Effects of microviscosity, dry electron scavenging, and protein mobility on the radiolysis of albumen hydrogel

Aggregation of Albumins under Reductive Radical Stress

The reactions of radicals with human serum albumin (HSA) under reductive stress conditions were studied using pulse radiolysis and photochemical methods. It was proved that irradiation of HSA solutions under reductive stress conditions results in the formation of stable protein aggregates. HSA aggregates induced by ionizing radiation are characterized by unique emission, different from the UV emission of non-irradiated solutions. The comparison of transient absorption spectra and the reactivity of hydrated electrons (eaq-) with amino acids or HSA suggests that electron attachment to disulfide bonds is responsible for the transient spectrum recorded in the case of albumin solutions. The reactions of eaq- and CO2•- with HSA lead to the formation of the same products. Recombination of sulfur-centered radicals plays a crucial role in the generation of HSA nanoparticles, which are stabilized by intermolecular disulfide bonds. The process of creating disulfide bridges under the influence of ionizing radiation is a promising method for the synthesis of biocompatible protein nanostructures for medical applications. Our Raman spectroscopy studies indicate strong modification of disulfide bonds and confirm the aggregation of albumins as well. Low-temperature measurements indicate the possibility of electron tunneling through the HSA protein structure to specific CyS-SCy bridges. The current study showed that the efficiency of HSA aggregation depends on two main factors: dose rate (number of pulses per unit time in the case of pulse radiolysis) and the temperature of the irradiated solution.

Effect of high-intensity ultrasound on the technofunctional properties and structure of jackfruit (Artocarpus heterophyllus) seed protein isolate

The influence of high-intensity ultrasound (HIU) on the technofunctional properties and structure of jackfruit seed protein isolate (JSPI) was investigated. Protein solutions (10%, w/v) were sonicated for 15min at 20kHz to the following levels of power output: 200, 400, and 600W (pulse duration: on-time, 5s; off-time 1s). Compared with untreated JSPI, HIU at 200W and 400W improved the oil holding capacity (OHC) and emulsifying capacity (EC), but the emulsifying activity (EA) and emulsion stability (ES) increased at 400W and 600W. The foaming capacity (FC) increased after all HIU treatments, as opposed to the water holding capacity (WHC), least gelation concentration (LGC), and foaming stability (FS), which all decreased except at pH 4 for FS. Tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) showed changes in the molecular weight of protein fractions after HIU treatment. Scanning electron microscopy (SEM) demonstrated that HIU disrupted the microstructure of JSPI, exhibiting larger aggregates. Surface hydrophobicity and protein solubility of the JSPI dispersions were enhanced after ultrasonication, which increased the destruction of internal hydrophobic interactions of protein molecules and accelerated the molecular motion of proteins to cause protein aggregation. These changes in the technofunctional and structural properties of JSPI could meet the complex needs of manufactured food products.

Sonolysis of high macroviscosity systems: hen albumen hydrogel

To understand molecular effects of ultrasound on protein gels (cross-linked, hydrated macromolecular systems of immeasurably high macroviscosity, but low microviscosity), the thick fraction of hen albumen was sonicated. The immeasurably high viscosity of the intact thick fraction decreased to 2.5-4.0 mPa·s (depending on the sample) after a 12 min sonication (0.14 mM of radicals were produced and 19 J g(-1) of thermal energy absorbed) indicating that the 3D protein network was degraded. SDS-PAGE analysis indicated the breaking of intermolecular S-S bridges holding together the protein network rather than the primary structure of constituent proteins. Despite the relatively large concentration of OH radical produced in the sonication time range applied, no protein cross-linking was observed which can be attributed to the high degree of protein glycosylation and protein immobility. Differential scanning calorimetry (DSC) showed that both the amount of bound water and the enthalpy of denaturation of the constituent proteins are not affected by sonication, which is consistent with the SDS-PAGE results. A small increase in sample turbidity can be attributed to the small extent of thermal denaturation occurring in the vicinity of cavitation sites.