The present study was aimed to evaluate the impact of the co-culture on the output of malolactic fermentation and to further investigate the reasons of the antagonism exerted by yeasts towards bacteria during sequential cultures. The Saccharomyces cerevisiae D strain/Oenococcus oeni X strain combination was tested by applying both sequential culture and co-culture strategies. This pair was chosen amongst others because the malolactic fermentation was particularly difficult to realize during the sequential culture. During this traditional procedure, malolactic fermentation started when alcoholic fermentation was achieved. For the co-culture, both fermentations were conducted together by inoculating yeasts and bacteria into a membrane bioreactor at the same time. Results obtained during the sequential culture and compared to a bacterial control medium, showed that the inhibition exerted by S. cerevisiae D strain in term of decrease of the malic acid consumption rate was mainly due to ethanol (75%) and to a peptidic fraction (25%) having an MW between 5 and 10 kDa. 0.4 g l−1 of l-malic acid was consumed in this case while 3.7 g l−1 was consumed when the co-culture was applied. In addition, there was no risk of increased volatile acidity during the co-culture. Therefore, the co-culture strategy was considered effective for malolactic fermentation with the yeast/bacteria pair studied. 相似文献
This study evaluated survival of Escherichia coli O157:H7 strain ATCC 43895 during exposure to pH 3.5 following its habituation for 2 or 7 days at 10 degrees in fresh beef decontamination waste runoff fluid mixtures (washings) containing 0, 0.02, or 0.2% of lactic or acetic acids. Meat washings and sterile water (control) were initially inoculated with approximately 5 log CFU/ml of acid- and nonadapted E. coli O157:H7 cells cultured (30 degrees C, 24 h) in broth with and without 1% glucose, respectively. After 2 days, E. coli O157:H7 survivors from acetate washings (pH 3.7 to 4.7) survived at pH 3.5 better than E. coli O157:H7 survivors from lactate washings (pH 3.1 to 4.6), especially when the original inoculum was acid adapted. Also, although E. coli O157:H7 habituated in sterile water for 2 days survived well at pH 3.5, the corresponding survivors from nonacid water meat washings (pH 6.8) were rapidly killed at pH 3.5, irrespective of acid adaptation. After 7 days, E. coli O157:H7 survivors from acetate washings (pH 3.6 to 4.7) continued to resist pH 3.5, whereas those from lactate washings died off. This loss of acid tolerance by E. coli O157:H7 was due to either its low survival in 0.2% lactate washings (pH 3.1) or its acid sensitization in 0.02% lactate washings, in which a Pseudomonas-like natural flora showed extensive growth (> 8 log CFU/ml) and the pH increased to 6.5 to 6.6. Acid-adapted E. coli O157:H7 populations habituated in water washings (pH 7.1 to 7.3) for 7 days continued to be acid sensitive, whereas nonadapted populations increased their acid tolerance, a response merely correlated with their slight (< 1 log) growth at 10 degrees C. These results indicate that the expression of high acid tolerance by acid-adapted E. coli O157:H7 can be maintained or enhanced in acid-diluted meat decontamination waste runoff fluids of pH levels that could permit long-term survival at 10 degrees C. Previous acid adaptation, however, could reduce the growth potential of E. coli O157:H7 at 10 degrees C in nonacid waste fluids of high pH and enriched in natural flora. These conditions might further induce an acid sensitization to stationary E. coli O157:H7 cells. 相似文献
Gas chromatography/mass spectrometry was used to analyze the pyrolytic byproducts from an Army-unique propellant compound (AA2) that is composed of predominantly nitrocellulose and nitroglycerin. Compounds produced by AA2 pyrolysis were compared to compounds detected in the gaseous effluent from AA2 incineration. The light permanent gases and most of the higher molecular weight byproducts produced by AA2 incineration are replicated by laboratory pyrolysis on AA2. The reverse case also holds whereby 18 out of 24 high molecular weight AA2 pyrolytic byproducts are found in the incinerator emissions. Poor matching, however, was obtained between the two processes for the volatile, water-soluble species. None of these low molecular weight compounds produced under pyrolytic conditions were detected in the AA2 incinerator samples, likely indicating inefficient capture of these compounds from the effluent stream. Separate pyrolytic degradation of the individual components of AA2 provides evidence that nearly all of the incomplete combustion products detected during incineration originate not from the prevalent energetic ingredients but rather from the minor and trace additives in AA2. In addition, pyrolysis successfully identified the AA2 components capable of surviving the incineration process intact. This work illustrates the potential of bench-scale pyrolysis for predicting incineration behavior. 相似文献
2‐(3,5‐Dichlorophenylcarbamoyl)cyclohexanecarboxylic acid ( 1 ) is a potent and selective positive allosteric modulator of metabotropic glutamate receptor subtype 4 (mGluR4). The activity of 1 was reported to reside in the cis diastereomer with equal potency between its enantiomeric forms (Niswender et al., Mol. Pharmacol. 2008 , 74, 1345–1358). In the present study, the asymmetric synthesis of each of the cis enantiomers was performed, and their activities were compared with that of the racemic trans. In our assays, the cis enantiomers differ in potency, with one of them (1R,2S) higher and the other (1S,2R) lower than the racemic trans. High‐level quantum chemical calculations were carried out to characterize the structures of minimum energy in all‐isomer conformational space as well as particular intermediates between conformational transitions. Computational analysis identified structural features of 1 that can play a role in mGluR4 functionality and establish the basis for subsequent work, in which molecular chirality constructed on conformations derived from those found for the active (1R,2S) enantiomer can provide new ideas for drug discovery. Comparison between experimental and theoretical circular dichroism spectra confirmed both the absolute configuration of the (1R,2S) compound and its calculated most stable conformation, thereby supporting experimental and theoretical work. 相似文献
Core/shell nanoparticles containing the fungicide tebuconazole were prepared from amphiphilic copolymers of gelatin grafted with MMA. The grafting was performed in water at levels of 1.5–15 wt.‐% solids based on matrix mass, to give core/shell nanoparticles with median diameters ranging from ≈200 to 400 or ≈10 to 100 nm depending on composition, conditions used, and work‐up. The biocide‐containing nanoparticles were delivered into wood in up to 85% efficiency. Wood blocks treated with tebuconazole‐containing nanoparticles leached less tebuconazole than wood blocks treated with tebuconazole solutions. The best nanoparticle formulations afforded wood blocks with a biological efficacy comparable to solution‐treated wood block controls in soil jar decay tests.