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1.
Bioassay-directed fractionation of the organic extract of the Kenyan pyrethrum flowers (Chrysanthemum cinerariaefolium Vissiani) resulted in the isolation of two natural pyrethrin esters, pyrethrin I (PI) and pyrethrin II (PII) as the major constituents. These esters elicited inhibition of the multiple drug resistant (MDR) Mycobacterium tuberculosis. The high-field (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of PI and PII were unequivocally assigned using modern two-dimensional (2D) proton-detected heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple-bond correlation (HMBC) experiments. The conformations of both esters were deduced from (1)H-(1)H vicinal coupling constants and confirmed by 2D nuclear Overhauser effect spectroscopy (NOESY). Computer molecular modeling (MM) studies revealed that PI and PII molecules adopt a "love-seat" conformation in chloroform (CDCl(3)) solution.  相似文献   

2.
In a screen of 1800 plant and fungal extracts for antiplasmodial, antitrypanosomal, and leishmanicidal activity, the n-hexane extract of Chrysanthemum cinerariifolium (Trevir.) Vis. flowers showed strong activity against Plasmodium falciparum. We isolated the five pyrethrins [i.e., pyrethrin II (1), jasmolin II (2), cinerin II (3), pyrethrin I (4), and jasmolin I (5)] from this extract. These were tested together with 15 synthetic pyrethroids for their activity against P. falciparum and Trypanosoma brucei rhodesiense and for cytotoxicity in rat myoblast L6 cells. The natural pyrethrins showed antiplasmodial activity with IC(50)s between 4 and 12 μM, and antitrypanosomal activity with IC(50)s from 7 to 31 μM. The pyrethroids exhibited weaker antiplasmodial and antitrypanosomal activity than the pyrethrins. Both pyrethrins and pyrethroids showed moderate cytotoxicity against L6 cells. Pyrethrin II (1) was the most selective antiplasmodial compound, with a selectivity index of 24.  相似文献   

3.
In this paper, pyrethrin levels during a postharvest treatment on stored durum wheat were studied. Two experiments were carried out at single and double the dose recommended by the manufacturer. In all trials, the initial deposition of pyrethrins levels was below the fixed maximum residue level of 3 mg/kg. The fate of pyrethrins in the two experiments was similar, and the total content of pyrethrins remained unchanged for 22 days with a complete dissipation in 8 months. In the single dose experiment, half-life times of pyrethrins I and II were 46 and 72 days, while for the double dose, pyrethrins I and II were 41 and 53 days, respectively.  相似文献   

4.
The stability of pyrethrins in formulations containing different combinations of antioxidant and sunscreen was studied with model system experiments. The mechanism of disappearance of pyrethrins was mainly due to photodegradation, but some loss by codistillation can occur. In formulations, the presence of mineral oil and emulsifiers determined a decrease on codistillation losses. The presence of the antioxidant in formulations even at high concentrations did not affect pyrethrin photodegradation rates, but rising amounts of sunscreen determined a progressive increase on half-life times of pyrethrins. A combination of sunscreen and antioxidant at low concentrations provided an effective protection against sunlight similar to that obtained by high amounts of sunscreen alone.  相似文献   

5.
Possible refining of crude hexane extract (CHE) from pyrethrum flowers and further refining of Pyrethrum Board of Kenya (PBK) pale product is investigated with both liquid and supercritical carbon dioxide. The experiments were carried out in a small pilot plant with a 200 mL extractor and three cyclonic separators in series. To understand the dynamics of pyrethrin extraction, CHE was extracted in a single step; pyrethrin concentration was found to be improved from 0.16 to 0.50 g/g. The effects of temperature and pressure on the quality of the extract were studied at 29 degrees C and 80 bar and at 40 degrees C and 100 bar. Liquid CO(2) processing (29 degrees C, 80 bar) yielded slightly better product quality. A comparison study of CHE and PBK pale processing with supercritical CO(2) (40 degrees C, 100 bar) showed that the final products were similar in terms of pyrethrin content. Extraction of both PBK pale and CHE in two steps with different operating conditions improved their purity.  相似文献   

6.
The behavior of pyrethrins and piperonyl butoxide (PB) on peaches has been studied after field treatment. Three experiments were carried out at 1, 5, and 10x the concentration recommended by the manufacturer. In all experiments, the initial deposition was below the maximum residue level (MRL), and the half-life time calculated in the 10x experiment for total pyrethrins within 2.3 days was in agreement with the preharvest interval (PHI) recommended. In a model system, the photodegradation rates of the pyrethrins in three commercial products were compared with pyrethrum pale (PP), with and without the presence of peach waxes. The pyrethrins in formulations containing PB showed higher half-life times but were not influenced by the presence of waxes, whereas in the case of PP that does not contain any PB, photodegradation was significantly affected by the presence of waxes.  相似文献   

