Low-resolution 1H Research Articles

Wholewheat bread: Effect of gradual water addition during kneading on dough and bread properties

Owing to the increasing demand for wholewheat flours (WWF) in bread-making, techniques are needed to improve WWF's poor technological properties and the resulting bread quality. We tested the effect of a common bakers' strategy to improve WWF performance: adding part of the water of the recipe during the kneading operation. First, the kneading operating conditions were optimized to perform the gradual water addition. The optimized dough sample was tested in a second trial to make an in-depth investigation of the effect of (i) the amount of water added during kneading and (ii) the total water content on dough molecular mobility (with Low Resolution 1H NMR), dough rheology and bread quality. The gradual addition of water caused significant variations in proton mobility and dynamics; it improved dough rheological properties, but did not affect the bread quality. A higher dough water content (i.e., 60%) than predicted by the Farinograph test significantly improved the bread quality in terms of bread and crumb specific volumes, and bread texture. Combining the gradual water addition with high water content could be a strategy to enhance the quality of WWF doughs and breads, promoting the consumption of fibre-enriched foods.

Use of the 1H NMR technique to describe the kneading step of wholewheat dough: The effect of kneading time and total water content

The kneading step of wholewheat flour (WWF) dough was monitored using low-resolution 1H nuclear magnetic resonance (NMR). The tested variables were kneading time and total water content. Two 1H Free induction decay (FID) (A and B) and four 1H T2 Car-Purcell-Meiboom-Gill (CPMG) (C, D, E and F) proton populations were observed and the attribution to the different proton domains was made based on the literature and data acquisition. Kneading time significantly increased the mobility and the relative abundance of popA, the relative abundance and strength of protons of popC, D and E, while significantly reducing the relative amount of popF and increasing its mobility. This evolution of the proton populations during kneading was interpreted as chemical/physical transformations of the flour constituents. The use of WWF may reveal the changes in molecular dynamics underlying the higher water requirements of unrefined doughs, often associated with improved bread quality.

Food protein network formation and gelation induced by conductive or microwave heating: A focus on hen egg white

Heat-induced protein polymerization, gelation and the associated molecular scale changes were investigated during conductive and microwave heating (CH and MH, respectively). Given identical temperature-time profiles, polymerization of bovine serum albumin, ovalbumin, egg white (EW) and wheat gluten protein occurred faster and to a greater extent with CH than with MH. Moreover, lanthionine cross-links were present in some MH but in none of the CH samples. Gelation of EW protein by CH or MH was studied in more detail. Differential scanning calorimetry and fluorescence spectroscopy indicated that EW proteins initially denatured to a larger extent with CH than with MH. Size exclusion high performance liquid chromatography demonstrated that CH resulted in more heavily cross-linked EW protein networks than MH. Homogeneous EW gels were obtained by 15 min CH at 80 °C while 120 min MH at this temperature still resulted in inhomogeneous (with liquid and solid zones) gels. This was affirmed by low resolution 1H nuclear magnetic resonance measurements which indicated more mobile water in MH than in CH samples. However, MH gels had higher firmness than the corresponding CH gels. Thus, MH here led to less covalent cross-linking than CH, but still resulted in firmer gels most likely because its protein network relied heavily on non-covalent interactions. Industrial relevanceThis study highlighted differences between microwave and conventional, conductive, heating of different protein materials. While literature is divided about the origin of differences noted between these different heating modes, it is clear from our data that heating mode, given identical temperature-time profiles, impacts the changes that proteins undergo during heating. The knowledge that microwave heating favors protein unfolding, aggregation and cross-linking to a lower extent than conductive heating can likely be exploited in industrial applications.

Stability of the Meat Protein Type I Collagen: Influence of pH, Ionic Strength, and Phenolic Antioxidant.

The water-holding capacity (WHC) is among the key factors in determining the quality of meat and its value, which is strongly influenced by the content and quality of the connective tissue proteins like collagen. Therefore, the factors that influence the proteins’ stability, e.g., pH, ionic strength, and the antioxidants which are used to increase the meat shelf-life, also affect the WHC. The interaction of collagen, whose structure is strongly influenced by the interaction with water molecules, can be studied following the behavior of water diffusion by low-resolution 1H NMR experiments. The present study is addressed to study the collagen stability as a function of pH, ionic strength, and phenolic antioxidants like catechin. The experimental study demonstrated how the 1H NMR time domain (TD) experiments are able to evaluate the hydration properties of collagen, not only as a function of ionic strength and pH, but also in determining the ability of catechin to interact both on the surface of the collagen fibrils and inside the fibrillar domain.

