1,720,983 research outputs found
Determinazione dei pigmenti e loro legame con parametri di qualità e autenticità dell'olio di oliva extravergine
No full textUna delle caratteristiche peculiari dell’olio di oliva extravergine è il suo colore, che è dovuto alla presenza di una classe di composti minoritari: i pigmenti. La determinazione quantitativa dei pigmenti, ovvero delle concentrazioni dei carotenoidi, delle clorofille e dei loro derivati, può essere fatta utilizzando vari metodi sperimentali, suddivisi in metodi cromatografici e metodi spettroscopici. In questo lavoro si passeranno in rassegna questi due approcci, soffermandoci sugli ultimi sviluppi che hanno consentito di analizzare molti campioni di olio di oliva extravergine di diverse cultivar, provenienze geografiche e sottoposti a varie condizioni di conservazione. Questi studi sono stati utili ad individuare dei parametri associati al contenuto dei pigmenti in grado di definire l’autenticità e la qualità di un olio aprendo a interessanti prospettive applicative
Pigments in extra virgin olive oils produced in different mediterranean countries in 2014: Near UV-vis spectroscopy versus HPLC-DAD
Full text linkCarotenoids and chlorophyll derivatives play a key role in Extra Virgin Olive Oils (EVOOs). Many factors,
such as cultivar, geographic origin, maturity of olives, climate and storage conditions, influence the
pigments’ content. The quantification of pigments is usually done by chromatographic techniques.
However, recent works evidenced the potentialities of UV-visible-related methodologies. In this
research, a selection of EVOO samples produced from olives harvested at the beginning of November
2014 in Greece, Tunisia, Italy and Spain, was investigated in terms of pigments by means of two methods.
The first one is a recent approach based on the mathematical treatment of near UV-vis absorption spectra
of olive oils to quantify in a fast, cheap and non-destructive way four main pigments, namely b-carotene,
lutein, pheophytin A and pheophytin B. The second one is a more standard HPLC-DAD method. From the
comparison between the two methods, we can conclude that the new near UV-vis approach gives
reliable results, with good precision and high reproducibility. Pigments quantified by these two methods
in EVOOs produced in four countries from different cultivars are analyzed by principal component
analysis (PCA). Results indicate that pigments can be correlated to several factors such as ripeness stage,
geographic origin and cultivars
Olio di Oliva Extravergine Toscano: uno studio sul contenuto dei pigmenti e prospettive per un nuovo indice di qualità
No full textNel 2014 il nostro gruppo di ricerca ha messo a punto un nuovo metodo di analisi degli spettri di assorbimento nella regione ultravioletto-visibile (UV-vis) dell’olio di oliva extravergine per ricavare, in modo rapido e semplice, la quantità di alcuni pigmenti, i principali, che conferiscono a questo tipo di olio di oliva alcune importanti caratteristiche. Il contenuto in -carotene, luteina, feofitina A e feofitina B dell’olio di oliva extra-vergine è legato infatti alla qualità, alla freschezza e allo stato di conservazione del prodotto. In questo articolo, descriveremo alcune recenti applicazioni di questo metodo ad un campione rappresentativo di oli di oliva extravergine prodotti in Toscana da olive toscane. Verranno discussi alcuni parametri derivati dall’analisi degli spettri UV-vis che possono essere correlati alle diverse annate (dal 2011 al 2015), alle condizioni di conservazione e al “tempo di vita” dell’olio di oliva extravergine. Queste ricerche sono importanti non solo per caratterizzare uno dei prodotti agroalimentari più legati alla cultura e alla cucina mediterranea, ma anche per evidenziare eventuali frodi e adulterazioni che rischiano di minare l’autenticità dell’olio di oliva extravergine prodotto nella nostra regione
Study of translational diffusion anisotropy of ionic smectogens by NMR diffusometry
No full textThermotropic ionic liquid crystals are considered very promising for a wide range of applications, such as anisotropic conductors as well as electrolytes in dye-synthesized solar cells. Their potential comes from the unique combination of ionic conductivity and high polarizability. In this paper we present a study of the diffusional properties of the ionic smectic A phase formed by the cationic smectogen, N-docecyl-N’-methyl-imidazolium (C12mim), with two different counter ions. Experimental translational diffusion data measured by NMR diffusometry are collected both for cations and anions and discussed in terms of their different anisotropy
Dynamics of a liquid crystal in its smectic A phase from angle dependent deuterium spin relaxation measurements
