Table of Content

15 April 2012, Volume 33 Issue 7
Basic Research
Separation and Identification of Chemical Constituents in Fallopia aubertii Stems and Leaves
2012, 33(7):  1-5.  doi:10.7506/spkx1002-6630-201207001
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Obiective: To separate and identify chemical constituents in the stems and leaves of Fallopia aubertii (L. Henry) Holub. Methods: The dried stems and leaves of the plant were extracted repeatedly with 95% methanol for four times, and then the pooled extract was re-extracted sequentially with ethyl acetate and n-butanol. At last, the two fractions obtained were separated using various column chromatographic techniques. In addition, the structure of the separated fractions was identified and elucidated according to their physicochemical properties and spectral data as well as relevant literature data. Results: Eleven compounds were isolated and identified as 5,7-dihydroxy-2-(n-heneicosyl) chromone (1), quercetin (2), kaempferol (3), luteolin (4), myricetin (5), myricetin-3-O-β-D-glucopyranoside (6), quercetin-3-O-α-L-rhamnoside (7), N-feruloyltyramine (8), p-coumaroyldopamine (9), β-sitosterol (10) and daucosterol (11), respectively. Conclusions: It is the first time that compounds 1, 5, 6 and 9 are isolated from the genus Fallopia and all identified compounds except compound 10 from Fallopia aubertii (L. Henry) Holub.
Comparison of Antioxidant Activities of Reduced Glutathione and Several Common Dipeptides
2012, 33(7):  6-10.  doi:10.7506/spkx1002-6630-201207002
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The antioxidant activities of reduced glutathione, L-carnosine, N-acetyl-L-carnosine, Gly-L-Tyr, L-Ala-Gln and Gly-Gly were measured by various chemical assays, including DPPH radical scavenging assay, ABTS radical scavenging assay, ferrous ion chelating assay and ferric thiocyanate method (for determining the inhibitory activity against linoleic acid peroxidation). The results showed that all these peptides had antioxidant activity, especially in linoleic acid system for peroxidation inhibitory activity. The antioxidant activity of reduced glutathione and Gly-L-Tyr were similar to those of BHA and VE and better than those of L-carnosine, L-Ala-Gln and Gly-Gly, and N-acetyl-L-carnosine had the weakest antioxidant activity. L-Carnosine, which contains histidine, was excellent in chelating ferrous ions, and the ability reached 92.51% at the concentration of 1 mg/mL, which was similar to that of EDTA.
Effect of High Hydrostatic Pressure Treatment on Enzymolysis Characteristics of Thermo-Denatured Rice Protein
2012, 33(7):  11-15.  doi:10.7506/spkx1002-6630-201207003
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Some enzymolysis properties such as solubility, hydrolysis degree, -SH content, molecular characteristics and microcosmic morphology of high hydrostatic pressure (HHP) treated thermal denatured rice protein during hydrolysis with alcalase were investigated. The results showed that the contents of soluble rice protein and free -SH in samples pretreated at high pressure 100-700 MPa were both increased (especially at 500 MPa), compared with that of untreated samples. The ratio of soluble rice protein in the hydrolysate obtained after HHP treatment at 500 MPa followed by 120 min of hydrolysis was 73.0% compared with only 53.6% for that obtained for non-HHP treated rice protein. However, no obvious difference in the degree of hydrolysis was found. The gel filtration chromatographic analysis indicated that soluble hydrolysates with lower relative molecular mass were obtained using HHP treatment and subsequent enzymatic hydrolysis compared to direct enzymatic hydrolysis. The SDS-PAGE analysis indicated that the content of high-molecular-mass components in insoluble hydrolysates of HHP treated rice protein decreased notably, while that of low-molecular-mass components increased distinctly. As observed under a scanning electron microscope (SEM), the morphology of HHP treated rice protein was relatively loose. Therefore, the appropriate HHP treatment was beneficial to the hydrolysis of rice protein and enzymatic hydrolysis characteristics were directly associated with structural changes in rice protein caused by HHP treatment.
Emulsifying Properties of Whey Protein Isolate-Chitosan Conjugates Prepared from the Primary Stage of Maillard Reaction
2012, 33(7):  16-19.  doi:10.7506/spkx1002-6630-201207004
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In this study, the conjugation of whey protein isolate (WPI) and chitosan through Maillard reaction under different dry heating conditions was studied. Emulsifying properties of WPI-chitosan conjugates were compared at different reaction temperatures, WPI-pectin mass ratios and reaction time by determining the changes in droplet size, emulsifying stability and turbiscan analysis. The fluorescence spectra of WPI-chitosan conjugates confirmed the conjugation of WPI and chitosan. Meanwhile, the primary stage of Maillar reaction was completed after 1-4 days of reaction under the conditions of 50 ℃ and a relative humidity of 79%, and reaction products with improved emulsifying properties were obtained. The product formed after 1 day of reaction between WPI and chitosan at a mass ratio of 1:4 at 50 ℃ showed a 10-fold increase in emulsion stability compared to their physical mixture.
Comparison of Antioxidant Activity between Six Kinds of Minor Cereals and Two Kinds of Staple Food Grains
2012, 33(7):  20-25.  doi:10.7506/spkx1002-6630-201207005
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Purpose: To compare the contents and existence form of polyphenols and flavonoids as well as antioxidant activities of edible parts between minor cereals (common buckwheat, tartary buckwheat, oat, coix, millet, corn and proso millet) and staple food grains (rice and wheat), and to explore the correlations between antioxidant properties and total phenolics or flavonoid contents. Methods: Total phenolic content was measured by Folin-Ciocalteu assay, and the content of total flavonoids was investigated by NaNO2-Al(NO)3 assay. Antioxidant properties were evaluated by DPPH free radical and ABTS+ · scavenging assay, reducing power and β-carotene-linoleic acid emulsion assay. Results: The content of total phenolics revealed a decreasing order as tartary buckwheat > common buckwheat> at>coix > corn>millet> proso millet> wheat > rice. Except for millet and proso millet, the major existence form of polyphenols was free phenolics (64.18%-98.70%). Additionally, the content of total flavonoids was the highest in coix, followed by oat, and existed mostly in a free form in both of them. The DPPH free radical and ABTS+ · scavenging capacity and reducing power of tartary buckwheat were higher than those of other cereals, while millet had the highest AAC value as determined by β-carotene-linoleic acid assay. In the present study, a significant correlation was observed between total phenolics and antioxidant activity. Conclusion: The antioxidant properties of minor cereals were higher than those of staple food grains, with the best antioxidant capacity in tartary buckwheat. Therefore, it can be suggested that minor cereals should be eaten more to improve the intake of dietary polyphenols, which are present in staple food grains in excessively small amounts.
