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25 March 2018, Volume 39 Issue 6
Food Chemistry
Effect of Fermentation of Buckwheat Sourdough with Different Exopolysaccharide-Producing Strains of Lactic Acid Bacteria (LAB) on Dough Microstructure and Bread Quality
CHEN Jiafang, TANG Xiaojuan, JIANG Hui, WU Yuxin, ZHANG Sijia, XU Yan, Huang Weining, LI Ning, Filip Arnaut
2018, 39(6):  1-6.  doi:10.7506/spkx1002-6630-201806001
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In this study, two high-yield exopolysaccharide (EPS)-producing strains of lactic acid bacteria (LAB), Weissella cibaria T5 and Weissella confusa J28, which were respectively isolated from Chinese rice wine koji and traditional sourdough, were used to make buckwheat sourdough. The aim was to investigate the effects of the two strains on dough microstructure and bread quality. Both J28 and T5 produced high molecular weight dextran. J28 produced higher amounts (11.87 g/kg vs. 9.36 g/kg) of EPS but significantly lowers amounts of acetic acid than did T5 in buckwheat sourdough. Compared with bread with the addition of 30% EPS-negative buckwheat sourdough, EPS produced by both T5 and J28 could improve the structure of the gluten network in dough and the specific volume and softness of bread, with the former being more effective. Compared with the control bread, the bread made from 30% EPS-positive buckwheat sourdough fermented by J28 had the best quality and was more favored by consumers.
Preparation and Characterization of Kafirin Microparticles Encapsulating Curcum by Anti-Solvent Method
LI Xiaohui, HUANG Wenjuan, ZHOU Wei, ZHANG Jinjie, XU Dalun, YANG Wenge
2018, 39(6):  7-12.  doi:10.7506/spkx1002-6630-201806002
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The encapsulation of curcum in kafirin microparticles by anti-solvent method was investigated in this study, and the physicochemical properties and stability of the microparticles were characterized. The results showed that the optimal curcumin/kafirin ratio (m/m) ratio was 1:10. The average particle size and zeta potential of the microparticles obtained under this condition were respectively 13.17 μm and 19.38 mV; the production yield was 87.51%, the entrapment efficiency was 62.61%, and the loading efficiency was 6.51%. Scanning electron microscopy (SEM) showed that kafirin microparticles encapsulating curcum were uniform spheres with a porous surface. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the peaks at 1 534 and 1 655 cm-1 red shifted; furthermore, the alpha helix and beta-sheet content were respectively reduced and increased. The stability of kafirin microparticles encapsulating curcum was significantly improved after being exposed to UV radiation for 24 h, and no significant changes were observed in their sizes or polydispersity index (PDI) after 30-day storage under ambient conditions. However, the microparticles were easily gathered at pH 5–6. Therefore, the kafirin microparticles encapsulating curcum can improve the stability of curcum, which will provide a theoretical basis for the high-value utilization of kafirin and curcum.
Impact of Calcium Hydroxide on Quality of Shannxi Traditional Buckwheat Noodles and Pasting Properties of Buckwheat Flour
ZHANG Jia, LI Xiaoping, HU Xinzhong, ZHAO Liu, WANG Fenghui, LI Qingqing, MAO Ning
2018, 39(6):  13-19.  doi:10.7506/spkx1002-6630-201806003
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This study investigated the effect of adding different proportions of calcium hydroxide (0%–1.0%) to buckwheat flour on its pasting properties as well as the quality of buckwheat noodles. The results showed that with increasing addition of calcium hydroxide, the lightness (L*) of buckwheat noodles was decreased, the redness (a*) was increased, and the yellowness (b*) value was increased firstly and then decreased. Buckwheat noodles with 0.6% calcium hydroxide showed a bright yellow, and had the lowest breaking rate (17.57%), lowest cooking loss (4.67%) and highest sensory score (80 points), with moderate hardness and good viscosity and flexibility. Addition of calcium hydroxide decreased the transmittance of buckwheat flour, increased the solubility and the, and resulted in an initial increase followed by a decrease in the final viscosity and setback. Moderate final viscosity and setback were obtained for noodles with 0.6% calcium hydroxide added. In conclusion, calcium hydroxide can improve the quality of buckwheat noodles by influencing the pasting properties of buckwheat flour.
Changes in Interfacial and Emulsifying Properties of β-Lactoglobulin Protein during Its Fibrillation
HUANG Ying, GAO Zhiming, WU Binxian, LIN Zhantuo, ZHAO Junjun, FANG Yapeng
2018, 39(6):  20-25.  doi:10.7506/spkx1002-6630-201806004
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When heated under acidic conditions, protein is self-assembled into fibrils. In this paper, the formation of β-lactoglobulin protein fibrils was characterized by fluorescence spectroscopy and transmission electron microscopy (TEM). Interfacial adsorption and interfacial viscoelasticity of the samples at different fibrillation stages were analyzed with an interfacial rheometer, and then their emulsifying behaviors were studied. Different interfacial and emulsifying properties of the dispersions from different fibrillation stages were observed. The interfacial adsorption ability and the viscoelasticity of the dispersions were increased as fibrillation progressed. Stable emulsions with average droplet size (D[3,2]) ranging from 8.5 to 10.5 μm could be formed from the fibrillation products at different stages, and the emulsifying capacity of the dispersions were shown to be increased with increasing degree of fibrillation. However, excessive fibrillation had a negative effect on the storage stability of the emulsions.
Effect of Natural Inulin on Dough Rheological Properties and Bread Quality
LUO Denglin, ZHAO Ying, XU Baocheng, XU Wei, LI Peiyan, REN Guangyue, YUAN Yunxia, LIU Jianxue
2018, 39(6):  26-31.  doi:10.7506/spkx1002-6630-201806005
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Rheology properties of wheat flour doughs with different levels of natural inulin were analyzed using rheofermentometer. Inulin addition, fermentation time and yeast inoculum size were investigated as independent variables using one-factor-at-a-time (OFAT) and central composite design (CCD) methods. The response variable was weighted average of bread specific volume, sensory score, hardness and elasticity. The results showed that with the increase of inulin addition, the total amount of CO2 was increased, the maximum expansion height was decreased, and the cavity-forming time of dough was significantly reduced. The retention coefficient of CO2 was increased by 18.0% after substitution of 10% flour by inulin, which was perhaps attributed to a certain amount of oligosaccharides in inulin and the ability to enhance the dough resistance to extension. According to the results of response surface analysis, addition of inulin reduced the hardness but had no significant effect on the springiness, and it slightly increased the specific volume of bread. Bread with the highest weighted average score (94.17) was obtained by addition of 4.43% inulin and 86 min fermentation with 1.08% dry yeast. The estimated values from the regression equation were in agreement well with the experimental data.
Effects of Non-Covalent/Covalent Interactions between Anthocyanins and Soybean Protein Isolate on Its Interfacial Function
LI Yang, SUN Hongbo, DONG Jixuan, LIU Yingjie, BI Shuang, ZHANG Qiaozhi, JIANG Lianzhou, SUI Xiaonan
2018, 39(6):  32-38.  doi:10.7506/spkx1002-6630-201806006
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The aim of this study was to compare the effects of different concentrations of anthocyanins on the functional properties of proteins through non-covalent/covalent interactions. The complexes of anthocyanins and soybean protein isolate (SPI) were studied by three-dimensional fluorescence spectroscopy. The relationship between the structural changes of protein-anthocyanin complexes and protein functional properties with non-covalent/covalent interactions was analyzed by determination of emulsifying properties and foaming properties, light microscope observation and measurement of sulfhydryl content. The results showed that the fluorescence intensities of the characteristic peaks of the proteins decreased, accompanied by the occurrence of unfolded polypeptide chains, with the increase of anthocyanin concentration after treatment at pH 7.4 for 2 h or at pH 9.0 for 24 h, and the covalent binding was stronger than the non-covalent one. The emulsifying properties and foaming properties of the complexes were improved as compared with SPI, and the content of sulfhydryl group was decreased, especially for sample 6 (treatment with 2 mg/mL anthocyanins at pH 9.0 for 24 h). The droplet sizes of emulsion systems 5 (with 1 mg/mL anthocyanins at pH 9.0 for 24 h) and 6 were homogeneous, and the emulsions were stable.
