1,721,021 research outputs found
Valutazione dell’interazione tra polifenoli della propoli e componenti della carta per alimenti per la realizzazione di un imballaggio attivo
No full textLa propoli è un composto di origine naturale, prodotto dalle api, che possiede diverse proprietà fra cui elevato potere antiossidante, antivirale e antimicrobico, grazie alla presenza d'innumerevole polifenoli. In questo lavoro si è voluto analizzare la stabilità dei polifenoli della propoli a contatto con carta per alimenti in un sistema di packaging attivo. La carta, infatti, è costituita da materiali cellulosici e da additivi chimici che potrebbero influire sulla stabilità dei polifenoli della propoli. In particolare, si sono effettuate laccature (coatings) di un preparato a base di propoli su due carte commerciali, una resistente ad umido ed una politenata, e per confronto su di un film di polietilentereftalato (PET). I campioni sono stati condizionati a temperatura e umidità costante (23°C e 55% UR) ed analizzati dopo 1, 15 e 30 giorni per valutarne la stabilità. E' stato utilizzato metodo DPPH per la valutazione del potere antiossidante.Da queste prime analisi è risultato che la matrice carta composta da fibre di cellulosa e diversi additivi è in grado di diminuire il potere antiossidante della propoli, disattivando parte dei polifenoli in percentuale del 15%. La disattivazione sembra avvenire al momento del contatto delle matrici per mantenersi poi stabile nel tempo (30 giorni). Sono stati eseguiti, quindi, coating su foglietti di carta monoadditivata, prodotti appositamente in laboratorio, per valutare il/i componenti maggiormente responsabili della disattivazione dei polifenoli. Dai risultati ottenuti si evince che la disattivazione di parte dei polifenoli avviene nella prima settimana di stoccaggio del materiale attivo con disattivazione variabile da un minimo di 5% per carte non additivate ad un massimo del 15% per carte additivate con colla a base di colofonia e resina poliamminoepicloridrinica (PAE). Si è proseguito il lavoro quindi applicando dei coating sulla parte politenata delle carte commerciali, in particolare formulando due tipologie di miscele al fine di modulare il rilascio dei polifenoli: la prima costituita da pasta di propoli italiana purificata e decerata e 0.5% di idrossipropilmetilcellulosa (HPMC), mentre la seconda da pasta di propoli e 35% di polivinilpirrolidone (PVP). Entrambe le tipologie di campione sono state poste a contatto con tre terreni colturali: un terreno PCA, un terreno simulate un prodotto carne (beef extract, bacteriological peptone, tryptone, glucosio, agar, pH = 6.9) e un terreno simulante prodotto lattiero caseario (PCA con il 5% di latte intero), sono state quindi effettuate le cinetiche di rilascio dei polifenoli quantificandoli tramite saggio di Folin-Ciocalteu. I risultati ottenuti presentano una percentuale di rilascio di polifenoli intorno al 20% per la formulazione con HPMC, mentre i polifenoli migrati dalla miscela con PVP raggiungono il 40% nel corso delle prime 24 ore, successivamente il rilascio si mantiene costante; il rilascio risulta inoltre modulato della composizione del terreno colturale
Sakacin-A antimicrobial packaging for decreasing Listeria contamination in thincut meat: preliminary assessment
Full text linkBACKGROUND: Minimally processed ready-to-eat products are considered a high-risk food because of the possibility of contamination with pathogenic bacteria, including Listeria monocytogenes from the animal reservoir, and the minimal processing they undergo. In this study, a sakacin-A anti-Listeria active package was developed and tested on thin-cut veal meat slices (carpaccio). RESULTS: Enriched food-grade sakacin-A was obtained from a cell-free supernatant of a Lactobacillus sakei culture and applied (0.63 mg cm−2) onto the surface of polyethylene-coated paper sheets to obtain an active antimicrobial package. The coating retained antimicrobial features, indicating that the process did not affect sakacin-A functionality, as evidenced in tests carried out in vitro. Thin-cut veal meat slices inoculated with Listeria innocua (a surrogate of pathogenic L. monocytogenes) were laid on active paper sheets. After 48 h incubation at 4 °C, the Listeria population was found to be 1.5 log units lower with respect to controls (3.05 vs 4.46 log colony-forming units (CFU) g−1). CONCLUSION: This study demonstrates the possibility of using an antimicrobial coating containing sakacin-A to inhibit or decrease the Listeria population in ready-to-eat products, thus lowering the risk of food-related diseases
Charge density quantification of polyelectrolyte polysaccharides by conductometric titration : an analytical chemistry experiment
No full textAn easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a negatively charged polysaccharide (pectin) and a positively charged biopolymer (chitosan), two biomacromolecules commonly used in food and biomaterials applications. This novel conductometric titration method can be easily applied in most analytical chemistry teaching laboratories, due to its ease-of-use, safety, and educational benefits. This analytical technique can also be used in a wide-range of laboratory activities and has extensive research applications in areas of chemistry involving charged biopolymers, such as food science, materials science, and physical chemistr
Study of cellulose-lysozyme interactions aimed to a controlled release system for bioactives
Full text linkThe potential use of cellulose based
materials for active food packaging applications was explored. For this purpose, the sorption of lysozyme in
a cellulose based paper pulp was optimized using the experimental design methodology. A Face-Centered Composite design was applied to investigate the effect of short/long fibers ratio and carboxymethyl cellulose concentration on linking lysozyme to the fibers surface and to optimize the cellulosic matrix composition. The related polynomial model showed good fitting ability (R2[0.9) as well as good prediction ability (Q2[0.8). The best combination of factors was 50 % short fibers, 50 % long fibers and at least 4 % carboxymethyl cellulose. Afterwards the lysozyme release was investigated using a mathematical model based on Fick’s second law. It was able to describe the release kinetics of lysozyme from the paper sheets made with the optimized cellulosic matrix into water at different temperatures (between 4 and 23 C), pH (from 4 to 7) and NaCl concentrations (from 0.2 to 2 M). The apparent diffusion coefficients for the
lysozyme were in the range of 3.1 X 10-16 6.6x10-14 and the Ea value was 22.1 kJ/mol at pH 5 and NaCl concentration of 0.5 M
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
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