Qiongying Wu

Production of ACE inhibitory peptides from sweet sorghum grain protein using alcalase: Hydrolysis kinetic, purification and molecular docking study.

In this study, sweet sorghum grain protein (SSGP) was hydrolyzed using alcalase yielding ACE inhibitory peptides. A kinetic model was proposed to describe the enzymolysis process of SSGP. The kinetic parameters, a and b, were determined according to experimental data. It was found that the model was reliable to describe the kinetic behaviour for SSGP hydrolysis by alcalase. After hydrolysis, the SSGP hydrolysate with DH of 19% exhibited the strongest ACE inhibitory activity and the hydrolysate was then used to isolate ACE inhibitory peptides. A novel ACE inhibitory peptide was successfully purified from this hydrolysate by ultrafiltration, ion exchange chromatography, gel filtration chromatography, and reversed-phased high performance liquid chromatography (RP-HPLC). The amino acid sequence of the purified peptide was identified as Thr-Leu-Ser (IC50=102.1 μM). The molecular docking studies revealed that the ACE inhibition of the tripeptide was mainly attributed to its C-terminal Ser, which can effectively interact with the S1 and S2 pockets of ACE. Our studies suggest that the tripeptide from the SSGP hydrolysate can be utilized to develop functional food ingredients or pharmaceuticals for prevention of hypertension.

Characterization, antioxidant and antitumor activities of polysaccharides from purple sweet potato.

Three polysaccharides, PSPP1-1, PSPP2-1 and PSPP3-1, were isolated from purple sweet potato. The three polysaccharides belonged to β-type polysaccharides and contained low proportions of proteins and uronic acids. PSPP1-1 and PSPP3-1 with molecular weights of 33.3 and 75.3 kDa, respectively, were composed of rhamnose, xylose, glucose and galactose, whereas PSPP2-1 with molecular weight of 17.8 kDa was composed of rhamnose and galactose. The three polysaccharides possessed in vitro antioxidant (scavenging DPPH radicals, chelating ferrous ions and reducing power) and antitumor activities (against SGC7901 and SW620 cells) in a dose-dependent manner. Among the three polysaccharides, PSPP2-1 exhibited the strongest reducing power, scavenging activity on DPPH radicals and chelating capability on ferrous ions. PSPP1-1 showed the strongest inhibitory activities on the growth of SGC7901 and SW620 cells. In addition, flow cytometry results showed that PSPP1-1 could induce apoptosis in SGC7901 and SW620 cells. These results suggest that polysaccharides from purple sweet potato are potential natural antioxidant and antitumor agents that can be used as drugs or functional food ingredients.

A novel angiotensin-І converting enzyme (ACE) inhibitory peptide from gastrointestinal protease hydrolysate of silkworm pupa (Bombyx mori) protein: Biochemical characterization and molecular docking study

Silkworm pupa (Bombyx mori) protein was hydrolyzed using gastrointestinal endopeptidases (pepsin, trypsin and α-chymotrypsin). Then, the hydrolysate was purified sequentially by ultrafiltration, gel filtration chromatography and RP-HPLC. A novel ACE inhibitory peptide, Ala-Ser-Leu, with the IC50 value of 102.15μM, was identified by IT-MS/MS. This is the first report of Ala-Ser-Leu from natural protein. Lineweaver-Burk plots suggest that the peptide is a competitive inhibitor against ACE. The molecular docking studies revealed that the ACE inhibition of Ala-Ser-Leu is mainly attributed to forming very strong hydrogen bonds with the S1 pocket (Ala354) and the S2 pocket (Gln281 and His353). The results indicate that silkworm pupa (B. mori) protein or its gastrointestinal protease hydrolysate could be used as a functional ingredient in auxiliary therapeutic foods against hypertension.

Rapid detection of Rosa laevigata polysaccharide content by near-infrared spectroscopy.

A method of rapid detecting Rosa laevigata polysaccharide content on the basis of near infrared spectroscopy (NIRS) was established to achieve the purpose of controlling quality of R. laevigata. A total of 129 batches of R. laevigata samples were randomly divided into calibration set and prediction set, number of which were 65 and 64 respectively. The polysaccharide content was measured according to the method provided by Chinese pharmacopoeia, and was 26.05±5.44(%). The Near-infrared diffuse reflectance spectra of R. laevigata were preprocessed by first-order derivative and autoscaling, and was built model with PLS. When 6 Latent variables (LVs) were used in model, the smallest root mean square error of cross validation (RMSECV) was 1.18%, and root mean square error of prediction (RMSEP) was 1.21%. The uninformative variables in spectrum were eliminated by UVE-PLS, and 383 variables were obtained. The prediction accuracy was improved, and RMSECV and RMSEP were 0.90% and 0.99% respectively. Then, 383 variables were further optimized by genetic algorithm (UVE-GA-PLS), and 179 variables were obtained; under this condition, the RMSECV and RMSEP were 0.93% and 1.07% respectively. In this work, result of UVE-PLS was the best. Analyzing variables VIP score in PLS, variable selected by UVE-PLS and UVE-GA-PLS, spectrum region from 7200 cm(-1) to 6700 cm(-1) of the combinations of first and second overtone of C-H and from 5300 cm(-1) to 5000 cm(-1) related to the first overtone of O-H could play an important role in the detection R. laevigata polysaccharide by NIR. Therefore, it was feasible of rapid detection of R. laevigata polysaccharide content by NIRS.

Isolation and characterization of an antimicrobial endophytic bacterium ME-2 from mulberry twig in China

An antimicrobial endophytic bacterium strain, ME-2, was isolated from fresh mulberry twig tissues, and was identified. In addition, antimicrobial activities of the isolated strain were evaluated against Bacillus thuringiensis, Escherichia coli, Staphylococcus aureus, Beauveria bassiana and Mycoid bacillus using the antagonism test method. The results showed that, strain ME-2 was gram-positive, aerobic, motile, nitrate-reduction-positive, spore-formation-positive, methyl-red-negative, 0.6-0.7 × 1.5-1.6 μm long and rods. The strain could utilize D-glucose, D-lactose, sucrose, starch, citrate, gelatin and casein, and it was slightly halophilic with growth occurring at 10% (w/v) NaCl. According to the morphological, biochemical and physiological properties and sequence analysis of 16S rRNA gene, the strain was identified as Bacillus subtili (GeneBank accession No. JQ900623). Moreover, the results also showed that strain ME-2 exhibited strong antimicrobial activities against B. thuringiensis (76.0%), E. coli (69.8%), S. aureus (45.8%), B. bassiana (64.2%) and M. bacillus (86.3%). It was concluded that, strain ME-2 and its antimicrobial materials might be considered as a potential antimicrobial agents in the food and pharmaceutical industries.