Oxygen and superoxide-mediated redox kinetics of iron complexed by humic substances in coastal seawater

Complexes with terrestrially derived humic substances represent one of the most reactive pools of dissolved Fe in natural waters. In this work, redox kinetics of Fe-humic substance complexes (FeL) in simulated coastal seawater were investigated using chemiluminescence techniques with particular attention given to interactions with dioxygen (O2) and superoxide (O2?-). Although rate constants of FeIIL oxidation by O2 (5.6-52 M-1 · s-1) were 4-5 orders of magnitude less than those for O2?- (6.9-23 × 105 M-1 · s-1),O2 is likely to outcompete O2?- for FeIIL oxidation in coastal seawaters where steady-state O2?- concentrations are generally subnanomolar. Rate constants for FeIIIL reduction by O2?- of 1.8-5.6 × 104 M-1 · s-1 were also determined. From the balance of FeIIL oxidation rates and O2?- -mediated FeIIIL reduction rates, steady-state FeIIL concentrations were estimated to be in the subpicomolar to picomolar range, which is generally lower than measured in situ Fe(II) concentrations under relevant conditions. This suggests that (i) processes other than O2?- -mediated reduction (such as photochemical ligand-to-metal charge transfer) may be responsible for Fe(II) formation, (ii) the in situ ligands differ significantly from the humic substances used in this work, and/ or (iii) the influence of other environmental factors such as pH and temperature on Fe redox kinetics may have to be considered.     

Isolation and investigation of emulsifying properties of surface-active substances from rice bran

Surface-active substances were isolated from defatted rice bran. They were 70:30 w/w ethanol/water soluble and could be further divided into n-hexane soluble fraction (fraction A) and n-hexane insoluble fraction (fraction B). For both the fractions emulsifying properties (i.e., interfacial tension, emulsion droplet diameter, emulsifying activity, and emulsion stability), were investigated and compared to those of a commercial emulsifier Atmos 150 or Tween 20. It was found that fraction A produced lower interfacial tension data and smaller droplet sizes than those of fraction B and showed, at concentrations ⩾0.7 wt%, similar emulsifying properties to those of Atmos 150. Fraction B, however, was found to have inferior emulsifying properties to those of the fraction A and Tween 20. The main substances in fraction A responsible for the emulsifying properties and mechanisms involved need to be studied.     

泡沫分离提取多粘菌素E的工艺研究

重点研究了泡沫分离提取多粘菌素E的工艺。考察了表面活性剂种类、溶液pH、气速、SDS浓度、无机盐浓度等操作参数对分离过程的影响。确定的最佳操作条件为:使用SDS作为静电亲和物质,pH4～5,气速220mL/min,SDS浓度0.06g/L,此条件下收率达到80%,富集比达到4.2。通过微生物实验证明本方法分离多粘菌素E对其生物活性没有影响。使用正丁醇萃取泡沫液中的SDS,脱除率达到99.4%,使目标产物多粘菌素E得到较好的纯化。     

乳酸菌对棒曲霉素的脱除作用

将3株乳酸菌(A1-5、ATCC19434、DSM7134)的活菌、热灭活菌分别作用于棒曲霉素,作用不同时间后用HPLC对其脱除效果进行检测。结果表明,3株乳酸菌对棒曲霉素均有脱除作用,A1-5菌株作用10 h效果最好,脱除率为52.86%;ATCC19434菌株作用48 h时效果最好,脱除率为74.28%;DSM7134菌株作用48 h脱除效果最好,脱除率为58.96%。在相同作用时间下,同一菌株的活菌比热灭活菌的脱除效果好,说明这3株乳酸菌对棒曲霉素既有吸附作用亦有代谢降解作用,均可用于棒曲霉素的脱除。ATCC19434菌株吸附脱除效果最佳,A1-5菌株则代谢降解能力最强,进一步对A1-5菌株进行鉴定,明确其为植物乳杆菌。     

Removal of Pseudomonas putida biofilm and associated extracellular polymeric substances from stainless steel by alkali cleaning

