Volume 31,Issue 5,2015 Table of Contents

1 Protective Effect of Eucalyptus Polyphenols on Acute Ethanol-induced Oxidative Damage in Rats

TANG Jie , CHEN Yun-jiao , CHEN Hong-zhang , ZHOU Ai-mei , ZHAO Li-chao , LIU Xiao-juan , CAO Yong , XIAO Su-yao

2015, 31(5):1-5. DOI: 10.13982/j.mfst.1673-9078.2015.5.001

[Abstract](1163) [HTML](0) [PDF 700.69 K](1189)

Abstract:
To evaluate the protective effect of Eucalyptus polyphenols on acute ethanol-induced oxidative damage in Kunming rats, Eucalyptus leaves were fed to Kunming rats, and a rat model of acute oxidative damage was established by ethanol feeding. The total antioxidant capacities (T-AOC) of the blood and liver, activity of each antioxidant enzyme, and liver tissue lesions of the rats were examined. Eucalyptus polyphenols enhanced the total antioxidant capacity, to a maximum of 33.12% and 56.83% in the serum and liver, respectively. The malondialdehyde (MDA) content was effectively reduced; the largest reductions in the serum and liver were 23.89% and 50.73%, respectively. The total superoxide dismutase (T-SOD) activity was increased to some extent. The glutathione peroxidase (GSH-Px) activity was decreased in the experimental group, but there was no significant difference from the positive control group. The observation of liver slices showed that the cells of three liver tissues from the experimental group were arranged regularly, the number of irregular vacuoles was reduced, and lobular inflammatory cell infiltrations and local necrosis were rarely found, indicating that acute ethanol-induced oxidative damage was inhibited and the liver tissue was protected by Eucalyptus polyphenols. In summary, Eucalyptus polyphenol confers in vivo antioxidant protection, which provides a research basis for the use of Eucalyptus polyphenols as an antioxidant.

2 Protective Effects of Crude Polysaccharide in Insect Tea against Carbon Tetrachloride-induced Hepatic Damage in Mice

WANG Rui , SUN Peng , ZHAO Xin

2015, 31(5):6-11. DOI: 10.13982/j.mfst.1673-9078.2015.5.002

[Abstract](986) [HTML](0) [PDF 836.20 K](1212)

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In this study, the protective effects of crude polysaccharides in insect tea (CPIT) against hepatic damage were investigated. Following treatment with CPIT, the serum levels of aspartate aminotransferase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), malondialdehyde (MDA) decreased and the glutathione (GSH) level increased in mice with carbon tetrachloride (CCl4)-induced hepatic damage. CPIT also decreased the MDA and triglyceride (TG) levels and increased the GSH level in the hepatic tissues of mice with CCl4-induced hepatic damage. In addition, these effects were more pronounced following 100 mg/kg CPIT treatment and were similar to those of the common hepatic therapeutic drug, silymarin. The levels of serum cytokines such as interleukin (IL)-6, IL-12, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ in CPIT-treated mice were lower than those of the control group, and the levels were similar to those of the normal and silymarin treatment groups. Histopathological results also showed that CPIT could reduce the CCl4-induced hepatic damage and protect the liver cells in mice. The inflammation-related genes, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 were down-regulated in CPIT treated mice, and were lower than that in the control group. The mRNA expressions of iNOS and COX-2 were further down-regulated by CPIT (100 mg/kg) compared to that by 50 mg/kg CPIT treatment. These experimental results have shown that CPIT had a good protective effect against hepatic damage.

3 Hepatoprotective Effect of Essential Oil of Rubia cordifolia

QUAN Mei-ping , TIAN Chen-rui

2015, 31(5):12-17. DOI: 10.13982/j.mfst.1673-9078.2015.5.003

[Abstract](1269) [HTML](0) [PDF 743.49 K](1115)

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Rubia cordifolia Linn (Rubiaceae) has been used as a traditional Chinese medicine for centuries and is officially listed in the Chinese Pharmacopoeia for the treatment of diverse diseases. The hepatoprotective effects of R. cordifolia essential oil extracted using hydrodistillation against carbon tetrachloride (CCl4)-induced hepatic damage in rats were evaluated. R. cordifolia essential oil was administered at doses of 100, 200, and 400 mg/kg orally and once daily for 21 days before CCl4 administration. CCl4 treatment significantly increased the activities of various serum enzymes and markers, such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol (TC), and total triglycerides (TC), which were dose-dependently restored to normal levels after the administration of R. cordifolia essential oil. The liver and spleen indices, as well as catalase (CAT), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) levels in the mice treated with the essential oil were similar to those of the normal control group. These results, together with the results of liver histopathology, showed that R. cordifolia essential oil exhibited hepatoprotective effects against CCl4-induced injury, and these effects were comparable to the effects of biphenyl dimethyl dicarboxylate (DDB) used as standard reference. The results of this study strongly indicate that R. cordifolia essential oil has a potential hepatoprotective action against CCl4-induced hepatic damage in rats.

4 Relaxation Characteristics of Water-ethanol System by Low-field-nuclear Magnetic Resonance

LIU Min , WANG Xin , LIU Bao-lin

2015, 31(5):18-24. DOI: 10.13982/j.mfst.1673-9078.2015.5.004

[Abstract](1458) [HTML](0) [PDF 1.08 M](1439)

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The 1H LF-NMR and molecular simulation methods were adopted to investigate the water-ethanol solution with different water concentrations. The results indicated that the interaction between hydrogen bond association and water content in water-ethanol solution can cause the relaxation characteristics change. In low concentration of water-ethanol (0%≤XW≤ 10%) system, when adding water to ethanol, part of the water and ethanol tend to form H2O(EtOH)n clusters through hydrogen bonding, multi-component relaxation time T21 at first increases, then decreases and remains relatively constant, while T2W decreased. For the high concentration of water-ethanol (10%≤XW≤100%) system, after minor reduction, T2W increased when the water concentration increased. When 10%≤XW＜30%, due to ethanol self-association and corresponding (H2O)m(EtOH)n clusters, T21 decreases after showing a relatively constant stage. When 30%≤XW≤60%, the saturation of single water molecule combined with ethanol self-association clusters could be reached, T21 turned to be relatively constant. When 60%≤XW≤100%, water self-association would be found and (H2O)m(EtOH)n clusters dissociated, then T21 appeared to increase.

5 Spectroscopic Studies of Interaction between Hapten and Monoclonal Antibody (McAb) against Iso-tenuazonic Acid

WANG Ya-li , WANG Feng , WANG Hong , YANG Jin-yi , XU Zhen-lin , SHEN Yu-dong , XIAO Zhi-li , LEI Hong-tao , SUN Yuan-ming

2015, 31(5):25-30. DOI: 10.13982/j.mfst.1673-9078.2015.5.005

[Abstract](1406) [HTML](0) [PDF 994.23 K](1185)

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The interaction between iso-tenuazonic acid (ITeAH) hapten and monoclonal antibody (McAb) against ITeAH was studied by ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, and circular dichroism (CD). Fluorescence results were verified using enzyme-linked immunosorbent assay (ELISA). The results suggested that fluorescence intensity of McAb was quenched by ITeAH, while the quenching mechanism was based on static quenching and nonradioactive energy-transfer theory. The binding constants (Ka) at 298, 310, and 318 K were calculated as 1.9 × 106, 1.6 × 106, and 1.4 × 106 L/moL, respectively, consistent with the values determined by ELISA. The binding point (n) number was about 1, while the average binding distance (r) was 3.35 nm. Furthermore, thermodynamic parameters evaluated during the binding process showed that the binding force between ITeAH and McAb constituted of mainly electrostatic attraction, which affected the extent of binding between ITeAH and McAb, when studied under different pH conditions by using ELISA. The synchronous fluorescence spectra indicated that the addition of ITeAH did not change the microenvironment of tyrosine and tryptophan residues in the McAb, and that the binding site for ITeAH was more inclined to tyrosine residues. CD analysis showed significant changes in the secondary structure of McAb after interaction with ITeAH.

6 Mechanism and Antibacterial Activity of Cinnamaldehyde against Escherichia coli and Staphylococcus aureus

ZHANG Yun-bin , LIU Xiao-yu , JIANG Ping-ping , LI Wei-di , WANG Yi-fei

2015, 31(5):31-35. DOI: 10.13982/j.mfst.1673-9078.2015.5.006

[Abstract](2964) [HTML](0) [PDF 626.72 K](2547)

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The antibacterial activity of cinnamaldehyde against Escherichia coli and Staphylococcus aureus, and the underlying mechanism were evaluated. Antibacterial activity was determined based on the diameter of inhibition zone (DIZ) that was measured by the disc diffusion method, and by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), measured to a series of doubling dilutions. Furthermore, the antibacterial mechanism was explored using scanning electron microscopy, cell membrane permeability and integrity, as well as membrane potential. The DIZ values of E. coli and S. aureus were 21.75 mm and 29.37 mm, respectively. The MIC (0.25 μL/mL) and MBC values (0.5 μL/mL) were the same for both bacteria. Scanning electron microscope images showed that the structure of the bacterial cell was damaged by cinnamaldehyde with consequent morphologxical changes. With increasing concentration of cinnamaldehyde, the relative electric conductivity increased rapidly, indicating that the permeability of the cell membrane was affected by cinnamaldehyde. Furthermore, the multi-fold increase in nucleic acids and proteins in the cell suspension revealed that cinnamaldehyde damaged the integrity of the bacterial membrane, decreased the membrane potential, and affected the metabolic activity, thus inhibiting bacterial growth. Cinnamaldehyde exerts its main effect on the bacterial cell membrane, and is suitable as a natural preservative to inhibit the growth of food-spoilage and pathogenic bacteria, thus extending the shelf life of food.

