1,721,111 research outputs found
Quantification of polyols in sugar-free foodstuffs by qNMR
No full textWe present a qNMR method for the determination of low calories sweeteners (erythritol, mannitol, maltitol, sorbitol, isomalt and xylitol) in sugar-free foodstuff. The structural similarities of these compounds determine often a severe spectral overlap that hampers their quantification via conventional 1D and 2D NMR spectra. This problem is here overcome by exploiting the resolving capabilities of the CSSF-TOCSY experiment, allowing the quantification of all six polyols, with satisfactory results in terms of LoQ (2.8-7.4 mg/L for xylitol, mannitol, sorbitol, 15 mg/L for erythritol, 38 mg/L for maltitol and 91 mg/L for isomalt), precision (RSD% 0.40-4.03), trueness (bias% 0.15-4.81), and recovery (98-104%). Polyol's quantification in different sugar-free confectionary products was performed after a simple water extraction without any additional sample treatment. While these results demonstrate the robustness of the proposed method for polyols quantification in low calories foods, its applicability can be further extended to other food matrices or biofluids
Conformation and interactions of bioactive peptides from insect venoms: The bombolitins
No full textBombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee, acting at membrane level and able to enhance the activity of Phospholipase A(2). The biological activity of this class of natural peptides seems to be related to the their ability to form amphiphilic helical structures in the presence of phospholipid aggregates or related membrane model systems. We have carried out systematic investigations on a series of bombolitins and their synthetic analogs in order to establish the conditions in which amphipathic helices are formed and to elucidate the details of the interaction with phospholipids and related model systems. We have shown that bombolitins and their analogs interact with phospholipid aggregates and detergent micelles forming amphiphilic helices. By means of the Langmuir film balance technique, coupled with fluorescence microscopy, we have shown that bombolitins perturbe the structure of phospholipid monolayers, forming phase separated peptide domains. In aqueous solution, in the absence of detergent or phospholipids, bombolitins form oligomeric aggregates with consequent conformational transition from a random coil to an ct-helical structure. In the aggregate structure, evidence was obtained that helices are oriented in an antiparallel fashion. In this article we summarize the most recent results of conformational studies by CD, NMR and computer simulations on a series of bombolitins and retro-, all-D- and all-D-retro-analogs. (C) 1998 John Wiley & Sons, Inc
1H Nuclear Magnetic Resonance Spectra of Chloroform Extracts of Honey for Chemometric Determination of Its Botanical Origin
No full textIn this work, we present a new NMR study, coupled with chemometric analysis, on nonvolatile organic honey components. The extraction method is simple and reproducible. The 1H NMR spectra of chloroform extracts acquired with a fast and new pulse sequence were used to characterize and differentiate by chemometric analysis 118 honey samples of four different botanical origins (chestnut, acacia, linden, and polyfloral). The spectra collection, processing, and analysis require only 30 min. The 1H spectrum provides a fingerprint for each honey type, showing many characteristic peaks in all spectral regions. Principal component analysis (PCA) and projection to latent structures by partial least squares-discriminant analysis (PLS-DA) were performed on selected signals of the spectra to discriminate the different botanical types and to identify characteristic metabolites for each honey type. A distinct discrimination among samples was achieved. According to the distance to model criterion, there was no overlap between the four models, which proved to be specific for each honey type. The PLS-DA model obtained has a correlation coefficient R2 of 0.67 and a validation correlation coefficient Q2 of 0.77. The discriminant analysis allowed us to classify correctly 100% of the samples. A classification index can be calculated and used to determine the floral origin of honey as an alternative to the melissopalinology test and possibly to determine the percentage of various botanical species in polyfloral samples. Preliminary data on the identification of marker compounds for each botanical origin are presented
Determination of the secondary structural elements of chicken liver Fatty Acid Binding Protein by two-homonuclear NMR
No full textA conformational study in solution of the fatty acid binding protein from chicken liver is presented. The nearly complete sequence-specific 1H resonance assignment was achieved from homonuclear two-dimensional nmr experiments using a sample of native protein. The principal elements of secondary structure were identified: 10 antiparallel beta-strands and one helical segment followed by a turn comprising 5 residues. These elements correspond closely with those of the crystal structure of the related protein, and two new secondary structural features obtained from the nmr data are the beta-sheet conformation between the first and the last beta-strand in the protein sequence, as well as a helical loop at the N-terminus of the polypeptide chain
