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61.
Luciana Juncioni de Arauz Angela Faustino Jozala Gabriel Soares Pinheiro Priscila Gava Mazzola Adalberto Pessoa Júnior Thereza Christina Vessoni Penna 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):325-328
BACKGROUND: Nisin is a commercially available bacteriocin produced by Lactococcus lactis ATCC 11454 and used as a natural agent in the biopreservation of food. In the current investigation, milk whey, a byproduct from dairy industries was used as a fermentation substrate for the production of nisin. Lactococcus lactis ATCC 11454 was developed in a rotary shaker (30 °C/36 h/100 rpm) using two different media with milk whey (i) without filtration, pH 6.8, adjusted with NaOH 2 mol L?1 and without pH adjustment, both autoclaved at 121 °C for 30 min, and (ii) filtrated (1.20 µm and 0.22 µm membrane filter). These cultures were transferred five times using 5 mL aliquots of broth culture for every new volume of the respective media. RESULTS: The results showed that culture media composed of milk whey without filtration supplied L. lactis its adaptation needs better than filtrated milk whey. Nisin titers, in milk whey without filtration (pH adjusted), was 11120.13 mg L?1 in the second transfer, and up to 1628‐fold higher than the filtrated milk whey, 6.83 mg.L?1 obtained in the firstt transfer. CONCLUSIONS: Biological processing of milk byproducts (milk whey) can be considered a profitable alternative, generating high‐value bioproducts and contributing to decreasing river disposals by dairy industries. Copyright © 2008 Society of Chemical Industry 相似文献
62.
Stanisaw Koter 《Separation and Purification Technology》2008,60(3):251-258
The experimental results of the separation of acetic acid (HA) from the sulfuric acid by the electro-electrodialysis (EED) method and the modeling of process have been presented. The Neosepta membranes CMX and ACM have been used. It has been found that the efficiency of retention of HA is high (>0.9) when the process is conducted below the limiting current density with respect to HSO4− or SO42− anions. The observed current efficiency of the H2SO4 removal was rather low (CES = ca. 0.7, when the initial concentration of H2SO4 in the mixture was 1 or 2 M) which was caused by the nonideal selectivity of the anion-exchange membrane. The experimental results have been described by the model based on the extended Nernst-Planck equation and the Donnan equilibrium. Since the efficiency of the process depended mainly on the selectivity of anion-exchange membrane (ACM), the concentration of fixed charges of that membrane, , and the ratio of volume fraction of pores to their squared tortuosity, Vp/θ2, have been chosen as the main fitting parameters. It has been found that the fitting of the EED data depends mainly on , whereas in the modeling of diffusion experiment (or an EED experiment conducted at low current density) both parameters are important. The best fit has been obtained for , i.e. ca. one order smaller than that determined experimentally. The obtained optimal value of Vp/θ2, equal to 0.013, is consistent with those previously obtained for other Neosepta anion-exchange membrane. 相似文献
63.
We report here a non-enzymatic detecting electrode strip for fast monitoring of uric acid in human whole blood. A single-use amperometric uric acid sensor strip, incorporating a three-electrode configuration, has been fabricated on a polypropylene substrate using low cost screen-printing (thick-film) technology. Both the working and counter electrodes were prepared by screen-printing commercial carbon ink. The integration on the same support of pseudo-reference electrode was obtained by screen-printing a commercial silver ink and subsequent electrochemical pretreatment. Simply by placing a 20 μl human whole blood drop on the strip is enough for uric acid analysis by square-wave voltammetry. Real human whole blood samples were analyzed by this method and compared to the phosphotungstic acid clinical test procedure with satisfactory results. 相似文献
64.
详细研究了以乙酸乙酯和环己烷为溶剂,丙烯酸为单体,BPO,LPO,AIBN为引发剂,聚烯基多醚为交联剂,合成增稠能力强、透明度高的聚丙烯酸树脂。于混和溶剂存在下制得的聚合物,消除了以往由二氯甲烷为溶剂的反应介质中所得产品的毒性,可广泛应用于医药及日用化工等行业。 相似文献
65.
66.
Y. Murat Elin Mehmet Saak 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(2):174-180
This paper presents the results of urease immobilization onto methacrylic acid–acrylamide grafted poly(ethyleneterephthalate) fibres. The graft yield strongly affected the maximum activity of the immobilized enzyme up to a value of 70·2%. Higher grafting caused a decline in urease activity and led to the degradation of the fibres. The minor changes observed in Km and Vmax demonstrated that the conformational changes existed during immobilization were not extensive. However, 70·2% methacrylic acid–acrylamide-g-fibres containing urease were more stable towards acidic and alkaline pH, high temperature and storage conditions compared with free enzyme. Apart from the increase in stability to heat inactivation, the initial enzymatic activity of the urease–fibre system remained almost unchanged even after 40 repeated assays corresponding to 10 h of operation in 4 months, indicating the excellent durability of the system. 相似文献
67.
68.
An in situ NMR study of tert-butanol dehydration in 95 and 85% sulfuric acid did not indicate the formation of tert-butyl cations as active reaction intermediates. Instead, only NMR lines from oxonium ions under the condition of fast exchange with water and the acid were observed. It is most likely that, in the concentrated acid, the active intermediates of this reaction are represented by tert-butyl sulfuric ester which probably is a precursor of invisible tert-butyl carbenium ions representing short-lived excited or transition states. 相似文献
69.
M. Ardizzi N. Ballarini F. Cavani E. Chiappini L. Dal Pozzo L. Maselli T. Monti 《Applied catalysis. B, Environmental》2007,70(1-4):597-605
The properties of catalysts with (i) Brønsted-type acidity (H-mordenite and Al/P mixed oxide), (ii) Lewis-type acidity (Al trifluoride) or (iii) basic characteristics (Mg/Fe mixed oxide) were investigated in the gas-phase methylation of catechol. When methanol was used as the methylating agent, H-mordenite and AlF3 gave high selectivities to guaiacol (the product of O-methylation) under mild reaction conditions, that is at very low catechol conversions. An increase in temperature led to the transformation of guaiacol to phenol and cresols, and to considerable catalyst deactivation. The basic catalyst Mg/Fe/O also favored an extensive degradation of guaiacol to phenol. On the mildly acidic catalyst Al/P mixed oxide a stable catalytic performance and a high selectivity to guaiacol at 40% catechol conversion were obtained. When methylformate, a more reactive methylating agent, was used with AlF3 and Mg/Fe mixed oxide as catalysts, higher catechol conversions and slower deactivation rates could be achieved under mild reaction conditions, with a low extent of guaiacol degradation. However, methylformate rapidly decomposed when temperatures above 350 °C were used. Finally, tests were made by reacting catechol and diethoxymethane with acid catalysts, with the aim of synthesizing methylenedioxybenzene. The latter product was obtained with high selectivity, but with very low yield, due to both catalyst deactivation and decomposition of diethoxymethane. 相似文献
70.
Reinhard Effenberger 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,58(2):129-133
The preparation of 2,6-dibromophenol is described. This compound, useful as raw material for brominated poly(phenyleneoxide) and pyrogallol or derived pharmaceuticals/pesticides, was prepared in 80% (isolated) yield by a transalkylation reaction between tetrabromobisphenol-A and toluene. The catalyst, trifluoromethanesulphonic acid, can be simply recovered and recycled. Perfluorinated resin sulphonic acid (NAFION-H®, DuPont) did not effectively catalyse this transalkylation. 相似文献