Preparation of Tea Polyphenols-Loaded Inverse Microemulsion Using Edible Oil as Continuous Phase
CHEN Mengjie, WANG Daoyuan, LI Zhiyong, YANG Ying, WU Jinhong, ZHONG Yaoguang, WANG Zhengwu
2018, 39(6):  39-44.  doi:10.7506/spkx1002-6630-201806007
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Tea polyphenols-loaded water-in-oil microemulsion (ME) of polyoxyethylene (10) oleyl ether (Brij97)-glyceryl monooleate (GMO)-ethanol-edible oil-water to envelop was prepared successfully in this paper. The phase behavior, particle size, and oxidative stability were investigated by pseudo-ternary phase diagram method, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The results showed that the optimal mass ratio of Brij97 to GMO was 2:8; the optimal mass ratio of water to ethanol was 4:1. Higher tea polyphenol (TP) concentration resulted in smaller mean particle size and higher polydispersity index of ME system. Moreover, the mean particle size of 5 kinds of ME systems with 0.10 g/mL TP in the aqueous phase remained between 8.00 and 12.00 nm for 30 days. The results of DSC showed that the incipient oxidation temperature of blank soybean oil ME was 163.40 ℃, while those of ME with 0.01 and 0.10 g/mL TP added were 175.77 and 210.88 ℃, respectively.
Effect of Xanthan Gum on Pasting, Rheological and Texture Properties of Lotus Root Starch
LIU Min, ZHAO Xin, KAN Jianquan, ZHANG Fusheng, ZHENG Jiong,
2018, 39(6):  45-50.  doi:10.7506/spkx1002-6630-201806008
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The aim of this work was to explore the influence of adding different proportions of xanthan gum as a hydrophilic colloid to lotus root starch on its pasting, rheological and textural properties and microstructure. The results showed that final viscosity and peak time of starch paste were increased while peak viscosity, setback value and breakdown value were reduced by adding xanthan gum. The mixed system had better thermal stability and aging resistance. Shear stress was declined to different degrees with increasing addition of xanthan; furthermore, the consistency coefficient K was increased whereas the fluid index n was decreased. The starch paste was still a pseudoplastic fluid after addition of xanthan gum, but the mixed system had higher thickening capacity. G’ and G” were improved and tanδ was reduced by addition of xanthan gum; viscoelasticity and stability were increased as well. A 8.0:2.0 (m/m) mixture of xanthan gum and lotus root starch had the best thickening capacity, viscoelasticity and stability. The hardness, cohesion, gumminess and chewiness of mixed systems were decreased, and the elasticity was increased compared with neat starch. The texture of xanthan gum-starch mixed gels was softer. A more uniform and stable structure was observed after adding xanthan gum under scanning electron microscope (SEM).
Effect of Freeze-Thaw Cycles on Properties of Hen Egg White Proteins
BI Haidan, CUI Xuhai, YU Bin, GUO Ying
2018, 39(6):  51-56.  doi:10.7506/spkx1002-6630-201806009
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The aim of this study was to investigate the effect of freeze-thaw cycles on functional and structural properties of egg white proteins (EWP). The functional, physicochemical, rheological properties and secondary structures of EWP subjected to different cycles of freeze-thaw were analyzed. The results showed that gelling and foaming properties of EWP were improved by appropriate freeze-thaw cycles. Freeze-thaw cycles resulted in the exposure of hydrophobic residues, protein unfolding and intermolecular aggregation. Moreover, dynamic rheological results revealed that the elastic and viscous modulus was strongly dependent on freeze-thaw cycles. Fourier transform infrared (FT-IR) spectra indicated that more β-sheet and random coil structures were formed with the decrease of α-helix and β-turn. The structure and properties of EWP could be changed by freeze-thaw cycles, which would be used in the processing of egg white.
Influence of Different Batter Ingredients on the Quality Characteristics and Water Distribution of Pre-Fried Microwave Reheated Popcorn Chicken
ZHANG Huan, DONG Fujia, CHEN Qian, KONG Baohua
2018, 39(6):  57-62.  doi:10.7506/spkx1002-6630-201806010
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Water migration and oil impregnation during microwave reheating can reduce the crispness of popcorn chicken. In order to solve this problem, the effect of addition of hydroxypropyl methylcellulose (HPMC) and maltodextrin to batter on oil content, moisture and distribution, crispness, color and sensorial characteristics of popcorn chicken after pre-frying and microwave reheating were investigated. Our results showed that adding 2% hydroxypropyl methylcellulose (HPMC) and 6% maltodextrin to batter significantly reduced the increase of crust water content and the decrease of inner meat moisture in microwave reheated product (P < 0.05). Meanwhile, there was a decrease in the T22 of inner meat, indicating that the mobility of free water was reduced. The A22 of popcorn chicken prepared with HPMC and maltodextrin was significantly higher than that of the control (P < 0.05), indicating that the crust crispness and the inner meat juiciness could be improved by inhibiting water migration from the inner meat to the outer crust. The crispnesses of popcorn chicken prepared with 2% HPMC and/or 6% maltodextrin were all significantly higher than that of the control (P < 0.05). However, the crust hardness of popcorn chicken with 2% HPMC was the highest, and the crust of popcorn chicken with 6% maltodextrin had the highest oil content (P < 0.05). Popcorn chicken with 2% HPMC together with 6% maltodextrin had the best crispness and moderate hardness, without an oily taste. These results provide a basis for improving the crispness and quality of battered products.
Isolation, Purification and Structural Analysis of Iron-Binding Peptides from Casein Hydrolysate
JI Xiaowen, WANG Zhigeng, KAN Wenhan, MEI Lin, XUE Xiuheng
2018, 39(6):  63-68.  doi:10.7506/spkx1002-6630-201806011
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Iron-binding peptides from tryptic casein hydrolysate were separated by immobilized metal affinity chromatography or anion exchange chromatography followed by purification by Sephacryl S-100 HR gel chromatography. The purified peptide was structurally elucidated by UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results showed that a fraction with high iron chelating capacity of 39.56 μg/mg purified by affinity chromatography followed by gel filtration chromatography was obtained, which was better than that purified by anion exchange chromatography. The formation of peptide-iron chelate was confirmed by UV-Vis and FT-IR spectra, and some changes at the carboxyl site occurred after chelating. Besides, three peptide fragments were identified by MS, whose amino acid sequences were HIQKEDVPSER, ITVDDKHYQK and TRLHPVQER, respectively. Asp, Glu and Gln were found to be abundant in these peptide fragments with each of them containing carbonyl group, suggesting that the carbonyl site of the peptide is among the main iron-binding sites.
Bioengineering
Cloning, Expression and Purification of the Nitrite Reductase Gene from Bacillus cereus LJ01
CHEN Simin, LUO Tonghui, FEI Yongtao, WU Jianfeng, LIU Dongmei
2018, 39(6):  69-74.  doi:10.7506/spkx1002-6630-201806012
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A nitrite reductase (NiR) gene was cloned from Bacillus cereus LJ01 and expressed in Escherichia coli. The recombinant enzyme was purified by His-Tag nickel affinity chromatography (Ni Sepharose 6 Fast Flow) and DEAE Sepharose Fast Flow ion exchange chromatography for characterization. The results showed that the recombinant NiR gene contained a 1 623 bp-length ORF encoding 540 amino acids, and the molecular weight was about 67 ku. Iron and copper ions were simultaneously present in the enzyme and their contents were 51.0 and 184.5 mg/kg, respectively. The results of circular dichroism showed that the helix structure accounted for the largest proportion of the recombinant NiR.
Effects of Environmental Stress on LuxS/AI-2 Quorum Sensing Systerm of Enterococcus faecium 8-3
GU Yue, LI Bo, WU Rong, TIAN Jianjun, WU Jing, HE Yinfeng
2018, 39(6):  75-81.  doi:10.7506/spkx1002-6630-201806013
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Enterococcus faecium 8-3, which was isolated from koumiss and screened for autoinducer-2 (AI-2), was used to study the effects of growth conditions (pH value, temperature, osmotic pressure, and nutrient condition) on the LuxS/AI-2 quorum sensing system. The production of AI-2 was detected by a biological method and the expression levels of luxS and pfs genes were detected by real-time quantitative PCR. The results showed that mild acid stress induced E. faecium 8-3 to produce the AI-2. Under alkaline conditions, the cell grew better, and the cell density mainly induced the production of AI-2. Under osmotic and low temperature stresses, the growth of E. faecium 8-3 and the production of AI-2 were both inhibited. Cell density controlled AI-2 production. Low nutrient stress could induce E. faecium 8-3 to produce AI-2. The expression of luxS and pfs genes in E. faecium 8-3 under different environmental stresses varied to different degrees, indicating that the LuxS/AI-2 quorum sensing system mediates stress resistance in E. faecium 8-3.
