叠氮活化烟草多酚氧化酶Ⅱ的机理

至今人们一直报道叠氮作为金属蛋白(特别是铜蛋白)的一种抑制剂,本研究表明叠氮也可以作为烟草多酚氧化酶Ⅱ(简称PPOⅡ)的激活剂.在天然PPOⅡ、叠氮-PPOⅡ络合物和过氧化物-PPOⅡ络合物的方波电位学研究中,从硝基蓝四唑(nitro bluetetrazolium)能被酶还原和PPOⅡ能被过氧化物激活的试验结果可以看出,叠氮与PPOⅡ的结合诱导了天然PPOⅡ活性中心的CuO2-Cu生成了CuO22-Cu活性中心结构.叠氮作为激活剂的原因应归因于叠氮分子与PPOⅡ的络合反应导致了CuO2 2-Cu的生成,它恰是过氧化物-PPOⅡ络合物的活性中心,其实质是过氧负离子起到激活剂的作用.     

氯化钙对机械伤番茄果实生理特性的影响

为研究氯化钙处理对具有机械伤的番茄果实生理特性的影响,本实验用1 mmol/L氯化钙(CaCl₂)处理机械伤的番茄果实,将处理后的番茄于20℃贮藏,测定贮藏期间番茄生理品质和抗氧化酶活性的变化。结果表明:经过CaCl₂处理含有机械损伤的番茄果实,可以维持番茄在贮藏期间的感官品质,降低腐烂率;与对照组相比,CaCl₂处理可维持番茄果实的硬度和色度,延缓贮藏期间维生素C(V_C)含量的下降;同时,抑制丙二醛(MDA)的积累,提高过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)、多酚氧化酶(PPO)的活性。因此,1 mmol/L CaCl₂处理具有机械损伤的番茄可以有效维持其在贮藏期间的品质,延长货架期。     

气调贮藏对“徐香”猕猴桃采后保鲜效果影响

为研究不同气调贮藏条件对猕猴桃采后保鲜效果的影响,以"徐香"猕猴桃为试材,分别用2% O₂+3% CO₂、2% O₂+5% CO₂、5% O₂+3% CO₂、5% O₂+5% CO₂四种不同气体成分结0℃贮藏猕猴桃,并测定贮藏期间猕猴桃果实的硬度、可溶性固形物含量、维生素C含量、总酚含量、丙二醛(MDA)含量、过氧化物酶(POD)活性和多酚氧化酶(PPO)活性等指标。结果表明:气调贮藏能够有效保持果实的硬度,延缓可溶性固形物含量、V_C含量、总酚含量的下降,抑制MDA含量的上升以及PPO活性的增加,并保持较高的POD活性,有效延长了猕猴桃果实的贮藏期。综上,2% O₂+5% CO₂的气调条件对猕猴桃的保鲜效果最好,能够较好地保持果实品质,提高抗氧化物质含量,延缓果实的衰老速度。     

气调包装技术在鲜切肉苁蓉保鲜中的应用

针对鲜切肉苁蓉易出现褐变和品质劣变的问题,该研究以新疆荒漠肉苁蓉为研究试材,在(4±0.5)℃条件下,采用气调包装(4%O₂+2%CO₂+94%N₂、4%O₂+4%CO₂+92%N₂、4%O₂+6%CO₂+90%N₂)进行处理,采用L^*值、ΔE、褐变度、硬度、水分含量、呼吸强度、维生素C含量、总酚含量和菌落总数等指标评价气调包装对鲜切肉苁蓉褐变及品质的影响。结果表明,气调包装处理能有效抑制鲜切肉苁蓉在贮藏过程中褐变和品质劣变,且以4%O₂+6%CO₂+90%N₂气调包装保鲜效果最佳。该处理能有效抑制贮藏期间鲜切肉苁蓉多酚氧化酶(polyphenol oxidase, PPO)、过氧化物酶(peroxidase, POD)活性(P<0.05)、延缓其褐变过程。此外,该条件可显著抑制鲜切肉苁蓉呼吸强度,...     

