基于烟草水提物的Maillard反应产物影响因素

为充分利用烟叶资源,提高其使用价值,以亚临界萃取后的烟叶残渣为原料制备了烟草水提物,利用GC-MS法对Maillard反应产物进行定量分析,系统探讨了氨基酸种类及用量、反应时间对Maillard反应产物化学组成及卷烟感官质量的影响;并探讨了Maillard反应产物中的18种成分与卷烟感官指标的相关关系。结果表明:①谷氨酸和天冬氨酸的Maillard反应产物与水提物自身的Maillard反应相似,以5-羟甲基糠醛为主,其次为羟基丙酮、2-乙酰基吡咯;脯氨酸参与的反应产物则以羟基丙酮、糠醇和5-羟甲基糠醛为主。②以感官作用为依据,基于烟草水提物Maillard反应的最佳条件为还原糖（以葡萄糖计）与谷氨酸的摩尔比n_还原糖:n_谷氨酸=1:0.5、反应温度110 ℃、反应时间2 h。③18种成分中,2-甲基四氢呋喃-3-酮与烟气浓度相关关系密切,糠醛、5-甲基糠醛、2-呋喃基羟基甲基酮和5-羟甲基糠醛与透发性关系密切,羟基丙酮和3-甲基-1, 2-环戊二酮与烘焙香关系密切。      

NDMA formation during chlorination and chloramination of aqueous diuron solutions

Formation of the potent carcinogen N-nitrosodimethylamine (NDMA) during chlorine disinfection of water containing secondary amines is now generally acknowledged. The phenylurea herbicide diuron is one of the most widely used herbicides in California, has been frequently detected in California's water sources with a transient nature of appearance, and has a structure that suggests it might be an NDMA precursor. This study sought to quantify the potential for NDMA formation from aqueous diuron solutions under varied chlorine and chloramine conditions. NDMA formation was consistently observed even in the absence of added ammonia, which has usually been the source of the nitroso-nitrogen during chloramination of other precursors. It appears that both nitrogen atoms in NDMA are donated by diuron during chlorination in the absence of added ammonia. For a given chlorine and diuron dose, NDMA formation increased in the order OCl- < NH2Cl < NHCl2, a result consistentwith previous NDMAformation studies. Significant quantities of NDMA (170 ng/L) were produced during dichloramination of diuron using a low dichloramine concentration and a diuron concentration at the upper end of typically detected concentrations in California (20 microg/L), suggesting a need for further investigation to accurately assess the human health risks posed by diuron with respect to NDMA formation potential. A reaction pathway is proposed to provide a possible explanation for NDMA formation from diuron during chlorination or chloramination. The findings in this study identify a specific potential precursor of NDMA formation, one that arises from nonpoint sources. This further highlights the difficulties associated with determining the environmental safety of chemicals and their associated byproducts.     

Antioxidant and antiradical properties of maillard reaction products in both aqueous and ethanolic fructose-glycine oligomer solutions

The purpose of this study was to evaluate the antioxidant and antiradical properties of Maillard reaction products (MRP) in both aqueous and ethanolic fructoseglycine oligomer solutions. Antioxidant and radical scavenging activities of MRPs were investigated using different in vitro assays: the ferric ion (Fe³⁺) reducing ability, cupric ion (Cu²⁺), ferrous ion (Fe²⁺) chelating effects, DPPH and ABTS radical scavenging activities, and Fe³⁺-TPTZ reducing ability. MRPs derived from fructose-diglycine (GG) were found to be effective antioxidants in different in vitro assays. The antioxidant activity was higher in ethanolic solutions than in aqueous MRP solutions.     

