1,721,026 research outputs found
Physical preteatment on plums (Prunus domestica). Note II. Effect on the quality characteristics of different prune cultivars
No full textThe effects of an alternative physical pre-treatment for enhancing the drying rate of different plums (Stanley, Angeleno(R), and Empress), are evaluated by means of the principal chemical parameters and by skin colour. The pre-treatment consists of the superficial abrasion of the plums' peels using an inert abrasive material to remove the cuticular waxy layer, the limiting factor for moisture loss. The drying process was carried out at 60 C to reduce the plums' quality loss, the latter being assessed by analysing the changes in skin colour, sugars by HPLC, total phenols, total anthocyanins, and reactive substances to the vanillin-HCl reagent. The proposed physical pre-treatment, without significantly altering the other qualitative characteristics of the plums, markedly reduced the dehydration time and, as a result, caused a smaller loss of sugars in Empress and Angeleno than Stanley plums. (C) 2002 Elsevier Science Ltd. All rights reserved
Evolution of phenolic and volatile compounds during bottle storage of a white wine without added sulfite
No full textBACKGROUND: Bottle storage can affect color, aroma and phenolic composition of white wine. Very little information is reported about the bottle evolution during storage of white wines without added sulfites and/or using other antioxidants. This work is aimed at studying the evolution of the main enological parameters, phenolic and volatile profiles of a white wine without added sulfites, during 15 months of storage in bottle at different light and temperature conditions, compared with a control stored with sulfur dioxide. Dark storage at 12 °C (D12-S, D12-NS) and 30 °C (D30-S, D30-NS) were compared to investigate the temperature effect, meanwhile uncontrolled temperature and light condition (UTL-S, UTL-NS) simulated improper storage conditions. RESULTS: Volatile acidity, absorbance at 420 nm and total phenols were higher in UTL-NS and D30-NS wines. The trans forms of hydroxycinnamic esters decreased, whereas, the cis forms, as well as caffeic acid derivatives, significantly increased in samples without added sulfites. The storage without sulfites also accelerated the hydrolysis of acetate esters. However, it did not affect most of the ethyl esters whose content remained almost the same between sulfite added (S) and no sulfite added (NS) wines. CONCLUSION: The presence of sulfites in the bottle helped to preserve the volatile compounds of young wines; however, even more important seemed to be the optimal storage (dark and low temperature), as unsuitable conditions favored aroma degradation of bottled wine, regardless of sulfite protective action. © 2019 Society of Chemical Industry
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.[...
I componenti polifenolici del vino. Nota II: gli antociani in relazione a differenti sistemi di vinificazione.
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Lysozyme immobilized on chitosan beads: Kinetic characterization and antimicrobial activity in white wines
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BIOELECTROCHEMICAL DETERMINATION OF LACTIC AND MALIC-ACIDS IN WINE
No full textElectroanalytical methods based on biosensor technology and differential PH measurement for the determination Pf L-lactic and L-malic acids in wine were developed. Lactic acid was determined according to two procedures consisting of the use of two lactate electrochemical biosensors, one based on a Clark 02 probe and the other based on the H2O2 probe. The two probes were assembled employing a polymeric membrane where the enzyme lactate oxidase was previously immobilized. Both sensors exhibited high storage and operational stabilities, and good reproducibility when used in wine matrix. Measurement of lactate was carried out using two different flow-through cells assembled with the lactate probes. The low detection limit of these probes and the relatively high concentration of lactate in wine samples required a serial dilution in the range 1:100 to 1:200, thus eliminating all potential electrochemical or enzyme interferences present in the sample. Malic acid was determined using a differential commercially available pH-meter and an enzymatic procedure. For this analysis, we employed the malic enzyme (EC 1.1.1.40) and the NADP+ cofactor. The pH variation due to the action of this enzyme on malic acid was found to be proportional to the malic acid present in the sample. Experimental parameters such as pH, temperature, and co-factor concentration were optimized, resulting in malate determination in less than 1 min with good reproducibility. Various samples of wine and wine musts were assayed for lactate with the two biosensor procedures, and for malate with differential pH-metry. The results when compared with those obtained with the commonly used spectrophotometric procedure 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
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