采后氯化钙处理对红树莓保鲜的影响

以红树莓为试材,研究了1%、2%和4%的氯化钙(CaCl₂)处理对采后低温(0℃)贮藏下红树莓果实品质影响。结果表明:1%和2% CaCl₂处理均可降低果实在贮藏期间的呼吸强度,减缓果实硬度、可滴定酸(titritable acidity,TA)含量、可溶性固形物(total soluble solids,TSS)含量、维生素C(vitamin C,V_C)含量、总酚含量的下降与丙二醛(malondialdehyde,MDA)含量的上升,抑制果实多酚氧化酶(polyphenol oxidase,PPO)的活性,同时提高过氧化物酶(peroxidase,POD)活性及过氧化氢酶(catalase,CAT)活性,而4% CaCl₂处理则有相反结果。因此,适宜浓度的CaCl₂处理可以有效维持采后红树莓果实的贮藏品质,以2% CaCl₂处理效果最佳。     

气调处理对茭白贮藏品质的影响

目的:明确气调贮藏对茭白的保鲜效果。方法:以常压冷藏为对照,在0℃和相对湿度为85%～90%的贮藏条件下,比较4种不同比例气体组分(CA1:2%O₂+7%CO₂+91%N₂,CA2:5%O₂+10%CO₂+85%N₂,CA3:5%O₂+7%CO₂+88%N₂,CA4:2%O₂+10%CO₂+88%N₂)对茭白感官品质、质构(硬度、咀嚼性、剪切力)、色泽(L^*、W_H值)、蛋白质、木质素和纤维素、苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)活性的影响。结果:气调处理可以显著延缓茭白感官品质、L^*值、W_H值的下降及可溶性蛋白质的消耗(P<0.05),气调处理中CA2的保鲜效果最好。贮藏90 d, CA2处理茭白PAL、PPO活性显著低于对...     

薇菜天然复配保鲜剂配方的优化及其对薇菜贮藏期生理指标的影响

为了保持薇菜的品质,延长其货架期,本实验以薇菜为研究对象,在单因素实验的基础上采用L₉(34)正交试验考察三种天然保鲜剂茶多酚、川陈皮素、壳聚糖复配对薇菜感官品质、叶绿素含量、V_C含量的影响。结果表明,筛选出的复合保鲜剂配方为茶多酚0.8 g/L、川陈皮素2.5 g/L、壳聚糖2 g/L。与不添加保鲜剂的薇菜相比,该配方对于能够提升薇菜的感官品质,维持薇菜的叶绿素、V_C、可溶性糖含量,对多酚氧化酶(PPO)、过氧化物酶(POD)的活性具有抑制作用,在4 ℃条件下较未用保鲜剂处理的薇菜能延长5~7 d贮藏时间。     

商标保鲜卡对巨峰葡萄采后果梗褐变的抑制作用

针对鲜食葡萄电商和物流技术需求，以巨峰葡萄为试验材料，采用商标保鲜卡T₁(0.8 g焦亚硫酸钠+0.2 g缓释剂)、T₂(0.8 g焦亚硫酸钠+1.0 g层状硅酸盐+0.2 g缓释剂)进行处理，在(12±1)℃、相对湿度(85±5)%货架条件下，研究商标保鲜卡处理对巨峰葡萄采后货架期间果梗褐变的抑制作用。结果表明，商标保鲜卡T₂能够抑制果梗乙烯释放量和呼吸强度；延缓巨峰葡萄果梗过氧化物酶(peroxidase, POD)、超氧化物歧化酶(superoxide dismutase, SOD)、过氧化氢酶(catalase, CAT)和抗坏血酸过氧化物酶(ascorbate peroxidase, APX)、多酚氧化酶(polyphenol oxidase, PPO)活性的下降；抑制超氧阴离子自由基(·O^-₂)的产生速率、H₂O₂含量、相对电导率以及丙二醛含量的上升；能够提高果梗的总酚含量，延缓葡萄果梗发生褐变。研究表明商标保鲜卡能够延缓...     