A New Amino Acid Descriptor SVHEHS and Its Application in QSAR of Bioactive Peptides
2012, 33(7):  26-31.  doi:10.7506/spkx1002-6630-201207006
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Totally 457 physicochemical variables of 20 kinds of natural amino acids were classified according to hydrophobic properties, electronic characteristics, hydrogen bonds contributions and steric properties, and analyzed by principal component analysis (PCA). A new amino acid structure descriptor, SVHEHS, was achieved. The descriptor was used to characterize the structures of a series of ACE inhibitory dipeptides and bitter dipeptides. A multiple linear regression (MLR) model was established on the basis of bioactivity. The correlation coefficients (R2), cross-validation correlation coefficients (Q2LOO) and root mean square errors (RMSE) for the models established for ACE inhibitory dipeptides and bitter dipeptides were 0.936, 0.854, 0.259, and 0.949, 0.886, 0.136, respectively. External validation was also conducted to validate the prediction capability of the models. The results showed that the models obtained with the descriptor had good fitting and prediction capability and consequently could be used for QSAR studies.
Effect of Glycine on Maillard Reaction System and Meat Flavor Compounds
2012, 33(7):  32-36.  doi:10.7506/spkx1002-6630-201207007
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The effect of glycine addition on the residual substrate concentration, pH and color of a glucose-cysteine Maillard reaction system as well as meat flavor compounds including 1,2-ethanedithiol, 2-ethylpyrazine, 2,4,5-trimethylthiazole and 2-acetylfuran was investigated. The results demonstrated that with increasing glycine addition, residual cysteine concentration remained basically unchanged, while residual glucose concentration slightly decreased. Besides, large amounts of colored compounds were formed, and the pH became lower. Meanwhile, both 1, 2-ethanedithiol and 2, 4, 5-trimethylthiazole exhibited an initial increase and subsequent decrease, 2-ethylpyrazine revealed a gradual decrease, and 2-acetylfuran revealed an increase first and then remained basically unchanged. As for sensory evaluation, the meat flavor of the system revealed an increase due to the addition of glycine at 0.20 mol/L.
Extraction and Physical and Chemical Properties of Collagen from Urechis unicinctus
2012, 33(7):  37-40.  doi:10.7506/spkx1002-6630-201207008
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Acid-soluble collagen (ASC) was prepared from the body wall of Urechis unicinctus through extraction with 0.5 mol/L acetic acid followed by precipitation with 0.9 mol/L NaCl and its physical and chemical properties were primarily studied. Ultraviolet spectral analysis showed that the characteristic absorption wavelength of ASC was 228 nm, suggesting that it is a typical collagen. Amino acid composition analysis indicated that ASC was a typical type Ⅰcollagen. SDS polyacrylamide gel electrophoresis (SDS-PAGE) suggested that ASC contained two alpha chains (α1 and α2), one β chain and oneγ chain. It also contained disulfide bonds. Fourier-transform infrared (FTIR) spectral analysis revealed the existence of helical arrangements in the collagen. The thermal denaturation temperature (td) and the thermal shrinkable temperature (ts) were 33.6 and 67.5 ℃, respectively.
Pattern Recognition and Classification of Geographical Indication Rice Based on Chemical Components
2012, 33(7):  41-45.  doi:10.7506/spkx1002-6630-201207009
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Principal component analysis (PCA) and Fisher linear discriminant analysis were both applied for the pattern recognition and classification of Zengcheng mew rice from Guangdong province as a geographical indication (GI) product. A classification model between GI and non-GI products was established based on inorganic elements and organic compounds including amino acids, fat, starch and protein by Fisher linear discriminant analysis. The results showed that Fisher linear discriminant analysis was a simple and fast method for the classification and identification of geographical indication rice and could allow rapid establishment of a classification model for identification and reorganization between GI and non-GI products based on relatively complicated data.
Effect of Postmortem Aging on Microstructure of Different Beef Muscles
2012, 33(7):  46-50.  doi:10.7506/spkx1002-6630-201207010
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To investigate the effect of postmortem aging on beef microstructure and the underlying mechanism, we herein examined three muscles, namely longissimus dorsi (LD), rectus abdominis (RA), and semitendinosus (ST), from Qinchuan beef carcasses. Meat samples were vacuum packaged and aged at 4 ℃ for 72 h. Subsequently, shear force, paraffin hematoxylin-eosin (HE) staining and atomic force microscopy were used to examine changes in different parts, muscle fiber and myofibril fragmentation. Environmental scanning electron microscopic observations were also performed to examine sarcolemma, and immunohistochemistry was employed to study the localization of μ-calpain in muscle fibers. The results indicated that the shear force of different parts ranked in the following descending order: ST > RA > LD. LD muscle fiber and myofibrils exhibited the most severe fragmentation, and ST fiber showed the least changes during postmortem aging. No significant changes were observed in sarcolemma. Furthermore, μ-calpain was detected mainly in sarcolemma and cytoplasm; high levels of μ-calpain were found in red muscle fiber (slow muscle), whereas white muscle fiber (fast muscle) showed low levels of expression. Therefore, μ-calpain appears to be important for beef tenderization during postmortem aging. In different parts of Qinchuan cattle carcass, the ratio of red to, white muscle fiber could significantly affect microstructural changes in muscle fibers and impovement in beef tenderness during postmortem aging.
Comparison of Material Characteristics among Conventional Freshwater Fish Species
2012, 33(7):  51-54.  doi:10.7506/spkx1002-6630-201207011
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The material characteristics of such conventional freshwater fish species as snail carp, grass carp, silver carp, bighead carp, carp, crucian carp and bream were studied. The weight percentage of each part, meat-producing rate, basic components, pH, protein composition and texture profile analysis (TPA) of back muscle were investigated. The results indicated that the weight percentages of viscera and head in seven species of freshwater fish were significantly different. The meat-producing rate of black carp was the highest, 54.33%, while bighead carp was the lowest, 32.80%. Little difference in basic components was observed except for higher crude fat content in bream (4.08%) compared with other fish species. The highest percentages of non-protein nitrogen, water-soluble protein, salt-soluble protein, alkali-soluble protein and alkali-insoluble protein were found in silver carp (1.67%), carp (4.68%), grass carp (9.91%), carp (2.45%) and bream (0.83%), respectively. Based on the TPA parameters, better textural characteristics were observed in black carp and crap.
Suitability of Different Melon Cultivars for Fresh-Cut Processing
2012, 33(7):  55-58.  doi:10.7506/spkx1002-6630-201207012
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Hardness, soluble solid content (SSC), sensory quality, VC content, and marketable fruit percentage were measured on melon fruits from four different cultivars, reticulate melon (Zhongmi No. 55 and Huami No. 2) and smooth rind melon (Zhongmi No. 116 and Yujinxiang) at days 0, 14 and 28 of post-harvest storage at 10 ℃. Meanwhile, grey correlation analysis was used to evaluate the experimental data. The suitability of the melon cultivars for fresh-cut processing followed the decreasing order of Huami No. 2 > Zhongmi No. 55 > Zhongmi No. 116 > Yujinxiang. Huami No. 2 was characterized by higher marketable fruit percentage at the early harvest stage, better sensory quality and higher VC content, and Zhongmi No. 55 showed the characteristics of higher marketable fruit percentage and better sensory quality and storage tolerance.