7 Changes in Morphological Characteristics, Crystallinity, and Thermodynamic Properties of Starches during Deep-fat Frying

ZHANG Ling-wen , JI Hong-fang , LOU Shi-yao , MA Han-jun , YANG Ming-duo

2015, 31(5):36-42. DOI: 10.13982/j.mfst.1673-9078.2015.5.007

[Abstract](1348) [HTML](0) [PDF 1.08 M](1528)

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A deep-fat-frying (DFF) model was employed to study the changes in morphological characteristics, crystal structure, and thermodynamic characteristics of starches during the DFF process using advanced analytical methods, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffractometry (XRD). The SEM results indicated that there were significant changes in the morphological characteristics of starch granules with increasing frying temperature and time. During the initial frying, the granules expanded. As frying proceeded, the starch granules disintegrated, moved close to each other, and ultimately merged to form large aggregates. Simultaneously, the iodine blue value of starch decreased gradually. The DSC results showed that a certain degree of gelatinization occurred in starch molecules during the first 25 s and 50 s of initial frying; the starch was completely gelatinized after 75 s and 100 s of initial frying, and an amylose-lipid complex was formed after 20 s of repeated frying. XRD indicated that after 75 s of initial frying, the degree of crystallinity of the starch was higher than that after 25 s of initial frying. After 40 s of repeated frying, the crystallinity of starch decreased with frying time.

8 Ethanol Treatment Enhances Expression of Thermostable Direct Hemolysin Gene by Vibrio parahaemolyticus

WU Kui , WU Qing-ping , ZHANG Ju-mei , LE Xian-song

2015, 31(5):43-48. DOI: 10.13982/j.mfst.1673-9078.2015.5.008

[Abstract](1029) [HTML](0) [PDF 991.39 K](1077)

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The effect of ethanol on thermostable direct hemolysin (TDH) production and corresponding tdh gene expression by Vibrio parahaemolyticus was studied. Two tdh-positive V. parahaemolyticus strains, ATCC33847 and SZ32 were separately treated with 0.5%, 1.0%, 2.0%, 4.0%, and 8.0% ethanol solutions. The effects on aerobic or anaerobic growth of V. parahaemolyticus were monitored, while changes in TDH production and tdh gene expression were studied with 1.0% ethanol treatment. TDH concentration in V. parahaemolyticus culture supernatant was quantitatively analyzed using a TDH detection kit (KAP-RPLA, Denka Seiken Co., Japan), while tdh gene expression was analyzed by real-time fluorescence-based quantitative polymerase chain reaction. The results showed that V. parahaemolyticus growth was not influenced by the presence of ethanol at low concentrations (0.5%, 1.0%, and 2.0%). On the other hand, 4.0% and 8.0% ethanol caused significant and total inhibition of bacterial growth, respectively. With ethanol treatment, TDH titers of culture supernatants showed a significant increase under aerobic as well as anaerobic conditions and intracellular tdh expression was also elevated. Moreover, ATCC33847 strain showed an increase in tdh expression by 6.6- and 5.7-fold, while SZ32 strain showed an increase by 5.9- and 8.6-fold under aerobic and anaerobic conditions, respectively. Thus, ethanol treatment enhanced tdh gene expression, which may have resulted in an increase in TDH production. The effects of methanol, ethanol, and n-propanol on tdh gene expression were also compared and the results showed increased tdh gene expression by all three alcohols, however, the effects were not significantly different.

9 Regulation of 2,4-dinitrophenol and Adenosine Triphosphate on Disease Development, Energy Status, and Respiratory Metabolism of Phomopsis longanae Chi-infected Longan Fruit

CHEN Meng-yin , LIN He-tong , HUNG Yen-Con , ZHANG Shen , LIN Yi-fen , CHEN Yi-hui

2015, 31(5):49-58. DOI: 10.13982/j.mfst.1673-9078.2015.5.009

[Abstract](1359) [HTML](0) [PDF 1008.87 K](1310)

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The DNP treatment increased the contents of nicotinamide adenine dinucleotide (NAD) and reduced NAD (NADH), decreased NAD kinase (NADK) activity in the pericarp, and led to lower contents of NAD phosphate (NADP) and reduced NADP (NADPH) and a lower level of energy charge. By contrast, ATP treatment reduced the disease index and pericarp-browning index for P. longanae-inoculated longans, and decreased the respiration rate of the fruit as well as the activities of COX, AAO, and PPO in the pericarp. Additionally, ATP treatment reduced the contents of NAD and NADH, increased NADK activity in the pericarp, and led to higher contents of NADP and NADPH and a higher level of energy charge. These results suggest that DNP treatment accelerates the development of postharvest disease in P. longanae- infected longans through exacerbating energy deficiency, decreasing pentose phosphate pathway activity in respiration and metabolism, and increasing the activities of respiratory terminal oxidases such as COX, AAO, and PPO. On the other hand, ATP treatment likely delayed the development of postharvest disease in P. longanae-infected longans through maintaining a relatively high level of energy charge, increasing PPP activity in respiration and metabolism, and decreasing the activities of respiratory terminal oxidases such as COX, AAO, and PPO.

10 Molecular Structure and Rheological Properties of Common Microcapsule Wall Materials

XIE Yan-li , ZHU Xiao-lu , WANG Fen

2015, 31(5):59-64. DOI: 10.13982/j.mfst.1673-9078.2015.5.010

[Abstract](1170) [HTML](0) [PDF 1007.83 K](1627)

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The molecular structure and rheological properties of five common materials, namely modified starch, gum arabic, gelatin, soybean protein isolate (SPI), and carboxymethyl cellulose (CMC), which are used to prepare microcapsule walls by spray drying were studied. The molecular weight distributions of the materials were determined by gel permeation chromatography (GPC), the functional groups and secondary structures were determined by Fourier transform infrared spectroscopy, while the apparent viscosity, dynamic modulus, and creep compliance were measured by a rotational rheometer. The results showed shear-thinning behavior in all five wall material pastes. The apparent viscosity of wall material pastes gradually decreased with temperature. The elastic modulus G' and viscous modulus G' increased with increasing oscillation frequency. With constant time, creep compliances J(t) values were in the following order: modified starch > gum arabic > gelatin > CMC > SPI. The higher the molecular weight, the greater the apparent viscosity. For the wall materials with molecular weight in the same order of magnitude, the non-Newtonian shear-thinning phenomenon was more obvious with a wider molecular weight distribution. Additionally, the apparent viscosity was higher when the molecular structure was more rigid and molecules had a higher polarity.

11 Adsorption Characteristics of Affinity-ultrafiltration Escort to His-tagged Recombinant AxCeSD

LIU Guang-yi , LIU Guang , CHEN Ping , LI Lin , HU Song-qing

2015, 31(5):65-70. DOI: 10.13982/j.mfst.1673-9078.2015.5.011

[Abstract](874) [HTML](0) [PDF 772.17 K](1004)

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N-terminal histidine (His)6-tagged recombinant protein AxCeSD was purified by affinity chromatography. The affinity- ultrafiltration escort, Cu2+-IDA-Dextran T2000 specifically able to adsorb the His-tag of recombinant protein, was synthesized using water-soluble Dextran T2000 as the matrix (molecular weight 2000 ku), iminodiacetic acid as the chelating agent, and Cu2+ as the affinity ligand. The effects of pH, ionic strength, adsorption time, and reaction temperature on the adsorption characteristics of the escort with N-terminal His-tagged recombinant AxCeSD were investigated. The results showed that the adsorption capacity of the affinity-ultrafiltration escort for AxCeSD increased with the increases in pH and temperature within a certain range, but decreased as the ionic strength increased. Moreover, the adsorption equilibrium could be achieved within 30 min. The isotherm adsorption curve was fitted to the Langmuir model. The maximum adsorption yield was 125.15 mg/g and the dissociation constant was 3.259×10-6 mol/L, indicating that the specific adsorption of the affinity-ultrafiltration escort to recombinant AxCeSD was mainly from chelation.

12 Gene Cloning and Expression of the Catalytic Region of Glycosyltransferase B from Streptococcus mutans UA159

YU Jia-nan , TIAN Jing , LI Bao-li , ZHANG Yong-xia , LIU Rui

2015, 31(5):71-75. DOI: 10.13982/j.mfst.1673-9078.2015.5.012

[Abstract](1333) [HTML](0) [PDF 954.65 K](1074)

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Water-soluble, catalytic region of glycosyltransferase B (GTFB/CAT) with good bioactivity, was obtained from Streptococcus mutans UA159 (Ingbritt c). The primers were designed based on the conservative sequences of GTFB gene in S. mutans UA159 (Ingbritt c), as listed in the National Center for Biotechnology Information database and the sequences at the ends of GTFB/CAT. The GTFB/CAT gene was amplified by polymerase chain reaction from S. mutans UA159 (Ingbritt c) and then cloned into vector pET-28b(+) to construct the recombinant pET-28b(+)-GTFB/CAT, which was then transformed into Escherichia coli BL21. Optimal induction conditions were as follows: temperature at 37 ℃ or 30 ℃; time for 4 h; 1 mmol/L of IPTG for induction. The product was purified by Ni2+-NAT resin-affinity chromatography and insoluble inclusion body GTFB/CAT was obtained. Subsequent denaturing and refolding produced the water-soluble protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a clear band at 44 ku, which is consistent with the expected molecular weight, and the purity of protein was approximately 80%. The specific activity of the protein was found to be 1.66 IU/mg by the Somogyi method. The results indicated that water-soluble proteins with biological activity were obtained through the expression of cloned GTFB/CAT gene in Escherichia coli BL21. This will lay a basis on further study of GTF antagonists and their effect as well as mechanism of action in prevention of dental caries.

