Ice-Binding Protein from Shewanella frigidimarinas Inhibits Ice Crystal Growth in Highly Alkaline Solutions.

The ability of a natural ice-binding protein from Shewanella frigidimarina (SfIBP) to inhibit ice crystal growth in highly alkaline solutions with increasing pH and ionic strength was investigated in this work. The purity of isolated SfIBP was first confirmed via sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and size-exclusion chromatography with an ultraviolet detector (SEC-UV). Protein stability was evaluated in the alkaline solutions using circular dichroism spectroscopy, SEC-UV, and SDS-PAGE. SfIBP ice recrystallization inhibition (IRI) activity, a measure of ice crystal growth inhibition, was assessed using a modified splat assay. Statistical analysis of results substantiated that, despite partial denaturation and misfolding, SfIBP limited ice crystal growth in alkaline solutions (pH ≤ 12.7) with ionic strength I ≤ 0.05 mol/L, but did not exhibit IRI activity in alkaline solutions where pH ≥ 13.2 and I ≥ 0.16 mol/L. IRI activity of SfIBP in solutions with pH ≤ 12.7 and I ≤ 0.05 mol/L demonstrated up to ≈ 66% reduction in ice crystal size compared to neat solutions.

On-Demand Microwave-Assisted Fabrication of Gelatin Foams.

Ultraporous gelatin foams (porosity >94%, ρ ≈ 0.039⁻0.056 g/cm³) have been fabricated via microwave radiation. The resulting foam structures are unique with regard to pore morphology (i.e., closed-cell) and exhibit 100% macroporosity (pore size 332 to 1700 µm), presence of an external skin, and densities similar to aerogels. Results indicate that the primary foaming mechanism is governed by the vaporization of water that is tightly bound in secondary structures (i.e., helices, ß-turns, ß-sheets) that are present in dehydrated gelatin films but not present in the foams after microwave radiation (700 Watts).

Evaporation-based method for preparing gelatin foams with aligned tubular pore structures.

Gelatin-based foams with aligned tubular pore structures were prepared via liquid-to-gas vaporization of tightly bound water in dehydrated gelatin hydrogels. This study elucidates the mechanism of the foaming process by investigating the secondary (i.e., helical) structure, molecular interactions, and water content of gelatin films before and after foaming using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. Experimental data from gelatin samples prepared at various gelatin-to-water concentrations (5-30 wt.%) substantiate that resulting foam structures are similar in pore diameter (approximately 350 µm), shape, and density (0.05-0.22 g/cm(3)) to those fabricated using conventional methods (e.g., freeze-drying). Helical structures were identified in the films but were not evident in the foamed samples after vaporization (~150 °C), suggesting that the primary foaming mechanism is governed by the vaporization of water that is tightly bound in secondary structures (i.e., helices, ß-turns, ß-sheets) that are present in dehydrated gelatin films. FTIR and TGA data show that the foaming process leads to more disorder and reduced hydrogen bonding to hydroxyl groups in gelatin and that no thermal degradation of gelatin occurs before or after foaming.