Alkali (NaOH)-based compounds are commonly used in the food industry to clean food contact surfaces. However, little information is available on the ability of alkali and alkali-based cleaning compounds to remove extracellular polymeric substances (EPS) produced by biofilm bacteria. The objectives of this study were to determine the temperature and NaOH concentration necessary to remove biofilm EPS from stainless steel under turbulent flow conditions (clean-in-place simulation) and to determine the ability of a commercial alkaline cleaner to remove biofilm EPS from stainless steel when applied under static conditions without heat. Biofilms were produced by growing Pseudomonas putida on stainless steel for 72 h at 25 degrees C in a 1:10 dilution of Trypticase soy broth. The biofilms were treated using NaOH at concentrations of 1.28 to 6.0% and temperatures ranging from 66 to 70 degrees C. Other biofilms were treated with commercial alkaline cleaner at 25 or 4 degrees C for 1 to 30 min. Removal of EPS was determined by direct microscopic observation of samples stained with fluorescent-labeled peanut agglutinin lectin. Treatment with 1.2% NaOH at 66 degrees C for 3 min was insufficient to remove biofilm EPS. A minimum of 2.5% NaOH at 66 degrees C and 2.0% NaOH at 68 degrees C for 3 min were both effective for EPS removal. Commercial alkaline cleaner removed over 99% of biofilm EPS within 1 min at 4 and 25 degrees C under static conditions. Selection of appropriated cleaning agent formulation and use at recommended concentrations and temperatures is critical for removal of biofilm EPS from stainless steel.     

乳杆菌代谢所产生的抑酵母活性物质的分离纯化

从内蒙古传统乳酸发酵食品中筛选出具有抑酵母作用的乳杆菌,对其代谢产生的抑菌物质进行分离纯化。结果表明:ALAC-3和ALAC-4菌株的代谢产物粗提液通过Sephadex G-100凝胶过滤层析分离纯化后,分别得到抑菌活性组分G100-3和G100-5,经过SDS聚丙烯酰胺凝胶电泳检测均达到电泳纯,相对分子质量分别为80.49 ku和40.32 ku。经过薄层色谱法证明G100-3和G100-5为单一成分的抑菌物质。      

Inactivation and magnetic separation of bacteria from liquid suspensions using electrosprayed and nonelectrosprayed nZVI particles: observations and mechanisms

Here, nonelectrosprayed nanoscale zerovalent iron (NE-nZVI), electrosprayed nZVI (E-nZVI) and preoxidized nZVI (O-nZVI) particles were applied to inactivating Bacillus subtilis, Escherichia coli as well as bacteria in various wastewater samples. In addition, magnetic separation was applied to the mixture of 0.2 mL bacterial sample and 1.8 mL E-nZVI or NE-nZVI suspensions. Bacterial concentrations and optical density of the supernatants were analyzed using culturing, optical adsorption and qPCR tests. In general, for wastewater samples the inactivations were shown to range from 1-log to 3-log. PCR-DGGE analysis indicated that no gene mutation occurred when bacteria were treated with nZVI. Using magnetic separation, significant physical removals, revealed as a function of nZVI type (NE-,E- and O-nZVI) and bacterial concentration, up to 6-log were obtained. E-nZVI and NE-nZVI were shown to react differently with B. subtilis and E. coli, although exhibiting similar inactivation rates. qPCR tests detected higher amount of DNA in the supernatants from mixing E. coli with NE-nZVI, but less for E-nZVI. However, the opposite was observed with B. subtilis. Our data together with optical adsorption analysis suggested that the inactivation and magnetic separation mainly depend on Fe(0)/Fe(3)O(4) shell compositions, the type of bacteria (aerobic and anaerobic) and their concentrations.     