13 Microbial Transformation of Polydatin by Endophytic Fungi Isolated from Polygonum cuspidatum and Antioxidant Activity of the Products

LONG Li-lin , YI You-jin , ZHOU Jin-wei , CHENG Yuan-du , XIA Yan-bin

2015, 31(5):76-83. DOI: 10.13982/j.mfst.1673-9078.2015.5.013

[Abstract](1478) [HTML](0) [PDF 928.59 K](1117)

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The microbial transformation of polydatin by endophytic fungi isolated from Polygonum cuspidatum and the antioxidant activity of the transformed products were investigated. Screening of endophytic fungi for microbial transformation of polydatin was carried out using thin-layer chromatography (TLC). Fungi were identified by morphological characteristics and analysis of the ITS-5.8S rDNA region. Polydatin transformation products were isolated and purified by macroporous adsorption resin, preparative TLC, and high-performance liquid chromatography. Using vitamin C (Vc), BHT, polydatin, and five types of polydatin derivatives as standard substances, the DPPH? and OH? radical-scavenging capacities of transformation products were investigated. An endophytic strain J3, capable of transforming polydatin was identified preliminarily as Aspergillus fumigatus (Genbank accession number: KM434883) by morphological characteristics and analysis of the ITS-5.8S rDNA region (573 bp). The transformed product, A-2, showed DPPH? and OH? radical-scavenging capabilities in vitro, while the OH? radical-scavenging ability was higher than that of substrate polydatin. However, transformed product, A-1, did not show DPPH? and OH? radical-scavenging capabilities in vitro. Endophytic fungus Aspergillus fumigatus isolated from Polygonum cuspidatum was thus shown to transform polydatin into products with antioxidant property.

14 Emulsifying Properties of Soy Protein Isolate at pH near the Isoelectric Point

LIU Yong-chuang , YANG Xiao-quan , GUO Jian , ZHOU Qian

2015, 31(5):84-89. DOI: 10.13982/j.mfst.1673-9078.2015.5.014

[Abstract](1509) [HTML](0) [PDF 944.73 K](1663)

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At pH near the isoelectric point (pI), soy protein exhibits reduced electric charge and enhanced hydrophobic interactions, causing aggregation that results in poor solubility. Therefore, the emulsifying properties of soy protein under these conditions have received little attention. In this study, a soy protein isolate (SPI) was used to prepare stable emulsions at pH 5.0, which was near the pI, and pH 7.0, which was far from the pI. Soy protein aggregate particles were used to stabilize the emulsion. The interfacial properties of SPI under such conditions and the storage stability of the resulting emulsions were investigated. The results indicated that the solubility of SPI was 4.70 ± 0.15% at pH 5.0, which was much lower than that at pH 7.0 (93.28 ± 1.89%). At a concentration of 0.5% SPI, higher surface tension was observed at pH 5.0 when compared with that at pH 7.0. Moreover, the surface protein adsorption capacity of the emulsion prepared at pH 5.0 was 87.04 ± 1.28%, which was significantly higher than that prepared at pH 7.0 (36.15 ± 1.48%). After two months of storage, the average size of the droplets in the emulsion prepared at pH 5.0 was 63.15 ± 0.30 μm, which was similar to that of the droplets in freshly prepared emulsion (62.36 ± 0.41 μm). In the case of the emulsion prepared at pH 7.0, the average size of the droplets increased from 45.78 ± 0.38 to 55.19 ± 1.86 μm after storage for two months. Thus, we conclude that SPI prepared at pH near its isoelectric point can be used as an efficient emulsifier.

15 Microfloral Diversity and Dynamics in the Sourdough of Northeast Sticky Bean Buns and Homemade Sourdough

YAO Di , SUN Da-qing , LI Hong-fei

2015, 31(5):90-95. DOI: 10.13982/j.mfst.1673-9078.2015.5.015

[Abstract](1328) [HTML](0) [PDF 604.23 K](1196)

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The Northeast sticky bean bun is a popular traditional food in Northeast China with a long history and unique flavor. However, little research has been conducted on the sourdough used to prepare Northeast sticky bean buns. In this study, the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique was employed to study the diversity and dynamic changes of the microflora in homemade sourdough and samples of sourdough used for Northeast sticky bean buns collected from different Northeast provinces. There were six genera and 11 species of bacteria identified from the sourdough of Northeast sticky bean buns, and Lactobacillus fermentum and Lactobacillus plantarum were estimated to be the dominant species during fermentation. Moreover, three genera and four species of fungi were identified from the sourdough of Northeast sticky bean buns, and Saccharomyces cerevisiae was estimated to be the dominant species during fermentation. The microfloral diversity of the homemade sourdough was relatively rich. However, the microfloral diversity and dominant bacterial species continuously changed at different fermentation stages.

16 Experimental Study on Stress Relaxation Characteristics and Associated Damage of Litchi

JIANG Zhi-lin , CHEN Yan , TAN Jian-hao , LI Bo , ZOU Xiang-jun

2015, 31(5):96-101. DOI: 10.13982/j.mfst.1673-9078.2015.5.016

[Abstract](1040) [HTML](0) [PDF 765.67 K](1312)

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In order to investigate the stress relaxation characteristics of litchi as well as the damage patterns induced in the relaxation condition, a compression stress relaxation test and statistical analysis on the associated damage were carried out under different experimental conditions. The stress relaxation model was confirmed, and the influence of experimental factors on model parameters and litchi damage was analyzed. The results indicated that the stress relaxation characteristics of litchi could be described by a five-element generalized Maxwell model with a coefficient determination (R2) of 0.98. Within the test range, deformation did not significantly affect the elastic modulus of the model, but loading direction had a significant impact. All of the experimental factors affected the relaxation time and viscosity coefficient of the model, and although the elastic moduli and relaxation time were not significantly correlated, each factor showed a significant correlation independently. The prominent damage factors were in the order of compression deformation, loading direction, loading rate, and relaxation time. For the increment of 1 mm in deformation, 10 s in relaxation time, and 10 mm/s in load rate, the average increase of the absorbed energy in litchi were 3.3 mJ, 0.26 mJ, and 0.2 mJ, respectively. The viscosity coefficient was not significantly correlated with the absorbed energy in litchi. With the increase of compression deformation, absorbed energy and the damage degree of litchi also increased; there was an approximate quadratic relationship between damage degree and absorbed energy in litchi.

17 Changes in and Correlations between Textural Properties and Chemical Components of Grass Carp during Broad Bean Feeding

AN Yue-qi , XU Wen-jie , LI Dao-you , XONG Shan-bai

2015, 31(5):102-108. DOI: 10.13982/j.mfst.1673-9078.2015.5.017

[Abstract](1169) [HTML](0) [PDF 856.91 K](1236)

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Changes in textural properties and chemical components of grass carp during broad bean feeding and their correlations were investigated. The start and end times of grass carp crisping were determined. Experimental results indicated that the hardness and chewiness of grass carp increased significantly with the duration of feeding. After 80 days of feeding, hardness was equivalent to that of common carp and after 100 days of feeding, it was of crisping standard. Chewiness and springiness were stable after 80 days of feeding, wherein the springiness of the dorsal muscles increased significantly during feeding. The maximum level of resilience was at 40 days of feeding and subsequently, decreased significantly. Content of crude protein, matrix protein, collagen, and alkali-soluble protein of grass carp dorsal muscle increased significantly during feeding. Moisture content showed a decreasing trend with maximum level at 20 days of feeding. Content of crude fat, soluble solid, water-soluble protein, and salt-soluble protein of grass carp dorsal muscle were maximum at 40 to 60 days of feeding. Variations in chemical components of grass carp abdominal muscle were similar to that of the dorsal muscle. Correlational analysis showed that changes in the textural properties of grass carp correlated significantly with changes in crude protein, salt-soluble protein, matrix protein, and collagen content.

18 Major Components and Functional Properties of Changbai Mountain Hazelnut Protein Isolate

DU Yan-ping , LIU Chun-lei , MIN Wei-hong , LI Jing-jing , LIU Jing-sheng

2015, 31(5):109-115. DOI: 10.13982/j.mfst.1673-9078.2015.5.018

[Abstract](1019) [HTML](0) [PDF 880.53 K](1224)

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Proteins were isolated from Changbai Mountain hazelnut and their functional properties were analyzed in this study. Osborne protein extraction was performed to obtain albumin, globulin and glutenin with purities of 72.32%, 68.72%, and 40.60%, respectively, while an alkali-solution and acid-isolation method was used to obtain a protein isolate with a purity of 90.31%. Functional properties of the four protein types were comparatively analyzed. The results showed that the protein isolate contained the highest total sulfhydryl content (6.71 μmol/g), while albumin extract contained the highest content of exposed sulfhydryl and disulfide groups (2.28 and 60.40 μmol/g, respectively). The emulsifying ability and emulsion stability of all four proteins showed opposite trends with increasing pH. For instance, at pH 5, the emulsifying ability was the lowest, while emulsion stability was the highest. Under acidic or alkaline conditions, emulsifying ability was good, while emulsion stability was poor. The water and oil absorption capacities of glutenin were the highest at 3.40 and 2.52 mL/g, respectively, while those of albumin were the lowest at 0.63 and 1.79 mL/g, respectively. Solubility, emulsifying ability, and emulsion stability trends with changes in pH were similar and the isoelectric point was at the minimum for all four protein types. The total amino acid content in albumin, globulin, glutenin, and the protein isolate was 29.83%, 32.14%, 35.23%, and 30.32%, respectively. Except for methionine, the amino acid content for the other three protein types met the FAO/WHO regulations for required intake in adults.

19 Effect of a Hydroxyl Radical-generating System on the Characteristics of Proteins from Hairtail (Trichiurus haumela)

JIANG Qing-qing , LU Jun , HU Yue , CHEN Shi-guo , YE Xing-qian , HU Ya-qin

2015, 31(5):116-123. DOI: 10.13982/j.mfst.1673-9078.2015.5.019

[Abstract](1319) [HTML](0) [PDF 909.86 K](1450)

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General nutritional components and amino acid composition from fresh hairtails were investigated by national standard methods. The results showed that in fresh hairtails, crude protein accounted for 88.19% of dry weight, the essential amino acid index (EAAI) was 1.64, and the amino acid score (AAS) was relatively high, implying high nutritional value. In the simulated system, the value of thiobarbituric acid-reactive substances (TBARS), which is an indicator of lipid oxidation, as well as carbonyl and sulfhydryl content, which are indicators of protein oxidation, were measured. Additionally, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was used to explore the effect of lipid oxidation and protein oxidation on protein solubility and digestibility. With prolonged oxidation time, TBARS value and carbonyl content of myofibrillar proteins increased significantly (p < 0.05), while those of sulfhydryl content dropped after the initial increase and the peak value was reached after 1 h oxidation. The SDS-PAGE pattern showed that aggregation of myosin heavy chains occurred after oxidation. With increasing degree of oxidation, the solubility of proteinates decreased significantly (p < 0.05), while the in vitro protein digestibility of hairtail reached the highest value (92.09%) after 1 h of oxidation and then decreased gradually. The results indicated that the hydroxyl radical-generating system promoted lipid and protein oxidation in hairtail, and caused a decline in the solubility of proteinates, but moderate oxidation enhanced in vitro protein digestibility.