7.
The effect of storage conditions on compost suppressiveness against fusarium wilt of melon, caused by Fusarium oxysporum f. sp. melonis (FOM) was studied in relation to the dynamics of compost microbial activity and biodegradability. For this purpose, mature suppressive compost, prepared from tomato plants and separated cow manure, was divided into four portions and stored for one year under cool/warm (12 or 28 °C) or dry/wet (15-35 or 55-65% moisture content) conditions, in four different combinations: cool-dry, warm-dry, cool-wet and warm-wet. All composts retained and even enhanced their suppressive capacity during storage, with no significant differences among them by the end of the storage period. However, significant differences were found in the dynamics of some of the measured chemical and microbial properties. The microbial activity of composts stored under wet conditions was higher than that of those stored under dry condition, which resulted in a substantial decrease in dissolved organic matter content (expressed as dissolved organic carbon; DOC) and increase in its recalcitrance to biological degradation, decrease in basal heat emission, slower response to added glucose or citric acid, and higher NO3 concentration, indicating increased nitrification under wet conditions. The DOC significantly correlated with several microbial properties as well as with compost suppressiveness of fusarium wilt of melon seedlings, and may be regarded as a most suitable general index for compost maturity. A best-subset multiple linear regression analysis revealed that the three best predictors, namely dissolved organic carbon (DOC), basal heat, and mesophilic bacterial counts, could explain as much as 83% of the total variance in compost suppressiveness. The generally agreed association between compost maturity and suppressiveness was verified in this case. It appears that compost microbial populations might compete and interfere with the saprophytic stage of FOM conidia, between germination and host invasion. In conclusion, it was demonstrated that compost suppressiveness against fusarium wilt of melon can be maintained for at least one year under a wide range of storage conditions, without any loss of suppressive capacity. This fact has positive logistical implications for the use of suppressive composts against FOM.  相似文献   

8.
The effect storage had on the microbial biomass in two soils (Trevino and Fargo) was compared to the effect storage had on each soil's capacity to degrade metsulfuron-methyl. Soils were collected from the field and used fresh (<3 weeks old) or stored at 20 and 4 degrees C for 3 or 6 months. The phospholipid fatty acid content of the soils was used to monitor changes in the microbial biomass during storage and incubation in a flow-through apparatus. In both soils, [phenyl-U-14C]metsulfuron-methyl was used to monitor changes in the route and rate of degradation along with 14CO2 evolution (mineralization). Total microbial biomasses in both soils were significantly reduced for soils incubated in the flow-through apparatus, whereas only the Trevino soil's microbial biomass was significantly reduced as a result of storage. The microbial communities of both soils were significantly different as a result of storage as shown by discriminant analysis. In both soils, degradation rate, pathway of degradation, and mineralization of metsulfuron-methyl were significantly affected by storage compared to fresh soil. The half-life of metsulfuron-methyl increased significantly (P < 0.05) in the Trevino soil from 45 days (fresh) to 63 days (stored soil), whereas in the Fargo soil half-lives increased significantly (P < 0.05) from 23 days (fresh) to 29 days (soils stored for 6 months). In both soils, mineralization of [14C]metsulfuron-methyl was significantly (P < 0.05) higher in fresh soils compared to stored soils. The degradation pathways of metsulfuron-methyl changed with storage as evidenced by the loss of formation of one biologically derived metabolite (degradate) in stored soils compared to fresh soils.  相似文献   

9.
为明确茄果类蔬菜秸秆原位还田对设施土壤综合质量的影响,该研究以番茄、茄子和辣椒秸秆为试材,设置了秸秆不还田（CK）、秸秆原位还田（SR）、秸秆原位还田+氰氨化钙（SR+C）和秸秆原位还田+微生物菌剂（SR+M）4个处理,研究了茄果类蔬菜秸秆不同原位还田方式对土壤化学性质、微生物群落和秸秆降解率的影响,并通过计算土壤质量指数（soil quality index,SQI）对土壤质量进行了综合评价。结果表明：与CK相比,SR、SR+C和SR+M处理均可提高土壤阳离子交换量,增加土壤有机碳库,改善土壤养分条件,并调节土壤细菌和真菌的群落结构。添加氰氨化钙抑制了辣椒秸秆的降解,但对番茄和茄子秸秆没有影响;添加微生物菌剂能够促进3种蔬菜秸秆的降解。秸秆原位还田处理均提高了设施菜田SQI,相较于CK,SR、SR+C和SR+M处理的SQI分别提高了15.8%～32.5%、8.8%～56.8%和21.8%～51.4%。研究结果为茄果类蔬菜秸秆资源化利用和设施蔬菜可持续生产提供了理论参考。  相似文献   