食品风味物质的分离研究进展与应用

介绍了一些常用食品风味物质的分离抽提方法,主要包括分子蒸馏法、超临界流体抽提法、超滤法、直接萃取法,并举实例说明这些方法的应用。     

Inhibition of Clostridium tyrobutyricum by bacteriocin-like substances produced by lactic acid bacteria

Lactic acid bacteria were selected for their inhibitory activity against Clostridium tyrobutyricum under conditions that eliminate the effects of lactic acid and hydrogen peroxide. Four strains were isolated belonging to the species Lactococcus lactis ssp. lactis. The sensitivity of the inhibitory substances to pronase and trypsine indicates that they are proteins or peptides different from nisin. Their resistance to phospholipase D indicates that they are also different from lactostrepcin. The inhibitory substances are produced during the exponential phase of growth. Their activity is bactericidal and directed toward some strains of Clostridium tyrobutyricum, Lactobacillus helveticus, and Streptococcus thermophilus, but strains used as dairy starters, Lactobacillus lactis, Streptococcus thermophilus, and Propionibacterium shermanii, are not all affected by the inhibition.     

Two-stage foam separation technology for recovering potato protein from potato processing wastewater using the column with the spiral internal component

For recovering potato protein from potato processing wastewater, the effects of temperature, pH, volumetric airflow rate, liquid loading volume and sparging time on the foam separation performances were investigated using the column with the spiral internal component (SIC). A two-stage foam separation technology was designed to improve both the enrichment ratio and recovery percentage of potato protein. The results showed that the SIC and specially the increase of temperature were effective for improving the enrichment ratio of potato protein. A best enrichment ratio of potato protein of 4.69 was obtained under the optimal conditions of temperature 45 °C, pH 7, volumetric airflow rate 100 mL/min, liquid loading volume 300 mL and sparging time 90 min. The total recovery percentage of potato protein was as high as 73.4% by using the two-stage foam separation technology. So the two-stage technology was effective for the protein recovery from potato processing wastewater.     

Preliminary characterization of bacteriocin-like substances from lactic acid bacteria isolated from organic leafy vegetables

This study presents the characterization of new strains of lactic acid bacteria (LAB) from organic vegetables. Forty-five strains of LAB isolated from vegetables were investigated by its antimicrobial activity against taxonomically related microorganisms. Genetic identification of selected LAB was performed by means of PCR method. These strains were Enterococcus faecium, Lactococcus lactis, Enterococcus hirae and Enterococcus canis. Bacteriocin-like substances were active against Gram-positive bacteria and Gram-negative foodborne pathogens (Listeria monocytogenes and Escherichia coli, respectively). The antimicrobial activity of LAB strains was inactivated by the addition of proteases, thus confirming the proteinaceous nature of the inhibition. In all four strains the bacteriocin activity was stable after extended refrigerated storage and freezing-thawing cycles. This fact suggests that bacteriocin produced by the four LAB strains may find application as biopreservatives in minimally processed vegetables.     

Removal of ionic dyes from water by solvent extraction using reverse micelles

Several methods (e.g., UV/H2O2 oxidation, adsorption, flocculation-precipitation) are normally employed to remove dye from water. A new technique based on liquid/liquid extraction using reverse micelles is proposed whereby recovery of solvent and reuse of dye is possible. Experiments were conducted by mixing a known quantity of dye in aqueous phase and solvent-containing surfactants in a simple mixer. The separation of solvent phase, containing encapsulated dye in reverse micelles, from aqueous phase due to gravity results in separation of dye from water. The removal of different ionic dyes (e.g., eosin yellow, methylene blue, malachite green, methyl orange, orange G) from aqueous phase in the presence of different cationic and anionic surfactants [e.g., sodium dodecylbenzene sulfonate, sodium bis(2-ethylhexyl) sulfosuccinate, hexadecyltrimethylammonium bromide, and cetyl pyridinium chloride] in different solvents (e.g., amyl alcohol, benzyl alcohol, methyl benzoate, and isooctane) were studied by conducting experiments. The percentage removal of dye from aqueous phase increases with the decrease in dye concentration or with the increase in surfactants concentration. Furthermore, the percentage COD removal of dye is increased with the increase in surfactant concentration. The nature of solvent has minimal effect on percentage removal of dye. The ratio of solventto aqueous phase volume required for the removal of dye decreases with the increase in surfactant concentration. It is possible to back-extract dye into aqueous phase and recover solvent by using counterionic surfactants. The separation of aqueous phase from the aqueous-phase solvent dispersion is faster for amyl alcohol as compared to benzyl alcohol and methyl benzoate. A theoretical model based on ion-exchange reaction between surfactants and dye is used to analyze the experimental data.     

