对与居民生活息息相关的住居领域内所产生的能源消费与CO2排放的地区间差异性进行研究,并在此基础上对产生这一差异性的影响因素进行了深入的分析。以人均碳排放量为因变量,分别从人口、社会和经济特征及区域环境特征两大方面出发选取了10个影响因素作为自变量构建了从2002—2011年10年间以全国28个省份为对象的4个均衡面板数据模型并进行了估计分析。从模型估计结果来看,个人属性以及家庭结构等都对住居领域的碳排放有着显著性的影响;城镇居民的人均住宅建筑面积越大其碳排放量就越高。基于此,研究认为在制定有关节能减排措施时,要充分考虑到个人属性、家庭结构等人口和社会经济性因素以及住宅类型、城市形态等区域环境因素所带来的影响,根据各个地区不同的经济发展水平和实际情况因地制宜地制定和实施节能减排政策。