1,720,981 research outputs found
Instrumental GC-MS analysis of virgin olive oils already subjected to sensory evaluation
Full text linkThe aroma plays an important role in the olive oil consumer preference and it is one of the parameters used to classify olive oils. The oils of lower quality have an aroma very different rather than that of an extra virgin olive oil, due to the presence of metabolic pathways different from the Lipoxygenase (LOX) one. Depending on the relevant pathway, different odorants are produced giving rise to unpleasant sensory perception whose intensity is related to the amounts of some aroma components.
The sensory evaluation, also called “panel test” is the only normed method to assess the quality of the oils relying on their aroma, but this procedure, although carried out by a trained assessor, has some drawbacks. The use of analytical techniques consists in an objective approach, able to identify and quantify the odorants in the volatile fraction of both extra virgin and virgin oils.
In this work, 77 olive oils were analyzed; 21 were extra virgin while 56 were virgin olive oils characterized by different sensory defects with different intensities. SPME-GC-MS techniques and the “Find by Chromatogram Deconvolution” algorithm were applied, in order to extract the most compounds as possible.
The results obtained were subjected to some statistical analysis, from the simple Principal Component Analysis (PCA) to the more complex Partial Least Square (PLS) regression, to find some correlations between sensory evaluation and chemical composition, with the final aim to develop a method suitable to verify the results of the panel test. The PCA was not so useful to reach the goal, so the PLS regression was applied. The models obtained highlighted the compounds characterizing the defected samples analyzed, each one with a specific importance. The models developed have been composed by a high number of variables because, instead to consider the compounds concentration, the variables subjected to this analysis have been the chromatographic signal detected at each time of the analysis. To simplify, only the relevant variables were taken into account and some relations between the specific compound content and the median of the defects have been foun
Le molecole del gusto: metodi di analisi della frazione aromatica degli alimenti
No full textFoods usually undergo to sensory evaluation: in some cases (olive oils, butter) it has become a legal evaluation within the frame of EU regulations, in some
other cases (e.g. honeys) they have reached a fully standardized level. Analytical chemistry applied to foods, however since a number of years devoted
efforts to characterize food volatile compounds which are responsible of the so said “flavor”. In this paper some details will be described concerning
improvements and trends in foods volatile compounds, enclosing trials carried out to study relationships between these and sensory evaluation
Methods for triacylglycerols analysis in vegetable oils
No full textTriacylglycerols analysis is a powerful tool to assess purity of vegetable oils, mainly applied to olive oils. Official methods by EU and IOC standardized RP-HPLC analysis of triacylglycerols to evaluate the amount of ECN42 terms, even if, in many cases, the obtained separation was not satisfactory, the method was adopted to check for extraneous oils with high amounts of oleic acid. An improvement of the method suitable to check for admixtures with several oils had been proposed by substitute acetone/acetonitrile with propionitrile. Ratios between selected TAGs were then calculated. The ECN42 value obtained by using the two different eluting solvents were compared and some discrepancies were highlighted.
Some peculiar mixtures of seed oils and olive oil, however, cannot be detected even by this approaches, while gas chromatography can be a suitable approach.
Capillary GC on short column coated with non polar stationary phase was applied and results suggested that some limits can be proposed for C48 and C60.
Care must be applied to the injection method, as thermal degradation can easily take place
Evolution of Eight Biogenic Amines in Raw and Preserved Mackerel (Scomber scombrus) Fillets Monitored by UHPLC-PDA
Full text linkThe presence of biogenic amines (BAs) in seafood can pose a health risk to consumers, as they have been linked to adverse reactions such as histamine poisoning. Although the only biogenic amine for which maximum limits have been set is histamine, it is also important to regulate the presence of other amines associated with certain adverse effects. In this study, the official method for determining histamine was slightly modified and adapted for a UHPLC-PDA system and applied to analyze raw and preserved mackerel fillet samples. The evolution of biogenic amines during the storage period under refrigerated conditions revealed that, within two days, the limit for the content of histidine of 100 mg/kg was exceeded in raw fillets, while the histidine content in preserved mackerel (in oil and marinated) remained more stable. The thawing phase, whether in the fridge or at room temperature, did not significantly affect the BA content. Additionally, three different cooking methods (steaming, oven-baking, and boiling) significantly decrease the levels of BAs in highly contaminated raw mackerel fillets
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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