20 Physicochemical Properties and Antioxidant Activity of Chlorogenic Acid-lecithin Complex

GENG Sheng , MA Yu-xiang , MO Hai-zhen , MA Han-jun , GE Xiao-hong , LI Gang , LIU Ben-guo

2015, 31(5):124-129. DOI: 10.13982/j.mfst.1673-9078.2015.5.020

[Abstract](1256) [HTML](0) [PDF 866.13 K](1293)

Abstract:
Chlorogenic acid exhibits bioactivities including antioxidant, antibacterial, and antitumor. Therefore, it has several applications in the food industry; however, its scope is limited by low liposolubility. Here, chlorogenic acid-lecithin complex was prepared by a solvent method and physicochemical properties were studied by ultraviolet-visible spectrometry, infrared spectrometry, scanning electron microscopy, differential scanning calorimetry, and X-ray diffractometry. Additionally, the antioxidant activity of the complex were also evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay and Rancimat test. The results indicated that the physical phase of chlorogenic acid significantly changed after forming a complex with lecithin, where it remained in an amorphous state and completely dispersed in lecithin. The solubility of chlorogenic acid in n-octanol at 25 ℃increased from 34.73 to 4715.84 μg/mL after complex formation, and the liposolubility of chlorogenic acid significantly improved. The antioxidant assay showed that the DPPH scavenging activity of the complex was inferior to that of chlorogenic acid and BHT. On the other hand, antioxidant activity of the complex in oil was close to that of BHT and superior to that of chlorogenic acid, which suggested that antioxidant activity of chlorogenic acid in oil could be significantly improved by forming a complex with lecithin.

21 In Vitro Antioxidant Activity of Abalone Viscera Hydrolysates Isolated by Ultrafiltration

YE Yan-jun , CHEN Jun , WENG Wu-yin

2015, 31(5):130-136. DOI: 10.13982/j.mfst.1673-9078.2015.5.021

[Abstract](1381) [HTML](0) [PDF 810.34 K](1407)

Abstract:
Abalone viscera hydrolysates were separated by ultrafiltration, and the chemical composition and antioxidant activity of the hydrolysates in different ranges of molecular-weight were investigated. Four fractions (FA, FB, FC, and FD) were obtained by membrane ultrafiltration with molecular weight cut-off (MWCO) of 10000, 3000, and 500 u. In fraction FA, total sugar and protein contents were 34.06% and 17.20%, respectively. However, fractions FB, FC, and FD were mainly composed of proteins, and the free amino acid content was 23.20, 25.47, and 28.68 g/10 g, respectively. Based on the results from tricine-sodium dodecyl sulfate polyacrylamide gel electrophoresis and β-elimination, the high molecular-weight fraction (HMWF) of FA in the spacer gel contained glycoproteins with N-glycosidic linkage, and components with molecular weight of 25 ku were proteins. Gel permeation chromatography data indicated that molecular weight of the fractions FB, FC, and FD were each approximately 300 u. Additionally, the result of in vitro antioxidant assay indicated that fraction FA had a relatively strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging ability and reducing power at low concentration. When the concentration was increased above 5 mg/mL, there were no significant differences in the DPPH radical-scavenging abilities among these fractions, but the reducing power of fraction FA was lower than that of other fractions. In both, low and high concentrations, the hydroxyl radical-scavenging abilities of fractions FB, FC, and FD were stronger than that of FA.

22 Antioxidant Activity of (-)-Epigallocatechin Gallate-phospholipid Complex

CHEN Jin-yu , ZHANG Xin , WU Zu-fang , WENG Pei-fang

2015, 31(5):137-143. DOI: 10.13982/j.mfst.1673-9078.2015.5.022

[Abstract](1166) [HTML](0) [PDF 1.06 M](1495)

Abstract:
The in vitro antioxidant activity of (-)-epigallocatechin gallate (EGCG)-phospholipid complex (EPC) was studied. First, EPC was prepared by dissolving EGCG and soybean lecithin in ethanol. High-performance liquid chromatography showed that the complexation rate of EGCG in EPC was more than 99%, and the structure of EPC was characterized by ultraviolet spectroscopy, infrared spectroscopy, and X-ray powder diffractometry. The in vitro antioxidant activity of EPC, as evaluated by diphenylpicrylhydrazyl and ferric reducing ability of plasma and Trolox equivalent antioxidant capacity methods, was found to be significantly higher (p < 0.05) than that of VE. Indicators reflecting the oxidation of soybean oil at different storage times (3, 6, 9, 12, and 15 days) were also evaluated after the addition of EPC. The results showed that the inhibitory effect of EPC on the oxidation of soybean oil was dose-dependent as well as significantly higher (p < 0.05) than that of butylated hydroxytoluene after a 15-day storage. These results suggest that the prepared EPC has strong antioxidant activity and can effectively inhibit the oxidation of soybean oil.

23 Mutation Screening to Detect Strains that Produce Bacterial Cellulose at High Yield by N+ Ion Beam Irradiation

ZHANG Wen , LI CHENG-tao , LI Yan-jun , LIU DONG-wen

2015, 31(5):144-149. DOI: 10.13982/j.mfst.1673-9078.2015.5.023

[Abstract](1025) [HTML](0) [PDF 939.29 K](1219)

Abstract:
In order to obtain strains that produce a high yield of bacterial cellulose (BC) and improve the properties of BC, N+ ion beam irradiation was used to conduct mutation screening in Acetobacter xylinum. A plate-96-well plate-cuvette screening system was established, in which parameters such as the size, smoothness, density, wettability and rate of the colony formation, pliability, and yield of the BC film were chosen as the screening criteria. Two target strains, 5D and 2D, were obtained that could produce BC with improved product properties at an enhanced yield. The BC yields of 5D (4.84 g/L) and 2D (4.53 g/L) were 89.06% and 76.95% higher than that of the original strain, respectively. Fourier transform-infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and a tensile test were used to study the properties of BC. The results showed that the BC produced by the target strains had higher crystallinity and tensile strength, a smaller elongation at break, a denser layered structure, and a clearer three-dimensional network structure compared with the product from the original strain, indicating that they had superior mechanical properties. The success in obtaining the target strains lays a foundation for improving the BC yield and properties.

24 Characteristics of Mint Essence Microcapsule Prepared by Emulsification-internal Ionotropic Gelation

WU Yan , ZHANG Hui-qin , GAO Hao-feng , ZHU Hu-jian , AI Lian-zhong , WANG Guang-qiang , XIA Yong-jun

2015, 31(5):150-156. DOI: 10.13982/j.mfst.1673-9078.2015.5.024

[Abstract](1983) [HTML](0) [PDF 952.65 K](1429)

Abstract:
Mint essence is widely used while preparing food, however, characteristics such as volatility and environmental sensitivity reduce the duration of its aroma and shelf life. Spray drying is the most common method to prepare essence microcapsules, but the heat treatment following spray drying results in partial loss of the essence. Therefore, it is necessary to develop a preparation method that can be carried out at room-temperature. In this study, an emulsification-internal ionotropic gelation method was used to prepare mint essence microcapsules at room temperature, using calcium alginate to coat the core containing mint essence. The resultant product was spherical, with uniform particle size distribution. Fourier transform infrared spectroscopy was used to confirm that the mint essence was adequately embedded within calcium alginate. Embedding ratio and particle size distribution using single factor and orthogonal experiments were carried out to determine optimal conditions, as follows: mass ratio of the core material and sodium alginate was 1:3; mass fraction of sodium alginate was 4%; amount of added Span-80 was 2%; molar ratio of glacial acetic acid and calcium carbonate was 2:1; mass ratio of calcium carbonate and sodium alginate was 7:40; and emulsification time was 15 minutes. Under these optimized conditions, encapsulation efficiency was 59.63 ± 0.47%, and the average particle diameter was 290.70 μm. Thermal stability was measured using differential scanning calorimetry and it was found that the microcapsules contributed to sustained release of the essence.

25 Separation, Purification, Cellular Antioxidant Activity, and In Vitro Bile Salt-Binding Ability of Dihydromyricetin

MA Ling , YANG Ji-guo , LIAO Wen-zhen , YIN Xue-ru , QIU Xiao-bin , TAN Kai-yuan , NING Zheng-xiang

2015, 31(5):157-162. DOI: 10.13982/j.mfst.1673-9078.2015.5.025

[Abstract](1007) [HTML](0) [PDF 777.49 K](1416)

Abstract:
Dihydromyricetin (DMY) was separated and purified from Ampelopsis using water extraction and recrystallization. The crystal morphology was analyzed by scanning electron microscopy and the cellular antioxidant activity (CAA) was determined by CAA assay. Meanwhile, in vitro bile salt-binding ability of DMY was determined by in vitro simulation of the human gastrointestinal environment. The results showed that separation and purification techniques with multiple recrystallizations produced high-purity DMY, and the yield was 43%. An EC50 of 6.17 ± 0.08 μmol/L and CAA of 74.90 ± 0.90 μmol QE/100 μmol were obtained, which indicated that DMY exhibited strong CAA. DMY also exhibited relatively strong binding to sodium cholate, sodium glycocholate, and sodium taurocholate, with binding capacity of 1.24 ± 0.02, 0.97 ± 0.06, and 1.06 ± 0.002 μmol/m1, respectively, with strongest binding capacity for free sodium cholate.