一种多金属氧酸盐对多酚氧化酶的抑制活性评价及在南美白对虾保鲜上的应用

目的:研究新型多酚氧化酶抑制剂对南美白对虾的保鲜效果。方法:通过紫外和红外光谱表征合成的多酚氧化酶抑制剂H₈[P₂Mo₁₇Ni(OH₂)O₆₁](P₂Mo₁₇Ni),研究其对蘑菇多酚氧化酶(PPO)相对酶活的影响及抑制机制和抑制类型;再测定经P₂Mo₁₇Ni处理后的南美白对虾在贮藏过程中的感官评分、色差(L^*)值、总色差(ΔE)值、菌落总数、酸碱度(pH)值和总挥发性盐基氮(TVB-N)值的变化情况,评价P₂Mo₁₇Ni在南美白对虾保鲜上的作用。结果:P₂Mo₁₇Ni对体外蘑菇PPO的活性具有抑制作用,其半抑制浓度(IC₅₀)为(0.377±0.004) mmol/L,且对PPO的抑制模式为竞争型可逆抑制,抑制常数K_I为0.185 mmol...     

二氧化氯处理对低温贮藏鲜切仔姜品质的影响

为探讨二氧化氯(Chlorine dioxide,ClO₂)处理对鲜切仔姜贮藏品质的影响，以鲜切‘竹根姜’为实验材料，分别用蒸馏水和20、40、60 mg/L的ClO₂溶液浸泡5 min，监测4℃贮藏条件下，鲜切仔姜的色泽、硬度、丙二醛(MDA)、总酚、姜辣素、多酚氧化酶(Polyphenol oxidase,PPO)及过氧化物酶(Peroxidases,POD)活力等指标的变化。结果表明，与对照相比，不同浓度ClO₂处理可有效维持鲜切仔姜良好的色泽和硬度，减少质量损失和MDA累积，延缓姜辣素及总酚含量的降低，同时抑制PPO和POD的活力。贮藏至11 d时，40 mg/L ClO₂处理组的硬度最高，分别比对照、20 mg/L和60 mg/L组高28.3%、15.9%和9.3%(P<0.05)，而质量损失率和MDA含量最小，分别为对照的44.4%和76.6%(P<0.05)，姜辣素、总酚含量分别比对照高27.3%和35.3%(P<0.05),PPO和POD活力则分别比对照低38.1%...     

Mineralization of CCl4 with copper oxide

Experimentally, CCl4 was effectively mineralized by CuO to yield stable inorganic species of CO2 and CuCl2 (CCl4 + 2CuO --> 2CuCl2 + CO2). High CCl4 conversions (63-83%) were found in the mineralization process performed at 513-603 K for 10-30 min. Using X-ray-absorption near edge structure (XANES) and X-ray photoelectron spectroscopies, we found that most CuCl2 was encapsulated in the CCl4-mineralized product solid (mineralization at 513 K for 30 min). At higher mineralization temperatures (563-603 K), CuCl2 was found to be predominant on the surfaces of the mineralization product. Speciation of copper in the mineralization product solid was also studied by extended X-ray absorption fine structure (EXAFS) spectroscopy. Bond distances of Cu-O and Cu-Cl in the CCl4-mineralized product solid were 1.93-1.94 and 2.10-2.12 , respectively, which were greater than those of normal CuO and CuCl2 by 0.03-0.07 A. The increase of the bond distances for Cu-O and Cu-Cl might be due to Cl insertion and concomitant structural perturbation of unreacted CuO in the mineralization process. Forthe second shell around copper atom, bond distances of Cu-(O)-Cu also increased by 0.03-0.05 A, and the coordination numbers of Cu-O and Cu-(O)-Cu decreased, as expected, in the mineralization process. In addition, stoichiometrically excess oxygen atoms were found on the solid surfaces, and they might play an important role in the mineralization of CCl4, leading to the formation of CO2 and Cl. Chloride atoms might be further captured by CuO, yielding CuCl2 in the mineralization process. This work exemplifies the utilization of X-ray spectroscopies (XANES, EXAFS, and XPS) to reveal the speciation and possible reaction pathway in a very complex mineralization process in detail.     

