Formation of Peptide Bound Pyrraline in the Maillard Model Systems with Different Lys-Containing Dipeptides and Tripeptides.

Peptide-bound advanced glycation end-products (peptide-bound AGEs) can be formed when peptides are heated with reducing saccharides. Pyrraline is the one of most commonly studied AGEs in foods, but the relative importance of the precursor peptide structure is uncertain. In the present study, model systems were prepared by heating peptides with glucose from 60 °C to 220 °C for up to 65 min, and the amounts of peptide-bound pyrraline formed were monitored to evaluate the effect of the neighboring amino acids on the peptide-bound pyrraline formation. The physico-chemical properties were introduced to explore the quantitative structure-reactivity relationships between physicochemical properties and peptide bound formation. 3-DG content in dipeptide-glucose model system was higher than that in the corresponding tripeptide-glucose model systems. Dipeptides produced higher amounts of peptide-bound pyrraline than the corresponding tripeptides. The peptide-bound pyrraline and 3-DG production were influenced by the physico-chemical properties of the side chain of amino acids adjacent to Lys in the following order: Lys-Leu/glucose > Lys-Ile/glucose > Lys-Val/ glucose > Lys-Thr/glucose > Lys-Ser/glucose > Lys-Ala/ glucose > Lys-Gly/glucose; Lys-Leu-Gly/glucose > Lys-Ile-Gly/glucose > Lys-Val-Gly/glucose > Lys-Thr-Gly/glucose > Lys-Ser-Gly/glucose > Lys-Ala-Gly/glucose > Lys-Gly-Gly/glucose. For the side chain of amino acids adjacent to Lys in dipeptides, residue volume, polarizability, molecular volume and localized electrical effect were positively related to the yield of peptide bound pyrraline, while hydrophobicity and pKb were negatively related to the yield of peptide bound pyrraline. In terms of side chain of amino acid adjacent to Lys in tripeptides, a similar result was observed, except hydrophobicity was positively related to the yield of peptide bound pyrraline.

Highly selective and sensitive nucleic acid detection based on polysaccharide-functionalized silver nanoparticles.

Polysaccharide-functionalized silver nanoparticles (Oc-AgNPs) with a mean diameter of 15 nm were utilized as a novel and effective fluorescence-sensing platform for nucleic acid detection. Tests on the oligonucleotide sequences associated with the human immunodeficiency virus as a model system showed that the Oc-AgNPs effectively absorbed and quenched dye-labeled single-stranded DNA through strong hydrogen bonding interactions and slight electrostatic attractive interactions. The proposed system efficiently differentiated between complementary and mismatched nucleic acid sequences with high selectivity and good reproducibility at room temperature.

Effect of extraction media on preliminary characterizations and antioxidant activities of Phellinus linteus polysaccharides.

Three partially purified polysaccharides were extracted from Phellinus linteus mycelia using hot water, 1% (NH4)2C2O4, and 1.25M NaOH/0.05% NaBH4, and the extracts were named PL-W, PL-A, and, PL-N respectively. PL-N mainly comprised xylose and arabinose with a high molecular weight (Mw) and the highest carbohydrate and uronic acid contents. PL-W and PL-A were mainly composed of glucose with high and low Mw fractions in various ratios. All three polysaccharides existed as compact coils in aqueous solutions and exhibited strong scavenging capacity and antioxidant activities in a concentration-dependent manner. The polysaccharides also had high uronic acid and carbohydrate contents and strong antioxidant activities. The Mws, monosaccharide compositions, and chemical structures of the polysaccharides also affected their antioxidant activities. PL-A and PL-N had better antioxidant activities and could thus be developed as potential natural antioxidant agents for applications in food additives and biomedical industries.

Structural characteristics and antioxidant activities of different families of 4-acetamido-TEMPO-oxidised curdlan.

Regioselective oxidation was applied to commercial curdlan for the preparation of its water-soluble derivatives with improved antioxidant activities, using a 4-acetamido-2,2, 6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaClO2 system at pH 4.8 and 40°C. The structural features, molecular properties, and chain conformations of the oxidised curdlans were determined using Fourier transform (FT) infrared and FT Raman spectroscopy, carbon nuclear magnetic resonance, X-ray diffraction, and size-exclusion chromatography with multi-angle laser-light scattering analyses. The C6 primary hydroxyls of curdlan were successfully oxidised into carboxylate groups with less depolymerization, and no aldehyde groups were formed during oxidation. The crystalline region of curdlan was destroyed after oxidation. The oxidised curdlans formed random coils in aqueous solution, and the chain became more flexible and expanded with increasing carboxylate contents from 2.07mmol/g to 4.87mmol/g. The high polyglucuronic acid derivative (Cur-24) showed the best antioxidant activity in TEAC and FRAP assays, thus it could be explored as novel potential antioxidants for dietary and therapeutic applications.