No abstract

Antifreeze proteins have characteristics of inhibiting the growth of crystals, decreasing the injury of cells and can retain the structure, texture and quality of productions. The purpose of this study is to obtain natural antifreeze peptides, and to investigate the hypothermia protection activity on bacteria. Gelatin derived from shark skin was hydrolysed to obtain antifreeze peptides. The most appropriate protease and hydrolysis time was selected with the index of the hypothermia protection activity on bacteria. The hydrolysate was subsequently added on to Sephadex G-50 gel filtration column and SP-Sephadex C-25 column to acquire high activity fractions. The fraction of cationic peptides termed P2 shows higher antifreeze activity. The hypothermia protection assay shows that the survival rate of E.coli was 80.8 % when the concentration of peptides complexes was up to 500 μg/mL.

A 9 kDa non-specific lipid-transfer protein (nsLTP) from mung bean (Phaseolus mungo) seeds, displaying antifungal activity, antibacterial activity and lipid-transfer activity, was crystallized at 297 K using ammonium sulfate as a precipitant by means of the hanging-drop vapour-diffusion method. Native X-ray diffraction data were collected to a resolution of 2.4 A. The crystals are rhombohedral, belonging to space group P2(1)2(1)2(1), with unit-cell parameters a = 38.671, b = 51.785, c = 55.925 A. Assuming the presence of one molecule in the crystallographic asymmetric unit results in a Matthews coefficient (V(M)) of approximately 3.0 A(3) Da(-1), corresponding to a solvent content of about 58%.

In this study, cryoprotective effects of sericin enzymatic peptides (SEP) on the freeze-induced denaturation of grass carp surimi were evaluated on the basis of sulfhydryl content and surface hydrophobicity of actomyosin, as well as the SDS-PAGE pattern of myosin heavy chain (MHC) of myofibrillar proteins. Results show that SEP, containing a high polar amino acid content and abundant in amino acids with hydroxyl-containing side chain (Ser and Thr), was effective in preventing the decrease of SH content, slowing down the exposure of buried hydrophobic residues on the protein surface, and retarding the degradation of MHC in a non-linear dosage-dependent way. These findings suggest that SEP obtained in our study appear to be a promising cryoprotectant applied in the frozon storage of surimi.

To optimum the chelation technology of whey protein hydrolysate with calcium, the response surface method was used to investigate optimized technological conditions. The result showed that the optimum process parameters for the whey protein hydrolysate-calcium chelation were whey protein peptide and CaCl2 ratio of 24 : 1 (w/w), whey protein hydrolysate concentration 3.5 %, pH 7.5, reaction time 20 min, reaction temperature 30 °C. Finally, the optimum level was established and whey protein hydrolysate-calcium chelate was obtained, which can provide basic theories for the following function and activity evaluation of this potential calcium supplement.