Rapid, biomimetic degradation in water of the persistent drug sertraline by TAML catalysts and hydrogen peroxide

Iron TAML activators (oxidation catalysts based upon tetraamido macrocyclic ligands) at nanomolar concentrations in water activate hydrogen peroxide to rapidly degrade sertraline, the persistent, active pharmaceutical ingredient (API) in the widely used drug Zoloft. Although all the API is readily consumed, degradation slows significantly at one intermediate, sertraline ketone. The process occurs from neutral to basic pH. The pathway has been characterized through four early intermediates which reflect the metabolism of sertraline, providing further evidence that TAML activator/peroxide reactive intermediates mimic those of cytochrome P450 enzymes. TAML catalysts have been designed to exhibit considerable variability in reactivity and this provides an excellent tool for observing degradation intermediates of widely differing stabilities. Two elusive, hydrolytically sensitive intermediates and likely human metabolites, sertraline imine and N-desmethylsertraline imine, could be identified only by using a fast-acting catalyst. The more stable intermediates and known human metabolites, desmethylsertraline and sertraline ketone, were most easily detected and studied using a slow-acting catalyst. The resistance of sertraline ketone to aggressive TAML activator/peroxide treatment marks it as likely to be environmentally persistent and signals that its environmental effects are important components of the full implications of sertraline use.     

Environmentally persistent free radicals (EPFRs). 1. Generation of reactive oxygen species in aqueous solutions

Reactive oxygen species (ROS) generated by environmentally persistent free radicals (EPFRs) of 2-monochlorophenol, associated with CuO/silica particles, were detected using the chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy. Yields of hydroxyl radical ((?)OH), superoxide anion radical (O(2)(?-)), and hydrogen peroxide (H(2)O(2)) generated by EPFR-particle systems were reported. Failure to trap superoxide radicals in aqueous solvent, formed from reaction of EPFRs with molecular oxygen, results from fast transformation of the superoxide to hydrogen peroxide. However, formation of superoxide as an intermediate product in hydroxyl radical formation in aprotic solutions of dimethyl sulfoxide (DMSO) and acetonitrile (AcN) was observed. Experiments with superoxide dismutase (SOD) and catalase (CAT) confirmed formation of superoxide and hydrogen peroxide, respectively, in the presence of EPFRs. The large number of hydroxyl radicals formed per EPFR and monotonic increase of the DMPO-OH spin adduct concentration with incubation time suggest a catalytic cycle of ROS formation.     

The purification and characterisation of polyphenol oxidase from green bean (Phaseolus vulgaris L.)

Four isoforms of polyphenol oxidases (PPOs) were characterised in purified extracts of coats (PPOIa and PPOIb) and pods (PPOIIa and PPOIIb) of green bean (Phaseolus vulgaris L.). The molecular weights of four isoforms have been estimated to be from 57.5 to 39.0 kDa by SDS–PAGE. The PPOII (mixture of PPOIIa and PPOIIb) was used to characterise the PPO of green bean pods. All isoforms activities were stable between pH 6.8 and pH 7.2. PPOIa and PPOII have similar thermal inactivation profiles, and PPOIb has higher thermal stability than that of PPOIa and PPOII. PPOs showed the highest affinity to pyrogallol in all selected substrates. Although activities of PPOs were markedly inhibited by l-ascorbic acid, the activity of PPOI (mixture of PPOIa and PPOIb) was significantly activated by MnSO₄ and CaCl₂.     

