1,720,966 research outputs found
Development of a biosensor for monitoring of glycerol during alcoholic fermentation
No full textA biosensor for the measurement of glycerol in FIA was constructed using covalently immobilized glycerokinase and glycerol-3-phosphate oxidase in conjunction with a Pt based hydrogen peroxide probe. Different immobilization strategies have been studied including random and asymmetric immobilization onto a polymeric support and immobilization onto two different membranes. The latter resulted in the best configuration for batch measurement. The most effective configuration for measurement in FIA was the immobilization of glycerokinase in a glass beads reactor coupled with glycerol-3-phosphate oxidase on a preactivated Immobilon AV membrane kept at the electrode surface. Using a 250-mu l injection loop, 3 mmol ATP(Mg (+) (2)) in 0.1 M berate buffer pH 8.5 and a flow rate of 0.5 ml/min, a linear response in the 2 x 10(-6)/10(-3) mol/l range and a detection limit of 5 x 10(-7) mol/l were obtained for glycerol. Lifetime of the glycerol-3-phosphate membrane was extended up to 1 month by storage in the working buffer containing 1% DEAE-dextran and 5% lactitol. More than 350 samples can be assayed with this system. The biosensor was used to monitor off-line glycerol production during alcoholic fermentations carried out at different pHs and temperatures. (C) 1998 Elsevier Science S.A. All rights reserved.[...
A bienzyme electrode probe for malate
No full textA new amperometric malate enzyme electrode probe has been constructed using a hydrogen peroxide-based sensor coupled with malic and pyruvate oxidase enzymes. The first enzyme catalyzes the oxidation of malic acid, which in the presence-of NADP(+) yields pyruvate as product. The oxidation of pyruvate is catalyzed by pyruvate oxidase, which yields H2O2 as product in the presence of O-2 and phosphate as cosubstrates and thiamine pyrophosphate and Mg2+ as cofactors. The H2O2 is then detected by the electrochemical transducer, and the output current changes are correlated to the concentration of malic acid in solution. Analytical parameters such as pH, temperature, buffer, substrate and cofactor concentrations, and response time have been optimized, Probe stability and reproducibility have been evaluated. The malic enzyme was used first in solution and then coimmobilized with pyruvate oxidase, Coimmobilization of the oxidase and dehydrogenase enzymes has been performed both randomly and asymmetrically on different supports, Calibration curves for malate have been constructed with all the analytical parameters optimized. The detection limit for this newly designed probe was 5 x 10(-7) mol/L, with a broad linear range between 10(-6) and 5 x 10(-4) mol/L. Recovery studies of malate in a wine matrix have been carried out. Malic acid has been determined in grape musts during grape maturation, Results correlated well when compared with those from a spectrophotometric procedure.[...
Curd-ripening evaluation by flow injection analysis of L-lactic acid with an electrochemical biocell during mozzarella cheese manufacture
No full textA flow injection analysis procedure was used for the determination of L-lactic acid during the production of mozzarella cheese. The apparatus consists of an electrochemical flow-through wall-jet cell assembled with a platinum sensor covered with the immobilized lactate oxidase enzyme and connected to an amperometer. This system was used to monitor the concentration of L-lactic acid produced by lactose fermentation catalyzed by selected starters during cheese manufacture. Lactate was detected in the range (5 x 10(-6))-(1 x 10(-4)) mol/L with a detection limit of 2 x 10(-6) mol/L. L-Lactate has been measured in raw milk and during the manufacture of cow and water buffalo mozzarella cheese. The starter used was a commercially available strain of Streptococcus thermophilus. Real time analysis of lactate allowed a control of the curd-ripening evolution at different pasteurization temperatures of the milk. Values of lactic acid were compared with pH variation during the process. This method proved to be more sensitive than the pH measurement procedure for the control of the continuous production of lactic acid particularly near the ''stretching point'' when very slight pH variations were observed.[...
Fast analysis of lysine in food using protein microwave hydrolysis and an electrochemical biosensor
No full textA fast procedure for lysine analysis in food was developed by coupling in sequence a microwave protein hydrolysis technique with a lysine enzyme electrode. Protein hydrolysis was carried out in 6N HCl using sealed vessels located in a microwave digestion system. Parameters such as irradiation power, pressure, time and temperature were varied to select the best conditions for the hydrolysis. The hydrolysate was then analyzed for lysine using an electrochemical biosensor based on an amperometric H2O2 transducer and the enzyme lysine oxidase covalently immobilized on a preactivated polymer support. Analytical parameters, such as pH, buffer and measurement system were studied in order to eliminate or minimize the enzymatic interferences. Bovine serum albumin and two farro (T. dicoccum) meals (whole and sieved) were processed for lysine content. The analysis was carried out with this new procedure (microwave hydrolysis + biosensor) and by traditional hydrolysis coupled with ion-exchange chromatography (IEC). Results obtained with the two procedures correlated well.[...
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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