Table of Content

25 June 2020, Volume 41 Issue 12
Food Chemistry
Scanning Electron Microscope Analysis of Cell Wall Breakdown of Buckwheat Bee Pollen and Release of Flavonoids during Its Simulated Gastrointestinal Digestion
SHEN Zhiyan, GAO Yuntao, ZHANG Haifen, JIANG Qiongfang, XIONG Huabin
2020, 41(12):  1-6.  doi:10.7506/spkx1002-6630-20190127-346
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Low-temperature energy-focusing ultrasound was used to break down the cell wall of buckwheat bee pollen and the process was analyzed using scanning electron microscope (SEM). In the microscopic field, the bee pollen cells were spited, ruptured along the germ ditch, and broken into pieces successively, which allows the establishment of an accurate method for calculating the efficiency of cell wall disruption. Based on SEM observation, the optimum experimental conditions that provided the maximum efficiency of cell wall disruption (98.33%) were determined as follows: initial temperature 0 ℃, ultrasound power 400 W, pulse duty factor 1:2, sonication time 30 min, and ratio of solid to solvent 1:30 (g/mL). Further study showed that the efficiency of cell wall disruption displayed a linear relationship with the release percentage of total flavonoids from the pollen when incubated in simulated gastric and intestinal fluid, which was fitted into the following equation was y = 0.363 8x + 27.172 with a correlation coefficient (R2) of 0.999 7.
Effects of Different Curing Methods on the Curing Rate and Quality of Duck Meat
CHEN Xing, SHEN Qingwu, LUO Jie
2020, 41(12):  7-13.  doi:10.7506/spkx1002-6630-20190603-016
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In order to shorten the curing time, reduce the production cost, improve the product quality and guide rapid curing of duck meat, we examined the effects of normal pressure curing (control group), vacuum tumbling curing and variable pressure static curing on the curing rate and quality of duck meat. The results showed that vacuum tumbling curing significantly increased the curing rate (P < 0.05) as compared to two other curing methods, which did not significantly differ from each other. After vacuum tumbling curing for 2 h, brightness (L*) significantly increased (P < 0.05), and redness (a*) and yellowness (b*) significantly decreased (P < 0.05), suggesting improved color. Shear force and hardness were significantly reduced (P < 0.05), and meat tenderness was improved. However, at this time, vacuum tumbling curing resulted in a significantly higher cooking loss (P < 0.05) than did the other curing methods. Variable pressure static curing for 4 h gave the lowest chewiness, cohesiveness and resilience, and there was no significant difference in other quality attributes as compared with normal pressure curing for 6 h (P > 0.05). Low field nuclear magnetic resonance (NMR) results showed that curing for 8 h with vacuum tumbling significantly reduced the transverse relaxation time of immobile water (P < 0.05), and the difference between variable pressure static curing and atmospheric pressure curing was not significant (P > 0.05). The maximum peak area percentage of immobile water occurred after 2 h for vacuum tumbling curing, 6 h for variable pressure static curing, and 6 h for normal pressure curing. To sum up, the best curing time was less than 2 h for vacuum tumbling curing, 4 h for variable pressure static curing and 6 h for normal pressure curing. Vacuum tumbling curing for an appropriate period of time could effectively improve the meat tenderness, shorten the curing time and reduce the production cost.
Interaction of Rosmarinic Acid with Myosin in Aqueous Buffer Solution and Its Effect on Protein Physicochemical Properties
ZHOU Yang, CHEN Xueke, DAI Hongjie, YU Yong, ZHU Hankun, WANG Hongxia, ZHANG Yuhao
2020, 41(12):  14-21.  doi:10.7506/spkx1002-6630-20190523-275
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Fluorescence spectroscopy, circular dichroism and electrophoresis were used to study the interaction between myosin and rosmarinic acid (RA) in an aqueous buffer solution and the effect of RA addition on the conformation and physicochemical properties of myosin at different NaCl concentrations. The results showed that RA exhibited a strong static quenching effect on the endogenous fluorescence of myosin and they combined mainly by hydrophobic interaction without covalent cross-linking. RA could promote the unfolding of myosin, resulting in a reduction in α-helix content, exposure of more active groups and an increase in surface hydrophobicity. At each NaCl concentration, the addition of RA reduced the absolute value of the Zeta potential, resulting in decreased solubility as well as increased turbidity and particle size of myosin. The emulsifying properties of myosin was reduced by RA addition at low salt concentration (0.2–0.4 mol/L NaCl), but was little affected at moderate and high salt concentrations (0.6–1.0 mol/L NaCl).
Effects of Alkali Extraction Conditions on Monosaccharide Composition, Physicochemical Properties and Rheological Properties of Arabinoxylan from Wheat Bran
LU Zhenjie, LI Juan, CHEN Zhengxing, LI Cheng, WANG Li, LI Yanan
2020, 41(12):  22-27.  doi:10.7506/spkx1002-6630-20190611-115
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In this paper, arabinoxylan was prepared from wheat bran by an alkali extraction method. The influences of NaOH concentration, extraction temperature and time on the monosaccharide composition, molecular mas distribution and viscosity of arabinoxylan were investigated by high-performance liquid chromatography, high performance gel filtration chromatography and rheological analysis. The results showed that with increasing alkali concentration, the purity of arabinoxylan decreased first and then increased, while the yield showed the opposite trend. As the extraction temperature and time increased, the purity and yield of arabinoxylan increased until reaching a plateau. Their values were respectively 88.72% and 32.8% under the optimized conditions: NaOH concentration 0.5 mol/L, extraction temperature 85 ℃ and extraction time 120 min. The molecular mass of arabinoxylan decreased significantly with increasing extraction temperature. The viscosity of arabinoxylan solution was positively correlated with NaOH concentration but negatively correlated with extraction temperature and time. The results of this study indicated that arabinoxylans obtained under different alkali extraction conditions were distinct in their properties. Our results in this paper can provide a theoretical basis for the alkali extraction and application of arabinoxylan from wheat bran.
Freeze-Thaw Properties and Structural Characterization of Covalent Complexes of Soy Protein Isolate with Monosaccharides, Disaccharides and Polysaccharides
WANG Yuying, ZHANG Anqi, ZHOU Guowei, WANG Lin, WANG Xibo
2020, 41(12):  28-35.  doi:10.7506/spkx1002-6630-20190310-112
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In order to study the effect of sugar type on the freeze-thaw properties of soy protein isolate (SPI)-sugar covalent complex, this experiment examined and compared the emulsifying properties, creaming index, oiling off, degree of grafting, Fourier transform infrared (FTIR) spectra and fluorescence spectra of SPI complexes with glucose (G), maltose (M) and dextran (D). The results showed that under the conditions of reaction temperature 80 ℃, reaction time 3 h, protein concentration 4%, and SPI-to-M ratio 4:1, SPI-M complex was obtained whose emulsifying activity and emulsion stability were 1.41 and 1.29 times as high as those of the control sample, respectively. After one, two and three freeze-thaw cycles, the creaming index decreased by 29.68%, 28.3%, and 29.57%, respectively, and the oiling off decreased by 4.8%, 16.8%, and 22.6%, respectively. The freeze-thaw stability of SPI-M was significantly improved relative to the control group, and its emulsifying activity and freeze-thaw stability were better than those of SPI-G and SPI-D. The grafting degree of SPI-M was significantly higher than that of SPI-G and SPI-D. FTIR spectroscopy indicated that the sugar molecules were inserted into the SPI molecule through covalent bonds. Fluorescence analysis indicated that the protein structure changed.