26 Testing Apparatus Design for Tomato Pomace Separation after Tomato Sauce Processing

RAN Bing , WANG Li-hong , KAN Za , LI Cheng-song , DU Xiang

2015, 31(5):163-168. DOI: 10.13982/j.mfst.1673-9078.2015.5.026

[Abstract](1002) [HTML](0) [PDF 814.39 K](1310)

Abstract:
To optimize the performance of separating equipment to process tomato pomace in terms of separation rate and degree of separation cleanliness of tomato seeds and skin, a double-action pomace-separation test apparatus was developed. Core operating components in this design included a centrifugal screening device, inclined plate sedimentation unit, and a feeding system. The combined modular design showed installation and replacement compatible with the test apparatus, while structure and motion parameters of the operating components were fully adjustable. The relationship model between various factors under different working conditions and quality indices (such as the separation rate and degree of separation cleanliness) was established, and flow field distribution in the settling chamber was acquired. Verification test results showed that the test apparatus exhibited a stable performance and parameters were easy to adjust. The degree of pomace separation cleanliness (64% to 98%) was significantly affected by feed rate of the centrifugal screening device (F = 5329.00, P < 0.01), speed (F = 841.00, P < 0.05) and angle (F = 1225.00, P < 0.05) of the scraper, and interaction of feed rate and scraper angle (F = 225.00, P < 0.05). This test apparatus design provides parameter basis to optimizing the design of separating equipment based on double-action that can be applied to tomato pomace processing.

27 Preparation and Identification of Cronobacter Single-chain Variable Fragment Antibody using ELISA

ZHANG Xiu-yuan , HUANG Zhi-hong , WANG Li-xia , CHEN Yi , ZHAO Rui-ping

2015, 31(5):169-174. DOI: 10.13982/j.mfst.1673-9078.2015.5.027

[Abstract](911) [HTML](0) [PDF 943.17 K](1320)

Abstract:
Specific single-chain variable fragment (scFv) against Cronobacter was generated using genetic engineering. Genes coding for variable regions of the heavy and light chains (VH and VL) were amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) of total RNA from hybridoma cells secreting Cronobacter monoclonal antibody. VH and VL were fused together by Splice Overlap Extension (SOE)-PCR with flexible polypeptide linker (Gly4Ser)3 to construct the scFv genetic fragment. The scFv-pET-26b recombinant plasmid was constructed by double-digestion with restriction endonucleases XhoI and EcoRI, followed by cloning into plasmid vector pET-26b. Positive clones were selected for extraction of scFv-pET-26b, which was transformed into Escherichia coli BL21 for expression using IPTG as an inducer. The expressed recombinant protein was purified by His affinity chromatography and identified by sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS-PAGE) and enzyme-linked immunosorbent assay (ELISA). Genetically engineered strains expressing Cronobacter scFv were successfully constructed. SDS-PAGE and ELISA results showed that the molecular weight of the expressed scFv was approximately 30 kDa and that the obtained scFv could specifically bind to Cronobacter and is a potential candidate antibody for the detection of Cronobacter.

28 Preparation and Catalytic Properties of Immobilized Thermoalkaliphilic T1 Lipase from Geobacillus sp. Strain T1

WANG Pu , WANG Fang-hua , TANG Qing-yun , WANG Yong-hua , YANG Bo

2015, 31(5):175-180. DOI: 10.13982/j.mfst.1673-9078.2015.5.028

[Abstract](900) [HTML](0) [PDF 700.40 K](1130)

Abstract:
Using glucan as carrier, thermoalkaliphilic T1 lipase from Geobacillus sp. strain T1 was immobilized via covalent binding. The optimized conditions for enzyme preparation were established and catalytic properties of the immobilized T1 lipase were determined. In a single-factor experiment, specific activity of immobilized T1 lipase reached 50.25 U/mg matrix by using optimal conditions including 1.23% 2-iodoxy benzoate, immobilization temperature of 50 ℃ and time for 2 h. Immobilized T1 lipase was used to catalyze the alcoholysis of olive oil and methanol, yielding 14.08% fatty acid methyl esters after 60 h. Meanwhile, the thermostability and organic solvent tolerance of the immobilized T1 lipase were also studied. The results indicated that the immobilized T1 lipase could maintain more than 70% of its activity after a 7-h incubation at 60 ℃, and the activity increased to 120% to 140% after treatment with n-butanol, n-propanol, and isopropanol, in addition to methanol and ethanol. These results demonstrate that immobilized T1 lipase has a potential to catalyze the reaction involving methanol to produce biodiesel and exhibits good thermostability and organic solvent tolerance; therefore, it has potential for industrial application.

29 Growth Kinetic Parameters of Multi-drug and Single-drug Resistant Vibrio parahaemolyticus Strains in Pure Culture and in Penaeus vannamei

LOU Yang , ZHANG Zhao-huan , XIAO Li-li , GUO Dan-feng , LIU Hai-quan , PAN Ying-jie , ZHAO Yong

2015, 31(5):181-186. DOI: 10.13982/j.mfst.1673-9078.2015.5.029

[Abstract](942) [HTML](0) [PDF 746.71 K](1252)

Abstract:
The variations in growth kinetic parameters of single- and multi-drug resistant Vibrio parahaemolyticus strains were investigated, and the relationship between bacterial resistance and risk was explored. A Bioscreen-C automated growth curve analysis system combined with the serial dilution method was employed to compare and analyze the maximum specific growth rates (μmax) of V. parahaemolyticus strains with varying degrees of drug resistance cultured in trypticase soy broth (TSB). Furthermore, Penaeus vannamei was inoculated with the VPD18 strain, which is resistant to six antibiotics, and the VPD43 strain, which is only resistant to ampicillin. Growth curves at different temperatures were established and then the growth dynamics parameters were calculated using the Baranyi model. There was no significant difference in μmax values between the single- and multi-drug resistant strains grown in TSB (P > 0.05). However, in P. vannamei, the μmax of the single-drug resistant strain was higher than that of the strain resistant to six antibiotics, but the latter strain had a shorter lag time (λ). These results suggest that the increase of antibiotic resistance may lead to a shortened λ, but has no significant effect on the μmax. The results of this study can provide basic data for the development of a quantitative risk assessment of V. parahaemolyticus in China.

30 Effect of Repeated Marination and Cooking on Quality of Marinades

TANG Chun-hong , LI Hai , LI Xia , ZHANG Chun-hui , CHEN Lin-li

2015, 31(5):187-192. DOI: 10.13982/j.mfst.1673-9078.2015.5.030

[Abstract](1135) [HTML](0) [PDF 668.79 K](1309)

Abstract:
Chinese traditional marinated meat is very popular among consumers due re-useable marinades. Numerous taste-enhancing, active compounds are enriched by repeated use, which provides the marinade a characteristic strong flavor that delivers a unique flavor to marinated foods. Using chicken drumsticks from white-feathered broilers, changes in nutrients such as proteins, free amino acids, flavor nucleotides, and equivalent umami concentration (EUC), as well as harmful substances such as heterocyclic amines were analyzed in the marinades used for Chinese traditional marination with different marinating time. The results showed that compared with the control group (unused marinade), the marinade used for the 9th time showed protein content increased to 3.86% from 0.09%, total free amino acid content increased to 601.92 from 68.57 mg/100 g, flavor nucleotides increased to 22.97 from 0.78 mg/100 g, and EUC value increased to 1.32 from 0.068 g MSG/100 g; whereas heterocyclic amine content increased as well, to 28.64 from 12.29 ng/g. Therefore, content of both nutrients and harmful substances were found to continuously rise, with each marination use.

31 Changes in Biochemical Parameters and Organic Acid Content during Liquid Fermentation of Peach Vinegar

XIANG Jin-le , DU Lin , LIU Zhi-jing , LI Xin-ling , LUO Lei , ZHU Wen-xue

2015, 31(5):193-198. DOI: 10.13982/j.mfst.1673-9078.2015.5.031

[Abstract](1205) [HTML](0) [PDF 1003.47 K](1243)

Abstract:
Pear vinegar was produced from ripe peaches by liquid-state fermentation and changes in biochemical parameters were monitored during the “two-step” fermentation process. “Skin-on” fermentation was carried out after pulping and inoculation with 0.05% wine yeast. Fermentation lasted for 80 h at a constant temperature of 20 ℃, with an alcoholic content of 6.07% (V/V). Acetic fermentation was carried out in a self-priming, submerged fermentation tank after inoculation with 10% acetic acid bacteria. Acetification lasted for 60 h at 34 ℃ with titratable acidity of 3.54% (m/V). Nine organic acids were found in the peach wine fermentation liquor, including oxalic acid, formic acid, malic acid, α-ketoglutaric acid, lactic acid, acetic acid, citric acid, fumaric acid, and succinic acid. The organic acid content was constantly changing during fermentation, which significantly contributed to the acidity and quality of the fermentation liquor. During alcoholic fermentation, lactic acid was produced and accumulated, while the concentration of malic acid and citric acid decreased significantly. Acetic acid bacteria transformed alcohol to acetic acid, the concentration of which increased significantly, while the concentration of the majority of the remaining organic acids, such as lactic acid and malic acid, decreased during acetification. Thus, the “two-step” fermentation method used in this study is suitable for the production of peach vinegar.