Survival of Frozen Escherichia coli O157:H7 after Thawing
JI Saisai, WANG Xianjing, MA Jingjing, JIANG Xiaoyan, YUAN Huanyun, YU Jinlong, JIANG Yun
2018, 39(6):  82-87.  doi:10.7506/spkx1002-6630-201806014
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The objective of this study was to investigate the survival of frozen Escherichia coli O157:H7 during thawing. The injury and death of four E. coli O157:H7 strains doe to freezing were compared and the effect of different thawing methods on the survival of frozen E. coli O157:H7 in nutrient-free phosphate buffer saline (PBS) solution was determined. The results showed that after being frozen at ?20 ℃ for 24, 48 or 72 h, cell injury and even death occurred in all the four strains and the severity was time dependent and varied among strains. After being frozen for 72 h, strain CICC21530 showed the highest injury rate (87.70%). When a mixture of four strains was frozen in PBS and then immediately thawed at 20, 30 or 37 ℃, cell death was aggravated with increasing thawing temperature. The colony counts of 72 h frozen E. coli cells were significantly reduced at 48 h of thawing at each temperature (P < 0.05). Additionally, to explore the effect of slow thawing on the survival of E. coli O157:H7, the frozen strains were thawed slowly at 4 ℃ for different durations (0, 2, 6, and 12 h), and then kept at 37 ℃ for 5, 10, and 30 min, respectively. The results showed that slow thawing for a longer time was more beneficial to bacterial survival. Frozen E. coli were thawed at 4 ℃ for 12 h/37 ℃ for 5–30 min and then cultured on sorbitol macconkey agar (SMAC). As a result, higher bacterial counts were found compared with they were cultured on tryptose soya agar (TSA), indicating that the injured cells existed. This study suggests that slow thawing is conductive to bacteria surviving freeze and more attention needs to paid to the detection and control of surviving bacteria, especially injured bacteria during the risk assessment of frozen food.
In Vitro Screening of Lactic Acid Bacteria for Cholesterol-Lowering Activity and the Underlying Mechanism
HUANG Yanyan, GUO Jun, LI Hengxi, YANG Aijun, FENG Like, PENG Xiaoxia, LIU Dongmei
2018, 39(6):  88-94.  doi:10.7506/spkx1002-6630-201806015
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Objective: To screen 29 Lactobacillus strains isolated from kefir grains and fermented pickles for cholesterol-lowering activity and to explore the mechanism of action of the selected isolates in degrading serum cholesterol in rats. Methods: One of these isolates, identified as Lactobacillus plantarum DMDL 9010, was selected for its acid resistance, bile salt tolerance, hydrophobicity, bile salt hydrolase activity and cholesterol-lowering property. A feeding experiment was conducted on fifty eight-week-old Sprague Dawley rats, which were randomly divided into normal diet control, hyperlipidaemic diet control, positive (atorvastatin calcium) control, high-dose and low-dose DMDL 9010 groups. The rats were fed for 10 weeks. The serum levels of total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) were determined on the 28th and 70th day of the experiment. The real-time fluorescence reverse transcription PCR was used to detect the expression level of 3-hydroxy-3-methylglutaryl-CoA reducase (HMGCR) as the rate-limiting enzyme for cholesterol synthesis. Results: L. plantarum DMDL 9010 was capable of 37.58% degradation of cholesterol and showed 35.48% tolerance to bile salt and a hydrophobicity of up to 40%. It had good acid resistance. A hypercholesterolemic rat model was successfully constructed after feeding a high-cholesterol diet for 28 days. Administration of high-dose DMDL 9010 for 70 days significantly reduced serum TC (23.03%) and LDL-C (28.00%), but there was no significant difference between the low-dose and positive control groups. The positive control and high-dose groups significantly down-regulated the expression level of HMG-CoA mRNA in the liver (79.92% and 62.86%, respectively) (P < 0.05). Conclusion: It is possible to develop L. plantarum DMDL 9010 into a functional microecological agent.
Antimicrobial Activity and Mechanism of Lactic Acid on Enterobacter cloacae
WANG Fengting, SUN Zhilan, WU Haihong, XU Xiaoxi, LIU Fang, WANG Daoying, GENG Zhiming, ZHU Yongzhi, XU Weimin
2018, 39(6):  95-100.  doi:10.7506/spkx1002-6630-201806016
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The antimicrobial activity of lactic acid (LA) against a dominant strain of Enterobacter cloacae isolated from spoiled frozen chicken was examined in the study. The results showed that all the selected LA solutions (1.0%, 0.5%, and 0.25%) had bactericidal action against E. cloacae. The cell membrane potential and the leakage of intracellular ATP and ultraviolet-absorbing substances were increased in cells treated with 1.0% LA. The treated cells showed an irregular morphology under transmission electron microscope (TEM); furthermore, the cell wall was damaged and the intracellular contents were leaked out. The permeability of the cytoplasmic membrane was increased as shown by laser scanning confocal microscope and flow cytometry. Therefore, the bactericidal effect of LA against E. cloacae was mainly mediated by damaging the cell wall and consequently increasing the cell membrane permeability, thereby leading to leakage of the intracellular components.
Effect of Rhizoma gastrodiae Extract and Its Three Main Components on Production of Laccase and Mycelial Biomass by Submerged Fermentation of Grifola frondosa
LU Hongyun, WU Tianxiang, ZHONG Min, NIE Wenqiang
2018, 39(6):  101-106.  doi:10.7506/spkx1002-6630-201806017
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This study investigated the effect of exogenous addition of Rhizoma gastrodiae alcohol extract to the culture medium on the production of mycelial?biomass and extracellular laccase by Grifola frondosa in submerged culture. In addition, we identified the role of the key components of the extract, gastrodin (GA), p-hydroxylbenzaldehyde (HBA) and p-hydroxybenzyl alcohol (HA), in affecting the two parameters. These three compounds were quantified by high performance liquid chromatography (HPLC). It was revealed that the R. gastrodiae extract added at proper concentrations, as well as each of its key components at a concentration equivalent to 3 g/L R. gastrodiae extract, exerted a significant stimulating effect?on the growth of mycelial biomass and extracellular laccase activity. By supplementing 3 g/L R. gastrodiae extract to the medium, the maximum biomass and laccase activity of 10.03 g/L and 106.46 U/L, respectively were obtained, 1.62 and 7.41 times higher than those of the control group (P < 0.05), respectively. Both HA and HBA significantly promoted laccase activity and mycelial production. Compared with 3 g/L R. gastrodiae extract, the laccase activity and biomass of the experimental group containing HA increased by 10.25% and 9.17%, respectively. This experiment can provide evidence that R. gastrodiae extract and its purified components can promote fungal growth and laccase activity.
Screening of Aroma-Producing Yeast from Jiangshui, a Traditional Chinese Fermented Vegetable Food, and Optimization of Its Enrichment Medium
YAO Bo, YUN Jianmin, AI Duiyuan, YAN Haijiao, BAI Jie, LI Duojia
2018, 39(6):  107-115.  doi:10.7506/spkx1002-6630-201806018
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In this research, yeast strains were isolated and purified from Jiangshui, a traditional Chinese fermented vegetable food, by the streak plate method. The isolates were screened for aroma-producing ability by sensory evaluation, analysis of their fermentation properties and semi-quantitative analysis of the volatile compounds produced by them using gas chromatography-mass spectrometry (GC-MS). The selected strain was identified by physiological and biochemical tests and molecular biology. The enrichment culture for this strain was optimized using one-factor-at-a-time (OFAT) method and response surface methodology (RSM). A total of 16 yeast isolates were obtained. The strain Y16 was selected out of these and was identified as Hansenula anomala. The optimum medium formulation was determined to 10 °Be′ wort plus 11.0 g/L glucose, 2.3 g/L beef extract, and 0.8 g/L KH2PO4. In this enrichment medium, the final cell concentration reached 8.75 × 108 cells/mL, which was more than 4 times as high as that in the initial wort fermentation medium. Simultaneously, the ethyl acetate yield reached 256.35 μg/mL, and the limonene yield reached 0.083 μg/mL, which increased by 25.39% and 31.75% respectively in comparison with the initial fermentation medium. To sum up, the efficient aroma-producing strain could provide a source of direct vat set (DVS) starter culture for Jiangshui.
