1,720,964 research outputs found
Interfacial rheology study of espresso coffee foam structure and properties
No full textThe espresso coffee beverage is a polyphasic colloidal system, in which the liquid phase is topped by a wet foam of tiny sphere-shaped gas bubbles. Each sphere is surrounded by a liquid film (lamellae) that isolates it from its neighbours and that hosts biopolymers and natural surfactants. Foaming biopolymers of coffee (total fraction and its sub-fractions: proteins/melanoidins fraction and polysaccharides fraction) were extracted from defatted and raw, commercially roasted ground coffee. In order to study the viscoelastic behaviour of the surface-adsorbed layer, all the extracted fractions were analyzed using a commercial interfacial rheometer CIR 100 operating in time sweep mode. The growth of the interfacial elasticity of the lamella implicitly contains all the information about the molecular interaction at the foam air/liquid interface. These interactions are described to be responsible for the foam stabilization. Results indicate that the kinetics of the film formation is mediated by the polysaccharide component and that the protein/melanoidin component of the coffee foaming fraction exhibits the highest viscoelastic interfacial properties. Lipids play a major role in the interfacial film formation due to their interaction with protein-like macromolecules, the melanoidins. A correlation was established between air/water interface properties of the foaming systems and the respective foam volumes evaluated by means of the image analysis. A new mathematical description of surface viscoelastic phenomena, covering the terms of transport of surfactant biopolymers to the interface and describing the coagulation of particles here taking place, is proposed. The suggested equation overcomes the Warburton model, taking into account the complexity of real food systems as in the case of the espresso coffee beverage
Electrochemical signatures of multivitamin mixtures
Full text linkThe ability of cyclic square wave voltammetry to identify distinct
fingerprints of multiple vitamins, in a single voltammetric run, is
demonstrated. This method represents an efficient alternative to
more common techniques for fast screening of complex vitamin
mixtures or commercial tablets due to its low cost, high speed and
sensitivity
Estrazione e caratterizzazione strutturale della frazione polisaccaridica estratta dall’essudato di Launaea Acanthodes
No full textMediante analisi di light scattering, tecniche mono e bidimensionali di spettroscopia NMR e viscosimetria capillare la è stata caratterizzata la frazione polisaccaridica dell’essudato di Launaea Acanthodes. Le analisi strumentali hanno permesso di definire che il polisaccaride è costituito da unità di galattosio, ramnosio, arabinosio e residui di acido galatturonico. E’ stata dimostrata la presenza di strutture aggregate che vengono escluse nel calcolo della distribuzione del peso molecolare. I valori bassi dei raggi idrodinamico e di girazione indicano una compattezza strutturale delle macromolecole nelle condizioni di analisi. Il polimero possiede una conformazione random-coil ad elevata densità strutturale. Una via utile per investigare le capacità di strutturazione dell’arabinogalattano allo studio è stata la produzione di sottili pellicole di polimero ottenute per evaporazione dl solvente. I film ottenuti si presentano opachi e con scarse proprietà meccaniche: elevata fragilità, elasticità e resistenza alla trazione scarse. L’indagine morfologica tramite SEM indicano una struttura non uniforme, priva di una precisa orientazione dei polimeri
Electrospun Nanofibers as Selective Barrier to the Electrochemical Polyphenol Oxidation
No full textA tissue made of nylon-6 electrospun nanofibers has been fabricated and placed over a glassy carbon electrode. The resulting coating eliminates the passivation effect of the electrode surface caused by polyphenols oxidation, while the characteristic waves of small biological antioxidants are not affected
Rheological interfacial properties of espresso coffee foaming fractions
No full textLa stabilità e la velocità di formazione della schiuma del caffè espresso sono legate alla cinetica di formazione e alla viscoelasticità di tale film biopolimerico che si forma all’interfaccia delle bolle.
Le principali macromolecole responsabili della schiuma del caffè espresso, complessi melanoidine/proteine e polisaccaridi, sono state estratte dalla polvere di caffè ed analizzate sia per la loro attitudine alla formazione della schiuma (analisi della morfologia della schiuma) , sia per le proprietà di strutturazione all’interfaccia liquido/aria, valutate tramite reologia interfacciale
Adaptive nanowire–nanotube bioelectronic system for on-demand bioelectrocatalytic transformations
No full textAn integrated nanobioelectronic system, exploiting the distinct properties of nanowires and carbon-nanotubes, has been designed for triggering reversibly and on-demand bioelectrocatalytic transformations of alcohols
Nylon Nanofibrous Biosensors for Glucose Determination
No full textNanofibrous membranes have been produced by electrospinning to develop first generation glucose biosensors. The direct immobilization of glucose oxidase onto the polyamide nanofibrous surfaces by drop coating revealed a simple and efficient method for the development of sensitive, stable, and reproducible electrochemical biosensors. The biosensor showed a linear response over the range 1 – 9X10-3 glucose (R-2=0.9997) with a sensitivity of 1.11 muA/mM and a limit of detection of 2.5X10-6 M (S/N=3). The uncertainty of repeatability was 2% (RSD%, n=30). After one month of storage, the signal decreased of 35%. The recovery of glucose, evaluated in real samples of honey, was 98% (RSD%=1%, n=3)
Electrospun nonwoven nanofibrous membranes for sensors and biosensors
No full textThis review will focus on the recent advances on nanofibrous membranes (NFM) prepared by electrospinning (ES) applied to modify electrochemical sensors and biosensors. Most relevant applications of NFM include their used as selective barrier toward diffusion, protective coatings against fouling, conductive substrates for sensing applications, catalytic and biocatalytic membranes. The main advantages and drawbacks of these applications are critically assessed
On-demand protection of electrochemical sensors based on adaptive nanowires
No full textWe report here on the use of adaptive nanowires for addressing the key surface fouling problem of electrochemical sensors. Effective resistance against surfactant fouling is obtained by switching magnetically the surface orientation of alkanethiol-coated gold nanowires (containing a short nickel segment) between horizontal and vertical positions to allow the transducer to perform the measurement and reset it to the protection mode between successive measurements. This leads to "opening" and "closing" of the surface and hence switching between active (sensing) and passive (protection) modes. Such on-demand protection and minimization of surface-fouling are indicated from prolonged series of stripping-voltammetric measurements of cadmium in the presence of gelatin, albumin, or Tween80. Factors influencing the protective action of the adaptive nanowires, including the length of the alkanethiol layer or of the gold/nickel segments were examined and optimized. Such on-demand protection capability should facilitate practical sensing applications of electrochemical devices
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