32 Effect of Calf Chymosin Dose on Protein Degradation in Hard Cheese Made from Yak Milk

SONG Xue-mei , LIANG Qi , ZHANG Yan , ZHANG Wei-bing , WEN Peng-cheng

2015, 31(5):199-205. DOI: 10.13982/j.mfst.1673-9078.2015.5.032

[Abstract](1146) [HTML](0) [PDF 851.17 K](1154)

Abstract:
The effect of calf chymosin supplementation on degradation of protein in hard cheese made from yak milk during the three-month ripening process was studied by measuring content of various types of soluble nitrogen. Additionally, urea-polyacrylamide gel electrophoresis and sensory evaluation regarding bitterness in the cheese was conducted. The results showed that chymosin dosage had significant impact on content of soluble nitrogen in pH 4.6 acetate buffer and 12% trichloroacetic acid (p < 0.05). After one month of ripening, there were significant differences in soluble nitrogen content in pH 4.6 acetate buffer between samples with different chymosin dosages, and a strong linear correlation was found between chymosin dosage and soluble nitrogen content. However, chymosin dose had no significant effect on the content of soluble nitrogen in 5% phosphotungstic acid and free amino acid content (p > 0.05). Results of urea-polyacrylamide gel electrophoresis showed that degradation of αs-casein in cheese was dependent on chymosin dosage and was more extensive than that of β-casein. Chymosin dosage had a significant impact on cheese bitterness as well, which increased in intensity with increasing amount of chymosin, with most cheeses ranging from slightly to moderately bitter. The degree of cheese bitterness strongly correlated with soluble nitrogen content in 12% trichloroacetic acid as well as degree of αs-casein and β-casein degradation (Spearman correlation coefficient > 0.7, p < 0.01).

33 Effect of Multiple Freeze-thaw Cycles on the Microflora of Quick-frozen Dumplings

HAN Qi , SUN Qing-xiu , SUN Fang-da , ZHENG Dong-mei , KONG Bao-hua

2015, 31(5):206-211. DOI: 10.13982/j.mfst.1673-9078.2015.5.033

[Abstract](1866) [HTML](0) [PDF 862.64 K](1250)

Abstract:
The effect of temperature fluctuations caused by repeated freeze-thaw cycles on the number and diversity of microorganisms in quick-frozen dumplings was investigated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and traditional plate culture methods. The dumpling fillers were inoculated with Staphylococcus aureus to analyze the dynamic changes in S. aureus itself and its influence on the dumpling microflora. The results showed that the quantity and diversity of microorganisms in the dumplings increased significantly (p < 0.05) with increasing freeze-thaw cycles. At the last cycle, S. aureus count in the inoculated dumplings increased from 3.49 to 5.07 log10 CFU/g, which reached the minimum count for Staphylococcal toxicity, of 105 CFU/g. PCR-DGGE showed that lactic acid bacteria, Pseudomonadales bacterium and Brochothrix thermosphacta were the dominant strains in the dumplings during the freeze-thaw cycles, while the counts of S. aureus increased and finally became the dominant strain. The results of PCR-DGGE and the traditional culture method were generally consistent.

34 Effect of Changes in Cell Wall Enzyme Activity on Degradation of Pectin during Low-temperature Storage of Plum

LIANG Jie-yu , ZHU Dan-shi , ZHAO Li-hong , GE Yong-hong , CAO Xue-hui , FENG Xu-qiao , LI Jian-rong

2015, 31(5):212-218. DOI: 10.13982/j.mfst.1673-9078.2015.5.034

[Abstract](1211) [HTML](0) [PDF 778.38 K](1553)

Abstract:
Changes in cell wall enzyme activity are known to significantly affect pectin degradation and fruit softening. Changes in the pectin content and activity of cell wall polysaccharide-degrading enzymes (PE, exo-PG, endo-PG, and EG) during low-temperature storage (0 ℃ and 10 ℃) of “banbianhong” plum were investigated in this study. Correlation analysis was carried out to explore the effect of cell wall enzyme activity on pectin degradation. The results showed that the changes in the activities of four cell wall enzymes were different during low-temperature storage, indicating that lower temperatures inhibited enzyme activity to a certain extent. PE activity showed significant difference after 5 days storage under 0 ℃ and 10 ℃, while significant differences were found in exo-PG activity during the entire storage period. When the plum was stored at 0 ℃ and 10 ℃, activities of endo-PG and EG did not show significant difference during the first 10 days and the trend of changes in endo-PG activity was similar to that of EG, however, the peak value of endo-PG activity appeared later than that of EG. The results of correlation analysis between pectin content and cell wall enzyme activity showed that protopectin and SSP content showed a significant negative correlation with WSP content. The activity of PE exhibited a significant positive negative correlation with ASP and HSP content. Thus, PG played an important role in the conversion process from protopectin and SSP to WSP, while EG played a minor role on the degradation of pectin in plums.

35 Impact of Microwave Heating on the Water State and Distribution of Potato Starch Granules

MA Shen-yan , FAN Da-ming , WANG Li-yun , LIAN Hui-zhang , ZHAO Jian-xin , ZHANG Hao

2015, 31(5):219-225. DOI: 10.13982/j.mfst.1673-9078.2015.5.035

[Abstract](1073) [HTML](0) [PDF 967.93 K](1512)

Abstract:
In order to investigate the mechanism of microwave heating, potato starch was selected as the research sample because of its typical B-type crystalline structure. Based on the characteristics of the microwave heating process, a control heating model was established and evaluated. Using 1H NMR technique, Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence and principal component analysis (PCA) to obtain the original transverse relaxation curves of samples that underwent microwave, rapid, and slow heating. The transverse relaxation time (T2) was calculated through multi-exponential regression to analyze the variation patterns of water in the samples in order to study impact of microwave heating on the water state and distribution in potato starch granules. The results showed that there were significant differences in T2 with all three types of heating; microwave heating exerted a particularly significant impact on moisture distribution within the potato starch granules in the early stages of gelatinization. To a certain extent, this study showed that the special effects of microwave accelerated the destruction of hydrogen bonds at this stage.

36 Combined Effects of High-pressure and Thermal Treatment on Intramuscular Fatty Acid Composition in Pork

HUANG Tian , YAN Cheng , SUN Juan , HUANG Ye-chuan

2015, 31(5):226-236. DOI: 10.13982/j.mfst.1673-9078.2015.5.036

[Abstract](1030) [HTML](0) [PDF 944.47 K](1149)

Abstract:
Pork longissimus muscles were used to study the effects of high pressure and specific temperatures on intramuscular fatty acid composition. After treatments at different pressures (300~700 MPa), temperatures (20~50 ℃), or treatment durations (10~20 min), the changes in the fatty acid composition of total lipids, triglycerides, phospholipids, and free fatty acids were observed. The results showed that pressure, followed by temperature, had the most significant impact on the fatty acid composition of pork. The interaction of pressure and temperature was significant, while the effect of treatment duration was no significant. There were mainly changes in the fatty acid composition of phospholipids and free fatty acids, whereas the fatty acid composition of intramuscular total lipids and triglycerides did not change significantly throughout the treatment process. There was significant degradation of phospholipids at pressures ≥300 MPa combined with thermal treatment. Additionally, more PUFA was degraded, resulting in a significantly decreased percentage of PUFA in phospholipids, while SFA and MUFA increased significantly in phospholipids. Moreover, the changes in the free fatty acid composition were the opposite of those observed in the phospholipid composition. Therefore, high-pressure and thermal treatment of pork mainly affected the fatty acid composition of phospholipids and free fatty acids but not of total intramuscular lipids and triglycerides.

37 Effect of Water and Fat Migration during the Softening Process on the Texture of Cantonese-style White Gourd Mooncake

CHEN Xian , ZHANG Yan , TANG Xiao-jun , MA Yong-xuan , XU Wei-bing , ZUO Min-er

2015, 31(5):237-242. DOI: 10.13982/j.mfst.1673-9078.2015.5.037

[Abstract](1304) [HTML](0) [PDF 848.91 K](1539)

Abstract:
In order to objectively determine the end-point of the softening process of Cantonese-style white gourd mooncake, a correlation between water as well as fat content, in different parts of the mooncake, and texture profile analysis (TPA) parameters during the softening process was analyzed. Meanwhile, the effect of water and fat migration on the texture of Cantonese-style mooncake was explored. The study showed that during the five-day softening process, water and fat in the mooncake migrated gradually from inside to the cake skin. Thereby, the water and fat content in skin increased significantly, by 100.37 ± 1.31% and 31.33 ± 2.24%, respectively (p ≤ 0.05). Hardness decreased significantly, by 22.8 ± 2.4% (p ≤ 0.05). Cohesiveness and resilience increased by 11.8 ± 2.0% and 1.5 ± 0.2% (p ≤ 0.05) in the first two days of softening, but later decreased gradually by 8.7 ± 0.5% and 1.3 ± 0.3% (p ≤ 0.05). Hardness was significantly negatively correlated with water and fat content in the mooncake skin (p ≤ 0.01). Cohesiveness was significantly negatively correlated with fat content in the inner filling (p ≤ 0.01), while resilience showed no statistically significant correlation with water and fat content in different parts of the mooncake. The latter were introduced as independent variables into the regression model to conduct a regression analysis. A predictive model for the correlation between hardness of Cantonese-style white gourd mooncake and water content in the mooncake skin as well as that between resilience and fat content in the outer fillings was established.

38 Removal of Citrinin from Drinking Water by Powdered Activated Carbon in Emergency Pollution Incidents

LIU Shuang , ZHU Yao , TANG Shu-ze

2015, 31(5):243-247. DOI: 10.13982/j.mfst.1673-9078.2015.5.038

[Abstract](1034) [HTML](0) [PDF 721.53 K](1060)

Abstract:
The impact of different citrinin concentrations on pH, refractive index, conductivity and optical activity of drinking water was investigated. Additionally, the effect of activated carbon on removal of citrinin contamination from polluted drinking water was studied to provide technical support during emergency pollution incidences. The results showed that when the concentration of citrinin was in the range of 1 to 50 mg/L, pH of drinking water declined significantly, while the refractive index increased linearly. Conductivity increased significantly between 0.1 and 10 mg/L of citrinin, but no optical activity was observed. The impact of citrinin on pH, refractive index, and conductivity can be used as indicators for monitoring drinking water for contamination by citrinin. Comparison of two types of activated carbon showed that the powdered form removed citrinin more effectively than the granular one. The optimal conditions for removal of citrinin from drinking water included 0.8 g/L powdered, activated carbon and 5-min duration of treatment, resulting in 109.86% removal efficiency. Powdered, activated carbon removed citrinin rapidly and efficiently. Therefore, it has potential for use during emergency pollution incidents wherein drinking water is contaminated by citrinin.

