Xiaolan Liu

Preparation of antioxidative corn protein hydrolysates, purification and evaluation of three novel corn antioxidant peptides.

Corn gluten meal is a major co-product of corn wet milling. Corn gluten meal was hydrolyzed with Alcalase, Flavourzyme, Alcalase+Flavourzyme and Flavourzyme+Alcalase. At the substrate concentration of 10%, corn protein hydrolysate catalyzed by Alcalase had a degree of hydrolysis of 17.83%, which was higher than that by Flavourzyme (3.65%). The hydrolysate catalyzed by Alcalase+Flavourzyme exhibited better antioxidant activities and was further purified. Three novel antioxidant peptides were purified by a series of chromatographic techniques. Sequences of the three peptides were identified as Cys-Ser-Gln-Ala-Pro-Leu-Ala, Tyr-Pro-Lys-Leu-Ala-Pro-Asn-Glu and Tyr-Pro-Gln-Leu-Leu-Pro-Asn-Glu, respectively. Among the three peptides, Cys-Ser-Gln-Ala-Pro-Leu-Ala exhibited good reducing power and excellent scavenging capacities for DPPH radical and superoxide anion radical, with IC50 values of 0.116 and 0.39mg/ml, respectively. The results from our study indicate antioxidant potency of corn protein hydrolysates and peptides separated from corn gluten meal and can provide basic understanding for the application of corn protein hydrolysates as natural antioxidants.

Effect of hydrolysis time on the physicochemical and functional properties of corn glutelin by Protamex hydrolysis

The physicochemical and functional properties, such as surface hydrophobicity, disulphide bond content, thermal properties, molecular weight distribution, antioxidant properties, of corn glutelin hydrolysates catalysed by Protamex at different hydrolysis times were evaluated. The hydrolysis influenced the properties of corn glutelin significantly, and not only decreased its molecular weight and disulphide bond content, but also eventually transformed its insoluble native aggregates to soluble aggregates during the hydrolysis process. Corn glutelin hydrolysates were found to have a higher solubility, which was associated with their relatively higher foaming and emulsifying properties compared to the original glutelin. Corn glutelin and its hydrolysates maintained a high thermal stability. In addition, the hydrolysates exhibited excellent antioxidant properties measured through in vitro assays, namely DPPH and OH radical scavenging activity, Fe(2+)-chelating capacity and reducing power; the values were 58.86%, 82.64%, 29.92% and 0.236% at 2.0mg/mL, respectively.

Purification and biochemical characterization of a novel fibrinolytic enzyme from culture supernatant of Cordyceps militaris.

A novel fibrinolytic enzyme from Cordyceps militaris was produced by submerged culture fermentation, purified, and biochemically characterized. The enzyme was purified to homogeneity, with an overall yield of 4.0% and a specific activity of 1682 U/mg. The molecular weight and pI of the enzyme were 32 kDa and 9.3 ± 0.2, respectively. The optimal pH and temperature of the enzyme were 7.4 and 37 °C, respectively. The enzyme activity was inhibited by Fe(2+), phenylmethane sulfonyl fluoride (PMSF), aprotinin, and pepstatin but not by N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and ethylenediamine tetracetic acid (EDTA). Three internal peptides of the enzyme, APQALTVAAVGATWAR, EKNVGSTVNLLSYDGNK, and TDATSVLLDGYNVSAVNDLVAK, were obtained. The enzyme could hydrolyze fibrin(ogen) directly and cleave the α-chains more efficiently than β- and γ-chains, suggesting that it is a plasmin like protein. It degraded thrombin, which indicated that it can act as an anticoagulant and prevent thrombosis. Intravascular thrombosis is one of the major reasons of cardiovascular diseases. On the basis of these results, the purified enzyme can be developed as a natural agent for oral fibrinolytic therapy or prevention of thrombosis.

Biochemical characterization of a novel fibrinolytic enzyme from Cordyceps militaris.

A fibrinolytic enzyme was produced by the medicinal mushroom, Cordyceps militaris using submerged fermentation. The enzyme was purified from culture supernatant by hydrophobic interaction, ion exchange and gel filtration chromatographies. It was purified by 36 fold, with a specific activity of 1,467.4U/mg protein and the final yield was 5.8%. The molecular weight of the enzyme as determined by SDS-PAGE and gel filtration was 28kDa and 24.5kDa, respectively, and its isoelectric point (pI) was 9.0±0.2. It was found to be a glycoprotein with carbohydrate content of 1.67% (w/v). The enzyme was optimally active at 37°C and pH 7.2. The enzyme activity was strongly inhibited by soybean trypsin inhibitor (SBTI) and aprotinin which indicated it to be a serine protease, while other inhibitors like N-α-tosyl-l-phenylalanine chloromethyl ketone (TPCK), phenyl methane sulfonyl fluoride (PMSF), pepstatin and metal chelator EDTA did not inhibit its activity. Amino acid sequences of the purified enzyme were determined partially by Q-TOF2 and they were IEDFPYQVDLR; ANCGGTVISEK; YVLTAGHCAEGYTGLNIR; TNYASVTPITADMICAGFPEGK; KDSCSGDSGGPLVTGGK; VVGIVSFGTGCAR; ANKPGVYSSVASAEIR. Sequences of the seven peptides completely matched with those of a trypsin-like serine protease from Cordyceps militaris CM01 (accession no. EGX95217.1). The purified enzyme degraded α chains of fibrinogen first and then β and γ chains and also activated plasminogen into plasmin. It can act as an anticoagulant and prevent clot formation by degrading fibrinogen. Based on these studies, the purified enzyme has great potential to be developed as a natural agent for prevention and treatment of thrombolytic diseases.

