Modelling biological efficacy decrease and rate of degradation of chlorpyrifos-methyl on wheat stored under controlled conditions

Insecticide residue degradation and pest survival were observed in wheat treated with a low dose of chlorpyrifos-methyl. Treated wheat was stored in small batches at three controlled temperatures and two levels of moisture content of grain, in equilibrium with r.h. in order to stabilise the water activity in the grain during a storage period of 126 d after insecticide application. Every 3 weeks, samples were taken from treated and untreated control grain in each storage condition. Chlorpyrifos-methyl residues declined regularly with time of storage and an exponential negative regression was fitted with high correlation coefficients in most situations of storage temperature and grain water activity (Aw). A multivariate model to show the respective influence of controlled variables involved in the model of residues breakdown (time, Aw, and temperature) was built up through a multiple regression. This model showed the respective importance of the water activity of grain kernels, temperature and formulation of chlorpyrifos-methyl and their combinations on the decline of residues. Simultaneously, the effectiveness of the residues was checked through bioassays with two target species: Sitophilus oryzae and Tribolium castaneum. Taking into account the intentionally low initial applied dose of chlorpyrifos-methyl, the period after application achieving complete kill of the two test insects was rather short and did not exceed 105 d for S. oryzae in the best conditions for control, i.e. low moisture content and temperature. For high Aw (0.8) and storage temperature 30°C, T. castaneum was effectively controlled (more than 95% kill) only on the day after the treatment, survival occurring at the next test date 21 d after the application. High moisture content and temperature and their interactions were the main variables influencing the decrease in the biological effectiveness with time. The concentration threshold for insect survival was slightly below 1 ppm chlorpyrifos-methyl and was influenced by storage and grain conditions. Implications of these findings on storage pest management practices and on the ability to predict the period of biological effectiveness of residues of chlorpyrifos-methyl are discussed.     

滩羊肉宰后成熟期间ATPase活力变化对微观结构及保水性的影响

为研究宰后成熟期间ATPase活力变化对滩羊肉微观结构以及保水性的影响,以6 月龄滩羊背最长肌（Longissimus dorsi）为研究对象,分析其4 ℃成熟0、1、2、4、8 d时Na＋-K＋-ATPase、Ca2＋-ATPase、Caspase-3活力以及肌肉微观结构、pH值与滴水损失率的变化情况。结果表明：随成熟时间延长,Na＋-K＋-ATPase与Ca2＋-ATPase活力先升高后降低,成熟1 d时达到最大值;Caspase-3活力先升高后降低,成熟2 d时达到最大值;滴水损失率先升高后降低,pH值先降低后有所回升;总蛋白、低盐溶性蛋白及高盐溶性蛋白质量浓度均逐渐减少,水溶性蛋白质量浓度成熟2 d后显著降低（P＜0.05）;成熟至8 d时,肌原纤维断裂,肌纤维之间、肌束之间、肌纤维及肌膜之间形成间隙,Z线断裂,H带消失;相关性分析结果表明Na＋-K＋-ATPase活力与各指标均呈极显著相关性（P＜0.01）,Ca2＋-ATPase活力与pH值、Na＋-K＋-ATPase及Caspase-3活力均呈极显著相关性（P＜0.01）。结论：滩羊肉宰后成熟过程中Na＋-K＋-ATPase与Ca2＋-ATPase活力变化可能促使下游Caspase-3激活,Caspase-3水解结构蛋白可能导致肌肉组织在不同部位形成间隙,在重力作用下肌肉中的水分流入间隙中,引起滩羊肉滴水损失升高,保水性变差。     

Purification, characterization, and steady-state kinetics of a meta-cleavage compound hydrolase from Pseudomonas fluorescens IPO1

2-Hydroxy-6-oxo-7-methylocta-2,4-dienoate (6-isopropyl-HODA) hydrolase (CumD), an enzyme of the cumene biodegradation pathway encoded by the cumD gene of Pseudomonas fluorescens IP01, was purified to homogeneity from an overexpressing Escherichia coli strain. SDS-polyacrylamide gel electrophoresis and gel filtration demonstrated that it is a dimeric enzyme with a subunit molecular mass of 32 kDa. The pH optima for activity and stability were 8.0 and 7.0-9.0, respectively. The enzyme exhibited a biphasic Arrhenius plot of catalysis with two characteristic energies of activation with a break point at 20 degrees C. The enzyme has a K(m) of 7.3 microM and a k(cat) of 21 s(-1) for 6-isopropyl-HODA (150 mM phosphate, pH 7.5, 25 degrees C), and its substrate specificity covers larger C6 substituents compared with another monoalkylbenzene hydrolase, TodR Unlike TodF, CumD could slightly hydrolyze 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (6-phenyl-HODA). A mutant enzyme as to a putative active site residue, S103A, had 10(5)-fold lower activity than that of the wild-type enzyme.     

淀粉类酶降解鲜烟叶中淀粉的研究

为降低烤后烟叶中淀粉含量,研究了烘烤过程中外加淀粉类酶对淀粉降解的影响.结果表明,烘烤过程中,通过外加淀粉类酶来降解烤烟中的淀粉是有效的.烘烤变黄初期,不同外加淀粉类酶烟叶淀粉降解动态基本一致;变黄后期至定色前期,淀粉降解随外加酶量增加而加剧.烤后烟叶淀粉含量随外加酶量增加而减少,水溶性糖和还原糖含量随外加酶量增加而增加.方差分析表明,不同处理烤后烟叶之间淀粉含量存在极显著差异.多重比较结果表明,K326品种适宜的外加酶量为(6 60)U/g;HD品种适宜的外加酶量为(8 80)U/g.     