Does the presence of fibres affect the microstructure and in vitro starch digestibility of commercial Italian pasta?

Abstract • Dry pasta is a staple food in many countries of the world and it is traditionally made of durum wheat semolina. The aim of this study was to evaluate the impact of pasta composition on microstructure, water absorption and mobility during cooking and nutritional properties of two commercial spaghetti made of durum wheat semolina (S) and whole durum wheat semolina (WS). Scanning Electron Microscopy (SEM) revealed no significant microstructural differences between the uncooked pasta samples, whereas the presence of fibre altered the integrity of the protein network in the cooked samples. Moreover, the water absorption during cooking and the water mobility at molecular level were investigated as weight increase and by low-resolution 1H NMR experiments, respectively. Compared to durum wheat spaghetti, the presence of fibre increased the water absorption while decreased the proton relaxation times 1H T2 and 1H T1 indicating an increased degree of water-polymers interaction. Lastly, the rate of starch hydrolysis, evaluated by means of in vitro methods, increased in presence of fibre, resulting in higher RDS and estimated Glycemic Index (eGI) for whole durum wheat spaghetti compared to the traditional ones. These findings were quite unexpected.

Effect of sepiolite treatments on the oxidation of sepiolite/natural rubber nanocomposites prepared by latex compounding technique

Latex compounding technique is an economic and ecosustainable alternative to melt mixing for preparing nanocomposites in which fillers are directly mixed with natural rubber in the latex aqueous dispersion. Clay minerals are excellent potential fillers to be used in masterbatches prepared exploiting this technique, but their presence is associated to the occurrence of oxidative degradation phenomena of natural rubber. In this work, by exploiting a combination of high- and low-resolution 13C and 1H Solid State Nuclear Magnetic Resonance techniques, with the support of Fourier Transform Infrared spectroscopy and thermal analyses, we characterized for the first time the oxidation phenomena occurring in sepiolite/natural rubber masterbatches obtained by the latex compounding technique. Oxidized species were identified and quantified and the dynamic properties, molecular weight and thermal stability of the rubber were characterized. Moreover, the dependence of degradation phenomena on the filler treatment and on the masterbatch work-up procedure was assessed, identifying freeze-drying as the method able to effectively protect the rubber from oxidation.

Effects of starch from five different botanical sources on the rheological and structural properties of starch–gluten model doughs

Wheat, corn, tapioca, sweet potato and potato starches were independently mixed into starch–gluten model doughs containing 15% (w/w) vital gluten. Rheological properties, including linear viscoelasticity region, frequency dependence and recovery capacity, were studied by strain sweep, frequency sweep, and creep and recovery measurements. Structural properties were also investigated by measuring the disulfide bonds (–SS–) content, SDS-PAGE and low-resolution 1H nuclear magnetic resonance. Wheat starch (WS)–gluten dough had the greatest linear viscoelasticity region (0.190%), lowest frequency dependence (0.128) and greatest recovery capacity (67.39%), while potato starch–gluten dough had the smallest linear viscoelasticity region (0.126%), greatest frequency dependence (0.195) and lowest recovery capacity (54.97%). Furthermore, WS–gluten dough showed the highest disulfide bonds (–SS–) content (3.47μmol/g), lowest intensity of extracted glutenin bands and highest bond water content (23.20%). This suggested that WS–gluten dough formed stronger starch–gluten interactions compared with those of the other four starch–gluten model doughs.