Effect of Operating Conditions on Extraction Rate and Purity of Glycinin (11S) from Soybean
2012, 33(7):  59-63.  doi:10.7506/spkx1002-6630-201207013
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Low-fat soybean flakes were used to evaluate the effects of some operating conditions for glycinin (11S) extraction such as pH, reducing agent type and cold precipitation duration on the extraction rate and purity of glycinin. The pH adjustment of protein extract from 6.2 to 6.6 could decrease the extraction rate of glycinin by 16.71%, while the purity of the protein exhibited an increase by 4.60%. The contents of sulfhydryl and disulfide in proteins increased as the pH increased. Addition of sodium bisulfite (SBS) instead of dithiothreitol (DTT) or β-mercaptoethanol (ME) to the protein extract at pH 6.4 could increase the extraction rate of glycinin. The effect of DTT on the extraction rate of glycinin was the lowest among the reducing agents. The highest extraction rate and purity of glycinin were obtained after 10 h of cold precipitation. No significant difference was observed in the total content of sulfhydryl and disulfide as the precipitation duration was prolonged from 12 to 16 h (P ≥ 0.05), while the content of free sulfhydryl decreased as a result of partial oxidation to disulfide bonds.
Effect of Organic Acids on Storage Stability of Purple Corn Cob Pigment
2012, 33(7):  64-68.  doi:10.7506/spkx1002-6630-201207014
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The kinetic parameters of color change and the stability of purple corn cob pigment with the respective addition of several organic acids such as glycine were studied. The mechanism of the effect of glycine on the stability of purple corn cob pigment was also discussed. The results showed that glycine had the most pronounced effect on the stability of the pigment at pH 5. The results of uniform design optimization indicated that the retention rate of the pigment at 0.96 μg/mL after 10 d of storage at pH 5 and 75℃ in the presence of 160 mmol/L glycine and 256 mmol/L Fe2+ increased by 1.49-fold compared to the control without the addition of any organic acid. The possible mechanism may be mainly associated with the interaction between glycine and anthocyanins. It is speculated that glycine is bound to the pigment through ester bonds, resulting in an increased activation energy, thus enhancing the stability of the pigment.
Establishment of a Quality Control Method for Lu-Gui Tincture Based on 1H NMR-PLS-DA
2012, 33(7):  69-72.  doi:10.7506/spkx1002-6630-201207015
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Objective: To establish a new method of quality control for Lu-Gui Tincture. Methods: The 1H-NMR data of the whole composition were transformed to a matrix and analyzed by PLS-DA method using SIMCA-P software. Results: Authentic and imitated samples of Lu-Gui Tincture and its corresponding samples with shortage of one component could be distinguished by the scattering plots obviously. Conclusion: The 1H NMR-PLS-DA is a simple and useful method for the quality control of Lu-Gui Tincture.
Microscopic Structure Properties of Fat Particles in Meat Batters Prepared under Shearing Conditions
2012, 33(7):  73-77.  doi:10.7506/spkx1002-6630-201207016
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The distribution regularity and microstructure of fat particle in meat batters were investigated. Porcine longissimus muscle was used as raw material. After grinding and chopping for 3 min, the mash was chopped with pork fat for 5 min. Light microscope and electron microscope were used to observe the meat batter and the gel. The results showed that the fat was shearing into liquid fat droplets and solid fat granules of different sizes and shapes, some fat droplets and fat granules could even be aggregated into fat particle clusters. They were all covered with a layer of protein film and dispersing in the protein matrix individually or by a coalescent way.
Factors Affecting the Photochromism and Anti-oxidant Activity of Green Tea Infusion Brewed with Tap Water in Beijing
2012, 33(7):  78-82.  doi:10.7506/spkx1002-6630-201207017
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Water quality was measured on Beijing tap water with and without reverse osmosis membrane filtration and deionized water. In addition, the effect of selected ions showing a considerable difference on color parameters and DPPH free radical scavenging activity of tea infusion was discovered. Our results indicated that Beijing tap water was slightly alkaline, remarkably darkened the color of tea infusion compared with deionized water, and resulted in a distinct decrease in DPPH free radical scavenging activity. Calcium (70 mg/L), magnesium (30 mg/L) and sodium (18 mg/L) ions in Beijing tap water could reduce the color of tea infusion and its DPPH free radical scavenging activity. This suggests that the main reason for the darker color and decreased DPPH free radical scavenging activity of tea infusion brewed with tap water is that tea infusion is kept in a weakly alkaline environment during brewing due to the presence of HCO3- in tap water, thus causing oxidative degradation of tea phenols.
Influence of Thermalstable Ice-Structuring Proteins Extracted from Oat Flour and Chinese Privet Leaves on Freeze-Thaw Stability of Wheat Starch Gels
2012, 33(7):  83-87.  doi:10.7506/spkx1002-6630-201207018
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The effect of thermostable ice-structuring proteins extracted from oat flour and Chinese Privet (Ligustrum vulgare) leaves separately added at 0.5% on the freeze-thaw stability of wheat starch gels was investigated. The syneresis, freezable water content, microstructure and texture of starch gels after going through different freeze-thaw cycles were analyzed using centrifugation, differential scanning calorimetry, scanning electron microscopy and texture analyzer, respectively. The results showed that as freeze-thaw process happened repeatedly, the syneresis and freezable water content of starch gels increased obviously, the microstructure was damaged seriously, ice cell cavities became larger and uneven, the hardness increased markedly, and the springness decreased significantly. The introduction of TSISP extracted from oat flour and Chinese Privet (Ligustrum vulgare) leaves into wheat starch gels improved the freeze-thaw stability, which was indicated by a significant decrease in syneresis, freezable water content, the size of ice cell cavities and springiness and an increase in hardness.
Effect of Alcalase Hydrolysates of Soybean 7S Globulin on Gel Properties of Minced Pork
2012, 33(7):  88-92.  doi:10.7506/spkx1002-6630-201207019
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In this study, the influence of soybean 7S globulin hydrolysates with different degree of hydrolysis (DH) on gel properties of minced pork was investigated. Soybean 7S globulin was first hydrolyzed to different DH (3%, 6%, 9%, 12%, 15%) using alcalase. Hydrolysates were then added to minced pork to make pork sausage. Interactions to stabilize the gel structure of pork sausage were finally analyzed to determine the influence of hydrolysates on gel properties of minced pork. The results obtained showed that hydrophobic interaction was not significantly related to the gel strength of pork sausage, indicating it was not a principle interaction in maintaining the gel network of mined pork. While, disulfide bond and hydrophobic interactions were significantly related to the springiness and chewiness of pork sausage (P<0.01). Hydrogen bond was also significantly related to springiness of the pork sausage (P<0.05), indicating that disulfide bonds, hydrophobic interactions and hydrogen bonds were the principle forces to maintain pork gel network. Scanning electron microscopy (SEM) revealed that hydrolysates of soybean 7S globulin improved the gel properties of minced pork. With increasing DH added hydrolysates, the pork gel became more compact and uniform, with no noticeable pores in it.