Impacts of Metal Ions, Cysteine, Phosphate and Ethanol on Browning and Antioxidant Activity of Glycosylated Whey Protein Isolate-Inulin Conjugate
MA Ling, SUN Dongxue, LI Tianqi, WANG Yu, Abdul QAYUM, HOU Juncai, JIANG Zhanmei
2020, 41(12):  36-45.  doi:10.7506/spkx1002-6630-20190508-061
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The impacts of metal ions, cysteine, phosphate and ethanol on the browning and antioxidant activity of glycosylated whey protein isolate (WPI)-inulin conjugate were investigated in this study. With the increase in the concentrations of iron and zinc ions, the browning and antioxidant activity of glycosylated WPI-inulin conjugate increased initially and afterward decreased, whereas the content of free amino groups content firstly reduced and then increased. With increasing copper ion concentration from 0 to 150 mg/L, the browning and antioxidant activity increased whereas the content of free amino groups decreased. Cysteine could not only inhibit the browning, but also enhance the antioxidant activity of WPI-inulin conjugate. Phosphate buffer and ethanol could facilitate the glycosylation reaction, with the former being more effective. Therefore, the metal ions, phosphate and ethanol could promote the glycosylation reaction and enhance the antioxidant activity of WPI-inulin conjugate.
Effects of High Temperature Treatments on the Gel Properties of Fish Proteins Extracted Using Isoelectric Solubilization Precipitation versus Rinsing Method
SHI Liu, ZHANG Wei, ZHOU Junpeng, WANG Lan, LI Xin, DING Anzi, XIONG Guangquan, YANG Hong
2020, 41(12):  46-53.  doi:10.7506/spkx1002-6630-20190521-239
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The effects of heat treatment temperature (100, 110, and 120 ℃) and duration (15, 30, and 60 min) on the gel properties of proteins extracted from silver carp muscle using isoelectric solubilization precipitation (ISP) and those recovered from surimi wash water including gel strength, water-holding capacity, color, chemical interactions and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) pattern were analyzed and compared. The results showed that that ISP protein gels had weaker breaking force and higher deformation degree than did washed protein gels. The highest gel strength for washed protein gels and ISP protein gels were found under thermal treatments at 110 and 100 ℃, respectively. With increasing treatment time, breaking force and deformation degree decreased for the two protein gels. The water-holding capacity of ISP protein gels was not significantly affected by the treatments, while that of washed protein gels was decreased with increasing heating time. The water-holding capacity, L* value and whiteness of washed protein gels were higher than those of ISP protein gels. With the increase in treatment duration, L* value and whiteness of washed protein gels significantly decreased, while those of ISP protein gels showed an opposite trend. The concentrations of ionic and hydrogen bonds increased first and decreased later, while the concentration of hydrophobic interaction and total sulfydryl group showed a decline trend during the thermal treatment process. With raising temperature and time, the myosin heavy chain (MHC) bands disappeared and the band intensities of actin and myosin light chain gradually decreased in the SDS-PAGE patterns for both protein gels.
Effect of Apple Pomace Combined with Pre-emulsified Rice Oil on the Quality of Low-Fat Pork Meatballs
WANG Zhengrong, RUAN Xiaqing, MA Wentao, KANG Zhuangli, ZHU Mingming, ZHAO Shengming, MA Hanjun
2020, 41(12):  54-59.  doi:10.7506/spkx1002-6630-20181130-353
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In order to develop low-fat meat products, the effect of partially replacing pork back fat with apple pomace combined with pre-emulsified sesame oil on the water holding/oil binding capacity, color, texture profile analysis (TPA), fat content, dynamic rheology, and sensory properties of pork meatballs was examined. The results showed that partial replacement of pork back fat with apple pomace combined with pre-emulsified sesame oil increased the hardness and chewiness, and reduced the crude fat content of meatballs. An ascending trend in the water holding/oil binding capacity and yellowness (b* value) was observed with increasing level of apple pomace. The rheological analysis demonstrated that the storage modulus G’ progressively increased with increasing level of apple pomace. However, both a* value and sensory evaluation score increased firstly and then decreased with increasing level of apple pomace up to 3%. The sensory score of the sample with 2% apple pomace was closest to the control meatballs, 74.02 ± 1.04 versus 75.92 ± 0.85, without any significant difference between them (P > 0.05). From an economic perspective, 2% apple pomace combined with pre-emulsified sesame oil was determine to be optimum for partially replacing pork back fat in meatballs.
Pickering Emulsion Stabilized by Synergistic Effect of Starch Particles with Sodium Caseinate
WANG Ran, LIU Ying, LIU Yang, LIU Lihong, CAI Yong, ZHANG Chunyu, WEN Huiying
2020, 41(12):  60-66.  doi:10.7506/spkx1002-6630-20190730-408
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In this study, Pickering emulsions stabilized by the synergistic effect between starch particles and sodium caseinate were prepared. The hydrodynamic diameter, zeta potential, interfacial tension, particle size, surface protein concentration, fat partial coalescence rate, rheological behavior and optical microscopy were used as indicators to study the properties of Pickering emulsions with different concentrations of starch particles. Changes in starch particle content significantly affected the hydrodynamic diameter, zeta potential and interfacial tension of the synergetic system. The Pickering emulsion with 0.04 g/100 mL starch particles showed shear thinning characteristics. The average diameter of surface area and volume of the emulsion were the smallest, 3.50 and 1.97 μm, respectively. The highest interfacial protein concentration and fat partial coalescence rate were observed, 3.90 mg/m2 and 7.98%, respectively. The diameter of fat globules in the dispersed phase was the smallest, 4.11 μm. The results showed that starch particles could promote the interfacial activity of sodium caseinate in a certain concentration range, and their combination could synergistically maintain the stability of Pickering emulsion.
Preparation, Structural Characterization and in Vitro Antibacterial Activity of Water-Soluble Carboxymethyl Pachymaran with Different Degrees of Substitution
BIE Meng, XIE Bijun, SUN Zhida
2020, 41(12):  67-76.  doi:10.7506/spkx1002-6630-20190603-015
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To improve the water solubility and bioactivity of pachymaran, carboxymethylated pachymaran (CMP) was synthesized with monochloroacetic acid as carboxymethylation reagent. The structures of CMP with different degrees of substitution were characterized and their bacteriostatic activity were analyzed in vitro. The results showed that the optimum reaction conditions were as follows: temperature, 65 ℃; etherification time, 4 h; ethanol concentration, 80%; and molar ratio of pachymaran to sodium hydroxide to monochloroacetic acid, 1:3.5:1.75. Under these conditions, the average degree of substitution (DS) was 0.724. CMP with DS in the range of 0.350 to 0.728 could be prepared by controlling the reaction conditions. The results of Fourier transform-infrared (FT-IR) spectroscopy analysis showed that pachymaran was successfully derivatized. Gel permeation chromatography coupled online to multi-angle laser light scattering (GPC-MALLS) revealed that higher the DS, the smaller the molecular mass and the higher the absolute value of Zeta potential of CMP. In addition, the particle size increased first and then decreased, the content of neutral sugar decreased continuously, and the thermal stability firstly increased and then decreased. The results of nuclear magnetic resonance (NMR) showed that carboxymethyl derivatization mainly occurred at the hydroxyl position of C6. Scanning electron microscopy (SEM) showed that the higher the DS, the closer the spatial structure and the higher the degree of cracking. In vitro tests showed that the inhibition of CMP against foodborne pathogens was enhanced with increasing DS, and it was more active against Gram-positive bacteria than against Gram-negative bacteria.
Effect of Metmyoglobin Oxidation on Biochemical Characteristics of Myofibrillar Protein in Yak Meat
CUI Wenbin, SONG Yanyan, LI Minghua, ZHANG Li, YU Qunli, HAN Ling, WEI Jinmei, GUO Zhaobin
2020, 41(12):  77-83.  doi:10.7506/spkx1002-6630-20190320-268
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In this study, we investigated the effect of metmyoglobin (MetMb) oxidation on the biochemical characteristics of yak muscle myofibrillar proteins at 24 h postmortem. The pattern of change in the contents of carbonyl, sulfhydryl and disulfide bonds, surface hydrophobicity, Ca/K-ATPase activity and dimeric tyrosine in myofibrillar proteins was determined after 24 h of oxidative incubation of MetMb at different concentrations (0, 0.01, 0.05 and 0.5 mmol/L). A sample without any added oxidant was served as a control. The results showed that with the increase in MetMb concentration, the oxidation level of myofibrillar proteins varied. The contents of carbonyl, disulfide bond and dimeric tyrosine, surface hydrophobicity, and Ca-ATPase activity significantly increased (P < 0.05), whilst the opposite was true for sulfhydryl content and K-ATPase activity (P < 0.05). When MetMb concentration increased to 0.5 mmol/L, the carbonyl content increased by 5 flod, while the sulfhydryl content decreased by 31.5% as compared with the blank treatment group. In summary, the oxidation of MetMb promotes the oxidation of myofibrillar proteins. The results of this study provide a reference for protein oxidation control during the production and processing of yak meat.
