Isolation, Characterization, and Antioxidant Activity of Melanin from Auricularia auricula (Agaricomycetes).

The cell wall of Auricularia auricula fruit bodies is extremely tough, making it difficult to dissolve the melanin using the traditional preparation method. To investigate the efficient preparation of melanin and its resistance to oxidative stress, this paper first used ultrasound-assisted alkaline cellulase to optimize the optimal wall-breaking parameters through a Box-Behnken design based on a single-factor experiment. After optimization, the yield of melanin from A. auricula reached 3.201 ± 0.018%. Then, different types and different proportions of deep eutectic solvents (DES) were used for further extraction. When choline chloride and urea were selected and the ratio was 1:2, the melanin yield was up to 25.99% ± 2.36%. Scanning electron microscope (SEM) images showed that the melanin was amorphous mass with no crystal structure. X-ray photoelectron spectroscopy (XPS) analysis revealed that the melanin was mainly composed of C (5.38%), O (15.69%) and N (30.29%), as was the typical composition of eumelanin. The melanin had a concentration-dependent relationship with both ABTS+ and hydroxyl radical scavenging ability; at the concentration of 0.5 mg/mL, it significantly prolonged Caenorhabditis elegans survival under hydrogen peroxide and methyl viologen stress and increased the glutathione level and enzyme (total superoxide dismutase and catalase) activities in vivo compared with the negative control (P < 0.05), indicating that the melanin enhances oxidative stress resistance in C. elegans.

Analysis of the complexation process between starch molecules and trilinolenin.

Starch is a basic biomacromolecule, and an in-depth understanding of the process and mechanism of starch-lipid complexation has great significance for starch based food and pharmaceutical. In this study, molecular dynamics simulation was used to explore the complexation details between starch molecules and trilinolenin, such as complexation process, interaction forces, conformation changes and stability changes, which are difficult to be verified by using other characterization methods. The results show that, firstly, starch residues of one turn helix (8 residues) are enough to bind a trilinolenin molecule firmly. Secondly, the complex is maintained by Van der Waals and electrostatic interaction. Thirdly, the residues complexed with trilinolenin become more stable than the former or the free residues. In brief, the complexation process, interaction forces, conformation changes and stability changes of the starch-trilinolenin complex were clarified in this study. The results may create new insights for the research about the interaction of starch and lipid, then provide theoretical guidance for the research on starch based food and pharmaceutical.

Effect of repeated heat-moisture treatments on the structural characteristics of nanocrystals from waxy maize starch.

The effect of repeated heat-moisture treatment (RHMT) on the structural characteristics of waxy maize starch nanocrystals was investigated. Compared with native waxy maize starch (WMS), waxy maize starch nanocrystals (WMSNs) changed the crystalline pattern from A-type to B-type, and displayed the lower crystallinity (RC), molecular order (MO), enthalpy (∆H) and double-helix (DH) content, indicating a reduction in the long- and short-range orders of starch molecules. Single heat-moisture treatment significantly increased values, including RC, MO, α (power law exponent obtained by SAXS), ∆H, DH, and the melting temperatures (To, Tp and Tc), while repeated heat-moisture treatment further increased values of these parameters except ∆H, indicating the reinforcement of the long- and short-range orders of WMSNs. In addition, repeated heat-moisture treatment also caused a gradual conversion from B-type to "A + B"-type (Cb, Cc to Ca polymorphs in sequence) and finally to A-type crystallites.

Adsorption capacity and cold-water solubility of honeycomb-like potato starch granule.

Honeycomb-like granules, with 2-4 µm pores on the surface, were prepared by heating potato starch suspensions in water at the pasting temperature. These granules with a yield of 84% were most amorphous (relative crystallinity 1.9%). Their total pore area was 0.668 m2/g, porosity was 73.4%, and mean particle size (D50) was 154.3 µm. The molecular weights (MW) of honeycomb-like granules were: amylopectin, 8.7 × 107 g/mol; amylose, 3.1 × 105 g/mol, close to those of native starch. The chain length distribution profiles of honeycomb-like granules were similar to those of native starch, while the proportions of B2 and B3 chains were higher. The water and oil adsorption of honeycomb-like granules were about 1.5 and 2.4 times those of native starch, respectively; and the cold water solubility of honeycomb-like granules was 88.5%, while native starch showed no solubility in cold water. Thus honeycomb-like starch granules have the potential to be applied as adsorbents, thickeners and adhesives for their dispersibility, adsorption capacity and cold water solubility.