荔枝果皮总花色苷及降解指数的测定

本文研究了荔枝果皮总花色苷及其降解指数的含量测定。结果表明,当荔枝果皮发生褐变时,1％盐酸甲醇提取液花色苷及降解指数含量显著偏高。荔枝果皮总花色苷及花色苷降解指数可以很好地反映出提取液中花色苷的降解情况。     

食品加工工艺对大豆内源基因降解变化规律的影响

本文以转基因大豆和非转基因大豆为试验材料，运用定性PCR技术分析了磨浆、煮浆、调配、均质、点浆、杀菌、喷雾干燥等豆腐、豆奶、豆粉三种豆制品中关键加工工艺对大豆内源基因lectin的影响，探讨了转基因大豆加工食品在不同加工过程中DNA降解程度的变化。研究结果表明，大豆内源基因在三种加工食品中的各个加工过程中都会受到不同程度的破坏。在豆腐、豆奶、豆粉的加工过程中，片段大小为1883bp的lectin基因仅能在原料中检测到；磨浆、煮浆、均质等工艺，使lectin基因降解至1000bp以下；随着进行的点浆、高温杀菌或喷雾干燥等工艺对lectin基因的降解产生更显著的影响，豆腐终产品中lectin基因的片段大小在500bp以下，豆奶、豆粉中lectin基因片段大小仅为200bp左右。     

发酵酸化技术对乳饼蛋白质降解及蛋白肽生物活性的影响

通过发酵酸化技术研制发酵型乳饼,以传统的直接酸化技术为对照,通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE）、液相色谱-质谱测定乳饼蛋白质降解情况和游离氨基酸含量,通过用液相色谱-串联质谱鉴定乳饼蛋白肽。并通过测定体外抗氧化活性、α-葡萄糖苷酶抑制率和血管紧张素转换酶（angiotensin-converting enzyme,ACE）抑制率表征乳饼蛋白肽的生物活性。SDS-PAGE结果表明,两种酸化技术均能促进乳饼蛋白质的降解,发酵酸化技术对乳清蛋白的降解程度更高,能促进游离氨基酸的释放。从发酵酸化乳饼中鉴定出潜在的ACE抑制肽23?条、抗氧化肽6?条和降糖肽5?条,而传统的直接酸化乳饼中分别为13、4?条和1?条。发酵酸化技术能显著提升乳饼蛋白肽的α-葡萄糖苷酶抑制活性和ACE抑制活性（P＜0.05）,其中分子质量＜3?kDa超滤组分对二者抑制率的IC50分别为1.250?mg/mL和0.416?mg/mL。发酵酸化技术能促进乳饼蛋白质降解,释放生物活性多肽,同时产生游离氨基酸,提升乳饼的生物学价值。     

金属共掺杂纳米TiO2对甲基橙的催化降解

以硫酸钛、CoCl2·6H2O和FeCl3为原料,采用共沉淀法制备了掺杂不同量Co2+和e3+的TiO2纳米粒,通过X-射线衍射(XRD)、差热-热重(TG-DTA)和紫外-可见吸收光谱(UV-Vis)等分析手段对样品的晶体类型、光谱吸收特征进行了表征.结果表明,金属共掺杂TiO2纳米粒仍以锐钛矿相存在,粒子的粒径约为12 nm;Co2+和Fe3+掺入TiO2后,主要以替代的方式占据TiO2晶格中Ti4+的位置,并在TiO2禁带中产生掺杂能级,使原来位于380 nm的吸收带边红移至460 nm.以太阳光为光源,当Co2+掺杂量为0.025%,Fe3+掺杂量小于0.05%时,光催化剂TiO2的活性较高,对甲基橙的降解率接近100%.     

负载MIL-53(Fe)的改性聚丙烯腈纤维光催化剂的制备及其性能

针对MIL-53(Fe)粉末作为光催化剂的光响应范围窄、催化效率低和难回收利用等问题,以偕胺肟改性聚丙烯腈(PAN)纤维作为载体,通过表面原位合成法制备了负载不规则MIL-53(Fe)的纤维MIL-53(Fe)-PAN。借助扫描电子显微镜、X射线衍射仪、红外光谱仪和紫外-可见漫反射光谱仪对其表面形态、微观结构和光吸收性能进行表征,并对其在染料降解中的光催化性能进行了研究。结果表明:原位合成的MIL-53(Fe)能够均匀分布于改性PAN纤维表面,部分MIL-53(Fe)呈现出一定的结晶性能,且纤维配体的电荷转移(LMCT)效应将其光谱响应范围拓宽至800 nm;由于纤维配体和对苯二甲酸配体的协同作用,使得MIL-53(Fe)-PAN在染料降解中显示出极高的可见光催化活性,远优于MIL-53(Fe)粉末及其直接负载改性PAN纤维催化剂,为高效金属有机框架材料(MOFs)光催化剂的结构调控提供了新的思路。