Potential Application of Mixed Starter Cultures of Indigenous Pichia kluyveri and Saccharomyces cerevisiae to Wine Aroma Enhancement
ZHANG Wenjing, YANG Shini, DU Shuang, JIANG Jiao, YE Dongqing, LIU Yanlin
2020, 41(12):  84-90.  doi:10.7506/spkx1002-6630-20190418-232
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This study aimed to understand the potential application of indigenous Pichia kluyveri in winemaking and its impact on wine aroma. Mixed starter cultures of P. kluyveri HS-2-1 and Saccharomyces cerevisiae NX11424 at ratios of 1:1, 10:1 and 20:1 were separately used to ferment Cabernet Sauvignon wine. Results showed that HS-2-1 propagated well in the mixed culture fermentation. Compared with pure fermentation by NX11424, wines produced by mixed fermentation contained less volatile acid as well as significantly higher levels of esters and higher alcohols with the highest increase being 24.19% and 21.34% at 20:1 ratio, respectively. Additionally, the concentrations of isopentanol, ethyl butyrate, ethyl hexanoate, ethyl octanoate, ethyl 9-decenoate and ethyl lactate increased with increased proportion of HS-2-1 in the mixed inoculum, thus enhancing the fruity and floral aroma of the wine. To our knowledge, this study is the first to indicate that strain HS-2-1 exhibits good enological characteristics, and further highlight its potential application in wine-making by co-fermentation with S. cerevisiae NX11424 at a ratio of 20:1.
Purification and Preparation of Nanoparticles of Human H-chain Ferritin
XIA Xiaoyu, LI Han, WANG Zhenyu, TAN Xiaoyi, CHENG Shuzhen, DU Ming
2020, 41(12):  91-98.  doi:10.7506/spkx1002-6630-20191017-171
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In order to explore an efficient method for the preparation of reversible self-assembled active ferritin nanocage, we constructed prokaryotic expression system based on Escherichia coli for the recombinant human H-chain ferritin (BL21-pET3a-rHuHF) to express rHuHF efficiently in a fermentation tank. Three key parameters including stirring speed, air flux and induced expression time were optimized. A transmission electron microscope (TEM) and a light scattering instrument were used to characterize the nanostructure and particle size of rHuHF, respectively. The results showed that the optimum expression conditions were as follows: stirring speed 200 r/min, air flux 1.6 L/min, and expression time 9 h. According to the results of identification, ferritin existed in the soluble part of bacteria cells and had good self-assembly activity and monodisperse cage-like structure. The highest expression yield in 9 experiments was 290 mg/L, which was significantly higher than that in a shaking flask under the same conditions. The particle size of rHuHF was (11.23 ± 0.10) nm at pH 7 and (2.73 ± 0.10) nm at pH 2. This research can provide a scientific basis for the application of ferritinin nanometer-targeted delivery system.
Comparison of the Aroma-Producing Performance of Lactic Acid Bacteria from Qula as the Residue of Yak Milk after Ghee Making
WEN Pengcheng, CAO Lei, YANG Min, MA Ruijuan, ZHANG Zhongming, ZHANG Weibing
2020, 41(12):  99-105.  doi:10.7506/spkx1002-6630-20190708-094
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In this study, solid phase microextraction combined with gas chromatography-mass spectrometry (SPME-GC-MS) was used to detect and analyze the volatile flavor substances in milk fermented with each of 6 strains of lactic acid bacteria isolated from Qula. The key flavor substances were determined by relative odor activity value (ROAV). The results showed that a total of 60 volatile flavor substances were identified in this experiment, and the compositions and contents of key flavor substances produced by the isolated strains were significantly different. Strain G1 had strong ability to produce 2-heptanone; strains G1 and Q1 possessed strong ability to produce isoamyl alcohol and caproic acid; the ability of strain G2 to produce acetoin, sterol and 2-tridecanth was significantly higher than that of the other strains; strain G4 produced acetic acid and its ability to produce butyric acid was strong. The results of principal component analysis also showed that there were differences in the aroma-producing performance of the 6 strains. The research results can provide a theoretical basis for the application of lactic acid bacteria isolated from Qula.
Physiological Mechanism by Which Adaptive Evolution Improves the Resistance of Streptomyces diastatochromogenes T17 to Spontaneous Acid Stress
REN Xidong, YU Chao, WANG Chenying, LIU Xinli
2020, 41(12):  106-112.  doi:10.7506/spkx1002-6630-20190511-112
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The physiological responses of the ε-poly-l-lysine-producing strain Streptomyces diastatochromogenes T17 and its acid-resistant derivatives, S. diastatochromogenes AE44, S. diastatochromogenes AE51 and S. diastatochromogenes AE56, to spontaneous acid stress were investigated. The changes in relevant physiological indexes of the original and evolutionary strains were compared at two stages of acidic stress. The results showed that at 0 h (pH 6.5), there were no significant differences in the physiological indexes between the original and evolutionary strains. At 48 h (pH 3.2), compared to the original strain, the intracellular pH, ATP concentration and H+-ATPase activity of the evolutionary strains were significantly increased, accompanied by increased levels of intracellular aspartic acid, alanine, glutamic acid, lysine, glycine and proline. The ratio of unsaturated to saturated fatty acids (U/S ratio) in the cell membrane was also increased so that the membrane fluidity was improved. Collectively, we conclude that the evolutionary strains could achieve a balance during spontaneous acid stress.
Effect of CaCO3 on Sporulation of Bacillus coagulans CGMCC 9951
TIAN Jingjing, WU Ying, LI Changfu, ZHOU Yanlin, ZHOU Zilü, GU Shaobin
2020, 41(12):  113-119.  doi:10.7506/spkx1002-6630-20190505-021
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The effect of calcium carbonate on the sporulation of Bacillus coagulans CGMCC 9951 and its possible mechanism were studied in this investigation. The results showed that addition of 6% CaCO3 to the fermentation broth at 16 h not only ensured sufficient supply of calcium for sporulation, but also increased the pH of the fermentation broth from about 4 to over 6.5, quickly initiating sporulation. At (68 ± 2) h, the concentration of spores reached 4.53 × 107 CFU/mL, and sporulation was initiated about 100 hours earlier compared with the control group. Moreover, the heat resistance, acid resistance, bile salt tolerance and germination ability of spores were not significantly affected by CaCO3. Further we found that addition of CaCO3 effectively accelerated the sporulation process. The expression levels of kinC, kinE and spo0A genes related to sporulation initiation were significantly increased at 4 h after adding CaCO3, reaching levels 61.07, 23.49, and 17.32 times as high as the control group, respectively. This study revealed that the sporulation of B. coagulans was dependent upon environmental pH and neutral and weakly alkaline environments were conducive to the transcription of sporulation-related genes, thus accelerating the sporulation process.
Effects of Beef and Chicken Proteins on Human Fecal Microbiota under in Vitro Fermentation Conditions
ZHANG Guanghong, ZHOU Guanghong, XU Xinglian, LI Chunbao
2020, 41(12):  120-128.  doi:10.7506/spkx1002-6630-20191030-342
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In order to study the effects of addition of beef and chicken proteins on the composition of gut microbiota under in vitro conditions, we incubated human fecal microbes in the presence of beef or chicken proteins (0.01 g) at 37 ℃ for 48 h, then extracted DNA from the fermentation broth and sequenced the DNA on Illumina PE250 sequencing platform to analyze microbial community composition and structure. The results showed that addition of beef protein and chicken protein significantly affected the composition and structure of gut microbiota. At the phylum level, the beef protein and chicken protein groups had significantly higher abundances of Proteobacteria and Actinobacteria compared with the control group (P < 0.05). The abundance of Bacteroidetes was significantly decreased in the chicken protein group (P < 0.05). At the genus level, a total of 15 species of core microbes were found in the three groups. Compared with the control group, the relative abundance of Prevotella, Parabacteroides and Faecalibacterium in the beef protein and chicken protein groups was significantly decreased (P < 0.05), while the relative abundance of Megasphaera, Megamonas and Escherichia-Shigella was significantly increased (P < 0.05). In addition, significantly increased abundance of Sutterella and Ruminococcus torques was seen in the chicken protein group (P < 0.05), together with an increase in the abundance of Lactobacillus and Bifidobacteria. Under in vitro fermentation conditions, beef and chicken protein significantly but differently affected the composition and structure of human fecal microbiome.