Purification and Spectroscopic Analysis of Polysaccharide from Mango
2012, 33(7):  93-95.  doi:10.7506/spkx1002-6630-201207020
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Crude polysaccharide was extracted from Mexico mango using hot water extraction followed by ethanol precipitation. The polysaccharide concentration of crude extract was (46.3±1.75) mg/g as determined by phenol-sulfuric acid assay. After further purification by DEAE-52 and Sephadex G-75 column chromatography, a white flocculent polysaccharide was obtained. High performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to determine the monosaccharide composition. The results showed that the polysaccharide was composed of rhamnose, galactose and glucose with a ratio of (6.3±1.40), (11.9 ±1.76) mg/g and (13.8 ±1.52) mg/g, respectively. The purified polysaccharide exhibited the characteristic IR absorption of polysaccharide. The structure was pyranoid glucan with β-glycosidic bond.
Kinetic Modeling of Enzymatic Hydrolysis of Wheat Flour with α-Amylase
2012, 33(7):  96-100.  doi:10.7506/spkx1002-6630-201207021
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The effects of substrate concentration, enzyme concentration, pH and temperature on the hydrolysis rate of wheat flour by α-amylase were analyzed. Based on this, the Michealis constant (Km) and maximum rate (Vm) were deduced by Lineweaver-Burk plotting and Wilkinson statistical method. Results showed that, under the optimal conditions of pH 6.0 and temperature 60 ℃, the Km and Vm were.2.940 mg/mL and 0.348 mg/(mL ·min), respectively. The Michaelis-Menten equation was v =----. The model-predicted values were consistent with the actually measured values from confirmation tests. At temperatures ranging from 30 to 60 ℃, an enzymatic kinetic equation was obtained as v=---------[E]total[S].
Antioxidant and Antibacterial Activities of Polysaccharides from Chinese Surf Clam (Mactra chinensis)
2012, 33(7):  101-104.  doi:10.7506/spkx1002-6630-201207022
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Purpose: To investigate the antioxidant and antibacterial activities of polysaccharides from Chinese surf clam (Mactra chinensis). Methods: Polysaccharides from the whole viscera of the shellfish were extracted by alkaline extraction and alcohol precipitation and deproteinized by Sevag,s method. The purified extract was determined for its polysaccharide content, hydroxyl and superoxide anion free radical scavenging activity and antibacterial activity. A high extraction efficiency of polysaccharides from dried powdered material was obtained by using alkaline extraction, reaching 15.45%. Polysaccharides extracted from Chinese surf clam had strong antioxidant properties and the scavenging rates against superoxide anion and hydroxyl free radicals at 0.8 mg/mL were 86.49% and 49.31%, respectively. These polysaccharides had different antibacterial activity against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. The antibacterial activity against Staphylococcus aureus was the strongest, followed by Bacillus subtilis; they had the weakest antibacterial activity against Escherichia coli. The corresponding minimum inhibitory concentrations were 12.5, 25 mg/mL and 25 mg/mL. Conclusions: Polysaccharides from Chinese surf clam have scavenging activity against superoxide anion and hydroxyl free radicals in a concentration-dependent way in a certain range of concentrations and show stronger antimicrobial activity against Gram-positive bacteria than Gram-negative bacteria.
Hot Air Drying Characteristics and Mathematical Modeling of Sugar Infused Sweet Potato Slices
2012, 33(7):  105-109.  doi:10.7506/spkx1002-6630-201207023
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After 10 h of infusion in different concentration of sugar solution (10%, 15%, 20%, 30%, 40%, 50% or 70%), sweet potato slices were subjected to hot air drying and then examined for hot air drying characteristics and effective moisture diffusivity. The drying data were fitted to Newton, Page, and Henderson and Pabisnine models. The results showed that Page model fitted best with R2 value of 0.982. The sugar content c had a linear relationship with the parameter k, but no relationship with the parameter n. The effective moisture diffusivity Deff under various levels of c were calculated and compared. It was found that Deff had a significant cubic relationship with the initial sugar content value c, with R2 value of 0.984. The pre-exponential factor D0 and activation energy Ea were calculated based on the Arrhenius relationship. Both D0 and Ea value of sugar infused sweet potato slices were larger than those of slices without sugar infusion treatment.
Rheological Properties of Cold-Pressed Rapeseed Oils
2012, 33(7):  110-113.  doi:10.7506/spkx1002-6630-201207024
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Cold-pressed rapeseed oils (CROs) were obtained from three rapeseed samples with different erucic acid by cold-pressing. The rheological properties and characteristics of CROs were investigated, and the Bingham model was used to describe the rheological behavior of CROs. The results showed that CROs behaved as a shear-thinning pseudoplastic fluid at shear rates varying from 0.1s-1 to 200 s-1 and showed Newtonian behavior at shear rates greater than 5 s-1. It was also found that temperature was an important factor affecting the rheological properties of CROs. The viscosity, loss modulus (G'') and plastic consistency coefficients (ηp) of CROs decreased with the increase of temperature. The storage modulus (GO`) of CROs was less affected by temperature. Furthermore, the viscosities and GO` of CROs increased with increasing erucic acid content. The values of ηp of CROs were positively correlated with the level of erucic acid.
Effect of Hydrocolloids on the Stability of Wax Corn Juice
2012, 33(7):  114-117.  doi:10.7506/spkx1002-6630-201207025
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In order to improve the stability of wax corn juice, the influence of various hydrocolloids on the stability coefficient, centrifugal sedimentation rate, relative viscosity and sensory quality of the corn juice were investigated. The electrostatic stability of wax corn juice system was also evaluated in this study. The results indicated that xanthan gum had emulsifying effects on corn juice and inhibited lipid droplet formation. Addition of sodium alginates, guar gum and sophora bean gum improved the stability of wax corn juice. The stability coefficient and relative viscosity of corn juice increased with the increase of their concentrations. When xanthan gum and sophora bean gum were together added at a ratio of 1:4, the juice had the highest stability.
DSC Analysis of Heat-induced Changes of Thermal Characteristics for Perimysium and Endomysium Collagen from Beef semitendinosus Muscle
2012, 33(7):  118-122.  doi:10.7506/spkx1002-6630-201207026
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The main objective of this study was to investigate the heat-induced changes of thermal characteristics for perimysium and endomysium collagen from beef semitendinosus muscle. Muscle samples were heated to an internal core temperature of 20, 40, 50, 60, 70, 80 ℃ and 90 ℃ in water bath and in microwave oven respectively. The changes of thermal shrinkage temperatures (To: onset temperature; Tp: peak temperature; Te: end temperature) of perimysium and endomysium collagen for beef semitendinosus muscle during heating were analyzed by Differential Scanning Calorimeter (DSC). The results indicated that the thermal shrinkage temperatures (To, Tp and Te) of perimysium and endomysium collagen both showed significant differences at different internal core temperatures during water-bath and microwave heating. And an internal core temperature of 60 ℃ was the critical heating temperature which affects thermal shrinkage temperatures of perimysium and endomysium collagen for both water-bath and microwave heated meat. The significant differences in thermal shrinkage temperatures between water bath and microwave heated beef muscle samples were attributed to the heat-induced changes in thermal characteristics of perimysium and endomysium collagen.