Development of a low resolution 1H NMR spectroscopic technique for the study of matrix mobility in fresh and freeze-thawed hen egg yolk

Three experiments were conducted in developing a low resolution proton nuclear magnetic resonance (1H NMR) spectroscopic technique to study matrix mobility in fresh and freeze-thawed gelled yolk. The Carr–Purcell–Meiboom–Gill (CPMG) sequence was used to measure spin–spin relaxation times of proton pools representing major yolk constituents. A component identification test distinguished 3–4 pools. The least mobile pool was assigned to proteins, protein–lipid and protein–water interactions, and the most mobile to unbound water. The remaining pools were assigned to lipids, lipid–protein and lipid–water interactions. A stability test indicated that yolk had varied matrix mobility within the same sample across five days of refrigeration storage. A reproducibility test demonstrated high repeatability of fresh yolk measurements, but significant differences (p<0.05) were found within gelled yolk samples. This research determined that 1H NMR spectroscopy, a non-destructive technique, can identify yolk components and detect changes in the matrix.

Effect of Flour, Gelatin and Salt on Water Status of Tomato Sauce

Tomato pulp was added with flour, gelatin, and salt (and their binary and ternary mixtures), to obtain tomato sauces with different formulations. Water status of the mixes was characterized at different time-space levels by means of water activity, moisture content and 1H rotational and translational molecular mobility (low resolution 1H NMR, 1H D and 1H T2 relaxation times distributions). The effect of different ingredients and water status was very different on macroscopic and molecular indicators. In particular, moisture content decreased with addition of all ingredients, as expected, while water activity was significantly reduced only when salt was added into the formulation by itself or together with flour and/or gelatin. At a molecular level, flour was the most effective ingredient in reducing proton rotational mobility (1H T2 relaxation time), while gelatin further increased proton molecular mobility as compared to the standard. Proton translational mobility was reduced with the addition of all ingredients, more effectively in the presence of gelatin and flour. It is interesting to point out the different molecular dynamics developed by these two thickening agents although their similar macroscopic effect in tomato sauce. Changes in formulation strongly affected water status at all time-space levels investigated in a complex manner, and the effect of each single ingredient should be carefully considered in the production of tomato sauces as it can affect product properties and stability.

Dynamics in Crystallites of Poly(ε-caprolactone) As Investigated by Solid-State NMR

We investigate the molecular dynamics within the crystallites of poly(e-caprolactone), PCL, crystallized from the melt by means of high-field 13C and low-field 1H NMR spectroscopy, addressing the question of whether it can be classified as a “crystal-fixed” polymer without chain motion through the crystallites. We address fast, slow, and intermediate-regime (microseconds to milliseconds time scale) motions by means of high-resolution of 13C DIPSHIFT and CODEX MAS experiments as well as low-resolution static 1H FID and MSE measurements over a range of temperatures. The DIPSHIFT data provide information on motionally averaged 13C–1H dipole–dipole couplings and indicate the presence of fast (≤1 μs) methylene group librational motions within the crystalline phase, where the amplitudes increase with increasing distance from the rather rigid ester groups. The CODEX experiments, addressing slow (≥ms) local rotations of the chemical-shift anisotropy tensors, suggest the absence of slow intracrystallite chain dyna...

Physical state, molecular mobility and chemical stability of powdered dairy formulations

The chemical stability of valuable nutrients like the essential amino acid lysine is an important factor regarding the nutritional quality of dairy powders. So far, the stability concepts based on the water activity or on the glass transition temperature are mainly used to predict the stability of dairy powders. However, these concepts often only partly predict the stability of food products. Therefore, the aim of this study was to complement the established stability concepts by the molecular mobility as measured by low resolution 1H NMR to fill this gap. Glass transition and crystallization of lactose were measured by differential scanning calorimetry. The delay of lactose crystallization was a function of the glass transition temperature and could be modeled by the Williams–Landel–Ferry equation. Lactose crystallization kinetics could not be modeled by the Avrami equation which indicates the formation of different crystal forms. The molecular mobility measured by low resolution 1H NMR proved to be a fast and easy to handle method for the characterization of dairy powders. The transversal relaxation time showed a sharp increase above the glass transition temperature and increased further in the crystalline state. However, the crystallization conditions affected the transversal relaxation time in the crystalline state which indicated the formation of different crystal forms in accordance with the observations of the lactose crystallization kinetics. Furthermore, crystallization led to a step increase of the second moment. Hence, low resolution 1H NMR could also be used to analyze the crystalline structure. The extent of lysine loss in three different dairy formulations after a thermal treatment could be explained by taking into account the physical state together with the molecular mobility. Thus, it can be concluded that both the physical state and the molecular mobility are decisive for the chemical stability of dairy powders.

