Faiza Rasheed

Wheat gluten polymer structures : The impact of genotype environment and processing on their functionality in various applications

ABSTRACT For a number of applications, gluten protein polymer structures are of the highest importance in determining end-use properties. The present article focuses on gluten protein structures in the wheat grain, genotype- and environment-related changes, protein structures in various applications, and their impact on quality. Protein structures in mature wheat grain or flour are strongly related to end-use properties, although influenced by genetic and environment interactions. Nitrogen availability during wheat development and genetically determined plant development rhythm are the most important parameters determining the gluten protein polymer structure, although temperature during plant development interacts with the impact of the mentioned parameters. Glutenin subunits are the main proteins incorporated in the gluten protein polymer in extracted wheat flour. During dough mixing, gliadins are also incorporated through disulfide-sulfhydryl exchange reactions. Gluten protein polymer size and complexi...

Structural architecture and solubility of native and modified gliadin and glutenin proteins: non-crystalline molecular and atomic organization

Wheat gluten (WG) and its components, gliadin and glutenin proteins, form the largest polymers in nature, which complicates the structural architecture of these proteins. Wheat gluten, gliadin and glutenin proteins in unmodified form showed few secondary structural features. Structural modification of these proteins using heat, pressure and the chemical chaperone glycerol resulted in a shift to organized structure. In modified gliadin, nano-structural molecular arrangements in the form of hexagonal closed packed (HCP) assemblies with lattice parameter of (58 A) were obvious together with development of intermolecular disulphide bonds. Modification of glutenin resulted in highly polymerized structure with proteins linked not only by disulphide bonds, but also with other covalent and irreversible bonds, as well as the highest proportion of β-sheets. From a combination of experimental evidence and protein algorithms, we have proposed tertiary structure models of unmodified and modified gliadin and glutenin proteins. An increased understanding of gliadin and glutenin proteins structure and behavior are of utmost importance to understand the applicability of these proteins for various applications including plastic materials, foams, adhesives, films and coatings.

Commercial potato protein concentrate as a novel source for thermoformed bio-based plastic films with unusual polymerisation and tensile properties

Commercial potato protein concentrate (PPC) was investigated as a source of thermoformed bio-based plastic film. Pressing temperatures of 100 to 190 °C with 15 to 25% glycerol were used to form PPC films. The shape of the tensile stress–strain curve in thermoformed PPC was controlled by glycerol level and was independent of processing temperature. Tensile testing revealed that elongation at break increased with processing temperature while Youngs modulus was unaffected by processing temperature, both in contrast to previous results in protein based systems. Also in contrast to previous studies, Youngs modulus was found to be only sensitive to glycerol level. Maximum tensile stress increased with increasing processing temperature for PPC films. Maximum stress and strain at break correlated with the extractable high molecular weight protein content of the processed films measured with size exclusion chromatography. Infrared absorption indicated that the content of β-sheet structure increased from the commercial protein concentrate to that pressed at 100 °C, but did not further develop with increasing press temperature. Changes in structural arrangements were observed by small angle X-ray scattering indicating the development of different correlation distances with processing temperature but with no clear long range order at the supramolecular level. The novel Youngs modulus behaviour appears to be due to constant secondary structure or the effect of aggregated protein structure formed during protein production. Unique strain at break behaviour with processing temperature was demonstrated, likely due to new connections formed between those aggregates.

Macromolecular changes and nano-structural arrangements in gliadin and glutenin films upon chemical modification: Relation to functionality.

Protein macromolecules adopted for biological and bio-based material functions are known to develop a structured protein network upon chemical modification. In this study, we aimed to evaluate the impact of chemical additives such as, NaOH, NH4OH and salicylic acid (SA), on the secondary and nano-structural transitions of wheat proteins. Further, the effect of chemically induced modifications in protein macromolecular structure was anticipated in relation to functional properties. The gliadin-NH4OH-SA film showed a supramolecular protein organization into hexagonal structures with 65 Å lattice parameter, and other not previously observed structural entities having a characteristic distance of 50 Å. Proteins in gliadin-NH4OH-SA films were highly polymerized, with increased amount of disulfide crosslinks and β-sheets, causing improved strength and stiffness. Glutenin and WG proteins with NH4OH-SA showed extensive aggregation and an increase in β-sheet content together with irreversible crosslinks. Irreversible crosslinks hindered a high order structure formation in glutenins, and this resulted in films with only moderately improved stiffness. Thus, formation of nano-hierarchical structures based on β-sheets and disulfide crosslinks are the major reasons of high strength and stiffness in wheat protein based films.

Unraveling the Structural Puzzle of the Giant Glutenin Polymer—An Interplay between Protein Polymerization, Nanomorphology, and Functional Properties in Bioplastic Films

A combination of genotype, cultivation environment, and protein separation procedure was used to modify the nanoscale morphology, polymerization, and chemical structure of glutenin proteins from wheat. A low-polymerized glutenin starting material was the key to protein–protein interactions mainly via SS cross-links during film formation, resulting in extended β-sheet structures and propensity toward the formation of nanoscale morphologies at molecular level. The properties of glutenin bioplastic films were enhanced by the selection of a genotype with a high number of cysteine residues in its chemical structure and cultivation environment with a short grain maturation period, both contributing positively to gluten strength. Thus, a combination of factors affected the structure of glutenins in bioplastic films by forming crystalline β-sheets and propensity toward the ordered nanostructures, thereby resulting in functional properties with high strength, stiffness, and extensibility.