Identification and Mechanism of Action of Angiotensin-? Converting Enzyme Inhibitory Peptides from Hen Egg Proteins
YU Zhipeng, FAN Yue, ZHAO Wenzhu, ZHANG Xinyue, LIU Jingbo
2020, 41(12):  129-135.  doi:10.7506/spkx1002-6630-20190507-050
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In this study, in silico methods were used to discover novel angiotensin-? converting enzyme (ACE) inhibitory peptides from hen eggs for regulation of blood pressure. Hen egg proteins were in silico hydrolyzed using ExPASy PeptideCutter program. Potential activity, solubility, and absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the generated peptides were predicted using program online. Three novel ACE inhibitory peptides, FQK, WGK and ADW, were identified from hen egg protein with IC50 values of (250 ± 0.25), (222.74 ± 1.02) and (85.38 ± 0.54) μmol/L, respectively. The molecular docking studies revealed that the ACE inhibitory activity of FQK, WGK and ADW was mainly attributed to their ability to form very strong hydrogen bonds with the S1 an S2 pockets. This study provides a high-throughput screening method for the identification of food-derived ACE inhibitory peptides.
Identification of Dominant Postharvest Pathogens of Taro and Antifungal Activity of Hinokitiol against Them
ZHAO Lumiao, GAO Haiyan, LIU Ruiling, DING Yuting, HAN Yanchao, CHEN Hangjun
2020, 41(12):  136-142.  doi:10.7506/spkx1002-6630-20190521-248
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To provide evidence for the control of taro postharvest diseases, the main pathogens causing postharvest decay of taro and the antifungal effect of hinokitiol against these pathogens were investigated. In this study, the pathogenic fungal strains were isolated from naturally decaying taro grown in Fenghua, Zhejiang province by tissue separation method and identified by morphological characteristics and rDNA-ITS sequence analysis, and their pathogenicity was evaluated by Koch’s postulate. The antifungal activity of hinokitiol was investigated by evaluating its effects on the mycelial growth, spore germination, malondialdehyde content and ultrastructure of the dominant pathogens. The results showed that the two pathogenic strains isolated were identified as Fusarium sp. and Lasiodiplodia theobromae respectively. Hinokitiol exhibited obvious antifungal activity against the pathogens. It inhibited mycelial growth and spore germination, exacerbated membrane lipid peroxidation, and destroyed the subcellular structure of mycelia. Accordingly, this study indicated that hinokitiol can be a promising candidate for the control of postharvest diseases of taro.
Structure and Diversity of Culturable Yeast Populations in Different Maotai-flavor Liquor Brewing Regions of Maotai Town, Guizhou Province
LUO Fangwen, HUANG Yongguang, TU Huabin
2020, 41(12):  143-149.  doi:10.7506/spkx1002-6630-20190430-292
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The structure and diversity of cultural yeast populations in different Maotai-flavor liquor brewing regions of Maotain town, Guizhou province were studied. Yeast samples were collected from the brewing environment and the fermentation starter, Daqu. A total of 568 yeast strains were obtained and identified by 26S rDNA gene sequencing, 334 of which came from the brewing environment and identified as 25 species and 1 uncultured yeast strain in 14 genera, while the remaining 223 were derived from Daqu were identified as 20 species and 1 uncultured fungal strain in 12 genera. Ten yeast populations were common to both. The dominant species in the environment were Wickerhamomyces anomalus, Saccharomyces cerevisiae and Hyphopichia burtonii while those in Daqu were W. anomalus and Saccharomycopsis fibuligera. The diversity of yeast in the environment and Daqu was significant quantitatively but at the species level. To our knowledge, this study is the first to isolate Nectaromyces rattus, Wickerhamomyces sp. H1Y23, Issatchenkia sp. S612Y5, Wickerhamomyces pijperi, Trichosporon faecale, Kazachstania sp. IMB190R, Pseudozyma sp., Kazachstania solicola, Torulaspora sp. Z8Y10 and Helicoceras oryzae from the Maotai-flavor liquor brewing process.
Screening, Identification and Characterization of Aroma-Producing and Salt-Tolerant Yeast Strains from Pickles from South Sichuan, China
TANG Hongmei, WANG Haowen, WU Huachang, DENG Jing, LIU Yang, WANG Yijin
2020, 41(12):  150-157.  doi:10.7506/spkx1002-6630-20190509-092
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Four yeast strains with a broad tolerance to a wide range of salt concentration (3%–15% NaCl concentration) and high aroma-producing ability, named YB4, YB18, YC14 and YF17, were screened from pickles from south Sichuan, China. Based on their morphology and internal transcribed spacer (ITS) rDNA sequencing, YB4 was identified as Meyerozyma guilliermondii, YB18 as Debaryomyces hansenii, and YC14 as Candida parapsilosis, whereas YF17 could not be accurately identified. The growth curves and pH of the four strains were determined. The results showed that YF17 was the first to enter the stationary phase of growth, the cell stability of YB4, YC14 and YF17 was better than that of YB18, and pH was within the acceptable range for the growth of all these strains. The acid production capacity of the yeast strains was explored at different NaCl concentrations. The results showed that the acid production capacity of YB4 and YB18 was more inhibited in the presence of 12% and 15% NaCl compared with NaCl concentrations of 6% and 9%. The acid production ability of YC14 and YF17 was less inhibited by 6% NaCl than by the other three NaCl concentrations. The acid production capacity of YB18 and YC14 increased from 48 to 72 h. This may be due to the reason that the salt adaptability of strains was stimulated during the cultivation process. In conclusion, this research lays a theoretical foundation for the preparation of fermentation agent for pickles.
Composition Analysis
Effects of Yeasts on the Release of Glycosidically Bound Aroma Components from Wine Analyzed by Ultra-high Performance Liquid Chromatography-Quadrupole-Time-of-Flight-Mass Spectrometry
AN Xiaohui, MIAO Yingxin, CHEN Zhuo, ZHANG Xinke, DUAN Changqing, PAN Qiuhong
2020, 41(12):  158-165.  doi:10.7506/spkx1002-6630-20190709-122
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This study investigated the effects of two kinds of yeasts, Red Fruit and Zymaflore ST, on the release of glycosidically bound aroma compounds during the fermentation of ‘Beibinghong’ and ‘Vidal’ ice wine, as well as the variation in these aroma compounds in fresh and bottled ‘Beibinghong’ ice wine after aging for one year, by means of ultra-high performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-Q-TOF-MS). The results showed that ‘Vidal’ ice wine contained more abundant types and higher concentration of glycosidically-bound aroma compounds than did ‘Beibinghong’ ice wine. In ‘Beibinghong’ ice wine fermented with either yeast, the content of aroma pentosyl glucosides slightly decreased during fermentation, while Zymaflore ST had no significant impact on hexosyl glucosides. By contrast, in ‘Vidal’ ice wine fermented with Zymaflore ST, the contents of pentosyl glucosides, hexosyl glucosides and glucosides significantly dropped during fermentation, whereas Red Fruit appeared to have no effect on pentosyl glucosides or glucosides. After aging for one year, ‘Beibinghong’ ice wine showed a large decrease of the contents of glucosidically bound aroma compounds. Based on these results, it is considered that the effects of Red Fruit and Zymaflore ST on the release of glycosidically bound aroma compounds are limited during the fermentation of ‘Beibinghong’ ice wine, and these aroma precursors could be released mainly in the process of aging while Zymaflore ST fermentation was more favorable for the release of glycosidically bound aroma in ‘Vidal’ ice wine. The findings provide a reference for fermentation and aging process design of ice wine.