39 Effect of Vacuum-pressure Alternating Tumbling Aided by Ultrasonic Waves on the Quality of Marinated Chicken

FENG Ting , SUN Jing-xin , XU Xing-lian , HUANG Ming , LIU Xiao-ying

2015, 31(5):248-254. DOI: 10.13982/j.mfst.1673-9078.2015.5.039

[Abstract](1061) [HTML](0) [PDF 803.64 K](1552)

Abstract:
Effect of vacuum-pressure alternating tumbling, aided by ultrasonic waves on the quality of marinated chicken was investigated in this study. At 4 h post-mortem, fresh chicken breast samples without tendons (50 ± 1 g, 5 × 4 × 4 cm) were randomly divided into two groups, placed into separate Ziploc bags containing marinades, and treated with two different methods including atmospheric tumbling and vacuum-pressure alternating tumbling aided by ultrasonic waves. Subsequently, shear force, differential scanning calorimetry (DSC), and other indicators of different treatment samples were determined. The results showed that, compared with atmospheric tumbling, vacuum-pressure alternating tumbling aided by ultrasonic waves produced better indicator values in a relatively shorter time. For instance, the tenderness of chicken breast effectively improved and after a 100-min treatment, shear force reduced to 6.7 N and cooking loss reduced to 34%. With a longer treatment time, rate of marinade absorption (p < 0.05) and myofibrillar fragmentation index (MFI) value (p < 0.05) increased significantly. Sodium dodecyl sulfate-gel electrophoresis patterns showed that vacuum-pressure alternating tumbling aided by ultrasonic wave significantly shortened the time to degrade high-molecular weight proteins and generate low-molecular weight proteins. DSC results showed that proteins were more sensitive to heat after tumbling. Therefore, vacuum-pressure alternating tumbling aided by ultrasonic waves was shown to improve the quality of marinated chicken.

40 Effect of Different Drying Methods on Physical Properties of Sweet Potato Leaf Powder

SONG Zhen , MU Tai-hua , SUN Hong-nan , XI Li-sha

2015, 31(5):255-261. DOI: 10.13982/j.mfst.1673-9078.2015.5.040

[Abstract](1193) [HTML](0) [PDF 852.77 K](1069)

Abstract:
The effect of three different drying methods (hot-air drying, vacuum freeze-drying, and spray drying) on the physicochemical properties of sweet potato leaf powder from five cultivars (Ningzi No.1, Xu 053601, LangShu 7-12, Fushu No.2, and Jishu 65) were compared. Physicochemical quality evaluation indices for the powder samples were selected by principal component analysis. The results showed that the drying methods had significant influences on bulk density, water absorption, oil-holding capacity, and swelling capacity of sweet potato leaf powder. The highest bulk density was found in hot-air drying method and the values were in the range of 0.54 to 0.67 g/cm3. Spray-dried sweet potato leaf powder showed a higher water absorption index and oil-holding capacity, which were in the range of 13.73 to 17.40 and 3.0 to 5.0 g/g, respectively. However, the swelling capacity (only 0.58 to 3.64 mL/g) of spray-dried sweet potato leaf powder was significantly lower than that for the other two drying methods. The typical physicochemical quality evaluation indices for sweet potato leaf powder screened out by principal component analysis were oil-holding capacity, emulsifying activity, emulsion stability, and water absorption index. Xu 053601 was considered as the most suitable cultivar for preparing sweet potato leaf powder. In conclusion, spray drying was found to be the best method to prepare sweet potato leaf powder from those analyzed in this study.

41 Enzyme Catalytic Chromogenic Method for Determination of Calcium Peroxide in Wheat Flour

ZHANG Yu-rong , ZHANG De-wei , ZHOU Xian-qing

2015, 31(5):262-266. DOI: 10.13982/j.mfst.1673-9078.2015.5.041

[Abstract](1261) [HTML](0) [PDF 719.16 K](1088)

Abstract:
As calcium peroxide can generate hydrogen peroxide in an acidic medium, visual colorimetry for rapid qualitative analysis and spectrophotometry for quantitative analysis of calcium peroxide in wheat flour were established based on the principle that hydrogen peroxide can cause rapid oxidation and chromogenesis in quaternary amine [4,4′-(dimethyl amine)diphenyl methane] by using horseradish peroxidase (HPR) as the catalyst with KI as the sensitization agent. In this study, the experimental conditions for detecting calcium peroxide were optimized, and the experimental factors influencing chromogenesis, including the HPR content, KI content, quaternary amine content, pH, reaction temperature, and reaction time, were investigated. The results showed that under the optimum conditions, the color of the complex gradually deepened with increasing calcium peroxide content. Based on the relationship between the color gradients and concentration of calcium peroxide, a standard color card was created for visual colorimetric determination. Beer’s law was obeyed when the concentration range of calcium peroxide was within 0~9 mg/L. The linear regression equation was as follows: ΔA = 0.0052 + 0.107C, with a correlation coefficient of 0.9994. The recovery rate for spiked standards was within 96.3%–101.7%, and the relative standard deviation was 1.74%~3.15%. The range of calcium peroxide content was rapidly determined by visual colorimetry and its detection limit was 1.64 × 10-2 mg/L.

42 Molecular Comparison of Gel-permeation Chromatography Methods to Determine the Weight of Walnut Peptides

REN Jiao-yan , LU Yun-jun , LIAO Wen-zhen , LUO Wei , CAO Hong-xi , ZHAO Mou-ming

2015, 31(5):267-271. DOI: 10.13982/j.mfst.1673-9078.2015.5.042

[Abstract](1966) [HTML](0) [PDF 725.84 K](1353)

Abstract:
Methods involving gel-permeation chromatography used to determine the molecular weight of walnut peptides were studied by comparing two commonly used gel columns. These included a TSK-GEL G2000 SWXL 7.8 mm × 300 mm column, recommended by the national standard GB/T 22492-2008 Soy Peptide Powder and GB/T 22729-2008 Oligopeptide Powder of Marine Fish, and a Superdex Peptide HR 10/30 column, recommended by the industry standard SB/T 10634-2011 Freshwater Fish Collagen Peptide Powder by the Ministry of Commerce. Data were measured, analyzed, and compared for four pure standards and four walnut peptide samples with different molecular weights in each of the two chromatographic conditions. The results showed that for TSK- GEL G2000 SWXL 7.8 mm × 300 mm column, the separation of walnut peptides was achieved within 30 min under the recommended conditions. The results also showed a good linear relationship, with a correlation coefficient of 0.97 and a clear peak shape. The measured molecular weights were higher than the actual values in the regions of >10,000 u and <1,000 u. For the Superdex Peptide HR 10/30 column in comparison, the separation was achieved after 80 min, however the results showed a better linear relationship, with a correlation coefficient of 0.99; however, spilt peaks and broad peaks appeared in the chromatogram. Moreover, in this system, the measured molecular weights were lower than the actual values in the regions of >10,000 u and <1,000 u.

43 Detecting Starch Syrup in Adulterated Honey via Retention Index

CHEN Mei-lan , LIANG Shi-jun , LEI Mingi , ZHAO Ming-xia , WU Jie , HE Jin-zhe

2015, 31(5):272-277. DOI: 10.13982/j.mfst.1673-9078.2015.5.043

[Abstract](1021) [HTML](0) [PDF 791.98 K](1124)

Abstract:
The use of retention index (Kovats index) to detect adulteration of honey with starch syrup was studied. After dissolving the honey sample in water, fructose and glucose were removed by Gel (Bio-Gel ? Gel P-2) size-exclusion, oligosaccharides were concentrated, separated, and directly identified by anion-exchange chromatography using an electrochemical detector. Linear maltooligosaccharides are formed by condensation of glucose monomers, similar to n-alkanes. Using the chromatographic peaks of maltooligosaccharide (maltose to maltoheptaose) standards as reference, the retention indices of maltotetraose, maltopentaose, maltohexaose, and maltoheptaose were set at 400, 500, 600, and 700, respectively, while the retention index value of sample peak was calculated based on the retention time. The results showed similar functional retention index values for maltose standard samples as compared with fructose syrup, pure honey containing fructose syrup, and in some commercial honey samples, while they were not found in pure honey samples. This approach can be used to detect adulteration of honey with 1% sensitivity, and was validated using deliberately adulterated honey samples.

44 Analysis of the Copper Content in Four Main Wine Regions in China

SUN Xiang-yu , ZHAO Fang , MA Ting-ting , WANG Li-hua , WANG Cheng , SUN Yu-qiang , ZHAN Ji-cheng

2015, 31(5):278-284. DOI: 10.13982/j.mfst.1673-9078.2015.5.044

[Abstract](1122) [HTML](0) [PDF 775.83 K](1440)

Abstract:
The copper contents of wines from Helan Mountain East region, Hexi Corridor region, Huaizhuo Basin region, and Tonghua region were investigated using inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that the copper content of wines obtained from these four regions was in a good condition overall; the detection rate of excess copper content was 0.2%. Among the four regions, Tonghua region showed the highest copper content, followed by Helan Mountain East region, while Hexi Corridor region and Huaizhuo Basin region showed relatively lower copper contents. The distribution of the copper content in Tonghua wine was polarized. The copper content in the Helan Mountain East region ranged between 50~100 μg/L and 100~300 μg/L, while the Hexi Corridor region and Huaizhuo Basin region showed a more uniform distribution of copper content. Regional climate and terroir characteristics, winery and vineyard management, and winemaking technology exert large effects on the copper content of wines. The copper contents of different wine grape varieties in the same region were similar, but there were certain differences between the wine grape varieties of different regions. Vintage also had a certain influence on copper content, which was mainly related to the climate, especially to precipitation.

