E. Brosio

Proton NMR relaxation study of swelling and gelatinisation process in rice starch–water samples

Proton transverse magnetization decay curves of rice flour starch-water samples were measured and analysed for the presence of four components in the relaxation curve. T2 values were interpreted on the basis of the diffusive and chemical exchange model that provided evidence for extra granular bulk water and three more water populations whose relaxation rate is governed by diffusive and chemical exchange with starch components. The analysis of relaxation data provided information on dynamics of water molecules as well as on the size and dispersion of diffusive domains. Furthermore, by measuring solid to liquid ratio, transverse and longitudinal relaxation curves of starch-water mixtures at increasing temperatures - from 20 to 77°C - swelling and gelatinisation processes were monitored.

Investigation of water dynamic behaviour in poly(HEMA) and poly(HEMA-co-DHPMA) hydrogels by proton T2 relaxation time and self-diffusion coefficient n.m.r. measurements

Abstract Proton transverse relaxation time (T2) and molecular self-diffusion coefficient (D) n.m.r. measurements of water in three hydrogels based on poly(2-hydroxyethyl-methacrylate) (pHEMA) have been performed in order to investigate the state of water and its interaction with the polymer network. Measured T2 values are discussed and quantitatively interpreted by assuming the chemical exchange process between water protons and hydroxyl protons of polymer chains as the major relaxation source, with no recourse to the bound water concept. The pseudo first-order kinetic constants and the activation energies for the exchange process in the different hydrogels have been calculated. The Pulsed Field Gradient (PFG) spin-echo technique has been used to measure diffusivity of water internal to the hydrogels; for hydrogels surrounded by external water, PFG multiple spin-echo experiments at different echo times and subsequent Diffusion Analysis by Relaxation-Time-Separated (DARTS) have been performed in order to obtain simultaneous determination of both internal and external water diffusion coefficients.

Amino acid profile in the ripening of Grana Padano cheese : a NMR study

Among typical Italian cheeses, Grana Padano is the most famous, with the biggest production. The final step in the cheesemaking is the natural ripening, which involves many modifications of high complexity. In the present work, thermoanalytical and spectroscopic techniques are applied to Grana Padano cheese as a new analytical approach. These are thermogravimetry (TG) and derived thermogravimetry (DTG) to determine different types of water present in the cheese matrix, low-resolution nuclear magnetic resonance (NMR) to provide information on the water localization and displacements within the foodstuff and high-resolution nuclear magnetic resonance (NMR) to evaluate all the amino acids present in the cheese. Modifications in both water and free amino acid contents are observed, as a function of the ripening time and of the distance from the centre of the cheese wheel.

A pulsed low resolution NMR study on crystallization and melting processes of cocoa butter

Pulsed low resolution nuclear magnetic resonance (NMR) was employed to measure the «melting» curves of different series of cocoa butter samples. The samples were prepared from completely liquid phase by cooling and tempering them at different temperatures Tc for varying time Δt. The «melting» curves were measured while keeping the sample at a fixed temperature Tm. The complex shape of each curve was interpreted in terms of cocoa butter polymorphism, and the results were compared with data obtained by other techniques available in the literature. Using just two tempering temperatures (+7 C and −18C), we were able to distinguish four solid phases and identify them with the phases II, III, IV, and V described in literature. Our data are in full agreement with literature. Several novel results have been also found. These include the kinetic constants of the melting processes of phases II and III, the rate constants of solidification of phase V, the conversion of phase III into phase IV before melting at temperatures ≥30 C, and the growth of phase V out of phase II at −18 C (including the rate constant of this process). We are convinced that NMR may serve as a principal tool in fat polymorphism investigations, especially if it is combined with other techniques such as differential scanning calorimetry. Its advantage, apart from rapidity of measurement, is the fact that the measurement itself does not interfere with the melting or solidification process studied. On the other hand, it does not distinguish in a direct way between different solid phases present in the sample; this can be done only in inference from the behavior upon melting.

Quality Traits of Conventional and Transgenic Lettuce (Lactuca sativa L.) at Harvesting by NMR Metabolic Profiling

