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The present study displays a comprehensive investigation into the micro- and macrostructures of gluten and its responses to temperature-induced changes, employing various analytical techniques. The integration of time domain-nuclear magnetic resonance (TD-NMR), differential scanning calorimetry (DSC), size-exclusion high-performance liquid chromatography (SE-HPLC), field emission scanning electron microscopy (FESEM), solid-state nuclear magnetic resonance (ssNMR), and multiphoton laser microscopy (MLM) measurements facilitates the multidimensional examination of gluten’s phase distribution and structure across various scales. Notably, TD-NMR helps to refine prior T2 assignments for hydrated gluten through dynamic T2 measurements at sub-zero temperatures. The innovative application of TD-NMR uncovers insights into freezable water quantities and their changes under varying temperature conditions. Through real-time analyses utilizing not only TD-NMR but also MLM techniques, along with SE-HPLC measurements, the study highlights increased lacunarities in the gluten structure, particularly between 60 and 85 °C. These structural changes are attributed to heating effects that unfold and denature proteins and culminate in aggregation and crosslinking phenomena, leading to the release of water into macropores, hence changes in the water distribution in the gluten matrix.

During wheat seeds development, storage proteins are synthetized and subsequently form dense protein phases, also called Protein Bodies (PBs). The mechanisms of PBs formation and the supramolecular assembly of storage proteins in PBs remain unclear. In particular, there is an apparent contradiction between the low solubility in water of storage proteins and their high local dynamics in dense PBs. Here, we probe the interplay between short-range attraction and long-range repulsion of a wheat gliadin isolate by investigating the dynamics of liquid-liquid phase separation after temperature quench. We do so using time-resolved small angle light scattering, phase contrast microscopy and rheology. We show that gliadins undergo liquid-liquid phase separation through Nucleation and Growth or Spinodal Decomposition depending on the quench depth. They assemble into dense phases but remain in a liquid-like state over an extended range of temperatures and concentrations. The analysis of phase separation kinetics reveals that the attraction strength of gliadins is in the same order of magnitude as other proteins. We discuss the respective role of competing interactions, protein intrinsic disorder, hydration and polydispersity in promoting local dynamics and providing this liquid-like behavior despite attractive forces.

Major nutritional and agronomical issues relating to maize ( ) grains depend on the vitreousness/hardness of its endosperm. To identify the corresponding molecular and cellular mechanisms, most studies have been conducted on opaque/floury mutants, and recently on Quality Protein Maize, a reversion of an mutation by modifier genes. These mutant lines are far from conventional maize crops. Therefore, a dent and a flint inbred line were chosen for analysis of the transcriptome, amino acid, and sugar metabolites of developing central and peripheral endosperm that is, the forthcoming floury and vitreous regions of mature seeds, respectively. The results suggested that the formation of endosperm vitreousness is clearly associated with significant differences in the responses of the endosperm to hypoxia and endoplasmic reticulum stress. This occurs through a coordinated regulation of energy metabolism and storage protein (i.e., zein) biosynthesis during the grain-filling period. Indeed, genes involved in the glycolysis and tricarboxylic acid cycle are up-regulated in the periphery, while genes involved in alanine, sorbitol, and fermentative metabolisms are up-regulated in the endosperm center. This spatial metabolic regulation allows the production of ATP needed for the significant zein synthesis that occurs at the endosperm periphery; this finding agrees with the zein-decreasing gradient previously observed from the sub-aleurone layer to the endosperm center. The massive synthesis of proteins transiting through endoplasmic reticulum elicits the unfolded protein responses, as indicated by the splicing of bZip60 transcription factor. This splicing is relatively higher at the center of the endosperm than at its periphery. The biological responses associated with this developmental stress, which control the starch/protein balance, leading ultimately to the formation of the vitreous and floury regions of mature endosperm, are discussed.

Grain protein content constitutes a key quality trait for durum wheat end-products and may also impact grain protein composition. A total of sixteen durum wheat cultivars were analyzed in a field trial during two seasons at two nitrogen (N) levels to evaluate whether and to what extent the variation in total grain N was associated with variation in the quantity of the various protein fractions and grain quality parameters. Genotypic variation in grain N content correlated with the variation in the content of all three protein fractions, although the strength of the correlation with gliadin and albumin-globulin was higher than that with glutenins. Genotypic variation in gliadin and glutenin content was more tightly correlated with the variation in the sulfur (S)-rich protein groups than with the S-poor protein groups and subunits. The variation in the percentage of unextractable polymeric proteins (UPP%) among genotypes was independent of their glutenin allelic composition. The significant genotypic differences in UPP% and in the ratios between protein groups and subunits were not influenced by the corresponding variation in grain N content. The final grain N content can only account for part of the variation in quality parameters and in the partitioning of total grain N between protein fractions since genotypic differences other than grain N content also contribute to these variations.