Phenol chlorination and photochlorination in the presence of chloride ions in homogeneous aqueous solution

Phenol chlorination was studied in the presence of dissolved Fe(III) and chloride under irradiation and of hydrogen peroxide and chloride in dark acidic solutions. In the former case phenol photochlorination is most likely due to the formation of Cl2*- as a consequence of Fe(III) irradiation in the presence of chloride. The most efficient pathway is the photolysis of FeOH2+ producing hydroxyl, which oxidizes chloride to Cl*. The latter finally yields Cl2*- upon further reaction with chloride. The importance of the pathway involving FeOH2+ is higher at higher pH and moderately low chloride concentration. At pH 2.0 and [Cl-] > 0.03 M chlorophenol generation rate decreases with increasing [Cl-], due to the formation of the much less photoactive species FeCl2+/FeCl2+. The photolysis of FeCl2+/ FeCl2+ yielding Cl* is likely to play an important role at pH 0.5 and high chloride, but under such conditions chlorophenol formation rates are about an order of magnitude lower than at pH 2.0. Due to pH and kinetic constraints, under most environmental conditions the photochemistry of FeCl2+/FeCl2+ can be expected to play a minor role toward chlorination when compared with the one of FeOH2+, which leads to hydroxyl-mediated chloride oxidation. Hydrogen peroxide and chloride react in dark acidic solutions to yield HClO, involved in electrophilic chlorination processes. Chlorophenol formation rates under such conditions are directly proportional to [H+]. The described chlorination and photochlorination processes can take place in acidic aerosols of marine origin, naturally rich in chloride and Fe(III). Antarctic aerosol is also rich of hydrogen peroxide and often strongly acidic due to the presence of sulfuric acid of biogenic origin.     

Carbonation of steel slag for CO2 sequestration: leaching of products and reaction mechanisms

Carbonation of industrial alkaline residues can be used as a CO2 sequestration technology to reduce carbon dioxide emissions. In this study, steel slag samples were carbonated to a varying extent. Leaching experiments and geochemical modeling were used to identify solubility-controlling processes of major and trace elements, both with regard to carbonation mechanisms and the environmental properties of the (carbonated) steel slag. Carbonation was shown to reduce the leaching of alkaline earth metals (except Mg) by conversion of Ca-phases, such as portlandite, ettringite, and Ca-(Fe)-silicates into calcite, possibly containing traces of Ba and Sr. The leaching of vanadium increased substantially upon carbonation, probably due to the dissolution of a Ca-vanadate. The reactive surface area of Al- and Fe-(hydr)oxides increased with the carbonation degree, which tends to reduce the leaching of sorption-controlled trace elements. Sorption on Mn- (hydr)oxides was found to be required to adequately model the leaching of divalent cations, but was not influenced by carbonation. Consideration of these three distinct reactive surfaces and possible (surface) precipitation reactions resulted in adequate modeling predictions of oxyanion and trace metal leaching from (carbonated) steel slag. Hence, these surfaces exert a major influence on the environmental properties of both fresh and carbonated steel slag.     

Formation of chloroform and other chlorinated byproducts by chlorination of triclosan-containing antibacterial products

Triclosan is a widely used antibacterial agent found in many personal hygiene products. Although it has previously been established that pure triclosan and free chlorine readily react, interactions between triclosan-containing consumer products and free chlorine have not previously been analyzed in great depth. Sixteen double-blinded solutions including both triclosan-containing (1.14-3.12 mg triclosan/g product) and triclosan-free products were contacted with free chlorine at pH 7. Products detected included (chlorophenoxy) phenols, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and chloroform. The daughter product yields were found to be highly variable and were dependent on the antimicrobial product investigated, the free chlorine to triclosan ratio, and the temperature at which the study was conducted. Lowering the temperature from 40 to 30 degrees C resulted in a decreased average chloroform yield from 0.50 to 0.37 mol chloroform/mol triclosan consumed after 1 min of reaction time for an initial free chlorine concentration of 4.0 mg/L as Cl2. At 40 degrees C the average molar chloroform yields decreased to 0.29 and <0.1 when the initial free chlorine concentration was decreased to either 2.0 or 1.0 mg/L as Cl2, respectively. Field experiments, in which Atlanta, GA and Danville, VA tap waters were augmented with various soap products, exhibited results varying from the laboratory experiments in that different productyields were observed. These differences are attributed to the chlorine demand of constituents in the tap water. A simple exposure model suggests that exposure to chloroform can be significant under some conditions.     