No full textMesomorphic, structural, electro-optic and dynamic properties of lactic acid derivative and its selectively deuterated isotopomers by means of electro-optics, SAXS, H-2-NMR and neutron spin-echo spectroscopy
No full textIn this work, we present the synthesis of two analogues of a lactic acid derivative selectively deuterated on phenyl and biphenyl moieties together with a detailed investigation of their properties within the Twist Grain Boundary smectic A* (TGBA*), the ferroelectric Smectic C* (SmC*) and the crystal E phases. The main structural features of the two liquid crystalline phases, namely TGBA* and SmC* phases, were determined by polarising optical microscopy, differential scanning calorimetry, electro-optical techniques, Small Angle X-ray Scattering (SAXS) and H-2 Nuclear Magnetic Resonance (H-2 NMR) measurements. Preliminary results from Neutron Spin-Echo (NSE) spectroscopy, a technique rarely applied to study chiral liquid crystalline materials, are reported. The effect of the external magnetic field on the supramolecular structure of the ferroelectric phase was studied by means of H-2-NMR experiments under different external magnetic fields. The supramolecular and orientational ordering properties of this ferroelectric lactic acid derivative and its deuterated homologues are discussed in the frame of actual knowledge in the field of ferroelectric liquid crystal materials
Chimicambiente 2013: evento dedicato alla Chimica e agli Alimenti
No full textChimicambiente è un evento di formazione e di tipo culturale. Iniziato nel 2011, viene ospitato nel Comune di Rosignano Marittimo ogni anno. La terza edizione è stata centrata sul ruolo della Chimica nell'industria degli alimenti. In questa relazione sono riportati gli aspetti più significativi affrontati durante questo corso di formazione, in cui Università e Aziende si confrontano su tematiche legate alla sicurezza e all'analisi degli aliment
Pigments in Extra‐Virgin Olive Oil: Authenticity and Quality
Full text linkPigments, divided into carotenoids and chlorophyll derivatives, are responsible for the colour of extra‐virgin olive oil (EVOO). The concentration of pigments in EVOO depends on several factors, such as the maturity of olives before oil production, the cultivar and the geographic origin of olives. Pigments naturally degrade in olive oil (OO) during storage, and they may decompose due to light, temperature and oxygen exposure. The nature and concentration of pigments in EVOOs are different from seed oils, and this is a base of their use to reveal oil treatments and sophistication. In this chapter, the analytical methods, mainly chromatographic and spectroscopic, applied to identify and quantify pigments are overviewed. In particular, the applications of these methods to check the authenticity and the quality of extra‐virgin olive oil are discussed
The twist-bend nematic phase: translational self-diffusion and biaxiality studied by 1H nuclear magnetic resonance diffusometry
Full text linkRecently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (NTB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now seems to be clear that the NTB phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the NTB phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1′′,7′′-bis-4-(4′-cyanobiphenyl-4′-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase
Compatibilization and property enhancement of poly(lactic acid)/polycarbonate blends through triacetin-mediated interchange reactions in the melt
No full textTetrabutylammonium tetraphenylborate (TBATPB) and triacetin were added during extrusion to melt
blends of polylactic acid (PLA) and polycarbonate bisphenol A (PC) through a reactive compatibilization
approach in order to enhance the materials' mechanical properties and thermal resistance. Dynamic
mechanical thermal analysis revealed a new peak attributable to the glass transition temperature (Tg) of
the PLA-PC copolymer at a temperature lower than the Tg typical of PC and higher than the Tg of PLA. The
results of tensile tests, thermogravimetric analysis, differential scanning calorimetry, scanning electron
microscopy, transmission electron microscopy, size exclusion chromatography, and NMR analysis for the
compatibilized and uncompatibilized blends were, on the whole, in agreement with the formation of the
PLA-PC copolymer due to the action of the TBATPB and triacetin during the short extrusion time. The
mechanical behaviour, morphology, and thermal properties of the PLA/PC compatibilized blends were
investigated as a function of composition, with the intention of broadening the utility of these biobasedblends.
Finally, a general scheme for the reactions that occur during extrusion was proposed based on the
experimental results
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