Biomedical subjects

Iko Burgar

Publications and source records attributed to Iko Burgar.

3 recordsLinked to original sources

PubMed2006

Chemical modification of wheat protein-based natural polymers: cross-linking effect on mechanical properties and phase structures.

Chemical modification of wheat protein-based natural polymer materials was conducted using glyoxal as cross-linker, and the cross-linking effect was studied on mechanical properties under different humidity conditions, the molecular motions of each component, and the phase structures/components of the whole materials. The cross-linking significantly enhanced the mechanical strength of wheat gluten (WG) materials under RH = 50%. The elongation of materials was also increased, which was in contrast to many cross-linked protein systems. The reaction mainly occurred in proteins and starch components, resulting in the formation of a stable cross-linked network with restricted molecular motions and modified motional dynamics. Although the plasticizer glycerol could also take part in the reaction with glyoxal or other components in WG especially when the glyoxal content was higher, the amount of glycerol involved in such reactions was very little. Glycerol was predominantly hydrogen-bonded with the network. The lipid component did not seem to take part in the cross-linking reaction; its mobility was promoted while its interaction with the protein-starch network was weakened after cross-linking. The formation of the cross-linked network did not enhance the hydrophobicity of the materials; the materials still adsorbed a high level of moisture under high humidity conditions (ca. RH = 85%) with no improvement in mechanical strength. In addition, further increasing the amount of glyoxal did not generate an additional strength improvement even at RH = 50%, possibly because the enhanced mobility of lipid promoted the component to be phase-separated from the WG system. To improve the water-resistant properties, the hydrophobicity of the protein macromolecules requires enhancement by other chemical modifications.

Chemical Phenomena↗

PubMed2006

pH effect on the mechanical performance and phase mobility of thermally processed wheat gluten-based natural polymer materials.

The mechanical properties, phase composition, and molecular motions of thermally processed wheat gluten- (WG-) based natural polymer materials were studied by mechanical testing, dynamic mechanical analysis (DMA), and solid-state NMR spectroscopy. The performance of the materials was mainly determined by the denaturization and cross-linking occurring in the thermal processing and the nature or amount of plasticizers used. The pH effect also played an important role in the materials when water was used as the only plasticizer (WG-w). Alkaline conditions modified the chemical structure of WG, possibly via deamidation; enhanced the thermal cross-linking of WG macromolecules to form a more stable aggregation structure; and promoted intermolecular interactions between water and all components in WG (proteins, starch, and lipid), resulting in a strong adhesion among different components and phases. The saponification of lipid under alkaline conditions also enhanced the hydrophilicity of lipid and the miscibility among lipid, water, and WG components. However, when glycerol was used with water as a plasticizer (WG-wg), the phase mobility and composition of the materials mainly depended on the content of glycerol when the water content was constant. During thermal processing under either acidic or alkaline conditions, glycerol was unlikely to thermally cross-link with WG as suggested previously. The advanced mechanical performance of the WG-wg materials was attributed to the nature of hydrogen-bonding interactions between glycerol and WG components in the materials. This caused the whole material to behave like a strengthened "cross-linked" structure at room temperature due to the low mobility of glycerol. The pH effect on phase mobility and compositions of WG-wg systems was not as significant as that for WG-w materials.

Biopolymers↗

PubMedDate not supplied

Intermolecular interactions and phase structures of plasticized wheat proteins materials.

The intermolecular interactions and phase structures of thermally processed wheat proteins with glycerol and water as plasticizers were studied by dynamic mechanical analysis and solid-state high-resolution NMR spectroscopy. The results of phase structures at scales of molecular level to tens of nanometers were correlated with the mechanical properties of the materials. The strong hydrogen bonding intermolecular interactions between the components in wheat proteins and the plasticizers resulted in a significant change in molecular motions of wheat protein materials. The plasticized systems, however, still presented a wide distribution of chain mobility at a scale from the molecular level to 20-30 nm, and the plasticizing effect was different for each wheat protein system. High protein content systems tended to be plasticized relatively easily especially when lipid content is high, but the existence of residual starch would require more plasticizers to reach a similar level of chain mobility. On a scale of 20-30 nm, plasticized vital wheat gluten (WG) and the deamidated wheat proteins (WP-I) were heterogeneous with each component exhibiting its individual mobility, whereas the plasticized insoluble protein system (WP-II) with poor mechanical properties was homogeneous. Both WG and WP-I systems showed excellent mechanical polymeric properties in tensile strength and elasticity despite the heterogeneity. The strong intermolecular hydrogen bonding interactions and soluble protein components in the materials could provide an adhesion among different components and act as a continuous matrix in the systems. Therefore, these materials displayed excellent mechanical properties via coordination effects among different components.

Plant Proteins↗