Study of Maillard reaction products derived from aqueous model systems with different peptide chain lengths

Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 0.2 M glucose and 0.2 M each of glycine, diglycine, and triglycine, heated at 100 °C, for different times (10, 60, 120, 180 and 240 min), with an initial pH control set to 7.8. The browning and intermediate products of MRPs derived from the Glu-Di model system were the most prominent. The pH of all MRP samples decreased considerably as the heating time increased (P < 0.05). The loss of glucose in MRPs derived from the Glu-Di model system was the highest, while the degree of sugar enolisation in MRPs derived from the Glu-Tri model system was the highest. The amino acid group content in MRPs derived from the Glu-Di model system was decreased noticeably. All MRP samples showed different absorptions in the UV–vis spectra, although they possessed similar shapes. The molecular weights of all MRP samples showed rising intensities as a function of the heating time, whereas the major peaks of each MRP sample were eluted at different retention times according to peptide chain lengths.     

Interactions of fluoroquinolone antibacterial agents with aqueous chlorine: reaction kinetics, mechanisms, and transformation pathways

Kinetics, products, and mechanistic aspects of reactions between free available chlorine (HOCl/OCl-), ciprofloxacin (CF), and enrofloxacin (EF) were extensively investigated to elucidate the behavior of fluoroquinolone antibacterial agents during water chlorination processes. Although the molecular structures of these two substrates differ only with respect to degree of N(4) amine alkylation, CF and EF exhibit markedly different HOCl reaction kinetics and transformation pathways. HOCI reacts very rapidly at CF's secondary N(4) amine, forming a chloramine intermediate that spontaneously decays in aqueous solution by concerted piperazine fragmentation. In contrast, HOCl reacts relatively slowly at EF's tertiary N(4) amine, apparently forming a highly reactive chlorammonium intermediate (R3N-(4)Cl+) that can catalytically halogenate EF or other substrates present in solution. Flumequine, a fluoroquinolone that lacks the characteristic piperazine ring, exhibits no apparent reactivity toward HOCI but appears to undergo facile halodecarboxylation in the presence of R3N(4)-Cl+ species derived from EF. Measured reaction kinetics were validated in real water matrixes by modeling CF and EF losses in the presence of free chlorine residuals. Combined chlorine (CC) kinetics were determined under selected conditions to evaluate the potential significance of reactions with chloramines. CF's rapid kinetics in direct reactions with HOCl, and relatively high reactivity toward CC, indicate that secondary amine-containing fluoroquinolones should be readily transformed during chlorination of real waters, whether applied chlorine doses are present as free or combined residuals. However, EF's slower HOCl reaction kinetics, recalcitrance toward CC, and participation in the catalytic halogenation cycle described herein suggest that tertiary amine-containing fluoroquinolones will be comparatively stable during most full-scale water chlorination processes.     

Odorous products of the chlorination of phenylalanine in water: formation, evolution, and quantification

To explain some of the possible origins of an odor episode which took place in a drinking water supply in the region of Paris (France), the chlorination reaction in water of phenylalanine was studied. This amino acid was chosen for first experiments because of its physical and chemical particular properties. Changes in the different byproducts formed were followed by high-performance liquid chromatography (HPLC) over a period of time. N-chlorophenylalanine (mono-N-chlorinated amino acid) and then phenylacetaldehyde were the major products formed for the lower chlorine to nitrogen molar ratios. For Cl/N molar ratios of 1 and beyond, phenylacetonitrile and N-chlorophenylacetaldimine appeared and increased with the chlorination level. N-chlorophenylacetaldimine was quantified by using its difference of stability in various organic solvents. Our attention was first directed to the monochlorinated derivative but further examination indicated that it could not be responsible for odor troubles: it dissociated before reaching the consumer's tap and it was produced at consistently low yields under conditions relevant to drinking water treatment. On the contrary, chloroaldimine appeared to be a very odorous and water-stable product: it strongly smells of swimming pool with a floral background. The odor detection threshold is about 3 microg x L(-1) and it can persist for more than one week at 18 degrees C. It is now suspected of being a source of off-flavor concerns among consumers.