Low resolution 1H NMR assignment of proton populations in pound cake and its polymeric ingredients

Based on a model system approach, five different proton populations were distinguished in pound cake crumb using one dimensional low resolution 1H NMR spectroscopy. In free induction decay (FID) measurements, proton populations were assigned to (i) non-exchanging CH protons of crystalline starch, proteins and crystalline fat and (ii) non-exchanging CH protons of amorphous starch and gluten, which are in little contact with water. In Carr–Purcell–Meiboom–Gill (CPMG) measurements, three proton populations were distinguished. The CPMG population with the lowest mobility and the FID population with the highest mobility represent the same proton population. The two CPMG proton populations with the highest mobility were assigned to exchanging protons (i.e., protons of water, starch, gluten, egg proteins and sugar) and protons of lipids (i.e., protons of egg yolk lipids and amorphous lipid fraction of margarine) respectively. Based on their spin–lattice relaxation times (T1), two dimensional 1H NMR spectroscopy further resolved the two proton populations with the highest mobility into three and two proton populations, respectively.

P3HT/PCBM Photoactive Materials for Solar Cells: Morphology and Dynamics by Means of Solid-State NMR

P3HT/PCBM blends before and after annealing at 150 °C, as well as the corresponding neat materials have been deeply investigated by means of a multinuclear and multitechnique solid-state NMR approach. 13C CP/MAS spectra, high-resolution 1H T1 measurements and low-resolution 1H FID analysis allowed us to obtain information on the phase and morphological properties on a nanometric and subnanometric scale of both the blends and the neat materials. Variable-temperature 1H and 13C T1 measurements have been carried out and the experimental relaxation times have been analyzed using sophisticated models to obtain a detailed characterization of the dynamic behavior of P3HT in the MHz frequency range in both the blends and the neat polymer. The results obtained highlighted a decrease of mobility of the side chains in passing from P3HT to the blend before annealing, probably due to the intimate mixing with PCBM, and an increase of phase separation between P3HT and PCBM after annealing, correlated with an increase of...

Microstructure of cellulose: NMR relaxation study

The models of structural organization of cellulose are reviewed within the framework of the semi-crystalline concept. Special attention is given to two crystalline modifications of cellulose: Iα and Iβ. The results of low-resolution 1H NMR studies of the supramolecular structure of cellulose are considered. The mathematical model describing the line shape of the solid-state NMR spectrum of cellulose is presented. A scheme for the structure of cellulose microfibrils that fits most of the known model concepts is proposed. It is shown that this scheme can be used to determine the major supramolecular parameters of this polymer.

Glycerol as a reference material for fecal fat quantitation using low-resolution time domain 1H NMR spectroscopy

Objectives To assess glycerol as reference material for low-resolution time-domain 1H NMR analysis of fecal fat. Design and methods NMR analysis of fecal fat in stool samples with added glycerol was used to assess linearity, recovery, and relationship with NMR lipid signal. Results The study revealed for added glycerol excellent linearity (r = 0.9998), recovery (101–104%), and linear relationship with simulated fecal fat content. Conclusions Glycerol is an effective reference material for NMR fecal fat analysis.

Effects of Extrusion on the Emulsifying Properties of Rumen and Soy Protein

Defatted rumen protein and soy protein concentrate were extruded in a 15.5:1 L/D single-screw extruder at the optimum conditions for their expansion (150°C and 35% moisture, and 130°C and 35% moisture, respectively). Emulsions were produced with these proteins and studied by rheology and time domain low-resolution 1H nuclear magnetic resonance (TD-NMR). Extrusion increased storage modulus of rumen protein emulsions. The opposite was observed for soy protein. Mechanical relaxation showed the existence of three relaxing components in the emulsions whose relative contributions were changed by extrusion. Likewise, spin–spin relaxation time constants (T2) measured by TD-NMR also showed three major distinct populations of protons in respect to their mobility that were also altered by extrusion. Extrusion increased surface hydrophobicity of both rumen and soy protein. Solubility of rumen protein increased with extrusion whereas soy protein had its solubility decreased after processing. Extrusion promoted molecular reorganization of protein, increasing its superficial hydrophobicity, affecting its interfacial properties and improving its emulsifying behavior. The results show that extrusion can promote the use of rumen, a by-product waste from the meat industry, in human nutrition by replacing soy protein in food emulsions.