Effect of Reheating on Volatile Constituents from Linoleic Acid-Xylose-Cysteine Reaction System as Analyzed by GC-MS and Electronic Nose
ZHANG Zheqi, ZANG Mingwu, ZHANG Kaihua, LI Dan, WANG Shouwei, LI Xiaoman
2020, 41(12):  166-172.  doi:10.7506/spkx1002-6630-20191027-298
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The effect of linoleic acid on the formation of volatile compounds from xylose-cysteine Maillard reaction system and the effect of reheating on the formation of volatile compounds from linoleic acid-xylose-cysteine Maillard reaction system were analyzed by dynamic headspace sampling combined with gas chromatography-mass spectrometry (DHS-GC-MS) and electronic nose. The results showed that a total of 53 volatile compounds were detected of which 13 were common to all three groups. The total amount of volatile compounds was 1 598.61, 2 330.71 and 1 675.09 μg/kg in the control, linoleic acid addition and linoleic acid addition plus reheating groups, respectively. Addition of linoleic acid decreased the amount of Maillard reaction products, indicating that linoleic acid has an inhibitory effect on the Maillard reaction. The amounts of all volatile substances except acids and alcohols formed in the reaction system decreased after reheating. The analysis of odor activity value showed that the increase in 1-octene-3-ol content and the decrease in meaty flavor and fatty flavor compounds may be one of the causes of hot odor. Electronic nose analysis showed that inorganic sulfide may also be a source of odor caused by reheating.
Analysis of Characteristic Flavor Components in Different Kinds of Shandong Pancakes
FAN Yue, LIU Wei, XU Fen, HUANG Yanjie, ZHANG Nana, LI Kang, ZHANG Hong, HU Honghai
2020, 41(12):  173-179.  doi:10.7506/spkx1002-6630-20190513-132
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The volatile and non-volatile flavor compounds in five kinds of Shandong pancakes (incorporated with millet, chestnut, sesame, walnut and coarse cereals, respectively) were analyzed and compared by electric nose, electric tongue, solid-phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS), ion chromatography, and amino acid analyzer. The key flavor compounds were identified by relative odor activity value (ROAV). The results showed that the fingerprints of electronic nose and electronic tongue could clearly distinguish among the pancake samples. A total of 24 flavor compounds were identified by GC-MS, including aldehydes, alcohols, alkanes, acids and aromatic compounds. The key flavor compounds in pancakes incorporated with millet, sesame and coarse cereals were nonanal and 2-methoxy-4-vinylphenol. Trans-2,4-decadienoaldehyde and 2-methoxy-4-vinylphenol were the key flavor compounds in pancakes incorporated with chestnut. Nonanal, trans-2-nonylaldehyde and 2-methoxy-4-vinylphenol were the key flavor compounds in pancakes incorporated with walnut. The highest contents of glucose and maltose were found in pancakes incorporated with chestnut and millet, respectively. For all pancake samples, sweet amino acids were the most abundant class of amino acids, followed by umami amino acids, and glutamic acid was the most abundant amino acid.
Comparison of Three Extraction Methods Used to Determine the Characteristic Flavor of Garlic Frying Oil
LIU Haoyue, LI Meng, ZHU Qingzhen, CHEN Haitao, SUN Baoguo, ZHANG Ning, ZHANG Yuyu
2020, 41(12):  180-187.  doi:10.7506/spkx1002-6630-20190508-066
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In this comparative study, volatile flavor compounds were extracted from garlic frying oil by headspace solid-phase microextraction (SPME), simultaneous distillation extraction (SDE) and solvent-assisted flavor evaporation (SAFE) and analyzed by gas chromatography-mass spectrometry (GC-MS) based on retention index (RI). A total of 83, 31 and 27 volatile aroma compounds were identified by SAFE, SPME, and SDE, respectively. The SAFE method extracted more aroma substances from garlic frying oil compared with two other methods. A total of 54 odorant compounds were detected in the extract obtained by SAFE using gas chromatography-olfactometry-mass spectrometry (GC-O-MS). The flavor of the extract was closer to that of the frying oil because it contained relatively high contents of pyrazine compounds and unique ether compounds. A total of 29 aroma compounds with flavor dilution (FD) factor ≥ 9 were identified from the SAFE extract by aroma extract dilution analysis (AEDA). Fourteen key aroma compounds were accurately quantified using standard substances by an external standard method. By recombining these compounds together, the characteristic aroma of the oil was determined to consist of raw garlic-like aroma, salty aroma, fried aroma, burnt aroma, green aroma and spicy aroma, and this combination was similar to the frying oil in green aroma and spicy aroma.
HS-SPME-GC-MS Analysis of Volatile Components of Congou Black Tea Processed from Baojing Huangjincha 1 from Different Harvesting Seasons
HUANG Hao, YU Penghui, ZHAO Xi, ZHONG Ni, ZHENG Hongfa
2020, 41(12):  188-196.  doi:10.7506/spkx1002-6630-20190721-265
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In order to evaluate the aroma characteristics of Congou black tea from different harvesting seasons, Congou black tea were processed from one bud with one leaf from the cultivar Baojing Huangjincha 1 harvested in spring, summer and autumn and were analyzed for their volatile components by using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Meanwhile, sensory evaluation was conducted to investigate the effects of different harvesting seasons on the volatile aroma characteristics of Congou black tea. The results showed that the aroma of Congou black tea was mainly characterized as sweet and fragrant for all three seasons, specifically pure sweet aroma for spring tea, strong sweet aroma for summer tea, and sweet and flowery aroma for autumn tea. In addition, the flavor index (FI) of autumn tea was the highest and its aroma quality was the best, followed by summer and spring teas. This was consistent with the results of sensory evaluation. A total of 80 aroma components were detected and identified in the three samples, and 51, 63 and 66 in spring, summer and autumn teas respectively. In total, 40 aroma components were common to these samples mainly including alcohols, aldehydes, hydrocarbons, esters and ketones. The contents of aroma components in Congou black tea were analyzed by principal component analysis (R2X = 0.941, Q2 = 0.825), and we further established a partial least squares-discriminant analysis model (R2X = 0.972, R2Y = 0.994, and Q2 = 0.982) to effectively distinguish the three tea samples. There were 13 landmark compounds that differed among these samples, including methyl salicylate, benzaldehyde, myrcene, 3,7-octad iene-2,6-diol,2,6-dimethyl, 1-ethyl-1H-pyrrole-2-carbaldehyde, safranal, (E)-nerolidol, styrene, 2-octen-1-al, trans-2-decenal, phenylethyl alcohol, 2-[(2S,5S)-5-ethenyl-5-methyltetrahydrofuran-2-yl]propan-2-ol-2H-pyran, and (E)-2-nonenal.
Comparative Metabolite Characteristics of White Tea with Green Tea, Oolong Tea and Black Tea Based on Non-targeted Metabolomics Approach
LI Xinlei, YU Xiaomin, LIN Jun, ZHAO Xiaoman, ZHANG Yan, LIN Hongzheng, HAO Zhilong, JIN Xinyi
2020, 41(12):  197-203.  doi:10.7506/spkx1002-6630-20190128-358
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This study aimed to explore the metabolites characteristics of white tea and the mechanism for the formation of metabolites during processing. White tea, green tea, oolong tea and black tea were processed from one bud with two or three leaves from the tea cultivars Fuyun 6 and Huangdan. The abundance of all metabolites in fresh tea leaves and tea was determined by using ultra-high performance liquid chromatography coupled to quadrupole time of flight mass spectrometry (UPLC-Q-TOF MS). Metabolites that differed between white tea and other types of tea were selected and identified. A total of 152 and 148 differential metabolites were determined for Fuyun 6 and Huangdan, respectively. Among them, 33 metabolites were identified as major compounds in tea, including catechins and its derivatives, anthocyanidins, hydrolysable tannins, flavonols or flavone glycosides, phenolic acids and theaflavins. The results of principle component analysis showed that white tea was between oolong tea and black tea in terms of first principle component whereas it was clearly separated from other types of tea in terms of second principle component. The loading plot showed that the characteristic metabolites of white tea that made it discint from other tea types were flavonol or flavone glycosides, gallated catechin and catechin derivates. The abumdances of most of the identified flavonols or flavone glycosides in white tea were significantly higher than those of other types of tea. The abundances of catechins and anthocyanidins were significantly lower than in white tea than in green tea and approximated to black tea, especially non-gallated catechins. The abundances of theaflavin and theaflavin-3-gallate were significantly higher in white tea than in green tea while no significant differences in the abunadance of theaflavin-3’-gallate or theaflavin-3,3’-gallate were seen between white tea and green tea. Interestingly, the abundance of 8-C-ascorbyl-EGCG, an EGCG derivate, was significantly higher than in white tea than in other types of tea.