Fast Determination of Histamine in Cheese by Nuclear Magnetic Resonance (NMR)
No full textA rapid and quantitative 1H nuclear magnetic resonance (NMR) method was developed to analyze histamine in cheeses. The procedure is simple because the acid extract is analyzed directly, without any need for further filtration, derivatization, or other manipulation. This NMR method was demonstrated to be specific by 2D total correlation spectroscopy (TOCSY) and heteronuclear multiple-quantum coherence (HMQC) experiments and reliable in terms of linearity, accuracy, recovery, repeatability, and limits of detection (LOD). Good precision, with relative standard deviation (RSD) < 4%, recovery of 100%, and a range of 0.6−1 mg/kg for the LOD were obtained. The NMR method was successfully applied to different types of cheese, ranging from soft to hard. No interference from free amino acids, proteins, and other natural components was detected. The NMR method could be transferred to other kinds of food
Nuclear Magnetic Resonance as a Method for Prediction of Geographical and Entomological Origin of Pot Honey
No full text1H-Nuclear Magnetic Resonance (NMR) spectroscopy was used to analyze pot honey samples of different geographical and entomological origin. An NMR-based metabolomic approach, applied to 67 samples, tested and confirmed the validity of the multivariate statistical analysis in the discrimination. We developed an efficient tool to differentiate the honeys by their geographical origin; additionally, we showed that within limited geographical areas it is possible to distinguish honey samples in terms of the bee species that produced it. Furthermore, the structural identification of a geographical marker compound (in the Brazilian honeys) was achieved, and a specific region in the NMR spectrum was found to be responsible for the entomological separation
DETERMINAZIONE DI AMMINE BIOGENE AROMATICHE NEL FORMAGGIO MEDIANTE 1H-NMR
No full textLe ammine biogene sono basi organiche azotate a basso peso molecolare, presenti naturalmente nei cibi, quali formaggio, carne, pesce e nelle bevande, vino, birra ecc. Vengono prodotte per decarbossilazione enzimatica di amminoacidi o per transamminazione di aldeidi e chetoni. Le ammine biogene si trovano nei cibi come conseguenza di un'attività microbica endogena ma possono anche essere presenti per effetto di contaminazione microbica durante i processi di lavorazione del prodotto. Per questo motivo, le concentrazioni di queste sostanze nei cibi vengono anche considerate indicatori di igiene.
In letteratura sono presenti molti metodi per la determinazione delle ammine biogene negli alimenti basati sull'utilizzo della gas cromatografia, HPLC, elettroforesi capillare, ed altri; tutti i metodi richiedono, dopo la prima fase di estrazione, altre fasi di filtrazione e derivatizzazione con anche, in alcuni casi, l'utilizzo di solventi tossici. Inoltre, dipendentemente dalla complessità della matrice alimentare, in particolare dalla quantità di amminoacidi liberi che possono competere con la reazione di derivatizzazione, può rendersi necessaria anche un'ulteriore fase di estrazione con solventi prima della determinazione analitica. Tutti questi passaggi riducono la percentuale di recupero, aumentano il rischio di perdita di analita e contaminazione, oltre ad allungare il tempo di analisi.
I risultati preliminari descritti in questo lavoro illustrano la potenzialità di un nuovo metodo per la determinazione di ammine biogene aromatiche che utilizza la Risonanza Magnetica Nucleare. Il metodo è veloce e semplice in quanto l’estratto acquoso acido iniziale viene analizzato direttamente senza alcun passaggio di filtrazione né di derivatizzazione
Identification of the production chain of Asiago d'Allevo cheese by Nuclear Magnetic Resonance Spectroscopy
No full textIn the present work, a rapid and simple NMR method to discriminate Asiago d’Allevo cheese samples from different production chains is described. A fast and reproducible extraction of the organic fraction was employed. By applying chemometric analysis to NMR data, it is possible to differentiate PDO Asiago cheese produced in alpine farms from that produced in lowland and mountain industrialized factories. PCA of both 1H and 13C NMR spectra showed a good separation of alpine farm products from the other ones, whereas the lowland and mountain industrialized cheeses are undistinguishable. The samples were differentiated on the basis of a higher content of unsaturated fatty acids, principally oleic, linoleic, linolenic, and conjugated linoleic acids for the alpine farm cheeses and a higher content of saturated fatty acids for the industrialized products. Conjugated linoleic acid and 1-pentene are also discriminating components
Role of the guanidine group in the N-terminal fragment of PTH(1-11)
No full textA series of PTH hybrids containing a diamine [NH2(CH2) n NH2; n = 4, 5, 6] in the C-terminal position was synthesized based on the H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH2 (Har = homoarginine) template. The compounds were pharmacologically characterized at PTH1R receptors for agonist activity
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