Changes in Microflora and Organic Acid Contents during the Fermentation of Chopped Pepper
YE Ling, WANG Jingjing, WANG Rongrong, LI Yong, LIU Chengguo, JIANG Liwen, DENG Fangming, ZHOU Hui
2018, 39(6):  116-121.  doi:10.7506/spkx1002-6630-201806019
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Lactobacillus plantarum W-4 was used as a starter culture for the fermentation of chopped pepper and spontaneous fermentation was also performed as a control. The results obtained indicated that lactic acid bacteria dominated the fermentation process, and the pH of chopped pepper inoculated with L. plantarum W-4 was lower than that of spontaneous fermentation. The chopped pepper fermented with L. plantarum W-4 had higher numbers of lactic acid bacteria and colony count than spontaneous fermentation. The count and changing trend of yeast in the spontaneous fermentation were similar to those of inoculated fermentation, and?coliform?bacteria were present only in the early stage of fermentation but died at the later stage. The analysis of organic acids indicated that the chopped pepper fermented with the starter culture maintained higher content of lactic acid, while spontaneous fermentation had higher content of citric acid and malic?acid; acetic acid was present only in the early stage of spontaneous fermentation.
Optimization of Extraction Process for Trehalose from Baker’s Yeast for Strain Screening and High Density Culture
HONG Housheng, DOU Bingran, GUO Huiming
2018, 39(6):  122-129.  doi:10.7506/spkx1002-6630-201806020
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The microwave-assisted extraction of trehalose was optimized using one-factor-at-a-time and orthogonal array design methods. Intracellular trehalose in yeast cells was determined by 3,5-dinitrosalicylic acid (DNS) method after hydrolysis by trehalase. The optimum conditions for extracting trehalose from 1.5 g of active dry yeast were determined to be extraction at 55 ℃ for 150 min using 40 mL of 0.7 mol/L trichloracetic acid as the extraction solvent with microwave treatment duration of?40 s at 231 W power. Under these conditions, the yield of trehalose was 280.15 mg/g, 15.2% higher than that before optimization. Furthermore, one of the 10 baker’s yeast strains preserved in our laboratory was selected for high yield production of trehalose. In a 50 L self-priming fermenter, the selected strain was used to perform fed-batch fermentation. The maximum wet yeast biomass was 198.34 g/L by using feedback control of dissolved oxygen concentration through feeding molasses. By feeding a predetermined amount of molasses, urea and phosphoric acid as nutrient source, the maximum wet yeast biomass was increased to 264.82 g/L, which was increased by up to 33.52% compared with the original procedure and suggested high density culture of baker’s yeast. In the fermentation process, the alcohol content (V/V) was controlled between 0.7% and 1.0%, thereby effectively improving wet yeast biomass and simultaneously ensuring that the fermentation power is over 650 mL/h, and the modified process was confirmed to stable.
Lactic Acid Production by Fermentation of Soybean Molasses with Lactic Acid Bacteria and Carbohydrate Metabolism
JIANG Yangjuan, XU Li, CHEN Meisi, ZHOU Xiaomin, HAN Cuiping, WANG Song
2018, 39(6):  130-134.  doi:10.7506/spkx1002-6630-201806021
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Lactobacillus delbrueckii ssp. bulgaricus KLDS1.8501, L. acidophilus KLDS1.0327, L. acidophilus ATCC11975, L. plantarum subsp. plantarum CICC23168, L. casei ATCC393 and L. plantarum NAU322 were separately utilized to ferment soybean molasses to produce lactic acid. The lactic acid production and carbohydrate metabolism of these six strains were analyzed by high performance liquid chromatography (HPLC). The results indicated that L. plantarum subsp. plantarum CICC23168 showed better growth (6.66 × 109 CFU/mL), greater sugar consumption (22.48 g/L) and higher production (12.18 g/L) of lactic acid during 24 h incubation at 37 ℃ in 15 °Brix soybean molasses, compared to the other bacteria. Therefore, L. plantarum subsp. plantarum CICC23168 is a potential strain for producing lactic acid by using soybean molasses.
Isolation and Identification of a Strain for High-Yield Production of L-Lactic Acid and Optimization of Its Culture Medium
SUN Lihui, WANG Yunxiao, Lü Shiwen, LI Man, HE Leiyu, BAO Yongming
2018, 39(6):  135-140.  doi:10.7506/spkx1002-6630-201806022
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A strain, LB-103, which is capable of producing high concentration of L-lactic acid with high optical purity was isolated from kimchi. The optical purity of the produced lactic acid was measured to be 100% by using L-/D-lactic acid enzymatic test kit. The strain was identified as Lactobacillus rhamnosus based on its morphological features, physiological and biochemical properties (VITEK 2 automated microbial identification system), and 16S rDNA sequence analysis. It was named L. rhamnosus DLF-15038. Then the fermentation medium for L-lactic acid production was optimized, and the results showed that yeast extract (10 g/L) and cottonseed meal (15 g/L) were used as nitrogen sources to maintain high L-lactic acid yield and simultaneously reduce the cost. The optimal concentrations of inorganic salts in the medium were as follows: CH3COONa 3 g/L, KH2PO4 2 g/L, MnSO4 0.3 g/L and MgSO4 0.2 g/L. Finally, fed-batch fermentation was performed under the optimized conditions in a 5-L fermentor. We obtained 165.15 g/L L-lactic acid after 72 h fermentation by using the strain DLF-15038, with a yield of 93.34% (g L-lactic acid/g glucose), and a productivity of 2.29 g/(L·h).
Construction of a Stationary-Phase?Sigma?Factor?Gene (rpoS) Defective Mutant of Salmonella typhimurium and Function of RpoS Factor under Environmental Stress
LIANG Yungai, GUI Meng, WANG Shun, LIU Mi, ZHANG Qing, ZHOU Kang
2018, 39(6):  141-147.  doi:10.7506/spkx1002-6630-201806023
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Salmonella typhimurium adapts to environmental stresses through its own regulatory system, in which the stationary-phase?sigma?(RpoS) factor plays an important role. The objective of this study was to construct a rpoS-defective mutant strain (SL1344/DrpoS) of S. typhimurium SL1344 using Red homologous recombination technique and to compare the growth of SL1344/DrpoS and SL1344 under different stresses including 3.5% NaCl, 42 ℃, and pH 4.0. Besides, this research also focused on the effect of pre-treatment of Salmonella with different concentrations of salt on its growth in a medium containing 3.5% NaCl in order to demonstrate the effect of rpoS on the adaptability of S. typhimurium to the stressful environment. The results showed that the growth of both strains was inhibited by 3.5% NaCl, and SL1344/DrpoS was more significantly inhibited. The maximum growth rate of SL1344 was 2.49 times as higher as that of SL1344/DrpoS. Under the conditions of 42 ℃ and pH 4.0, the maximum growth rate of SL1344 was 1.33 and 2.77 times as higher as that of SL1344/DrpoS, respectively. There were differences in the growth of the two strains after stimulation by different salt concentrations for different times. The construction of SL1344/DrpoS can lay the foundation for further study on the role of RpoS of S. typhimurium in response to environmental stresses and for the prevention and treatment of salmonellosis.
Evaluation of Probiotic Properties of Lactobacillus plantarum Sc52 and Its Application in a Hypoglycemic Product
WEN He,, XIAO Fengyan, DUAN Cuicui, GAO Lei, ZHAO Yujuan, NIU Chunhua, ZHAO Quan, LI Shengyu
2018, 39(6):  148-154.  doi:10.7506/spkx1002-6630-201806024
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Objective: This study aimed to investigate the in vitro probiotic properties of Lactobacillus plantarum Sc52 and its application in a hypoglycemic product and to analyze the hypoglycemic effect of the product. Methods: The in vitro probiotic properties of L. plantarum Sc52 were evaluated by its acid and bile salt tolerance, surface hydrophobicity and aggregation ability and minimum inhibitory concentration (MIC) of antibiotics against it. A mixed culture of L. plantarum Sc52 and other probiotics was used to ferment a composite aqueous extract of different both edible and medicinal plant materials to develop a solid beverage. In order to evaluate the hypoglycemic activity of the product, a diabetic mouse model was established by feeding high fat diet combined with streptozotocin injection. All the mice were divided into three groups: control, model and treatment groups. The mice in the treatment group were continuously administered with the solid beverage by gavage for four weeks. The levels of fasting blood glucose, the area under the blood glucose curve, the levels of serum lipids, insulin and inflammatory factor were measured. Results: L. plantarum Sc52 exhibited excellent resistance to acid and bile salt. When it was cultivated for 3 and 4 h in a medium at pH 3.0 with 1 g/100 mL bile salt concentration respectively, the survival rates were higher than 55% and 32%. L. plantarum Sc52 possessed strong aggregation ability, which reached (89 ± 0.3)% after standing for 48 h, and showed high sensitivity to penicillin and rifampicin. Compared with the model group, the auxiliary hypoglycemic product could significantly decrease the levels of fasting blood glucose, blood lipid and tumor necrosis factor-α and significantly elevate insulin levels. Conclusions: L. plantarum Sc52 exhibited good in vitro probiotic properties, and the solid beverage developed in this study had obvious hypoglycemic effects.