Phenolic Composition and Antioxidant Activity of Seed Coats of Kidney Beans with Different Colors
WANG Hezhu, ZHU Yong, ZHU Yi, HE Youxun, QIN Likang, LIANG Yali, CHEN Yue
2020, 41(12):  204-210.  doi:10.7506/spkx1002-6630-20190509-093
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Free and bound phenolic compounds were extracted chemically from kidney bean seed coats with seven different colors. The total phenolics, total flavonoids, total anthocyanins and phenolic composition of the phenolic extracts were analyzed and their antioxidant activities were determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, 2,2’-azinobis (3-ethylbenzothi azoline-6-sulfonic acid) ammonium salt (ABTS) radical scavenging and ferric reducing assays. The results showed that the contents of total phenolics, total flavonoids and total anthocyanins in the seven samples ranged from 0.76 to 48.73 mg/g, from 2.93 to 201.2 mg/g, and from 0 to 2.57 mg/g dry mass (DW), respectively. The seed coats of black kidney bean had the highest contents of total phenolics and total anthocyanins, while total flavonoids content was the highest in the seed coats of red kidney bean. Gallic acid, chlorogenic acid, catechin, 3,4-dihydroxybenzoic acid and hydroxybenzoic acid were the main phenolic compounds in the seed coats of kidney beans, and quercetin only existed in the seed coats of red kidney bean (48.64 μg/g). The seed coats of white kidney bean contained the highest content of coumaric acid (65.40 μg/g). The seed coats of black kidney bean possessed the strongest antioxidant capacity with DPPH and ABTS cation radical scavenging capacities of 156.0 mg/g and 260.8 mg/g and ferric reducing power of 214.7 mg/g, respectively. The content of total phenols in the seed coats of kidney beans was significantly correlated with antioxidant activities (P < 0.01). The seed coats of black kidney bean was rich in phenolic compounds and exhibited antioxidant activities, making it a potential ingredient for functional foods.
Principal Component Analysis and Cluster Analysis for Evaluating the Free Amino Acid Composition of Inner and Outer Lily Bulb Scales from Different Cultivars
WANG Xinyu, WANG Rongrong, WANG Ting, YANG Lüzhu, LIU Jie, LI Huan, ZHANG Qun, SHAN Yang, DING Shenghua
2020, 41(12):  211-220.  doi:10.7506/spkx1002-6630-20190709-117
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This study aimed to analyze the differences in the composition of free amino acids (FAAs) in the inner and outer bulb scales of seven cultivars of lily. We determined FAAs by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A systematic evaluation was performed by measurement of taste activity value (TAV) as well as using principal component analysis (PCA) and cluster analysis (CA). The results showed that a total of 21 FAAs were detected in all samples at concentrations ranging from 4.10 to 10.10 mg/g. There were differences in the contents of total free amino acids (TFAAs), essential amino acids (EAAs), flavor amino acids, and medicinal amino acids (MAAs) among different cultivars. On the whole, the content of TFAAs in the inner bulb scale was higher than that of the outer one, with mean values of 7.00 and 6.18 mg/g, respectively. Among all cultivars, the content of TFAAs was higher in Lilium davidii var. unicolor (from Pinglu and Lanzhou), and L. davidii Duchartre, and the lowest in L. regale Wilson. The content of EAAs was high in L. lancifolium Thunb. and L. davidii Duchartre, accounting for more than 10% of TFAAs for both inner and outer bulb scales. Among the flavor amino acids, bitter and umami amino acids were predominant, and both glutamic acid and arginine were the main contributors. MAAs were rich in lily bulbs, accounting for 49.18%–70.15% of TFAAs. Five principal components were extracted through principal component analysis, which together explained 88.803% the total variance and could reflect the comprehensive information about FAAs. According to the comprehensive analysis, the inner bulb scale of L. davidii var. unicolor from Pinglu, and the inner and outer scales of L. davidii Duchartre ranked top three among all samples. The hierarchical cluster analysis divided the inner and outer bulb scales of the seven lily cultivars into five categories, and the results were consistent with the principal component analysis, which could reflect the differences between different lily germplasms.
Analysis of Characteristics, Structure and Composition of Protein in Donkey Milk Powder
FAN Yumei, TIE Hang, XIE Xiao, SHI Chuanchao, ZHOU Guangyun, SU Ning, LIAO Feng
2020, 41(12):  221-27.  doi:10.7506/spkx1002-6630-20190711-162
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Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism spectroscopy and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/TOF-MS) were used to reveal the properties, structure and composition of milk powder protein from Dezhou donkeys, aiming to provide a basis for the deep exploitation of Dezhou donkey milk. The results showed that the protein content of the milk powder was 16.10%, the isoelectric point was evenly distributed between 4.5 and 6.5, and the molecular mass was mainly concentrated in the range of 10–20 and 53–78?kDa for whey protein, and 28–36?kDa for casein. By matching against the equine protein library, 386 proteins were identified, 139 of which were first discovered in donkey milk. This study provides a theoretical basis for revealing the physiological effects of donkey milk.
Discriminating the Volatile Flavor Composition of Hengshun Vinegars of Different Ages Using Electronic Nose and Gas Chromatography-Mass Spectrometry
KUANG Geling, WANG Xinyu, LI Shu, WANG Hao, LI Xin, YU Yongjian, ZHAO Guozhong
2020, 41(12):  228-233.  doi:10.7506/spkx1002-6630-20190508-071
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In order to distinguish Hengshun vinegars of different ages and to establish their aroma characteristics, the volatile flavor compounds of 3-, 5-, and 10-year-old Hengshun vinegars were analyzed by gas chromatography-mass spectrometry (GC-MS) and their flavor characteristics were evaluated using an electronic nose. Principal component analysis (PCA) and loding analysis (LA) were performed to determine the contribution ratio of each principal component and the degree of differentiation among vinegars of different ages in terms of flavor. The results showd that the electronic nose could clearly discriminate the three vinegar samples with W2S and W5S being the most efficient sensors. In addition, GC-MS analysis showed that the relative contents of furfural and Ligustrazine contributed most to discriminate these vinegars. Therefore, our results support the combined use of electronic nose and GC-MS to discriminate Hengshun vinegars of different ages.
Process and Technology
Preparation of Actin from Siniperca chuatsi Muscle Using Aqueous Two-Phase System and Its Quantitative Analysis
WANG Yangyang, XU Mingfang, BAI Weibin, ZHENG Chunli, YE Lei, ZHENG Qinqin
2020, 41(12):  234-242.  doi:10.7506/spkx1002-6630-20190630-424
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In this study, a method for the extraction and purification of actin from Siniperca chuatsi myofibrillar protein by alcohol-inorganic salt aqueous two-phase systems was established. A new method for the quantitative detection of S. chuatsi actin was explored using high performance micellar electrokinetic capillary chromatography (MECC) with diode array detection (DAD). The results showed that an isopropanol/ammonium sulfate aqueous two-phase system was determined as the optimal separation system by actin purity detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and extraction efficiency. Using combination of one-factor-at-a-time method and response surface methodology, the optimal aqueous two-phase system was determined to be composed of 26% isopropanol and 11% ammonium sulfate at pH 9.0, giving an actin extraction yield of 11.04%, which was close to the predicted value of the model. The actin peak occurred at around 10 minutes in the capillary electrophoresis spectrum, whose baseline was smooth without any noise peak. The results from this study lay an experimental foundation for the identification of quality attributes of precious fish and for development of fish actin standard products, and also provide a theoretical basis for the development and utilization of fish protein functions and rapidquantitative detection of fish proteins.