Preparation of glycosylated zein and retarding effect on lipid oxidation of ground pork

The focus of the present work was to investigate the glycosylation of zein, partial properties of the glycosylated zein (GZ) and its retarding effect on lipid oxidation of ground pork. Zein was glycosylated with chitosan (MW 1500Da) by microbial transglutaminase, the reaction was verified by FT-IR. Under the optimized conditions, 97.48mg of glucosamine was covalently conjugated to 1g of zein, determined by HPLC. The solubility and the surface hydrophobicity of GZ were significantly improved. In vitro studies of GZ showed a dose-dependent scavenging activity against free radicals of DPPH, superoxide and hydroxyl radical, and the EC50 value for DPPH radical was 1.99μg TE/mg protein. In addition, reducing power and Fe2+-chelating capacity of it were 16.60 and 12.96μg TE/mg protein, respectively. GZ resulted in low levels of thiobarbituric acid-reactive substances and peroxide value of ground pork. These results suggest that GZ is a potential natural antioxidant.

Effects of Extrusion and Starch Removal Pretreatment on Zein Proteins Extracted from Corn Gluten Meal

ABSTRACT In this study, the structure and selected properties of zeins extracted from corn gluten meal (CGM) pretreated by extrusion and removal of starch were investigated. The structure and properties of the zeins from pretreated CGM changed significantly. Pretreatments can decrease the extraction yields of zeins and change the granule shape and size of zein aggregates. The studies indicated that extrusion and removal of starch can significantly decrease the thermal enthalpy (ΔH1 and ΔH2) of zein from 1.94 ± 0.20 to 0.19 ± 0.10 and from 107.20 ± 0.80 to 78.62 ± 2.30 and J/g, respectively. The SDS-PAGE results confirmed that the molecular weight of zeins from CGM was 24,000 and 27,000, and the molecular weight of zeins did not change with the pretreatment. On the other hand, the circular dichroism spectroscopy results showed that the processing of extrusion and removal of starch can change the secondary structure content of β-sheets and β-turns; these results indicated that extrusion and removal of starc...

Rumen Degradability and Small Intestinal Digestibility of the Amino Acids in Four Protein Supplements

The supplementation of livestock feed with animal protein is a present cause for public concern, and plant protein shortages have become increasingly prominent in China. This conflict may be resolved by fully utilizing currently available sources of plant protein. We estimated the rumen degradability and the small intestinal digestibility of the amino acids (AA) in rapeseed meal (RSM), soybean meal (SBM), sunflower seed meal (SFM) and sesame meal (SSM) using the mobile nylon bag method to determine the absorbable AA content of these protein supplements as a guide towards dietary formulations for the dairy industry. Overall, this study aimed to utilize protein supplements effectively to guide dietary formulations to increase milk yield and save plant protein resources. To this end, we studied four cows with a permanent rumen fistula and duodenal T-shape fistula in a 4×4 Latin square experimental design. The results showed that the total small intestine absorbable amino acids and small intestine absorbable essential amino acids were higher in the SBM (26.34% and 13.11% dry matter [DM], respectively) than in the SFM (13.97% and 6.89% DM, respectively). The small intestine absorbable Lys contents of the SFM, SSM, RSM and SBM were 0.86%, 0.88%, 1.43%, and 2.12% (DM basis), respectively, and the absorbable Met contents of these meals were 0.28%, 1.03%, 0.52%, and 0.47% (DM basis), respectively. Among the examined food sources, the milk protein score of the SBM (0.181) was highest followed by those of the RSM (0.136), SSM (0.108) and SFM (0.106). The absorbable amino acid contents of the protein supplements accurately reflected protein availability, which is an important indicator of the balance of feed formulation. Therefore, a database detailing the absorbable AA should be established.

A dual-function chymotrypsin-like serine protease with plasminogen activation and fibrinolytic activities from the GRAS fungus, Neurospora sitophila

In this study, we have isolated and characterized a fibrinolytic enzyme from the GRAS (Generally Recognized as Safe) fungus, Neurospora sitophila. The enzyme was purified by fractional ammonium sulfate precipitation, hydrophobic interaction, ion exchange and gel filtration chromatography to 45.2 fold with a specific activity of 415.6U/mg protein. The native molecular mass of the enzyme was 49kDa, while the denatured molecular mass was 30kDa and 17.5kDa, indicating that the enzyme was a hetero-dimer. It was optimally active at 50°C and pH 7.4 and stable at human physiological temperature and pH. It was found to be a chymotrypsin-like serine protease which cleaved the synthetic chromogenic substrate, N-Succinyl-Ala-Ala-Pro-Phe-pNA for which the apparent Km and Vmax values were 0.24mM and 4.17×10-5mM/s, respectively. The enzyme hydrolyzed all the chains of fibrinogen by cleaving α chain first, followed by β chain and then γ chain. Moreover, the enzyme possessed dual function of direct fibrinolysis as well as plasminogen activation. Due to its attractive biochemical and fibrinolytic properties and being from a GRAS fungus, the fibrinolytic enzyme has application as a safe and efficient thrombolytic drug.