Optimization of Preparation of Antimicrobial Peptides by Two-Step Enzymatic Hydrolysis of Fish Scales Using Response Surface Methodology and Antimicrobial Activity of Purified Antimicrobial Peptide
SHI Yongqing, WANG Qiaoqiao, WU Danli, LI Xiaoyu, CAI Luyun, LI Jianrong
2018, 39(6):  155-161.  doi:10.7506/spkx1002-6630-201806025
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This study aimed to prepare antimicrobial peptides (AMPs) by two-step enzymatic hydrolysis of crucian carp scales and to evaluate the antimicrobial activity of purified AMPs. Hydrolysis conditions were optimized by one-factor-at-a-time method and response surface methodology based on the diameter of inhibition zones against tested bacteria. The enzymatic hydrolysate prepared using optimized conditions was then purified by Sephadex G-25 column chromatography, yielding only a single peak (G2) with antimicrobial activity. The minimum inhibitory concentration (MIC) of G2 was tested. The results indicated that a solid-to-liquid ratio of 30 g/100 mL and sequential hydrolysis with alcalase at pH 9.5 and 55 ℃ for 62 min followed by acid protease at pH 3.0 and 34.4 ℃ for another 3 h were found to be the optimal conditions to obtain a greater diameter of inhibition zone against Vibrio parahemolyticus of 27.72 mm, which was well matched with the predicted value (27.37 mm). The MIC of G2 was 1.56 μg/mL against Pseudomonas and Shewanella putrefaciens, and 6.25 μg/mL against Escherichia coli, Staphylococcus aureus, Salmonella choleraescens, V. parahemolyticus and Bacillus subtilis. In conclusion, AMPs derived from freshwater fish scales by stepwise enzymatic hydrolysis possess strong antimicrobial activity.
Microbial Diversity of Berries, Leaves and Soil of Grapevine Plants Grown in Xinjiang Analyzed by High-Throughput Sequencing
WEI Yujie, ZOU Wan, MA Wenrui, YAN Yinzhuo, WU Yun, XUE Jie
2018, 39(6):  162-170.  doi:10.7506/spkx1002-6630-201806026
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This research aimed to analyze the diversity and composition of microbial communities in soils as well as on grapevine leaves and berries from three vineyards located in Xinjiang by high-throughput sequencing. A total of 1 043 102 fungal high-quality sequences were obtained from 27 samples, representing 237 fungal genera in 5 fungal phyla, as well as 2 422 188 high-quality bacterial sequences, representing 8 bacterial phylum and 314 bacteria genus were obtained. The soil samples showed the highest diversity and quantity of both fungi and bacteria followed by grape leaves and berries. The predominant fungi identified in the soil included Saccharomyces, Sordaria, Tetracladium and Geomyces, and the predominant bacteria included Arthrobacter, Kaistobacter and Skermanella. However, for both plant materials, the predominant fungi included Aureobasidium, Cryptococcus, Aspergillus and Sporospora, and the predominant bacteria included Pseudomonas, Sphingomonas and Adhaeribacter. Moreover, microbial diversity varied from vineyard to vineyard. In summary, understanding of the complex microbial communities in the vineyard can offer a theoretical basis for further exploitation and utilization of distinctive microorganisms in the wine industry.
Identification and Flavor Profile of a Thermoactinomycetaceae Strain Separated from Moutai-Flavor Daqu
LI Dounan, HUANG Wei, WANG Xiaodan, LUO Xiaoye, QIU Shuyi
2018, 39(6):  171-176.  doi:10.7506/spkx1002-6630-201806027
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A thermophilic actinomycete strain, FBKL4.010, was successfully isolated from Moutai-flavor Daqu. Using morphological, physiological method, 16S rRNA genephylogenetic analysis and phylogenetic analysis, it was identified as Laceyella sacchari. Its optimum growth temperature was 45 ℃. According to the liquor-making system, pure-culture solid-state fermentation experiments were designed with strain FBKL4.010 and its flavor components were detected by solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS). The results showed that this strain could produce a large number of pyrazine and aromatic substances with strong Douchi and nutty flavors in fermentation broth. Tetramethyl pyrazine, which was considered to be one of the main flavour components of Moutai-flavor liquor, accounted for 43.318% of total volatile components. This study is expected to lay a good foundation for further research on the relationship between this strain and the formation of Moutai flavour.
Biological Characteristics of Vibrio parahaemolyticus during Growth in Adverse Environment
GAO Lu, OUYANG Min, ZHANG Hui, RAO Shengqi, YIN Yongqi, YANG Zhenquan,, SHEN Mingjun
2018, 39(6):  177-182.  doi:10.7506/spkx1002-6630-201806028
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The objective of this study was to observe the growth characteristics of Vibiro parahaemolyticus under various environmental stresses. The survival, biofilm formation ability, hemolysin activity and extracellular protease production of V. parahaemolyticus (CICC21617) exposed to low salinity (0.9 g/100 mL NaCl), low pH (5.0) or high temperature (50 ℃) were investigated after 10 passages. It was found that the stressed and passaged strains had enhanced survival and biofilm formation ability and decreased hemolysin activity and showed significantly reduced extracellular protease production compared with the parental strain. The expression levels and types of low molecular weight outer membrane proteins of the stressed strains were also different between the parental and passaged strains. Thus, V. parahaemolyticus is capable of changing their own biological characteristics to adapt to adverse conditions. Furthermore, the tolerance of V. parahaemolyticus to environmental stress can be enhanced after adaptive training.
Optimization of Enzymatic Preparation of Antioxidant Peptides from Protein Hydrolysate of the Marine Microalgae Nannochloropsis by Response Surface Methodology
Lü Xiaojing, CAO Dequn, XU Nianjun
2018, 39(6):  183-188.  doi:10.7506/spkx1002-6630-201806029
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Protein from the marine microalga Nannochloropsis was extracted and hydrolyzed with pepsin to prepare antioxidant peptides. The effects of enzyme-to-substrate ratio, substrate concentration, hydrolysis temperature and pH on the degree of hydrolysis (DH) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of hydrolysates were investigated and the process conditions were optimized using one-factor-at-a-time (OFAT) method and response surface methodology (RSM). The optimal hydrolysis conditions were determined as follows: substrate concentration, 5.0 mg/mL; temperature, 32 ℃; pH, 1.36; and enzyme-to-substrate ratio, 6%. The hydrolysate prepared under these conditions could scavenge 51.85% of DPPH free radical.
Component Analysis
Quantification and Characterization of Polysaccharides from Different Aged Dendrobium officinale Stems
QIN Zifang, TAN Xiaoyan, NING Huijuan, HU Jing, Miao Yuxin, ZHANG Xiuqing
2018, 39(6):  189-193.  doi:10.7506/spkx1002-6630-201806030
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This study quantified and characterized polysaccharides from different aged Dendrobium officinale stems. The molecular weights of polysaccharides were measured by gel permeation chromatography, and their monosaccharide composition was analyzed by pre-column derivatization high performance liquid chromatography (HPLC). In addition, the structural characteristics and antioxidant activity of polysaccharides were investigated. The results showed that the stems of five-year-old D. officinale had the highest polysaccharide content (238.60 mg/g), followed by three-year-old D. officinale (232.74 mg/g). The molecular weight of the primary polysaccharide (1 383 kDa) in four-year-old D. officinale was the highest, followed by that (1 046 kDa) of three-year-old D. officinale. Mannose was the most abundant monosaccharide in one-year-old D. officinale, followed by the three-year-old one. The polysaccharides of three-years-old D. officinale had the strongest Fe3+ reducing power hydroxyl radical scavenging activity and total antioxidant capacity. Based on polysaccharide content and in vitro antioxidant activities, the quality of three-year-old D. officinale was the best.