45 Non-destructive Detection of Protein Content in Fresh Eggs by Visible/near-infrared Reflectance Spectroscopy

WU Jian-hu , HUANG Jun

2015, 31(5):285-290. DOI: 10.13982/j.mfst.1673-9078.2015.5.045

[Abstract](1362) [HTML](0) [PDF 955.90 K](1548)

Abstract:
Eggs are considered an important food item, containing protein as the main nutrient. The aim of this study was to non-destructively detect protein content in eggs by visible (VIS)/near-infrared (NIR) reflectance spectroscopy. VIS/NIR raw reflectance spectra of fresh egg samples were acquired in the wavelength range of 400 to 1000 nm. The raw spectrum was pretreated with multiplicative scatter correction (MSC) and first-derivative (1-D) methods and step-wise regression discrimination method was used to select the optimal wavelength combination to establish multi-linear regression (MLR) models. Full cross-validation was used to validate the model. The results showed that after MSC treatment of VIS/NIR reflectance spectra, the MLR model, based on ten optimal wavelengths (400, 403.16, 407.9, 714.6, 715, 715.58, 970.4, 970.75, 973, and 974.45 nm) produced optimum calibration and validation results. For the calibration result, the correlation coefficient (R) was 0.92 and the standard error of calibration (SEC) was 0.47%. The model provided good prediction values for egg protein content with the correlation coefficient of cross validation (Rcv) at 0.89 and standard error of cross validation (SECV) at 0.47%. This study demonstrated that the VIS/NIR reflectance spectral technique provides a good prediction of the protein content in fresh eggs, and the VIS/NIR technique has potential applications in rapid detection of egg nutrients.

46 Rapid Detection of Thiabendazole Pesticide Residue in Fresh Tea Leaves Using Surface-Enhanced Raman Spectroscopy

LIN Lei , WU Rui-mei , GUO Ping , LIU Mu-hua , WANG Xiao-bin , AI Shi-rong , YAN Lin-yuan

2015, 31(5):291-296. DOI: 10.13982/j.mfst.1673-9078.2015.5.046

[Abstract](1680) [HTML](0) [PDF 763.21 K](1419)

Abstract:
Surface-enhanced Raman spectroscopy (SERS) along with density functional theory (DFT) was used to develop a rapid detection method for thiabendazole residues in fresh tea leaves. Fe3O4 nanoparticles and graphitic carbon were used to eliminate the interference from fluorescent materials in fresh tea leaves, such as chlorophyll and theanine. The SERS enhancement effects of silver colloids and gold colloids for thiabendazole standard solutions were compared; the results showed that silver colloids produced better effects. By attributing and analyzing the Raman spectra of a thiabendazole molecule combined with the results of density functional theory, Raman peaks were obtained at 782, 1007, and 1576 cm-1, which could be the characteristic peaks of thiabendazole molecules. The minimum detection concentration of thiabendazole in fresh tea leaves was obtained as 1 mg/L by using the SERS method. The standard curve was plotted with the peak intensity at 782 cm-1. A good linear relationship was found between the peak intensity at 782 cm-1 and the concentration of thiabendazole within the range 0.5–20 mg/L. The recovery rate of SERS was 87.33%~93.04% and the relative standard deviation (RSD) was between 3.28 and 5.64, indicating that this method is highly accurate and reliable.

47 Rapid Detection of Total Phytosterol Content in Cereals, Oils, and Foodstuff by Electrochemical Analysis

LV Shuang-shuang , ZHANG Yuan-Yuan , LI Shu-guo

2015, 31(5):297-302. DOI: 10.13982/j.mfst.1673-9078.2015.5.047

[Abstract](1123) [HTML](0) [PDF 881.42 K](1381)

Abstract:
The electrochemical reaction process of plant sterols in a bare glassy carbon electrode was investigated to develop a new differential-pulse voltammetric method for rapid detection of phytosterols in cereals, oils, and other foodstuff. Cyclic voltammogram of phytosterols showed that the oxidation peak appeared at 1.72 V and no reduction peak was observed, which indicated that the electrode reaction process was irreversible. The electrochemical conditions were optimized for the detection of phytosterols. The results showed that the optimal conditions were: acetonitrile and 2-propanol (9:1,V/V) as organic solvent, 50 mmol/L LiClO4 as supporting electrolyte, pulse amplitude of 50 mV, potential increment of 3 mV, pulse width of 0.05 s, and pulse interval of 0.3 s. Under these optimized conditions, the calibration curves for determination of phytosterol demonstrated an excellent linear response within the range 160 to 800 μg/mL (r = 0.998), with the detection limit at 8.8 μg/mL (S/N = 3). The proposed method was successfully applied to the determination of phytosterol in corn germ oil deodorizer distillate and the recovery rate was 97.0% to 101.3%. The results indicate that the electrochemical analysis method is feasible for the detection of phytosterols in non-aqueous solvents, easy to perform, and does not require complicated pretreatment of samples.

48 Determination of Methyltestosterone Residue in Aquatic Products by Enzyme-linked Immunosorbent Assay

WANG Qiang , WANG Xu-feng , HUANG Ke , KE Chang-liang , YANG Jin-lan , LI Zhi-guang , LI Liu-dong

2015, 31(5):303-308. DOI: 10.13982/j.mfst.1673-9078.2015.5.048

[Abstract](874) [HTML](0) [PDF 815.26 K](1167)

Abstract:
An indirect, competitive enzyme-linked immunosorbent assay (icELISA) was developed for rapid determination of residual methyltestosterone (MT) in aquatic products. MT was reacted with succinic anhydride to obtain the hapten MT17, which was then coupled to keyhole limpet hemocyanin (KLH) as an immunogen (MT17-KLH). After animal immunization, the polyclonal antibody was successfully obtained and could specifically recognize MT (cross-reactivity with other structurally related chemicals was < 1%). The optimized assay conditions for icELISA were as follows: coating antigen concentration at 100 μg/L; dilution ratio of MT polyclonal antibody at 1:1.2 × 105; 40 min reaction time of antibody; phosphate-buffered saline (PBS) as dilution solution; extraction of aquatic product with acetonitrile, followed by purification by dispersive solid-phase extraction (DSPE) using ethylenediamine-N-propyl (PSA)-bonded sorbent. The half inhibition concentration (IC50) was 3.48 μg/L, while the linear range (IC20~IC80) was 0.77 to 13.06 μg/L. Recoveries from spiked aquatic products were in the range of 81.02% to 103.19%, with relative standard deviation ranging from 4.46% to 13.14%. The results showed good correlation with liquid chromatography-tandem mass spectrometry (R = 0.9971). The method developed in this study is suitable for rapid determination of methyltestosterone residues in aquatic products.

49 Early Detection of Aflatoxin B1 Contamination in Stored Corn by Monitoring CO2 Concentration

LIU Yan , ZHAI Huan-chen , CAI Jing-ping

2015, 31(5):309-315. DOI: 10.13982/j.mfst.1673-9078.2015.5.049

[Abstract](869) [HTML](0) [PDF 948.95 K](1108)

Abstract:
The characteristics of carbon dioxide (CO2) produced by fungi during corn storage were investigated. The results showed that CO2 concentration was elevated at a constant rate in the storage container upon development of xerophilic Aspergillus glaucus. The CO2 gas production rate accelerated upon development of fungi that show rapid growth and/or are toxigenic. For example, the CO2 gas production rate increased by 4.6 times after 10-day storage when A. flavus was the dominant fungus in the corn sample. Furthermore, the effects of the original dominant fungal groups, fungal growth rate, and storage temperature on CO2 gas production were evaluated during corn storage. The results showed that A. flavus could develop and produce aflatoxin B1 (AFB1) in corn samples with different original dominant fungi. AFB1 production of the group with A. flavus as the original dominant fungus was three to seven times higher than that of the other experimental groups, and showed an accelerated CO2 production rate. The production of CO2 gas and AFB1 was significantly affected by fungal growth rate and storage temperature, but the CO2 gas production rate increased in all corn samples contaminated with AFB1. Changes in the CO2 gas production rate occurred more than seven days earlier than when AFB1 could first be detected. Therefore, monitoring of the CO2 gas production rate can be used as an early warning of AFB1 contamination during corn storage.

50 Key Volatile Flavor Compounds of Grey Sufu, a Chinese Traditional Fermented Soybean Food Product

MA Yan-li , LIU Ya-qiong , XIA Ya-nan , SUN Jian-feng , MU Jian-lou , WANG Jie

2015, 31(5):316-321. DOI: 10.13982/j.mfst.1673-9078.2015.5.050

[Abstract](2657) [HTML](0) [PDF 681.68 K](2415)

Abstract:
Grey sufu is a Chinese traditional fermented tofu with a unique flavor. Research on the flavor compounds of grey sufu is generally poor, especially with respect to the key volatile flavor compounds. In this study, dynamic headspace extraction was used to extract the flavor compounds in grey sufu, the gas chromatography-mass spectrometry (GC-MS) technique was used to identify the volatile flavor compounds, and dynamic headspace dilution analysis (DHDA) and sniffing were further used to determine the key volatile flavor compounds. These results can provide a scientific basis for stabilizing the flavor quality of grey sufu products. There were 73 volatile flavor components identified by GC-MS, including 16 esters, 13 nitrogen-containing compounds, 12 alcohols, 12 acids, 10 aldehydes and ketones, and eight sulfur-containing compounds. No hydrogen sulfide was detected. Quantitative analysis using internal standards showed that the relative content of nitrogen-containing compounds, acids, esters, phenols, and alcohol compounds was relatively high, accounting for 19.66%, 18.7%, 14.79%, 10.35%, and 9.21% of the total flavor compounds, respectively. Twenty-five key volatile flavor compounds were identified by DHDA and sniffing technique , among which indole, phenol, dimethyl disulfide, trimethyl hydrazine, ethyl acetate, butyric acid, and dimethyl trisulfide were the most important compounds contributing to the flavor of grey sufu.

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Volume 31,Issue 5,2015 Table of Contents