Pasta is popular for its ease of cooking and its low glycaemic index (GI). This interesting nutritional property can be attributed to its specific compact structure generally described as a protein network entrapping starch granules. Despite this low GI, pasta is poor in fibres and lack some essential amino acids. To enhance its nutritional composition, pasta can be fortified with non-traditional ingredients such as legume flours. The objective of this study was to investigate the impact of legume flour addition on pasta structure and the inherent consequences on the in vitro digestibility of starch. The addition of a high level (35%, w/w) of legume flour, especially split pea flour, induced some minor structural changes in pasta. The inclusion of fibres, the dilution of gluten proteins by albumins and globulins, and the larger amount of thin protein films (in split pea pasta) may have favoured higher susceptibility of starch to digestive enzymes. At the opposite, the presence of some partially gelatinised starch granules in the core of fortified pasta may have favoured the decrease in the in vitro starch digestibility. As a consequence, a high level of legume flour addition in pasta did not have any significant impact on its in vitro starch digestibility. A high level of split pea and faba bean flours can thus be added to pasta to increase its nutritional composition while keeping its low glycaemic index.

The objective of our work was to characterize natural rubber (NR) samples with different macromolecular structures by measuring Mooney viscosities (VR) at variable rotor speeds ≤2 rpm, called variable speed Mooney viscosity (MVS). Model samples of technically specified rubbers of constant Mooney viscosity (TSR5CV) were prepared with chosen specific clones. The structures of the samples were characterized by size‐exclusion chromatography coupled with an online multi‐angle light‐scattering detector (SEC‐MALS). Rheological properties of the samples were also characterized by a dynamic moving die rheometer. Measuring monoclonal model samples by MVS showed three types of VR flow curves. The VR at high rotor speed (2 rpm) was correlated with number‐average molar mass (Mn), whereas VR at low rotor speed (0.05 rpm) was correlated with weight‐average molar mass (Mw). Measuring MVS revealed the rheological behaviors of samples and enabled discrimination between samples with different macromolecular structures and should thus help in predicting processability. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The influence of the network structure of wheat gluten on the barrier properties against enzymes was investigated in vitro. The changes in the network structure were introduced by different temperature treatments. The modifications were assessed with solubility studies of wheat gluten proteins in sodium dodecyl sulfate (SDS). The physical barrier properties of wheat gluten membranes were investigated with transport studies examining the transfer of a model protein with no enzymatic activity (BSA) through gluten membranes. The protein network was an effective barrier for BSA, although lightly cross-linked films were mechanically instable. Membrane breaks occurred in function of the cross-linking density (percentage of SDS-insoluble proteins) after only 24 hr for lightly cross-linked films (approximately equal to 30% SDS-insoluble proteins), while highly cross-linked membranes (approximately equal to 80% SDS-insoluble protein) were tight up to more than 33 days. The digestion experiments of the gluten films with pepsin showed that the hydrolysis of wheat gluten films with >72% of SDS-insoluble protein was significantly retarded. In conclusion, technological treatments to increase the cross-linking density of gluten have the potential to slow the digestion of cereal-based foodstuff and to reduce the degradation rate of composite biomaterials.

The rheological behaviour of a gluten plasticized with glycerol has been studied in oscillatory shear. The mixing operation in a Haake batch mixer leads to a maximum torque for a level of specific energy (500–600 kJ/kg) and temperature (50–60 °C) quite independent of mixing conditions (rotor speed, mixing time, filling ratio). The gluten/glycerol dough behaves as a classical gluten/water dough, with a storage modulus higher than the loss modulus over the frequency range under study. A temperature increase induces a decrease of moduli, but the material is not thermorheologically simple. Glycerol has a plasticizing effect, which can be classically described by an exponential dependence. Mixing conditions influence the viscoelastic properties of the material, mainly through the specific mechanical energy input (to 2000 kJ/kg) and temperature increase (to 80 °C). Above 50 °C, specific mechanical energy highly increases the complex modulus. The aggregation of proteins, as evidenced by size-exclusion chromatography measurements, occurs later as the dough temperature reaches 70 °C. The nature of network interactions and the respective influence of hydrophobic and disulphide contribution is discussed. A general expression is proposed for describing the viscous behaviour of a gluten/glycerol mix, which could seem simplistic for such a complex rheological behaviour, but would remain sufficient for modelling the flow behaviour in a twin screw extruder.

Particle size distribution, colour, morphology and chemical composition of chestnut (Castanea sativa Mill.) starches isolated from fresh chestnut fruits (S1), semi-dried chestnut fruits at room temperature (S2) and commercial chestnut flour (S3) were determined using several experimental techniques. All starches had a bimodal particle size distribution, particularly S1 showed two types of starch granules--small (1.5 µm diameter) and large granules (10.5 µm). Starch granule sizes depended on the moisture content of the samples, decreasing slightly in the following order S1 > S2 > S3; however, no significant differences were observed in the morphological analysis. Most of the granules exhibited round or oval shapes, and exceptionally, some of them featured trefoil shape, which is not usually found in other starches. Colour results indicated that S3 samples had the darkest colour, followed by S2 and S1. Tested chestnut starches showed significant differences in total starch content, with starch isolation being more selective in dried samples. All samples showed low damaged starch (<2.91%) and intermediate amylose (from 17.0 to 25.8%) content on dry mass basis. The lowest amount of amylose was obtained in S1, even though it was within the range of common commercial starches. Key words: gluten-free diet, optical microscopy, particle size, amylose, damaged starch