Molecular Properties of Flurbiprofen and its Solid Dispersions with Eudragit RL100 Studied by High- and Low-Resolution Solid-State Nuclear Magnetic Resonance

Investigation of the conformational and molecular dynamic properties of the acidic and sodium salt forms of Flurbiprofen and their solid dispersions with Eudragit RL100, obtained by two different preparation methods (physical mixtures and coevaporates), and of the mixing degree between the two components in the dispersions. 1H and 13C high-resolution solid state NMR techniques, including Single Pulse Excitation-MAS, CP-MAS, FSLG-HETCOR; low-resolution 1H FID analysis; 1H spin-lattice relaxation time measurements. Conformational, molecular packing and dynamic differences were observed between the two pure forms of flurbiprofen, as well as between the pure drugs and the corresponding coevaporates. In the coevaporates of the two flurbiprofen forms, drug and polymer appear intimately mixed; their chemical interactions were detected and characterized. A combined analysis of several 13C and 1H high- and low-resolution solid state NMR experiments allowed the investigation of the conformational and dynamic properties of the pure drugs and of the solid dispersions with the polymer, as well as of the degree of mixing between drug and polymer and of the chemical nature of their interaction. Such information could be compared to the in vitro drug release profiles given by these solid dispersions.

Solid State NMR Investigation of the Molecular Dynamics of Cocoon Silks Produced by Different Bombyx mori (Lepidoptera) Strains

Cocoons produced by different strains of Bombyx mori larvae were investigated by a combination of several high- and low-resolution 1H and 13C solid-state NMR techniques in order to characterize and compare their dynamic behavior at a molecular level. A detailed interpretation in terms of molecular motions in these very complex systems was possible thanks to the integrated analysis of different relaxation measurements and high-resolution selective experiments. Untreated cocoons of all strains were found to be mainly constituted by two different types of rigid domains and by a third one, more mobile, due to physisorbed water molecules. Dynamic processes in the MHz and kHz ranges were characterized by means of different 1H and 13C relaxation times. Cocoons arising from different strains exhibit a different content of physisorbed water and also slightly different dynamic behavior, especially in the MHz regime.

Low-resolution 1H spin–spin relaxation of n-decane/water emulsions stabilized by β-casein

A low-resolution 1H NMR relaxometry study on the dynamics of an n-decane/water emulsion stabilized by β-casein is presented. Spin–spin (transverse) relaxation time constants ( T 2) were used to assess relative mobilities of emulsion components, by a selective deuteration procedure. Data analysis allowed the emulsion investigated to be described by a heterogeneous collection of dynamically distinct populations. A major population of n-decane molecules presented an average mobility that very nearly approached that of pure solvent, which is compatible with its occurrence in the emulsion continuous microphase. β-Casein molecules displayed a prevalent population with significantly decreased mobility as compared to the free protein in solution, which is in accordance with the protein location at the oil/water interface. Also, a major H 2O population with significantly lower average T 2 as compared to the pure liquid was detected and has been assigned to interfacial water.

Water in Hydrogels. An NMR Study of Water/Polymer Interactions in Weakly Cross-Linked Chitosan Networks

A pulsed low-resolution 1H NMR relaxation study at 75 MHz was performed on chitosan and on two lightly cross-linked chitosan networks with a different degree of cross-link and different amount of added water. The spin−lattice relaxation time T1, the spin−spin relaxation time T2, and the free induction decay (FID) were measured in the 200−320 K temperature range. An aperiodic saturation recovery sequence was applied for measuring T1, while a CPMG sequence was used for measuring T2. A full deconvolution of FIDs allows a plethora of information. Lightly cross-linked chitosan chains form super adsorbing hydrogels. The amount of water in these gels at the swelling equilibrium is so high to hide completely the properties of bound water. Thus, dried samples of chitosan and of cross-linked chitosan derivatives were partially rehydrated and studied as a function of added water and of temperature. Data obtained from a 1H NMR relaxation study allowed us to measure the number of water molecules in different shells of...