Metabolism of genetically modified (GM) lettuce (Lactuca sativa L.) leaves was investigated by comparing NMR metabolic profiles of three lines (T(3)B12, T(7)B7, and T(7)B14) overexpressing the E. coli asparagine synthetase A gene with those of the wild type (WT) at 24, 56, and 64 days after sowing (DAS). Statistical analyses based on hydro-soluble compound profiles significantly and maximally discriminated the WT from GM-lines at optimal harvest time (56 DAS). The T(7)B14 metabolic variations were opposite to those of both T(3)B12/T(7)B7 lines, suggesting that unexpected effects of transgenesis had occurred. Compared to controls, the T(3)B12/T(7)B7 plants shared the leaf mass increase, higher amino acid (asparagine, glutamine, valine, and isoleucine) and protein levels, and lower nitrate contents, accompanied by a modest sink of organic acids (alpha-chetoglutarate, succinate, fumarate, and malate), sucrose, fructose, and inulins. Incongruously, the T(7)B14 butter heads were less leafy than the controls and showed lowered amino acid/protein contents and overstored inulin. To further investigate the metabolic discrepancies among the GM-lines, a set of key nitrogen and inulin genes was monitored. The T(3)B12/T(7)B7 lines shared comparable gene expression changes, including the induction of the endogenous asparagine synthetase1 and nitrate reductase1 that supported the targeted enhancement of nitrogen status. Transgene product malfunctioning and T-DNA rearrangements throughout generations were proposed to explain the decreased asparagine content and the complex expression pattern of N genes in T(7)B14 leaves. In the latter, the inulin accumulation was associated with the upregulation of fructan biosynthesis genes and the intense repression of fructan hydrolases.

Oil and water determination in emulsions by pulsed low-resolution NMR

A pulsed, low-resolution nuclear magnetic resonance (NMR) technique has been used for the oil and water determination in O/W emulsions. The method is based on the analysis of the longitudinal magnetization decay curve, that, due to the different relaxation times of oil and water, consists of 2 recognizable components. Correlation of NMR results with fat content is described. A good correlation between the NMR response and fat content by weight has been found. The rapidity and accuracy of the measurements are comparable to those of other techniques.

A stereochemical model for phospholipids: I. Conformational energy refinement and molecular packing of l-α-Dipalmitoyl lecithin (DPL)

Abstract The preferred conformations of L-α-dipalmitoyl-lecithin (DPL) have been refined using a steepest descent procedure throughout non-bonded potential energy calculations. The results indicate that energy differences between the conformers is very low and the energy parameters are quite constant around the minimum, suggesting a large degree of flexibility of this molecule. The molecular packing energy calculations have been performed by separating the two hydrocarbon chains from the polar head groups of the molecule. From the energy parameters for the packing of the aliphatic chains it results that for distances between adjacent chains up to 4·4 A the intermolecular forces allow the maximum degree of freedom. This suggests that hydrocarbon chains do not play the main role in the packing process of DPL molecule. Therefore the energy parameters of the polar segment have been calculated, assuming that the C 2 asymmetric carbon atom represents the points of the hexagonal lattice and the rotation centre for each molecule. For the internal symmetry of this segment of the molecule two non-equivalent conformers have been selected over all sets of allowed conformations (the GGG and GGG ∗ for the α 2 , α 3 and α 5 torsion angles). The energy packing calculation has been carried out for two independent sets of data, with and without the electrostatic contributions. In the first case a unique topological situation is allowed with the P-N dipole lying parallel to the lattice plane. In the second case different situations including that with the P-N dipole lying orthogonal to the plane are allowed. These data are discussed in relation to different physical conditions.

A stereochemical model for phospholipids. II: Conformational analysis and molecular packing of phosphatidylethanolamine (PE)

Abstract A partition energy method procedure was applied to select the energetically favoured conformations of phosphatidylethanolamine (PE) as polar constituents of phospholipid molecules. The result indicated a large degree of freedom for the two torsion angles of the ester bond of the phosphate and a gauche, gauche star conformation for the ethane bond. A packing process of the molecule was carried out through a potential energy calculation by considering the conformers selected above, using previously published procedure and conventions. All the arrangements which possess the best packing energy values were characterised by an orientation of the PN dipolar segment parallel to the lattice plain. Rotation of the internal torsion angles and rotation in the eulerian space of the molecule produced differences in the charged groups that interact. An additional minimum was present in the energy packing process of those conformers which have the first torsion angle of the phosphate in a trans conformation. This minimum, which corresponds to an orientation of the molecule orthogonal to the lattice plane, requires a complete neutralisation of the point charges on the system. The results of the calculation underline the importance of changes in the behaviour of the polar group of the phospholipids in the packing process.

Pulsed low-resolution nuclear magnetic resonance — an analytical tool in food science

Abstract Routine food analysis requires methods that are non-destructive, rapid and easy to use. Pulsed low-resolution NMR satisfies all these conditions and is increasingly being applied to determine the water, oil and protein content of a number of foodstuffs.

NUCLEAR MAGNETIC RESONANCE IN THE ANALYSIS OF DAIRY PRODUCTS

Nuclear Magnetic Resonance (NMR) is a non-invasive, multiparametric technique particularly suitable for the study of heterogeneous systems. In this paper some applications to the study of milk and milk derivatives are reviewed and discussed. Low resolution H NMR is primarily involved in spin-spin relaxation time and self-diffusion coefficient measurements of water and fat molecules in dairy products. From these parameters, information about molecule dynamics, chemical exchange kinetics and sample morphologies can be obtained. In addition, the time-dependence monitoring of such parameters