Non-Destructive Detection of Vitamin C Content in “Lingwu changzao” Jujubes (Zizyphus jujuba Mill. cv. Lingwu Changzao) Using Visible Near Infrared Hyperspectral Imaging
HE Jialin, QIAO Chunyan, LI Dongdong, ZHANG Haihong, DENG Hong, SHAN Qimei, GAO Kun, MA Rui
2018, 39(6):  194-199.  doi:10.7506/spkx1002-6630-201806031
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This study aimed to explore the feasibility of predicting the vitamin C (VC) content in “Lingwu changzao” jujubes using hyperspectral imaging and to find the best prediction model. Hyperspectral images of 100 jujube samples were collected in the wavelength range of 400 to 1 000 nm. Genetic algorithm (GA), successive projection algorithm (SPA) and competitive adaptive reweighted sampling (CARS) algorithm were used to extract the characteristic wavelengths from the original spectral data. Partial least squares (PLS) and least squares support vector machine (LSSVM) were separately used to establish VC prediction models based on the full and characteristic spectra. The results showed that standard normal variate (SNV) transformation was the best preprocessing approach. The cross validation correlation coefficient (Rcv) of the PLS model was 0.839 5, and the root mean square error of cross validation (RMSECV) was 16.248 2. GA, SPA and CARS methods were used to select 12, 5, and 26 characteristic wavelengths. The PLS model based on CARS method was the best among the models developed, and its Rc, Rp, RMSEC and RMSEP values were 0.896 2, 0.889 2, 10.746 2%, and 12.145 3%, respectively. These results confirmed the feasibility of using hyperspectral imaging for the non-destructive detection of VC content in “Lingwu Changzao” jujubes.
Isolation and Structural Identification of Chemical Constituents from Seeds of Raphanus sativus L.
JIN Hongguang, LI Yuquan, LING Yun, ZHANG Lifang, REN Jin, FANG Liang, JIANG Shenhua
2018, 39(6):  200-206.  doi:10.7506/spkx1002-6630-201806032
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This study was done to analyze the chemical constituents of Raphanus sativus L. seeds for exploring the material basis for consumption of raw Raphanus sativus L. seeds. Sixteen compounds were isolated and purified by chromatography on macroporous resin HP-20, high-porosity polystyrene (MCI gel), ODS, silica gel and LiChroprep RP-18 columns. Their structures were identified by spectroscopic methods as cis-13-docosenoic acid (1), stigmasta-4-en-3-one (2), (22E,24R)-ergosta-5,22-dien-3β-ol (3), β-stigmast-5-en-3β-ol (4), trans-methyl ferulate (5), trans-methyl sinapate (6), β-sitosterol-3-O-β-D-glucoside (7), α-D-galactopyranosyl-(1-6)-α-D-glucopyranosyl-(1-2)-β-D-fructofuranoside) (8), β-D-fructofuranosyl-α-D-(6-O-sinapoyl)-glucopyranoside (9), β-D-(3-O-sinapoyl)-fructofuranosyl-α-D-glucopyranoside (10), β-D-(3-O-sinapoyl)-fructofuranosyl-α-D-(6-O-sinapoyl)-glucopyranoside (11), β-D-(3,4-O-disinapoyl)-fructofuranosyl-α-D-(6-O-sinapoyl)-glucopyranoside (12), isorhamnetin, 3-O-β-D-glucoside (13), isorhamnetin 3,4’-di-O-β-D-glucoside (14), isorhamnetin, 3-O-β-D-glucoside-7-O-α-L-rhamnose (15) and 3’-O-methyl-(-)-epicatechin 7-O-β-D-glucoside (16), respectively. Among these, compounds 2, 3, 7–10, and 13–16 were isolated from the plant for the first time.
Determination of Anthocyanins in Red-Fleshed Walnut by Ultra Performance Liquid Chromatography-Electrospray Ionization Tandem Mass Spectrometry
LI Yongzhou, SHANG Junhua, ZHOU Yifei, WU Wenjiang, JIE Bo, WU Guoliang
2018, 39(6):  207-214.  doi:10.7506/spkx1002-6630-201806033
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This study was concerned with the identification and quantification of anthocyanins in tree leaves and peel of red-fleshed walnut harvested at different growing stages (early sprouting, leaf growth and fruiting) by ultra performance liquid chromatography with photodiode array detection coupled with electrospray ionization tandem mass spectrometry (UPLC-PDA-MS/MS). The samples were from the Fruit Experimental Station of the College of Horticulture of Henan Agricultural University. Leaves of ordinary walnut were used as control. The results showed that the limits of quantification (LOQs) for eight target compounds were in the range of 0.60–0.90 μg/mL. The calibration curves were linear in the range of 0–300 μg/L with correlation coefficient (R2) of 0.999 0–0.999 6. Walnut peel and leaves were statistically significantly different with respect to major anthocyanins, as determined by UPLC-PDA-MS/MS. The analytical method proved to be easy to operate, sensitive and repeatable and thus was useful for rapid identification and quantification of a variety of anthocyanins in walnut materials.
Analysis of Chemical Constituents in Male Flowers of Eucommia ulmoides by Liquid Chromatography Coupled with Electrospray Ionization-Triple Quadrupole-Time of Flight-Tandem Mass Spectrometry (LC-ESI-Triple TOF-MS/MS)
YAN Ying, ZHAO Hui, ZOU Lisi, LIU Xunhong, CHAI Chuan, WANG Shengnan, HUA Yujiao
2018, 39(6):  215-221.  doi:10.7506/spkx1002-6630-201806034
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The chemical constituents in male flowers of Eucommia ulmoides were analyzed by liquid chromatography coupled with electrospray ionization-triple quadrupole-time of flight-tandem mass spectrometry (LC-ESI-Triple TOF-MS/MS). The separation and analysis were carried out on a reversed-phase C18 column with gradient elution using 0.1% formic acid (A)-acetonitrile (B) under the negative ionization mode of ESI. According to the accurate mass of quasi-molecular and product ions provided by Triple TOF-MS/MS, a total of 32 constituents were identified or tentatively presumed by comparing with reference standards and literature data, including 2 lignans, 9 iridoids, 8 penylpropanoids, 12 flavonoids and one phenolic glycoside. This study may provide basic information for further research?on the pharmacodynamic material basis and intensive utilization of male flowers of Eucommia ulmoides.
Changes in Major Components and Antioxidant Activity of Papaya Beverage during Fermentation with Lactic Acid Bacteria
CHEN Ronghao, CHEN Wenxue, CHEN Haiming, ZHANG Guanfei, CHEN Weijun, TANG Hui, HU Yueying
2018, 39(6):  222-229.  doi:10.7506/spkx1002-6630-201806035
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This study aimed to evaluate changes in the quality and antioxidant activity during the fermentation of papaya juice by lactic acid bacteria (a mixture of Lactobacillus bulgaricus and Streptococcus thermophilus). The results showed that the strains exhibited good viability and high acid-producing ability after 48 h fermentation, as demonstrated by a pH decrease from 5.36 to 3.11 and a simultaneous decrease in reducing sugar content from 8.69% to 5.15%. The antioxidant activity was evaluated by four different assays. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of papaya juice decreased to a level higher than 50% after 48 h fermentation. Large amounts of organic acids were produced during the fermentation process, including 1 264.39 mg/100 mL of lactic acid. Esters were the most abundant volatile compounds in the fermented juice. The number of ketones was highest among the new compounds formed during fermentation. Thus, papaya juice fermented with lactic acid bacteria could be used as a novel functional beverage.
Analysis of Volatile Aroma Compounds of Heated Rosa roxbuighii Tratt Juice by Solid-Phase Microextraction Combined with Gas Chromatography-Mass Spectrometry and Principal Component Analysis
PENG Bangyuan, ZHANG Hongli, SUN Xiaojing, WANG Xueya, DING Zhuhong
2018, 39(6):  230-236.  doi:10.7506/spkx1002-6630-201806036
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Fuzzy comprehensive evaluation was employed in the present research to assess the sensory quality of heated Rosa roxburghii Tratt juice. Subsequently, the volatile aroma components of raw and heated juice samples were determined by solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) and analyzed by principal component analysis (PCA). Results showed that a total of 65 volatile components were detected from raw juice and 4 heated samples, dominated by aldehydes, alcohols and alkenes. The number and amount of volatile compounds in the heated samples increased first and then decreased; 70 ℃, 30 min heated juice contained the largest number (61) of volatile compounds, accounting for 89.22% of the total, and its volatie composition was most similar to that of raw juice. The main aroma components identified by PCA were esters and alkenes. These findings were consistent with fuzzy comprehensive evaluation. Therefore, heat treatment at 70 ℃ for 30 min were the optimal conditions for thermal processing of R. roxburghii Tratt juice.