泡沫分离法优化美味牛肝菌多糖分离工艺

采用间歇式泡沫分离法研究美味牛肝菌水提物中的多糖分离工艺条件。结果表明:常温下,每批投料量为200mL时,间歇式泡沫分离美味牛肝菌多糖的最佳工艺条件为pH6、原料液浓度0.640mg/mL、气体流速300mL/min、表面活性剂用量(0.02mg/mL)25mL、浮选时间55min,回收率可达83.1%。结果显示间歇式泡沫分离美味牛肝菌多糖是一种可行、有效的分离方法。     

基于微囊细胞耦合发酵生产Nisin泡沫分离条件的研究

研究嗜热乳链球菌（Streptococcus thermophilus）6032海藻酸盐-壳聚糖-海藻酸盐（ACA）液芯微囊细胞发酵生产Nisin泡沫分离的影响因素,探索最佳分离条件。在单因素试验的基础上,以Nisin富集比作为评价指标,采用正交试验对泡沫分离Nisin的条件进行优化。结果表明,通气速率和泡沫层高度是影响分离效果的显著因素。为获得较多的Nisin,且不影响发酵,同时兼顾分离效果,确定最佳分离条件为：分离pH值为6,泡沫层高11 cm,通气速率为0.15 L/min,分离时间60 min。在该最佳条件下,Nisin回收率为83.89%,Nisin富集比为8.4,细胞富集比为0.221。     

草果抑菌物质提取分离及GC-MS分析

采用超声波提取草果中的抑菌成分,以提取率和抑菌圈大小的乘积为考察指标,通过单因素实验和正交实验设计得出草果抑菌物质超声波提取的最佳工艺条件为:以60%乙醇为提取溶剂、料液比1∶16、浸泡时间20h,超声波温度55℃、超声波时间45min,得到的草果提取物提取率为10.5%,对金黄色葡萄球菌的抑菌圈大小为19.3mm。经液-液分离实验,得出乙酸乙酯部位抑菌活性最强,经GC-MS分析定性,共定性出了88种成分。     

分子印迹聚合物泡沫材料制备及选择性吸附分离三氟氯氰菊酯研究

利用疏水性二氧化硅粒子和少量的非离子表面活性剂Hypermer 2296构建稳定的油包水型Pickering HIPEs,以三氟氯氰菊酯(LC)为模板分子,丙烯酰胺(AM)和聚乙二醇二甲基丙烯酸酯(PEGDMA)为聚合前驱体,制备了具有规则开孔结构的分子印迹聚合物泡沫材料(MIPFs)。利用静态吸附研究了MIPFs选择性吸附分离LC的行为和机理,并考察MIPFs结构对于吸附作用的影响。结果表明,MIPFs对LC的吸附属于单分子层吸附,符合准二级动力学模型,MIPFs对LC具有较好的选择性识别能力,可以有效分离食品中残留的LC成分,提高聚酯类农残检测的精密度。      

Removal of cadmium and zinc from aqueous solutions using red mud

Red mud, an aluminum industry waste, has been converted into an inexpensive and efficient adsorbent. The product obtained has been characterized and utilized in batch and column operations for the removal of cadmium and zinc from aqueous solutions over a wide range of initial metal ion concentrations (1.78 x 10(-5) to 1.78 x 10(-3) M for Cd2+ and 3.06 x 10(-5) to 3.06 x 10(-3) M for Zn2+; contact time, 24 h) adsorbent dose (5-20 g/L), and pH (1.0-6.0). The removal of Cd2+ and Zn2+ was almost complete at low concentrations, while it was 60-65% at higher concentrations at optimum pH's of 4.0 and 5.0, respectively, with 10 g/L of adsorbent in an 8-10 h equilibration time. The adsorption decreased with increase in temperature. Kinetic studies have been used to describe the mechanism of adsorption. Chemical regeneration of the columns has been achieved with 1% HNO3.