Changes in Aromatic Components of Refrigerated Nanguo Pears during Shelf Period Analyzed by Electronic Nose Technique
2012, 33(7):  123-126.  doi:10.7506/spkx1002-6630-201207027
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The present study intended to investigate the changes in aromatic components of Nanguo pears after cold storage. Electronic nose technique was used to detect the changes of volatile compounds in refrigerated Nanguo pears with and without 1-MCP pretreatment during the normal shelf period after refrigeration. Loading analysis (LA), principal component analysis (PCA) and linear discriminant analysis (LDA) were used to establish characteristic radar charts. Results showed that electronic nose was sensitive to the changes of volatile compound in Nanguo pears. After refrigerated storage, Nanguo pears with and without 1-MCP pretreatment could both release unique volatile compounds. However, the change rate of volatile compounds in Nanguo pears with 1-MCP pretreatment was slower.
Antioxidant Stability of Total Flavonoids from Propolis
2012, 33(7):  127-130.  doi:10.7506/spkx1002-6630-201207028
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Total flavonoids in propolis were extracted with ethanol and the antioxidant capacity of propolis extract was evaluated. The major factors that affect antioxidant stability were identified as ethanol concentration, extraction time, extraction temperature and material-to-liquid ratio and their effects of the extraction efficiency of total flavonoids were evaluated using an L9 (34) orthogonal array design to determine optimal conditions for the extraction of total flavonoids from propolis. The antioxidant stability of propolis extract was evaluated by measuring the scavenging capacity against hydroxyl free radicals under various conditions of pH, temperature, metal ions and illumination. The optimal extraction conditions were ethanol concentration of 80%, extraction temperature of 80 ℃, material-to-liquid ratio of 1:10 and extraction duration of 2 h. The propolis extract was relatively stable in the presence of metal ions such as Na+, K+, Ca2+ or weak acid, while poor antioxidant stability of propolis extract was observed in the presence of strong acid, strong alkali, light or heat.
Symbiotic Fermentation Characteristics of Lactic Acid Bacteria and Yeast Isolated from Koumiss in Inner Mongolia
2012, 33(7):  131-137.  doi:10.7506/spkx1002-6630-201207029
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The co-cultivation of a strain of lactic acid bacteria and a strain of yeast isolated from koumiss in Ximeng region of Inner Mongolia was studied. The best fermentation conditions of two-strain system were preliminarily explored. The optimal conditions for maximum viable cell count of lactic acid bacteria were shake culture at 30 ℃ for 12 h and then stationary culture at 37 ℃ for another 20 h in a medium based on skim milk with the addition of 1 g/100 mL peptone, 0.5 g/100 mL sucrose and 0.5 g/100 mL yeast extract powder, while maximum viable cell count of yeast was achieved after stationary culture at 37 ℃ for 8 h and then shake culture at 30 ℃ for another 32 h in skim milk with the addition of 0.5 g/100 mL peptone, 0.5 g/100 mL sucrose and 0.5 g/100 mL yeast extract powder. The inoculum was a mixture of lactic acid bacteria and yeast at a ratio of 1:1 (m/m). In addition, the effect of secondary fermentation on the symbiotic interaction between the two species of microorganisms was explored under the optimal growth conditions. Active substances promoting the growth of lactic acid bacteria were formed during the first 12 h of shake culture of yeast in medium No. 5 at 30 ℃, while those promoting the growth of yeast were formed during the first 16 h of stationary culture of lactic acid bacteria in medium No. 1 at 37 ℃. During the secondary fermentation, the viable cell counts of yeast and lactic acid bacteria in co-cultures were both significantly higher than those in pure cultures (P < 0.01).
Inhibitory Activity of Methanol Extract from Spirulina platensis on Bacterial Quorum Sensing
2012, 33(7):  138-141.  doi:10.7506/spkx1002-6630-201207030
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The inhibitory activity of methanol extract from Spirulina platensis on quorum sensing in the mini-Tn5 mutant Chromobacterium violaceum CV026 was investigated. The violacein and biofilm production in CV026 and Shewanella spp. were also measured. The results indicated that 75% methanol extract from Spirulina platensis not only significantly reduced violacein production and biofilm formation at a concentration of 0.125-1.000 g/100 mL, but also inhibited violacein production induced by exogenous N-hexanoyl homoserine lactone (10 μmol/L C6-HSL). The inhibitory rates of methanol extract at the dose of 1.000 g/100 mL on violacein production and biofilm formation were 87.67% and 77.05%, respectively (P <0.05). The growth of CV026 was not affected by methanol extract at a concentration of 0.125-1.000 g/100 mL, indicating the reduction of CV026 on violacein was due to HSL-induced quorum sensing but not the inhibitory growth of CV026. In conclusion, methanol extract from Spirulina platensis can significantly inhibit bacterial quorum sensing activity, and can therefore used as an bacterial quorum sensing inhibitor for the storage of fresh and processed food.
Phenotype Diversity and Dominant Species of Yeasts during Spontaneous Fermentation Process of Musalais from Xinjiang
2012, 33(7):  142-147.  doi:10.7506/spkx1002-6630-201207031
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Objective: To investigate the phenotype diversity and dominant species of yeasts during spontaneous fermentation process of Musalais from Xinjiang, and explore the effect of traditional technology on yeast community. Methods: A total of 19 samples were collected from the traditional spontaneous fermentation process of Musalais (including grapes, grape juice, boiled juice and fermentation broth) to analyze yeast phenotype diversity and corresponding dominant species. The isolated strains from these samples were typed and representative strains were selected for colony characteristic analysis on Wallerstein laboratory nutrient agar (WL nutrient agar) and grouped by unweighted pair group method with arithmetic mean (UPGMA) method and primarily identified according to their morphological and physiological characteristics. Results: Totally 217 isolates, 13 types based on WL agar culture, and 8 phenotype groups from 13 representative strains were harvested. Meanwhile, 7 generaand 13 species were primarily identified. The diversity of yeasts was associated with spontaneous fermentation of Musalais. Hanseniaspora spp. was the dominant strain in grape skin, grape juice and boiled grape juice. Saccharomyces cerevisiae is a starter and the only dominant strain during spontaneous fermentation of Musalais; however, other yeast species were also occasionally observed in fermentation broth. Conclusion: Almost all yeasts from grapes are killed by boiling during the production of Musalais. S. cerevisiae may come from brewing utensils and locations, and has high adaptability to spontaneous fermentation of Musalais.