Comparison of Volatile Flavor Compounds and Qualities between Naturally Fermented and Inoculated Chinese Leaf Mustard (Brassica juncea Coss.) Grown in Hunan Province, China
HOU Aixiang, WANG Yiqi, HUANG Qing, LI Zongjun
2018, 39(6):  237-245.  doi:10.7506/spkx1002-6630-201806037
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Solid phase micro-extraction (SPME) and gas chromatography-mass spectrometry (GC-MS) were used to analyze the volatile flavor compounds of naturally fermented and artificially inoculated Chinese leaf mustard grown in Hunan province, China. The two samples were contrasted with respect to nitrite content, pH value and sensory quality. The results showed that the main volatile flavor compounds of naturally fermented and inoculated samples with temperature control, were similar, with esters being the most abundant constituents (over 40.02%). The volatile flavor composition of naturally fermented mustard at ambient temperature was significantly different from those of the former two samples, with the predominance of alcohols (only 5.51%). A total of 64 (11 classes) of volatile flavor compounds were identified in four fermented Chinese leaf mustard samples: A, inoculated with Lactobacillus plantarum and Pediococcu pentosaceus (21 volatile compounds including 7 esters belonging to 9 classes); B, inoculated with L. plantarum, P. pentosaceus and Leuconostoc mesenteroides (24 volatile compounds including 8 esters belonging to 10 classes); C, naturally fermented with temperature control (20 volatile compounds including 5 esters belonging to 9 classes; and D, naturally fermented at ambient temperature (32 volatile compounds including 7 alcohols and 6 esters belonging to 10 classes). The nitrite content and pH value of artificially inoculated Chinese leaf mustard were lower than those of natural fermentation, and the sensory scores of the samples from artificial inoculation and temperature-controlled natural fermentation were similar but higher than that of natural fermentation without temperature. Therefore, artificial inoculation can be useful to ensure the commerciality and safety of fermented Chinese leaf mustard and is promising for wide application.
Processing Technology
Optimized Pre-Treatment and Storage Properties of Low-Salt Pickled Cowpea
LIANG Li, DU Aruna, MA Tao, CHEN Fang, LIAO Xiaojun, HU Xiaosong, SONG Yi
2018, 39(6):  246-251.  doi:10.7506/spkx1002-6630-201806038
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Changes in the hardness and color value of fresh cowpea were investigated under different blanching conditions and at different concentrations of browning inhibitor. Then medium-short wave infrared drying technology was used for partial dehydration processing of the pretreated material to determine the effects of radiation temperature, power and distance on the drying characteristics of cowpea. Furthermore, the quality change of pickled cowpea during storage was investigated and two fermentation methods were compared for improving the color and hardness. Results showed that the softening and browning of cowpea could be delayed by blanching at 90 ℃ for 1 min and soaking in 20 g/L calcium lactate solution. The infrared drying conditions were as follows: 70 ℃, 900 W and radiation distance of 10 cm, 50 min. The critical moisture point of semi-dry cowpea was 70%. After 4 weeks of storage, the total number of colonies was 4.4 × 103 CFU/g and the most probable number (MPN) of coliforms was under 3 MPN/g, indicating good microbiological quality. The optimal rehydration condition of semi-dry cowpeas was 20 ℃ and 3 h. Pickle brine was more suitable to obtain improved cowpea pickle quality.
Optimization of Storage Conditions for Inhibiting Off-Flavor Formation in Adlay Seed
WANG Shasha, LI Changfeng, TAN Yue, XU Yao, XIA Ji, DING Yongbo, KAN Jianquan,
2018, 39(6):  252-257.  doi:10.7506/spkx1002-6630-201806039
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The effect of storage temperature, packaging method and antioxidant on the off-odor of adlay seeds was examined and the off-flavor compounds of stored adlay seeds were measured by head space solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). Meanwhile, optimization of storage conditions for inhibiting off-flavor formation in adlay seeds was carried out using orthogonal array design method. The results showed that off-flavor formation could be restrained by using the appropriate storage temperature, antioxidant and packaging method. The effects of the three factors on the off-flavor score of adlay seeds were in the following order: antioxidant > storage temperature > packaging method. The optimum conditions were determined as storage at 4 ℃ and opaque and vacuum packaging with addition of 0.01% blended antioxidants (BHA:TBHQ = 4:1). After 6 months of storage under the optimized conditions the off-flavor score was at the lowest level of 2.5.
Optimization of Heat Pump Drying Process for Long Cowpea
ZHANG Bo, JI Changying, JIANG Sijie, XU Weiyue, TIAN Guangzhao, GU Baoxing
2018, 39(6):  258-263.  doi:10.7506/spkx1002-6630-201806040
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This study aimed to improve the quality parameters of heat pump dried long cowpea such as rehydration characteristics and color, and simultaneously to lower energy consumption during heat pump drying and increase drying efficiency. The rehydration ratio, color difference, per-unit energy consumption and drying time were investigated with respect to three independent variables, namely drying temperature, blanching time and material density. A multiple regression model was developed for each of these response variables in order to optimize the selected independent variables. A blanching time of 3 min, a material density of 2 kg/m2 and a drying temperature of 50 ℃ were determined as the optimal conditions. Under these conditions, the experimental values of rehydration ratio, color difference, per-unit energy consumption and drying time were 1.15, 22.39, 14.31 (kW·h)/kg and 7 h, respectively, which were very close to the predicted ones. These optimized process conditions can provide a useful basis for heat pump drying of cowpea.
Preparation and Stability of Microcapsules Containing Functional Lipids
WANG Dawei, REN Huahua, YANG Jiadan, FAN Hongxiu, LI Guijie
2018, 39(6):  264-269.  doi:10.7506/spkx1002-6630-201806041
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The microencapsulation of functional lipids was optimized using one-factor-at-a-time and orthogonal array design methods. Sodium alginate was used as the wall material, and calcium chloride solution as the curing agent. The voltage was 2 000 V and the curing process lasted for 30 min at a stirring rate of 50%. The response variable was microencapsulation efficiency. A sodium alginate concentration of 1.6%, a frequency of 620 Hz, a CaCl2 concentration of 1.5% and a feeding rate of 4.0 mL/min were found to be the optimal conditions to obtain a higher microencapsulation efficiency of (88.32 ± 0.28)%. The microcapsules under scanning electron microscope (SEM) showed a uniform spherical shape with smooth surface. The microcapsules were yellowish in color and had a mononuclear structure under stereomicroscope. Fourier transform infrared spectroscopy showed that the microcapsules contained the characteristic peaks of lipids and the chemical structure of the core did not change. Thermogravimetric analysis showed that the microcapsules had good thermal stability at below 250 ℃. Moreover, the microcapsules significantly increased the oxidative stability of the core material under the accelerated storage conditions.
Optimization of Simultaneous Extraction of Cordycepin and Adenosine Produced by Solid-State Fermentation with Cordyceps militaris by Response Surface Methodology
YU Ge, WANG Li, HU Xinlei, SUN Yanan, ZHANG Xin, LI Ming, LI Wenxiang
2018, 39(6):  270-275.  doi:10.7506/spkx1002-6630-201806042
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Cordycepin and adenosine were simultaneously extracted from the solid-state culture of Cordyceps militaris with rice and brewer’s spent grain (BSG) as co-substrates. The extraction process was optimized using one-factor-at-a time method and response surface methodology (RSM). The total yield of cordycepin and adenosine was investigated as a function of four variables including extraction time, ethanol concentration, solvent-to-solid ratio and temperature. The optimal extraction conditions were found to be extraction at 45 ℃ for 87 min with water as a solvent at a solvent-to-solid ratio of 22:1 (mL/g). Under these conditions, The maximum total yield (2.491‰) of cordycepin and adenosine was experimentally obtained, which agreed with the predicted value (2.487‰). Accordingly, the regression model developed showed excellent goodness of fit. The solid-state culture of Cordyceps militaris is a promising rich of cordycepin and adenosine.