Poly(ethylene glycol)-alpha-chymotrypsin complex catalytically active in anhydrous isooctane

Enzymatic catalysis in predominantly organic media has undergone rapid expansions, particularly over the past decade. There are numerous potential advantages in employing enzymes in organic media. However, there are some crucial defects in the native enzyme-catalyzed biocatalyses, such as a decrease in their reaction rate due to diffusional limitations of substrates. To overcome these defects, enzymes modified chemically with polymers and physically with surfactants, which were soluble in organic solvents, were often used. However, they had inherent drawbacks. On the other hand, the enzymes modified physically with polymers were found to be soluble and catalytically active in organic media. To date, however, the effect of the amount of added polymers on the enzyme activity has not been clarified, even though this may be an important factor governing the activity of polymer-enzyme complexes in organic media. In this study, we obtained a complex of an enzyme and a hydrophilic polymer by lyophilizing an aqueous solution containing a polymer and an enzyme. We found that the polymer-enzyme complex was catalytically active in organic media even when the molar ratio of polymer/enzyme in its preparation stage was unity, and that the activity of the polymer-enzyme complex increased with an increase in the molar ratio of polymer/enzyme, reached the maximum activity (ca. 7200-fold higher than that of the native enzyme suspended in organic media) and then gradually decreased.     

Initiation of lipid peroxidation in biological systems

The direct oxidation of PUFA by triplet oxygen is spin forbidden. The data reviewed indicate that lipid peroxidation is initiated by nonenzymatic and enzymatic reactions. One of the first steps in the initiation of lipid peroxidation in animal tissues is by the generation of a superoxide radical (see Figure 16), or its protonated molecule, the perhydroxyl radical. The latter could directly initiate PUFA peroxidation. Hydrogen peroxide which is produced by superoxide dismutation or by direct enzymatic production (amine oxidase, glucose oxidase, etc.) has a very crucial role in the initiation of lipid peroxidation. Hydrogen peroxide reduction by reduced transition metal generates hydroxyl radicals which oxidize every biological molecule. Hydrogen peroxide also activates myoglobin, hemoglobin, and other heme proteins to a compound containing iron at a higher oxidation state, Fe(IV) or Fe(V), which initiates lipid peroxidation even on membranes. Complexed iron could also be activated by O2- or by H2O2 to ferryl iron compound, which is supposed to initiate PUFA peroxidation. The presence of hydrogen peroxide, especially hydroperoxides, activates enzymes such as cyclooxygenase and lipoxygenase. These enzymes produce hydroperoxides and other physiological active compounds known as eicosanoids. Lipid peroxidation could also be initiated by other free radicals. The control of superoxide and perhydroxyl radical is done by SOD (a) (see Figure 16). Hydrogen peroxide is controlled in tissues by glutathione-peroxidase, which also affects the level of hydroperoxides (b). Hydrogen peroxide is decomposed also by catalase (b). Caeruloplasmin in extracellular fluids prevents the formation of free reduced iron ions which could decompose hydrogen peroxide to hydroxyl radical (c). Hydroxyl radical attacks on target lipid molecules could be prevented by hydroxyl radical scavengers, such as mannitol, glucose, and formate (d). Reduced compounds and antioxidants (ascorbic acid, alpha-tocopherol, polyphenols, etc.) (e) prevent initiation of lipid peroxidation by activated heme proteins, ferryl ion, and cyclo- and lipoxygenase. In addition, cyclooxygenase is inhibited by aspirin and nonsteroid drugs, such as indomethacin (f). The classical soybean lipoxygenase inhibitors are antioxidants, such as nordihydroguaiaretic acid (NDGA) and others, and the substrate analog 5,8,11,14 eicosatetraynoic acid (ETYA), which also inhibit cyclooxygenase (g). In food, lipoxygenase is inhibited by blanching. Initiation of lipid peroxidation was derived also by free radicals, such as NO2. or CCl3OO. This process could be controlled by antioxidants (e).(ABSTRACT TRUNCATED AT 400 WORDS)     

亚麻织物的过氧化氢和过醋酸漂白

通过正交试验，优选出亚麻织物的过醋酸漂白工艺条件，并与过氧化氢的漂白效果进行对比，探讨采用过醋酸一过醋酸或过氧化氢，过醋酸工艺，对白度要求较高的亚麻产品进行复漂。     