Optimization of Preparation Conditions for Soybean Anticancer Peptides by Papain Hydrolysis
2012, 33(7):  148-152.  doi:10.7506/spkx1002-6630-201207032
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In this study, operating conditions for the enzymatic preparation of anticancer peptides from soybean protein isolate with papain were optimized for maximum inhibitory rate against the growth of human gastric cancer SGC-7901 cells. Peptides with the highest anticancer activity were obtained after 4 h of hydrolysis at pH 7.5 and 55 ℃ with papain at a dose of 7000 U/g and a substrate concentration of 6 g/100 mL. All hydrolysates collected at selected time points during the hydrolysis process had obvious anticancer activity, while no linear relationship between degree of hydrolysis and cell growth inhibitory rate was found. All substrate concentration, enzyme dose, hydrolysis temperature, hydrolysis time and pH could affect cell growth inhibition rate of hydrolysates.
Preparation and Properties of Immobilized Linoleate Isomerase
2012, 33(7):  153-157.  doi:10.7506/spkx1002-6630-201207033
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Sodium alginate and chitosan were used as the carriers for immobilizing linoleate isomerase by entrapment and cross-linking entrapment methods. The immobilization conditions of linoleate isomerase and properties of immobilized linoleate isomerase were investigated. The results indicated that the optimal conditions for immobilizing linoleate isomerase were 3 g/100 mL sodium alginate, 2 g/100 mL CaCl2 and 0.3 g/100 mL glutaraldehyde. The optimal temperature and pH for the conversion of linoleic acid (LA) to conjugated linoleic acid (CLA) were 50 ℃ and 5.0, respectively. The thermal and pH stabilities of immobilized linoleate iosmerase were better than those of native enzyme in the range of 20-60 ℃ and pH 2-8. The Km of immobilized linoleate iosmerase was 0.36 mg/mL. After sixth repeated use, the immobilized enzyme remained 70.6% of its original activity. It could increase CLA production by 50% when compared with native linoleate isomerase.
Effects of Oligo Saccharides and Chlorella on the Growth of Probiotics and Quality of Chlorella Yogurt
2012, 33(7):  158-162.  doi:10.7506/spkx1002-6630-201207034
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In order to explore the effects of oligo saccharides and chlorella on the growth of probiotics and quality of chlorella yogurt, the growth of probiotics in yogurt with the addition of sucrose, fructooligosaccharide, stachyose, their pariwise combinations or all of them (at a total level of 10%) was determined. It was found that fructooligosaccharide and/or stachyose could promote the growth of chlorella in yogurt. Meanwhile, the presence of chlorella was beneficial to the growth of probiotics and the flavor and nutrition of yogurt. Yeast fermentation method was used to remove the odor of chlorella, and pectin was used as stabilizer. As determined using an L9 (34) orthogonal array design, the optima formula of chlorella yogurt was 10% skimmed milk, 3% Lactobacillus bulgaria/Streptococcus thermophilus mixture (1:1), 1% chlorella, 5% sugar, 3% fructooligosaccharide and 1% stachyose.
Purification and Characterization of Leucine Aminopeptidase from Mucor
2012, 33(7):  163-167.  doi:10.7506/spkx1002-6630-201207035
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An aminopeptidase was purified and characterized from crude extracellular protease extract from wheat bran koji of Mucor through ammonium sulfate precipitation, ion exchange chromatography, hydrophobic chromatography, gel filtration chromatography and ultra-filtration. The purified aminopeptidase was identified as leucine aminopeptidase, which was very active in hydrolyzing N-terminal leucine of peptides. Its maximum activity was observed at pH 6.5 and 40 ℃. In addition, the leucine aminopeptidase was stable in the pH range of 5.0-8.0 and at temperatures below 40 ℃. However, it could be completely inhibited by the metal protease inhibitor EDTA, indicating that it belongs to the metal protease family. Ca2+ had an activating effect on it, while Zn2+, Cu2+ and Mn2+ were very active in inhibiting it. The enzyme was effective in removing bitter taste from soybean ploypeptides and basic elimination of bitter taste was achieved after 4 h of treatment with it.
Extraction, Purification and Characterization of Protease from Digestive Tract of Octopus vulgaris
2012, 33(7):  168-171.  doi:10.7506/spkx1002-6630-201207036
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An electrophoretically pure protease , named as OP-I, was obtained from the digestive tract of Octopus vulgaris by ammonium sulfate precipitation, cellulose CM-52 cation-exchange chromatography, DEAE-Sephadex A50 anion-exchange chromatography and SDS-PAGE. Its properties were also characterized. The results showed that the molecular weight of the protease was 80.5 kD and its optimal reaction temperature and pH were 55-60 ℃ and 7-9, respectively. OP-I could be completely inhibited by EDTA, a metalloproteinase inhibitor. In contrast, Mn2+, Ca2+ and Mg2+could stimulate OP-I activity. Moreover, the Km of OP-I was 0.33 mmol/L and Vmax was 66.7 mg/(mL ·min)as determined by kinetic studies.
Purification and Biological Characterization of S-Layer Proteins in Lactobacillus brevis M8, Isolated from Fresh Milk
2012, 33(7):  172-175.  doi:10.7506/spkx1002-6630-201207037
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The aim of this study was to purify S-layer proteins from Lactobacillus brevis M8, isolated from fresh milk, by Sephadex G-75 column chromatography and observe their surface morphology under atomic force microscope (AFM). Also, regeneration and adhesion characteristics were explored. Highly pure S-layer proteins were obtained by Sephadex G-75 column chromatography, which could form nano-cluster by self-assemblage. Lactobacillus brevis M8 cells without S-layer proteins could re-express the proteins after re-incubation. Lactobacillus brevis M8 could adhere to Caco-2 cells, which was mediated by the S-layer proteins.
Enzymatic Properties of Polyphenol Oxidase from Gordon Euryale Seed
2012, 33(7):  176-181.  doi:10.7506/spkx1002-6630-201207038
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Dehulled kernels of two varieties of Euryale ferox Slisb, Zihua Suqian and Zihua Ciqian from respectively Suzhou and Hongze, Jiangsu province of China, were used as raw materials to prepare and characterize crude polyphnol oxidase (PPO) extract. The results showed that PPO enzymes from both verities of gordon euryale had the highest activity at 45 ℃ and pH 6.5. Ferric and ferrous ions were highly effective in promoting PPO activity. Calcium inhibited PPO activity at low concentrations, but not at high concentrations. Aluminum ion and copper ion at low concentrations activated PPO activity, while high levels of copper ions inhibited it. PPOs were inhibited by organic acids, like citric acid, oxalic acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA), and the reductants sodium bisulfate and sodium thiosulfate.
Optimization of Low-Cost Culture Medium for Large-Scale Production of Lactobacillus plantarum YSQ
2012, 33(7):  182-187.  doi:10.7506/spkx1002-6630-201207039
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One-factor-at-a-time method, Plackett-Burman design and response surface methodology were employed combinedly to optimize a growth medium based on low-cost agricultural by-products, like soybean meal, corn flour, wheat middlings and tomato juice for large-scale cultivation of Lactobacillus plantarum YSQ. The results showed that: 1) According to the results of one-factor-at-a-time experiments, in the culture medium, the carbon source were composed of corn flour, wheat middlings, the nitrogen source was soybean meal, and tomato juice was added as a growth factor. 2) As identified by Plackett-Burman design, the main factor that affect the growth of Lactobacillus plantarum YSQ were wheat middlings, soybean meal, K2HPO4 and MnSO4. 3) Collectively, the results of steepest ascent tests, central composition design and response surface analysis indicated that the optimal growth medium was composed of corn flour 10 g/L, soybean meal 15.5 g/L, bran 1.2 g/L, sucrose 5 g/L, tomato juice 150 mL/L, K2HPO4 1.1 g/L, MnSO4 0.28 g/L, MgSO4 0.3 g/L. The total viable count was 2.68 × 1010 CFU/mL after 18 h of culture in the optimized medium, while that obtained with a medium composed of a mixture of corn flour, soybean meal and bran was only 8.73 × 108 CFU/mL.