Electrolyzed Water Extraction and Structural Characteristics of Pectin from Pomegranate Pomace
WANG Weiqing, ZHUANG Hu, WANG Kangping, WANG Ping, LI Shugang
2020, 41(12):  243-249.  doi:10.7506/spkx1002-6630-20190723-302
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In the paper, the ultrasonic-assisted electrolyzed water extraction of pectin from pomegranate (Punica granatum L.) pomace was optimized, and the composition and structural characteristics of the pectin were analyzed. Using combination of one-factor-at-a-time method and Box-Behnken design, the optimal extraction conditions were obtained as follows: ultrasonic power density, 1 W/mL; pH, 1.7; extraction temperature, 60 ℃; extraction time, 33 min; and material to liquid ratio, 1:18 (g/mL). Under these conditions, the pectin yield was 14.95%, which increased by 2.2% compared with the ultrapure water extraction process, and the pectin extracted with electrolyzed water (EWP) had a lower molecular mass (7.294 × 106 g/mol) and higher galacturonic acid content (70.29%). Analysis by combined use of the chemical titration method and Fourier transform infrared (FTIR) spectroscopy indicated that EWP had a higher degree of esterification. It can be seen that the ultrasonic-assisted electrolyzed water extraction method is an efficient and environmentally friendly method. This research provides technical support for producing value-added products from pomegranate fruit and realizing efficient and comprehensive utilization of by-products.
Preparation of Indicator Films Based on Sodium Carboxymethyl Cellulose/Starch and Purple Sweet Potato Anthocyanins for Monitoring Fish Freshness
JIANG Guangyang, HOU Xiaoyan, REN Wen, WU Hejun, LI Shanshan, SHEN Guanghui, CHEN Anjun, WANG Zhangying, ZHANG Zhiqing
2020, 41(12):  250-258.  doi:10.7506/spkx1002-6630-20190715-202
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Indicator films were prepared through using starch (S) and sodium carboxymethyl cellulose (CMC-Na) as the film forming material and purple sweet potato anthocyanins (PA) as the indicator. The effects of S/CMC-Na ratio, anthocyanin concentration and glycerol concentration on the tensile strength (TS), elongation at break (EAB), water solubility and color (a value) of films were investigated. Using the comprehensive score of indicator film performance was as the response value, the process parameters were optimized by the response surface methodology, and the optimal indicator film was characterized. The results demonstrated that the optimum formulation of indicator films was determined as follows: starch/CMC-Na ratio 6:4, anthocyanin concentration 0.5%, and glycerol concentration 0.6%. The overall score of the indicator film prepared using the optimized formulation were the highest, up to 63.8, and it showed tensile strength of (21.48 ± 0.12) MPa, elongation at break of (28.88 ± 0.08)%, water solubility of (19.24 ± 0.21)%, and a value of 4.95 ± 0.02. The results of Fourier-transform infrared (FT-IR) spectroscopy, X-ray-differentiation (XRD) and scanning electron microscopy (SEM) indicated that the cross section of the SCA film was smooth and showed a good compatibility among the ingredients. Furthermore, the indicator film was used to monitor the freshness of grass carp. When the total volatile basic nitrogen (TVB-N) value, pH and total viable count reached 21.55 mg/100 g, 7.58 and 7.3 (lg(CFU/g)), respectively, the indicator film changed from red to blue-violet. These research results provide a basis for the application of indicator films for food shelf life evaluation.
Microencapsulation and Quality Analysis of Tartary Buckwheat Flavonoids Using Polymerized Whey Protein as Wall Material
SUN Yali, ZHOU Wenmei, HUANG Yongguang, WANG Xiaoping, ZHOU Min
2020, 41(12):  259-266.  doi:10.7506/spkx1002-6630-20190624-291
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Polymerized whey protein (PWP), a thermally induced polymer, has good film-forming properties and gel properties. In this study, we attempted to fabricate microcapsules containing tartary buckwheat flavonoids with PWP as the wall material by piercing-solidifying incuber method. The optimization of process parameters for improved microencapsulation efficiency was done using one-factor-at-a-time method and response surface methodology. It turned out that the optimal experimental conditions were as follows: ratio of core to wall materials, 1:9.24 (g/g); concentration of CaCl2, 1.43% and stirring time, 52.23 min. Under these conditions, microcapsules with microencapsulation efficiency of 92.85%, drug-loading efficiency of 9.29%; and moisture content of 7.10% were obtained as spherical particles with a loose and porous surface. The microencapsuled tartary buckwheat flavonoids had good sensory quality, storage stability and sustained release capacity. It was rarely released in the gastric juice environment but exhibited good release performance in the intestinal environment. Thus, PWP could be used in the food industry as a novel microcapsule wall material.
Safety Detection
Fabrication of Non-enzymatic Amperometric Glucose Biosensor Based on Fe3O4-Poly-(γ-glutamic acid)@Au
GUAN Huanan, GONG Dezhuang, SONG Yan, LIU Bo, HAN Bolin, YANG Fan, CUI Linlin, ZHANG Na
2020, 41(12):  267-272.  doi:10.7506/spkx1002-6630-20190319-239
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Herein we report a novel highly sensitive and selective non-enzymatic glucose biosensor fabricated using a Fe3O4-poly-(γ-glutamic acid)@Au (Fe3O4-PGA@Au)-modified glassy carbon electrode. By a green reduction and adsorption method, Fe3O4-PGA@Au was successfully prepared and characterized by X-ray differentiation (XRD), Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The reaction temperature, pH value, scan rate and time were optimized. Cyclic voltammetry was used to investigate the biosensor performance. The results showed that Fe3O4-PGA@Au had good electrocatalysis performance. Good linearity was observed between the peak current density of the biosensor and glucose concentration in the range of 0.1–5.0 and 10–250 μmol/L with a detection limit (LOD) of 0.74 μmol/L (RSN = 3). In addition, the biosensor showed excellent reproducibility. It could efficiently resist the interference of coexistent substances.
Optimization of a Predictive Model for Rapid Detection of Egg Freshness Using Visible Near-Infrared Spectra Based on Combination of Feature Selection and Feature Extraction
DUAN Yufei, WANG Qiaohua
2020, 41(12):  273-278.  doi:10.7506/spkx1002-6630-20190213-060
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In order to improve the detection efficiency of egg freshness by visible near-infrared spectroscopy and develop an optimized predictive model, we optimized the modelling process by taking the advantages of a combination of wavelength feature selection and feature extraction. First derivative was used to preprocess the visible near-infrared transmittance spectral data in the range of 550–950 nm. Considering the influence of redundant spectral information on the model accuracy, a total of 45 sensitive characteristic wavelengths were selected from the preprocessed spectral data by competitive adaptive reweighted sampling (CARS) for support vector regression (SVR) modeling. The correlation coefficients of cross-validation (Rcv) and prediction (Rp) of the developed model were 0.880 5 and 0.888 9, and the root mean square errors of cross-validation (RMSECV) and prediction (RMSEP) were 8.59 and 8.42, respectively. In order to improve the calculation rate and the stability of the model, we used local tangent space alignment (LTSA) as a nonlinear feature extraction method to reprocess the selected characteristic wavelengths. In the new CARS-LTSA model, Rcv and Rp were 0.896 0 and 0.898 3, and RMSECV and RMSEP were 8.04 and 8.18. Compared with the CARS model, the CARS-LTSA model showed improved prediction accuracy and was simplified by eliminating 14 data dimensions. The results of this study illustrated that combined use of feature selection and feature extraction for visible near-infrared spectral data preprocessing not only improved the detection efficiency but also enhanced the accuracy of the predictive model and therefore could provide a reference method for the optimization of predictive modelling for detecting egg freshness based on infrared spectral data.