10.
《Cereal Chemistry》2017,94(3):497-501
The objectives of this research were to characterize dry matter loss of hybrid long‐grain rough rice during storage under reduced‐oxygen conditions and develop a new approach to predict the dry matter loss by using storage temperature and relative humidity data as input. Two long‐grain hybrid rice cultivars, CL XL745 and XL760, harvested in the year 2015 were stored in rough‐rice form in sealed glass jars at moisture contents of 12.5, 16, 19, and 21%, (wet basis) and temperatures of 10, 15, 20, 27, and 40°C for a total of 16 weeks, with samples taken at 2, 4, 6, 8, 10, 12, and 16 weeks of storage. Results revealed no differences in dry matter loss connected with the rough‐rice moisture content levels and temperature during the storage duration. However, the dry matter loss was statistically different based on rough‐rice cultivar. Experimental data were fitted to a dry matter loss equation for long‐grain rice found in literature. The dry matter loss equation developed for conditions of grain storage without oxygen limitation did not accurately predict rough‐rice dry matter loss under reduced‐oxygen conditions. Equation constants generated for reduced‐oxygen storage conditions were significantly lower than the typical constants used for long‐grain rice in literature. Hence, integration of rice cultivar and storage conditions such as oxygen supply is crucial for accurate determination of kinetics of dry matter loss during storage of hybrid long‐grain rough rice.  相似文献   

11.
 We investigated the soil organic C and N stocks, storage profiles and microbial biomass as influenced by different crop management systems in a tropical agricultural ecosystem. The different crop management systems significantly affected the C and N stocks and microbial biomass C and N at different soil depths. Amongst the systems evaluated, the rice-wheat system maintained a higher soil organic C content. Inclusion of legumes in the system improved the soil organic matter level and also soil microbial biomass activity, vital for the nutrient turnover and long-term productivity of the soil. Irrespective of the cropping system, approximately 58.4%, 25.7% and 15.9% of the C was distributed in 0–15, 15–30 and 30–60 cm depths, respectively. Received: 10 October 1999  相似文献   

12.
Study of Biodegradation Processes of BTEX-ethanol Mixture in Tropical Soil   总被引：1，自引：0，他引：1  
In Brazil, gasoline is currently blended with ethanol and both compounds may contaminate the environment when spills occur. Ethanol preferential biodegradation delays gasoline degradation in the aquifer, as previously observed; in unsaturated soil a delayed recovery of culturable bacteria and removal of residues in the presence of ethanol suggest a similar situation. This study monitors microbial degrading activity in unsaturated soil with BTEX and BTEX-ethanol mixtures under tropical conditions as well as the effects of bioventing on contaminants degradation. Enzymatic activity was quantified by measuring fluorescein-diacetate hydrolysis by microorganisms, which determines total degrading activity in soil. As microbial enhanced activity may alter soil electromagnetic properties, soil dielectric constant shifts were monitored using Time Domain Reflectometry (TDR), while chemical analyses evaluated contamination residues throughout the experiment. Results suggest that ethanol delays BTEX biodegradation and that bioventing may compensate for this delay by providing oxygen for the continuation of microbial activity. Contamination and bioventing stimulated soil microbiota, while culturable populations were inhibited by contamination, showing soil toxicity. The presence of ethanol caused a higher and longer-lasting boost in enzymatic activity; TDR measurements did not follow these activity shifts, proving not to be an adequate tool for evaluating microbial activity in these experimental conditions. Residual BTEX were detected only in ethanol-containing non-ventilated soils after contamination. The set of results suggests that ethanol could delay BTEX degradation because of its constitutive degradation by soil microbiota, but this effect may be bypassed by bioventing.  相似文献   

13.
为了探明磺胺嘧啶在水中的环境行为,通过室内模拟降解实验分别研究了磺胺嘧啶在湖水和猪场废水中的好氧和厌氧微生物降解,考察了供氧方式和有机质含量对磺胺嘧啶微生物降解的影响。结果表明：磺胺嘧啶在猪场废水中厌氧微生物降解速率高于其好氧组,而磺胺嘧啶在湖水中厌氧微生物降解速率低于其好氧组。磺胺嘧啶在湖水和猪场废水中的好氧或厌氧微生物降解均较缓慢,这可能与其较强的抑菌性和微生物的营养状况有关。通过微生物培养还研究了好氧降解时磺胺嘧啶对湖水中微生物种群生长的影响,数据显示：磺胺嘧啶对湖水和猪场废水中细菌的生长具有一定的刺激作用,而对真菌和放线菌的生长影响不明显。  相似文献   