Catalytic effect of CuO and other transition metal oxides in formation of dioxins: theoretical investigation of reaction between 2,4,5-trichlorophenol and CuO

Density functional theory (DFT) calculations have been carried out to explore the potential energy surface (PES) associated with the gas-phase reaction between 2,4,5-trichlorophenol and CuO. A gas-phase model was constructed to account, from a theoretical perspective, for the most important reaction steps reported experimentally for the interaction between chlorinated phenol and a CuO surface. This involves the facile production of the chlorophenoxy radical through hydroxyl H abstraction, formation of HOCu-2,4,5-trichlorophenolate complex, and reduction of Cu-(II) into Cu(I) through chlorophenoxy desorption from the chlorophenolate complex. The overall process: 2,4,5-trichlorophenol + CuO --> 2,4,5-trichlorophenoxy radical + CuOH is significantly exothermic and facile (unlike the strongly endothermic process of 2,4,5-trichlorophenol --> 2,4,5-trichlorophenoxy radical + H) suggesting that in the gas phase, at least, CuO would be an efficient catalyst for production of polychlorinated phenoxy radicals which are known precursors of dioxins. Hence, the present study should be an important preliminary to a detailed investigation of the efficacy of CuO surfaces toward catalysis of dioxin formation. Lastly, we estimate the reaction energies for the reaction 2,4,5-trichlorophenol + MO --> 2,4,5-trichlorophenoxy radical + MOH for the first-row transition metal monoxides. This reaction only becomes exothermic for elements which have at least a half-filled d shell. Although the results of the present thermodynamic analysis match the observed catalytic effect toward dioxin formation, kinetic considerations are expected to play a major role as well.     

Destruction of estrogens using Fe-TAML/peroxide catalysis

Endocrine disrupting chemicals (EDCs) impair living organisms by interfering with hormonal processes controlling cellular development Reduction of EDCs in water by an environmentally benign method is an important green chemistry goal. One EDC, 17alpha-ethinylestradiol (EE2), the active ingredient in the birth control pill, is excreted by humans to produce a major source of artificial environmental estrogenicity, which is incompletely removed by currenttechnologies used by municipal wastewater treatment plants (MWTPs). Natural estrogens found in animal waste from concentrated animal feeding operations (CAFOs) can also increase estrogenic activity of surface waters. An iron-tetraamidomacrocyclic ligand (Fe-TAML) activator in trace concentrations activates hydrogen peroxide and was shown to rapidly degrade these natural and synthetic reproductive hormones found in agricultural and municipal effluent streams. On the basis of liquid chromatography tandem mass spectrometry, apparent half-lives for 17 alpha- and 17 beta-estradiol, estriol, estrone, and EE2 in the presence of Fe-TAML and hydrogen peroxide were approximately 5 min and included a concomitant loss of estrogenic activity as established by E-Screen assay.     

Invited review: The effect of native and nonnative enzymes on the flavor of dried dairy ingredients

Dried dairy ingredients are used in a wide array of foods from soups to bars to beverages. The popularity of dried dairy ingredients, including but not limited to sweet whey powder, whey proteins and milk powders, is increasing. Dried dairy ingredient flavor can carry through into the finished product and influence consumer liking; thus, it is imperative to produce a consistent product with bland flavor. Many different chemical compounds, both desirable and undesirable, contribute to the overall flavor of dried dairy ingredients, making the flavor very complex. Enzymatic reactions play a major role in flavor. Milk contains several native (indigenous) enzymes, such as lactoperoxidase, catalase, xanthine oxidase, proteinases, and lipases, which may affect flavor. In addition, other enzymes are often added to milk or milk products for various functions such as milk clotting (chymosin), bleaching of whey products (fungal peroxidases, catalase to deactivate hydrogen peroxide), flavor (lipases in certain cheeses), or produced during the cheesemaking process from starter culture or nonstarter bacteria. These enzymes and their possible contributions will be discussed in this review. Understanding the sources of flavor is crucial to produce bland, flavorless ingredients.