Comparison of Vacuum Freeze-Drying and Spray-Drying Processes for Active Bifidobacterium longum Powder Production
2012, 33(7):  188-192.  doi:10.7506/spkx1002-6630-201207040
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For long term storage and to improve its stress resistance, Bifidobacterium longum was made into active bacteria powder by vacuum freeze-drying or spray-drying. In this study, we first optimized the technological conditions for active Bifidobacterium longum powder production and then compared these two processes in term of bacterial survival rate, cost, and ease of operation. The viable count, survival rate, moisture and viable count after storage for 90 days at 4 ℃ of vacuum freeze-dried active Bifidobacterium longum powder were 7.98 × 109 CFU/g, 90.9%, 3.8%, and 2.5 × 108 CFU/g, respectively. The powder dissolved easily in water. In contrast, the viable count, survival rate, encapsulation efficiency, moisture and viable count after storage for 90 days at 4 ℃ of spray-dried Bifidobacterium longum powder were 4.4 × 109 CFU/g, 82.2%, 71.9%, 5.6% and 4 × 108 CFU/g, respectively. It took longer time to dissolve in water when compared to vacuum-freeze dried powder. Vacuum freeze-drying was more complicated to operate, time-consuming and expensive than spray-drying. In conclusion, these two processes have both their advantages and disadvantages, which make them fit for different purposes.
Comparison of Bacterial Flora between Fermented Zaopei and Pit Mud from the Production of Luzhou-Flavor Liquor Based on 16S rDNA Library
2012, 33(7):  193-197.  doi:10.7506/spkx1002-6630-201207041
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In order to understand the differences in the bacterial flora between pit mud and fermented Zaopei samples from the production of Luzhou-flavor liquor, we have constructed bacterial 16S rRNA gene libraries of pit mud and fermented Zaopei, respectively. A total of 691 valid sequences were analyzed by software DOTUR1.53 and compared with those published in GenBank by BLAST and EzTaxon server 2.0. The results showed that bacteria in pit mud and fermented Zaopei presented plentiful diversity. Totally 180 sequences in pit mud (51.14% of pit mud sequences) revealed 100% similarity with 264 sequences (77.88% of Zaopei sequences) in fermented Zaopei; these sequences belonged to Lactobacillus, Staphylococcus, Serratia, Clostridium and some potential novel species. In summary, large-scale bacterial interdiffusion between pit mud and Zaopei may happen during the fermentation of Luzhou-flavor liquor. The moving,, bacteria include Lactobacillus, Staphylococcus, Serratia, Clostridium and some potential novel species.
Expression in Escherichia coli, Purification and Functional Characterization of Recombination Fusion Protein MBP-BSH
2012, 33(7):  198-203.  doi:10.7506/spkx1002-6630-201207042
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The protein BSH, from Lactobacillu plantarum Y1, can form inclusion body when expressed in E. coli. The fusion tag IF2 can improve its solubility on the basis of our previous studies. In the present study, five fusion tags such as SUMO, GST, NusA, MBP and IF2 were used to improve the solubility of BSH. The results showed that an obvious protein band of MBP-BSH in the culture supernatant of recombinant E. coli Rosetta (DE3) (pLS932-BSH)was observed during the examination of SDS-PAGE. However, after induction, its solubility was greatly improved. Meanwhile, Ni-NTA resin exhibited better purification efficiency for MBP-BSH protein than Amylose resin. In addition, His-Tag linked at the C-terminal was favorable for the binding of nickel ions and as a result, MBP-BSH containing less impurities was obtained in a higher yield. The enzymatic activity of purified BSH was 2.4282 U/mg (115.14 AU/mg) as determined by ninhydrin color reaction.
Breeding of a Glucoamylase-Producing Strain of Rhizopus from Sweet Rice Wine Starter by Ultraviolet Radiation
2012, 33(7):  204-208.  doi:10.7506/spkx1002-6630-201207043
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An excellent strain of Rhizopus with high HE value and saccharification power from sweet rice starter was screened through flat plate primary screening and mutagenized by UV radiation. An excellent mutant strain with an HE value of 1.76 and a saccharification power of 1281 mg/(h ·g) was obtained, which were increased by 5.4% and 59.5% compared to those of the original strain, respectively. The optimal culture conditions for the mutant strain were culture temperature of 30 ℃, culture time of 3 days and corn flour concentration of 8 g/100 mL. Under the optimal conditions, the saccharification power of the screened strain was up to 1317 mg/(h ·g).
Sequence Analysis and Induced Expression of Epithiospecific Protein (ESP) from Brassica napus
2012, 33(7):  209-214.  doi:10.7506/spkx1002-6630-201207044
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In order to explore the effect of plant hormones and environment stress on the expression of Brassica napus ESP (BnESP), a cDNA encoding BnESP was cloned from Zhongshuang No. 9 by homology cloning approach. Sequence analysis showed that BnESP had 343 amino acids, and revealed 99% identity with brassica oleracea ESP and a high homology with nitrile-specific proteins (NSP), MY-binding-like protein (MBP) and JA inducible protein (JIP). Quantitative RT-PCR analysis showed that the expression of BnESP were promptly activated by MeJA and by wound treatment, and suppressed by Benzothiadiazole and by Sclerotinia sclerotiorum. This study suggests that ESP is a JIP and plays an important role in crossing-talk between SA and JA signaling and in the molecular network of oilseed rape response against S. sclerotiorum. Meanwhile, this study can provide a cue for producing health foods through attenuating the expression of ESP in cruciferous plants.
Ethanol Production by Fermentation of Corncob Hydrolysate with High Ratio of Hexose Prepared with Cellulase
2012, 33(7):  215-218.  doi:10.7506/spkx1002-6630-201207045
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Corncobs were crushed into 1-2 cm3, moistened by spraying 15g/100mL sulfuric acid, extracted for the removal of pentose, and then subjected to three-step countercurrent enzymatic hydrolysis and extraction. Hydrolysate with a hexose content of 10.26 g/100 mL was obtained. The fermentation of the hydrolysate by Saccharomyces cerevisiae HF2.0 for ethanol production was investigated. Placktt-Burman (PB) design was used to analyze the effects of MgSO4, KH2PO4, CaCl2, soybean meal hydrolysate, wheat bran hydrolysate, and yeast mud added to the hydrolysate on ethanol production. MgSO4, KH2PO4 and soybean meal hydrolysate were identified as the main influential factors. As determined by steepest ascent tests and central composite design, the best fermentation results were obtained when the concentrations of MgSO4, KH2PO4 and soybean meal hydrolysate were 0.045, 0.135 g/100 mL and 7.34 g/100 mL, respectively, resulting in an ethanol yield of 88.64 g/L.