14.
氧浓度对复合菌系MC1纤维素降解能力的影响   总被引：1，自引：0，他引：1  
堆肥系统内氧浓度一直是影响堆肥进程的重要因子,它决定了堆肥系统中微生物活动的强弱,从而影响堆肥中复杂有机物的分解速率.该文研究了氧浓度对纤维素降解复合菌系MC1功能的影响.通过不同封口方式与不同大小容器培养实验,揭示静置培养条件下复合菌系MC1在纤维素降解过程中,氧浓度对该复合菌系分解纤维素能力的影响.得出复合菌系MC1在微耗氧条件下(＜0.05 mg/L)分解纤维素,分解纤维素最佳的氧浓度范围在0.01～0.02 mg/L,氧浓度过高或过低均不利于纤维素的分解.特定氧浓度有利于复合菌系MC1执行分解功能.  相似文献   

15.
Picric acid is an explosive historically produced and disposed at the Louisiana Army Ammunition Plant (LAAP) in northern Louisiana. The potential for natural degradation of picric acid was investigated by creating picric-acid slurries with four LAAP sediments of variable composition and monitoring for up to 98 days. The concentrations of picric acid decreased rapidly in all slurries during the first day, attributed to adsorption, followed by slower decreases in some samples due to degradation. Degradation in unsterilized slurries was nearly complete within 80 days for two of the four sediments. Increases in nitrite and nitrate concentration over time were proportional to the loss of picric acid and indicate that at least two of the three nitrite groups were removed from the picric acid molecule. The absence of significant concentrations of compounds with a mass greater than 100 amu in the final solutions suggests that all three nitrite groups were removed. No correlation was found between the degree of degradation and grain size, clay content, organic content, carbonate content, or a suite of element concentrations in the sediment. Degradation in sterilized samples was minimal for all sediment slurries, indicating microbial activity as the primary mechanism of degradation.  相似文献   

16.
Betanin is an antioxidant pigment found in djulis, a grain native to Taiwan, and is a natural source food coloring, but the bright red color degrades rapidly if submitted to light, heat, or oxygen. The effects of nanogrinding on the stability of pigments and bioactive components are unknown. In this study, the color characteristics and bioactivity (antioxidant capacity and enzyme activity) of nanoparticle (NP) djulis was compared with those of intact granules (IG) and microparticles (MP). Results showed that the NP samples exhibited the highest betanin content (2.04 mg/g), which was almost twice that of IG. It was observed that nanogrinding resulted in higher pigment extraction efficiency. However, during storage (5-35 °C for 56 days), NP samples showed the most serious pigment degradation, and this color degradation, as expected, had the lowest activation energy. This was more evident when the storage temperature was high. Antioxidant capacities showed the same trends. MP and NP exhibited significantly higher activity of superoxide dismutaste-like activity, lactoperoxidase (LPO), and lysozyme than IG. Gel permeation chromatography confirmed the degradation of larger particles during nanogrinding, which might favor enzyme extraction and their activities. Statistical analysis revealed a close relationship between betanin and antioxidant capacity.  相似文献   

17.
The effects of spray-drying of the unicellular microalga Dunaliella salina on its beta-carotene content and geometric isomer composition have been studied. The efficacy of a range of synthetic and natural antioxidants in preventing degradation of beta-carotene has been determined. Losses of beta-carotene and isomerization were minimal during processing for both the control (no exogenous antioxidants) and the samples containing butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ). However, the use of tocopherol-based antioxidants resulted in degradation of 52-72% of beta-carotene during the drying process. All dried powders of Dunaliella proved to be unstable during storage in the presence of light and air, with beta-carotene degraded according to a first-order kinetic model. Of the antioxidants studied, only TBHQ was successful in significantly minimizing degradation (degradation constants of 0.03 and 0.04 days(-)(1), compared to 0.53 days(-)(1) for the respective control). For control powders and those with BHT added to the feed, the degradation constants were reduced to values between 0.27 and 0.37 days(-)(1) by restricting light and flushing with nitrogen; however, storage in the dark alone had no effect. For more slowly degrading powders having TBHQ added to the feed, it was clear that degradation of beta-carotene was influenced by both light and oxygen. During storage the 9-cis isomer of beta-carotene was significantly more unstable than the all-trans form. TBHQ was, however, successful in reducing relative losses of this isomer for samples stored in the dark. The results suggest a dominant photodegradative mechanism for the loss of the 9-cis isomer of beta-carotene.  相似文献   