Safety Detection
Multiplex PCR Method for Detection of Four Foodborne Pathogens on Fresh-Cut Fruits and Vegetables
FENG Ke, HU Wenzhong, JIANG Aili, Sarengaowa, XU Yongping, SI Qi, MA Xinxiu
2018, 39(6):  276-283.  doi:10.7506/spkx1002-6630-201806043
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The objective of this study is to establish a multiplex PCR assay for the detection Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus and Escherichia coli O157:H7 on fresh-cut fruits and vegetables. Four pairs of specific primers were designed according to the inlA gene of L. monocytogenes, the invA gene of S. typhimurium, the nuc of S. aureus and the wzy gene of E. coli O157:H7, respectively. The limits of detection (LODs) for L. monocytogenes, S. typhimurium, S. aureus and E. coli O157:H7 were 3.5 × 106, 1.6 × 105, 2.4 × 105, and 4.8 × 105 CFU/mL, respectively. This assay was advantageous for saving labor, reagents and time (9–11 h vs. 5–7 d) over traditional culture method. The present method can provide a significant guidance for enterprises or analytical and testing centers to monitor massive samples.
Establishment of Simple Sequence Repeat Fingerprint for Identification of Mungbean Varieties (Vigna radiate L.) Grown in Liaoning
ZHAO Yanan, WANG Ying, ZHANG Dongjie
2018, 39(6):  284-290.  doi:10.7506/spkx1002-6630-201806044
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Objective: This study aimed to establish a DNA fingerprint for rapid and accurate identification of mung bean varieties grown in Liaoning. Methods: A total of 48 mung bean samples from different varieties were used to construct a fingerprint database and a DNA fingerprint with 15 pairs of polymorphic simple sequence repeat (SSR) primers. Results: A total of 58 alleles were detected, 2–7 of which, with an average of 3.9, were detected with each pair of the primers used, and 13 specific bands were obtained, accounting for about 22.4% of the total. The polymorphic information content (PIC) varied from 0.114 5–0.776 4, with an average of 0.378 4. Five pairs of efficient primers were selected. The discrimination rate obtained with their combination was as high as 75%, while a discrimination rate of 89.68% was obtained with a combination of all 15 primer pairs. Based on these results, the DNA fingerprint database composed of the digits 0 and 1 and the SSR fingerprint were established, which allowed unequivocal?identification of all the varieties except a few unique ones. Conclusion: The SSR fingerprint presented in this study can open up a new way of identifying mung bean varieties and provide a basis for mung resource evaluation and protection as well as breeding of new varieties.
Rapid Identification of Maca Quality Based on Odor Fingerprint
DANG Yanting, YUAN Peng, XIA Kai, HAN Xiaofeng, LIU Shiwei, ZHAO Kexin, ZHOU Wenxuan, WEN Lin, LI Aimin, DUAN Shenglin
2018, 39(6):  291-297.  doi:10.7506/spkx1002-6630-201806045
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This work focused on 36 maca samples collected from 24 producing regions. Headspace odors from maca samples were collected and analyzed by an electronic nose (E-nose) and total glucosinolate content was determined by high performance liquid chromatography (HPLC). The correlation between glucosinolate contents and E-nose responses was analyzed by SPSS 22.0 statistical analysis software in an effort to build a model to rapidly identify maca quality using a soft independent modeling of class analogy (SIMCA) algorithm. The results showed a significant correlation between three sensors, T30/1, P30/1 and P30/2, and glucosinolates level. According to the resulting SIMCA models, the samples could be divided into three grades: grade 1 (glucosinolates content ≥ 10 mg/g), grade 2 (5 mg/g ≤ glucosinolates content < 10 mg/g), and grade 3 (glucosinolates content < 5 mg/g). The SIMCA models based on electronic nose data could allow rapid grading of maca quality according to its glucosinolates content.
Development of a Rapid Strip Test for Detection of Reducing Sugar
LIU Xiao, MA Qianli, YANG Rendang
2018, 39(6):  298-301.  doi:10.7506/spkx1002-6630-201806046
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A rapid strip test for the detection of reducing sugar was developed based on the fact the chromogenic reaction of reducing sugar and 3,5-dinitrosalicylic acid (DNS) is triggered by the alkaline environment and the heat generated by the reaction between calcium oxide and aqueous samples. The experimental conditions were determined and the detection range of the test system was investigated. Standard colorimetric card was prepared. The results showed that the best base paper was rapid qualitative filter paper, the concentration of chromogenic agent was 6.0 g/L and drying temperature was 50 ℃. The test required only 5 min and the detection range was 0.01–3.00 mol/L. This method had the advantages of simple operation, time saving, rapid color development and convenience. It was suitable for fast semi-quantitative detection of reducing sugar in food and medicinal fields and fermentation industry.
Rapid and Quantitative Detection of Escherichia coli O157:H7 in Milk by Flow Cytometry
LIU Siyuan, GU Shaopeng, SUI Zhiwei, LIU Sizhang, XUE Lei, HUO Nairui
2018, 39(6):  302-306.  doi:10.7506/spkx1002-6630-201806047
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The purpose of this study was to develop a flow cytometry (FCM) method for rapid and quantitative detection of Escherichia coli O157:H7 in milk. E. coli O157:H7 was labeled with fluorescein isothiocyanate (FITC)-conjugated anti-E. coli O157 monocolonal antibodies and then detected by flow cytometry (green fluorescence channel). Serial 10-fold dilutions of E. coli O157:H7 in PBS were tested by FCM method under optimized reaction conditions. The detection range of this method was 2.57 × 103–1.12 × 108 CFU/mL and the sensitivity was 2.57 × 103 CFU/mL. Then the FCM method was applied to artificially contaminated milk samples with 2.31 × 104–1.48 × 108 CFU/mL E. coli O157:H7. The results were consistent with the plate counting method. The sensitivity of our method was 2.31 × 104 CFU/mL and the process required 35 min. This method allowed for rapid, efficient and sensitive detection of E. coli O157:H7 in milk samples. Thus, it has a great potential for application in rapid screening and monitoring of foodborne pathogens.
Determination of 35 Polychlorinated Biphenyls in Vegetables by Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) Extraction Coupled with Gas Chromatography-Tandem Mass Spectrometry
XIE Sisi, LU Junwen, LI Rong, ZHANG Xianchen, ZHANG Pengjie, RONG Yutang, CHEN Lisi, XIE Lifang
2018, 39(6):  307-314.  doi:10.7506/spkx1002-6630-201806048
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A quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed for the determination of 35 polychlorinated biphenyls (PCBs) in vegetables. The sample was extracted using a solid-phase extraction column and QuEChERS with ethyl acetate as the extraction solvent, and then the extract was dried with anhydrous magnesium sulfate and cleaned up with primary secondary amine (PSA)/graphitized carbon black solid-phase extraction cartridge before being analyzed by GC-MS/MS under the selective reaction monitoring (SRM) mode and quantified by internal standard method. The results showed that the calibration curves for all target analytes displayed good linear relationships over the concentration range of 10-1 000 μg/L, with correlations coefficients of more than 0.999. The limits of detection (LODs) were 0.65-18.12 ng/kg. The average recoveries of 35 compounds at three spiked levels of 0.01, 0.02 and 0.10 mg/kg ranged from 72.3% to 119.0%, with relative standard deviations of 0.4% to 9.8%. The simplicity, rapidity, sensitivity and accuracy of the method make it suitable for rapid detection of PCB residues in vegetables.
Determination of 23 Organophosphorus Pesticide Residues in Tea by QuEChERS Extraction with Multi-Walled Carbon Nanotubes (MWCNTs) Coupled to Gas Chromatography
HUANG Tiantian, TANG Hua, DONG Xiaoqian, LIU Songnan, XU Wenwen, WANG Hua, ZONG Qi
2018, 39(6):  315-321.  doi:10.7506/spkx1002-6630-201806049
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This study intended to develop a method for the determination of 23 organophosphorus pesticide residues in tea by gas chromatography (GC). The target pesticides in tea were extracted by a modified QuEChERS method with acetone as the solvent, followed by cleanup with N-propyl ethylenediamine (PSA) adsorbent and multi-walled carbon nanotubes (MWCNTs). The quantification was performed by the matrix external standard method. Good linearity was observed for all calibration curves with correlation coefficients (r) > 0.986 5 over the range of 0.02–1.00 μg/mL. The limits of detections (LODs) were 0.01–0.02 mg/kg, and the limits of quantitation (LOQs) were 0.03–0.06 mg/kg. The recoveries at three spiked levels (0.05, 0.50 and 1.00 mg/kg) varied from 81.8% to 107.2%, with relative standard deviations (RSDs) of 1.2%–7.2%. Compared with the traditional QuEChERS method, this method was easy, fast and solvent saving with good recovery and accuracy. Thus, it was suitable for the determination of 23 organophosphorus pesticide residues in tea.