Detection and Inactivation Modeling of Injured Aeromonas spp. in Thawing Pork
2012, 33(7):  219-222.  doi:10.7506/spkx1002-6630-201207046
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In order to detect injured Aeromonas spp. and establish its inactivation model on the surface of thawing pork, TSAYE containing 0.6% yeast extract was selected and TSAYE supplemented with NaCl at various concentrations (1.0%, 1.5%, 2.0%, 2.5% and 3.0%) were used to culture Aeromonas spp. The results showed that TSAYE supplemented with 1.5% NaCl was the optimal injury medium. The number of injured Aeromonas spp. colonies was counted based on difference between ordinary medium and injury medium. This study indicated that the restoration time of Aeromonas spp. during the thawing process of pork at 25 ℃ was approximately 75 min, and the inactivation curve could be fitted with Polynomial model (R2 =0.9937) and Boltzmann model (R2 =0.9884), respectively. Moreover, polynomial model could better fit the inactivation process. This result can provide a theoretical reference for the detection and prediction of injured Aeromonas spp. in meat and meat products.
Optimum Reaction Conditions for Rutin-Hydrolysis Enzyme (RHE) from Tartary Buckwheat Seeds and Inhibitory Effect of Cu2+ on Its Activity
2012, 33(7):  223-227.  doi:10.7506/spkx1002-6630-201207047
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A rutin-hydrolysis enzyme (RHE) was isolated from Fagopyrum tataricum (tartary buckwheat) seeds by extraction with 20 mmol/L acetate buffer acetate buffer, ammonium acetate fractionation, anion exchange chromatography and size exclusion chromatography. The molecular weight of RHE, as determined by SDS-PAGE, was 70 kD. The optimum hydrolysis pH was 5.0. The activity was not inhibited by an ethanol concentration of 20% in the reaction system, but an inhibitory rate above 90% was observed when ethanol concentration was higher than 50%. Fluorescence spectroscopic analysis indicated that Cu2+ could be bound to RHE at a molar ratio of 1:1 to generate a stable complex without fluorescence. Meanwhile, Cu2+ revealed an obvious inhibitory effect on the activity of RHE. These investigations provided a theoretical basis for future enzymatic preparation of quercetin.
Isolation, Identification and Lytic Characteristics of Listeria Phage
2012, 33(7):  228-231.  doi:10.7506/spkx1002-6630-201207048
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The aim of this study is to find a virulent Listeria phage that can inactivate Listeria monocytogenes (Lm) and achieve biological control of Lm in ready-to-eat foods using the phase. The phage was isolated from sewage by double layer plate assay with agar medium. The PEG/NaCl purified phage was analyzed by electron microscope after negative staining. Host range and biological characteristics of the phage were detected. In addition, the genomic DNA was analyzed by restriction enzyme digestion. Finally, the inactivation effect of the phage on Lm in ready-to-eat foods was evaluated. The isolated phage, named as LipG2-5, was a lytic member of the Siphoviridae family, which could effectively lyse its hosts. LipG2-5 had a wide range of hosts and revealed excellent tolerance to temperature and pH. According to genomic analysis by restriction enzyme digestion, LipG2-5 was double strand DNA phage. Lm in ready-to-eat foods could be inactivated within 24 h after LipG2-5 had been added into the foods.
Optimization of Phosphorylation Process for Exopolysaccharide from Lactococcus lactis subsp. lactis
2012, 33(7):  233-236.  doi:10.7506/spkx1002-6630-201207049
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One-factor-at-a-time and orthogonal array design methods were employed to optimize the phosphorylation of exopolysaccharide from Lactococcus lactis subsp. lactis. The amount of grafted phosphate was investigated with respect to several process conditions such as the amount of added phosphorylate, reaction temperature, reaction time and pH. The optimal phosphorylation conditions were determined as 1:6 of exopolysaccharide-to-phosphorylate ratio, 90 ℃ of reaction temperature, 4 h of reaction time and pH 6.0. Under these conditions, the amount of grafted phosphate was up to 1.639 mg/g.
Application of Osmotic Membrane for High Cell Density Culture of Selenium-Enriched Spirulina platensis
2012, 33(7):  237-241.  doi:10.7506/spkx1002-6630-201207050
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Selenium-enriched Spirulina platensis (Se-SP) was cultured in osmotic membrane tube (OT) and compared with air blowing bioreactor (AB) and shaking bottle (SB) cultures under the same conditions. Se supplementation was 100 μg/mL in the form of sodium selenite. Growth rate and maximum biomass were monitored and deduced according to dry weight at designated time points. Total Se, organic Se and inorganic Se in Se-SP as well as soluble and insoluble Se species in culture medium were determined using a fluorimeter. Total protein (TP), phycocyanin (PC), chlorophyll a (Chla), carotenoids (Caro), total polysaccharides (SPS) and sulfydryl groups (-SH) in Se-SP were also detected colorimetrically. The contents of inorganic carbon (IC) and dissolved organic carbon (DOC) in culture medium were measured using a TOC-5000A analyzer. The results showed that the maximum biomass of Se-SP was up to 9.6 g/L during cultivation in OT tube, which was increased by 3-5 fold compared with AB and SB cultures. The conversion rate of organic Se and the contents of TP, PC, Chla, SPS and SH group in Se-SP from OT culture were significantly higher than those from AB and SB cultures. Accordingly, OT culture produced lower IC residues and less accumulation of DOC, and higher soluble Se in the conditioned culture medium. In conclusion, OT can be used as a novel material for high cell density culture of Se-PS and it will have the advantages of high cell proliferation rate, high biotransformation of organic Se, high consumption of inorganic nutritional sources, low accumulation of organic carbon and less release of waster water.
Optimization of Batch Fermentation Conditions for Starter Cultures of Lactic acid Bacteria from Tibetan Kefir
2012, 33(7):  242-246.  doi:10.7506/spkx1002-6630-201207051
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Lactobacillus casei J1, capable of producing bile salt hydrolase, Streptococcus thermophilus Tx and Lactococcus lactis subsp. lactis P5 that were isolated from Tibetan Kefir, were used to explore the effect of fermentation conditions and growth factors on total viable count of lactic acid bacteria and ratio between Lactococcus and Lactobacillus. Meanwhile, key batch fermentation conditions were optimized by orthogonal array design method in a 5 L automatic fermentor. The results showed that the optimal fermentation conditions were fermentation 40 ℃ for 6 h in a medium at pH 6.5 added with carrot juice as growth factor at 5%. Under these fermentation conditions, the highest total viable count of lactic acid bacteria, 6.7 × 109 CFU/mL was obtained, which revealed an approximately 70-fold increase compared to pre-optimization.