18.
不同渗灌灌水对土壤酶活性的影响   总被引：11，自引：0，他引：11  
Various environmental conditions determine soil enzyme activities, which are important indicators for changes of soil microbial activity, soil fertility, and land quality. The effect of subsurface irrigation scheduling on activities of three soil enzymes （phosphatase, urease, and catalase） was studied at five depths （0-10, 10-20, 20-30, 30-40, and 40-60 cm） of a tomato greenhouse soil. Irrigation was scheduled when soil water condition reached the maximum allowable depletion （MAD） designed for different treatments （-10, -16, -25, -40, and -63 kPa）. Results showed that soil enzyme activities had significant responses to the irrigation scheduling during the period of subsurface irrigation. The neutral phosphatase activity and the catalase activity were found to generally increase with more frequent irrigation （MAD of -10 and -16 kPa）. This suggested that a higher level of water content favored an increase in activity of these two enzymes. In contrast, the urease activity decreased under irrigation, with less effect for MAD of -40 and -63 kPa. This implied that relatively wet soil conditions were conducive to retention of urea N, but relatively dry soil conditions could result in increasing loss of urea N. Further, this study revealed that soil enzyme activities could be alternative natural bio-sensors for the effect of irrigation on soil biochemical reactions and could help optimize irrigation management of greenhouse crop production.  相似文献   

19.
为了探究一种有效的小米储藏方法,以晋谷42号小米为试材,采用0.08 mm厚尼龙(polyamide,PA)复合聚乙烯(polyethylene,PE)袋包装,常温((20±2)℃)环境中储藏,研究小米在常规、常规密闭和真空包装储藏120 d品质指标的变化规律。结果表明:相对于常规包装,真空包装储藏有效降低脂肪氧合酶的活性(P<0.05),延缓小米脂质的氧化分解(P<0.05),抑制小米游离脂肪酸含量的升高(P<0.05),较好地保持了小米的水分(P<0.05),延缓了小米黄色素的损耗(P<0.05),较好地保持了小米的亮度(P<0.05)、米黄色(P<0.05)以及弹性(P<0.05)和黏附性(P<0.05);常规密闭包装具有一定的储藏效果,但不及真空包装。因此,常温下真空包装储藏可以有效延缓小米的陈化,保持小米的储藏品质。研究结果为小米储藏,提升小米储藏品质提供了理论依据和技术支持。  相似文献   

20.
Energy crops are increasingly cultivated in agricultural management systems world-wide. A substitution of food crops (e.g. cereals) by energy crops may generally alter the biological activity and litter decomposition in soil due to their varying structural and chemical composition and subsequently modify soil functioning. A soil microcosm experiment was performed to assess the decomposition and microbial mineralization of different energy crop residues in soil compared to a food crop, with or without earthworms. Residues of the energy crops winter rape (Brassica napus), maize (Zea mays), miscanthus (Miscanthus giganteus) and the food crop oat (Avena sativa) were each provided as food source for a mixed earthworm population, each consisting of one individual of Lumbricus terrestris, Aporrectodea caliginosa, and Octolasion tyrtaeum. After 6 weeks, the rate of litter loss from the soil surface, earthworm biomass, microbial biomass-C and -N, microbial activity, and enzyme activities were determined. The results emphasized, that litter loss and microbial parameters were predominantly promoted by earthworms and were additionally influenced by the varying structural and chemical composition of the different litter. Litter decay by earthworms was highest in N-rich maize litter treatment (C-N ratio 34.8) and lowest in the case of miscanthus litter (C-N ratio 134.4). As a consequence, the microbial biomass and basal respiration in soils with maize litter were higher, relative to other litter types. MBC-MBN ratio in soil increased when earthworms were present, indicating N competition between earthworms and microorganisms. Furthermore, enzyme activities responded in different ways on the varying types of litter and earthworm activity. Enzymes involved in the N-cycle decreased and those involved in the C-cycle tended to increase in the presence of earthworms, when litter with high C-N ratio was provided as a food source. Especially in the miscanthus treatments, less N might remain for enzymatic degradation, indicating that N competition between earthworms and microorganisms may vary between different litter types. Especially, an expansion of miscanthus in agricultural management systems might result in a reduced microbial activity and a higher N deficit for microorganisms in soil.  相似文献   

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