1,720,964 research outputs found
Study of antimicrobial and antioxidant properties of new materials for development of active food packaging
Full text linkThis work is focused on the design, production and characterization of sustainable active food packaging materials with antimicrobial and antioxidant properties to ensure the safety and quality of foods and prolong their shelf-life.
Firstly, a microfluidic device combining dielectrophoresis (DEP) and Raman spectroscopy was developed for a fast and dynamic characterization of different bacterial strains, including food-related pathogens (i.e. E. coli and S. aureus), directly in planktonic suspension. Predictive models to identify bacterial cross-induced resistance to antibiotic within few hours were built using this method, overcoming the overnight incubation required by classical microbiological assays. Furthermore, Raman imaging was employed to detect the spatial distribution of different biomolecules at single cell level.
Then, the antibacterial properties of innovative silver and carbon-based nanosystems and their inclusion in prototype packaging materials were studied.
Differently sized silver nanoparticles, from 6 to 50 nm, were compared for their antibacterial efficacy in suspension and immobilized on glass. For the first time, the surface minimal bactericidal concentration (SMBC) of silver needed to kill 99.9999% of bacteria, was determined by ISO 22196, thereby facilitating the comparison between measurements and minimizing the amount of silver on the materials surface (0.023-0.034 μg/cm2) as well as their cost of production and toxicity.
Colloidal carbon nanoparticles (CNP), obtained by a green chemistry synthesis, were tested against Gram + and a Gram – bacteria, by classical microbiological assays and the DEP-Raman system, revealing a rapid interaction with the bacteria but not significant bactericidal effects. Thus, CNP were loaded with an antimicrobial peptide which increased their antibacterial activity, especially against S. aureus.
Finally, new antioxidant packaging modified with grape and olive industrial waste products and Moringa oleifera leaves obtained by different extractive procedures were produced and characterized. The antioxidant efficacy of many fractions of the plants extracts were analyzed by multiple standard assays and the results were correlated with their content of polyphenols obtaining higher values for anti-solvent and maceration extract fractions. The latter, resulting from a more sustainable extraction procedure, were included in cellulose-based active packaging systems. The antioxidant properties of such films were measured by indirect and direct analytical methods demonstrating good free radical scavenging properties for all the three kind of active agents and a higher radical reduction capacity of moringa. Additionally, the ability of the packaging coated with moringa (5% w/w) of delaying fresh ground beef oxidation was tested. This film was chosen as the best alternative to obtain the highest oxidative protection of meat on the basis of the in vitro results and ensuring a direct food-contact mechanism of action. This packaging revealed to prevent meat from lipid oxidation by at least 60% after 16 days compared to simple cellulose. Additionally, in situ analysis of the meat performed by vibrational spectroscopies evidenced also a protective action against protein and lipid degradation.
This work could be considered valuable in the field of food packaging because the use of sustainable and degradable materials to prolong the food shelf-life perfectly fits in the actual compelling need to reduce pollution and global waste production. This is in accordance with the 12th Sustainable Development Goal of the European Green Deal purpose to halve the global food waste production per capita by 2030, ensuring an efficient and sustainable use of natural resources. Hence, an innovative way to recover food industry waste is proposed and their antioxidant efficacy in active food packaging was demonstrated even on real food matrices with many different techniques strengthening the reliability of the results
Study of Nanobiomaterials with Bio-based Antioxidants: Interaction of Polyphenol Molecules with Hydroxyapatite and Silica
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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
Hyperspectral Chemical Imaging of Single Bacterial Cell Structure by Raman Spectroscopy and Machine Learning
Full text linkIn this work, biomolecules, such as membrane proteins, lipids, and DNA, were identified and their spatial distribution was mapped within a single Escherichia coli cell by Raman hyperspectral imaging. Raman spectroscopy allows direct, nondestructive, rapid, and cost-effective analysis of biological samples, minimizing the sample preparation and without the need of chemical label or immunological staining. Firstly, a comparison between an air-dried and a freeze-dried cell was made, and the principal vibrational modes associated to the membrane and nucleic acids were identified by the bacterium’s Raman chemical fingerprint. Then, analyzing the Raman hyperspectral images by multivariate statistical analysis, the bacterium biological status was investigated at a subcellular level. Principal components analysis (PCA) was applied for dimensionality reduction of the spectral data, then spectral unmixing was performed by multivariate curve resolution–alternating least squares (MCR-ALS). Thanks to multivariate data analysis, the DNA segregation and the Z-ring formation of a replicating bacterial cell were detected at a sub-micrometer level, opening the way to real-time molecular analysis that could be easily applied on in vivo or ex vivo biological samples, avoiding long preparation and analysis process
Rapid determination of bacterial susceptibility to antibiotics combining Raman spectroscopy and Dielectrophoresis
Full text linkVariations 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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