Analysis of Element Content Characteristics and Risk Assessment of Boletus edulis from Different Geographical Origins in Yunnan Province
CHEN Fengxia, YANG Tianwei, LI Jieqing, LIU Honggao, FAN Maopan, WANG Yuanzhong
2020, 41(12):  279-284.  doi:10.7506/spkx1002-6630-20190724-317
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A comparative study was carried to analyze the mineral contents of Boletus edulis from different producing areas in Yunnan province and to evaluate the health risk of dietary exposure to mineral elements by consumption of B. edulis, aiming to provide a basis for the development of the edible fungi industry in the province and food safety evaluation of wild B. edulis. A total of 171 samples of B. edulis were collected from 8 producing areas in Yunnan province. The contents of 14 mineral elements were determined by inductively coupled plasma emission spectrometry (ICP-AES). The original data were standardized with SPSS statistical software to eliminate the dimension, and comprehensive scores from principal component analysis were calculated and correlation analysis was carried out. The results showed that 1) B. edulis was rich in mineral elements such as Ca, Fe, Mg and Na, and there were differences in the content of mineral elements in B. edulis from different habitats; 2) the correlation analysis indicated that the major elements in B. edulis interacted synergistically (there was good synergism of the enrichment of the toxic element Cd with Fe, Mg, Ba, Co, Cr, Mn, V and Zn), and some antagonistically; 3) the comprehensive scores from principal component analysis could reflect the difference in mineral element contents of B. edulis from different areas, and the enrichment of elements may be related to many ecological factors; and 4) there was a health risk associated with dietary exposure to Cd in B. eduli from Kunming, Yuxi, Dali, Qujing and other areas, and it is recommended that consumers should consume an appropriate amount of B. eduli. The mineral element content characteristics of B. edulis and correlation analysis can provide a scientific basis for the exploitation, utilization and food safety evaluation of wild B. edulis in Yunnan.
Hyperspectral Imaging for Non-destructive Determination and Visualization of Moisture and Carotenoid Contents in Carrot Slices during Drying
YANG Jia, LIU Qiang, ZHAO Nan, CHEN Jikun, PENG Jing, PAN Leiqing, TU Kang
2020, 41(12):  285-291.  doi:10.7506/spkx1002-6630-20190225-169
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In this experiment, hyperspectral images in different wavelength ranges were acquired for carrot slice samples during hot air drying. Subsequently, using multivariate statistical analysis combined with chemometrics, a predictive model for the non-destructive determination of moisture content (MC) and carotenoid content (CC) in samples was developed separately based on partial least squares (PLS) and support vector machine (SVM) algorithm. The results showed that the SVM models developed using multiplicative scatter correction (MSC) in the 400–1 000 nm had the best prediction performance for both MC and CC with coefficient of determination for prediction (R2P) of 0.984 and 0.911, and root mean square error for prediction (RMSEP) of 0.380 g/g and 34.836 mg/100 g, respectively. The optimal models with the feature wavelengths selected by successive projections algorithm showed R2P of 0.962 and 0.898 and RMSEP of 0.612 g/g and 37.544 mg/100 g for MC and CC, respectively. The residual predictive deviation (RPD) in the new models was over 3, indicating good accuracy and stability. Moreover, the spatial distribution of moisture and carotenoid during the drying process were generated and visualized as pseudo-color images. The results indicated that the hyperspectral imaging could be used to effectively predict the MC and CC in carrot slices, demonstrating the potential of hyperspectral imaging as an analytical tool in quality control of carrot slices during drying.
Development of a One-Step Reverse Transcriptase Droplet Digital PCR Assay for Detection of Rotavirus Group A Strains
XU Leirui, MA Dan, WEI Yongxin, LI Dan, WEI Haiyan, LIU Li, ZHANG Ximeng, WANG Qi, FU Pubo, ZHAO Xiaojuan, ZENG Jing
2020, 41(12):  292-297.  doi:10.7506/spkx1002-6630-20190218-091
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Objective: To establish a one-step reverse transcriptase droplet digital polymerase chain reaction (RT-ddPCR) assay for the detection of rotavirus (RV) group A strains. Methods: A set of specific primers and probes was selected for RT-ddPCR. The specificity of this assay was evaluated with RNA samples of other foodborne viruses. A reference material containing the target fragment of RV group A strains was prepared and diluted into several gradients for use in evaluation of the limit of quantitation (LOQ), accuracy, repeatability and reproducibility. Artificially positive samples were prepared by adding the diluted positive fetal sample to different food matrices. Viruses were separated and concentrated from the artificially positive samples, and viral RNA was extracted sufficiently. The effect of food matrices on the quantitative performance of RT-ddPCR was investigated. Results: The RT-ddPCR assay displayed a high accuracy, sensitivity, repeatability and reproducibility. Its LOQ ranged from 58 000.00 to 5.80 copies/μL. Statistically significant disparities (P < 0.05) in the detectable amount and recovery of virus among different food matrices were discovered at each contamination level. Conclusion: RT-ddPCR could quantitatively and accurately detect RNA of RV group A strains. However, the quantitative results were sufficiently affected by the type of food matrixes. The load of RV group A strains in food could be calculated from the recovery rate.
Dietary Exposure Assessment of Sulfur Dioxide Residue in Edible Fungi by Monte Carlo Simulation
LI Xiaobei, ZHAO Xiaoyan, LIU Haiyan, ZHOU Changyan, FAN Tingting, ZHANG Yanmei
2020, 41(12):  298-304.  doi:10.7506/spkx1002-6630-20191101-003
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The sulfur dioxide residues present in 10 species of edible fungi primarily consumed in China were analyzed by @Risk software based on Monte Carlo simulation and hazard quotient was used to characterize their dietary exposure risk. The results showed that the safety of dried edible fungi was extremely poorer than the fresh ones, because the mean values of sulfur dioxide residue in fresh and dried edible fungi were 2.94 and 43.70 mg/kg, respectively, and only some dried fungi had sulfur dioxide values higher than the maximum residue limit, especially Lentinula edodes and Tremella fuciformis. The results of risk assessment showed that the hazard quotient (HQ) for sulfur dioxide via consumption of dried and fresh edible fungi was far below 1, maximum being 0.007 3 at each percentile. At percentile greater than 10%, the HQ was increased by one order of magnitude via consumption of dried edible fungi as compared to the fresh ones. Accordingly, the dietary exposure risk of sulfur dioxide associated with consumption of edible fungi was at a relatively low level for Chinese residents. This research provides a scientific basis for quality and safety management of edible fungi in China.
Establishment of Droplet Digital PCR Assay for Quantitative Detection of Vibrio vulnificus in Aquatic Products
MA Dan, WEI Yongxin, LI Dan, WEI Haiyan, XU Leirui, WANG Qi, FU Pubo, ZHANG Ximeng, ZENG Jing
2020, 41(12):  305-311.  doi:10.7506/spkx1002-6630-20190222-144
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This study aimed to establish a quantitative assay method to detect Vibrio vulnificus in aquatic products based on droplet digital polymerase chain reaction (ddPCR). A pair of primers and probe were designed targeting the single-copy gene met in V. vulnificus. The specificity, sensitivity and repeatability of this method were tested through comparison with real-time PCR. The results indicated that the developed ddPCR method had good specificity, sensitivity and repeatability. In pure cultures, the limit of quantitation (LOQ) and limit of detection (LOD) of this method were 323 and 61 copies/mL, respectively. In artificially contaminated oyster samples, the sensitivity was 1.13 × 102 copies/g. The quantitative result of ddPCR was about 1.4 times as high as the plate counting result and was more stable and accurate than real-time PCR. Therefore, ddPCR is a rapid, specific and sensitive method for quantitative detection of V. vulnificus.
Quick Determination of Residues of Fipronil and Its Metabolites in Tea by QuEChERS Coupled with Gas Chromatography-Tandem Mass Spectrometry with Isotope Internal Standard Calibration
NI Yunchen, XU Xiaomin, HUANG Baifen, XU Meijia, LI Zuguang
2020, 41(12):  312-317.  doi:10.7506/spkx1002-6630-20190203-018
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Based on the quick, easy, cheap, effective, rugged and safe (QuEChERS) technique, a method for the simultaneous determination of the residues of fipronil and its metabolites in tea was developed by gas chromatography-tandem mass spectrometry (GC-MS/MS). The samples were added with the internal standard of fipronil-13C2,15N2, and then extracted with acetonitrile after water soaking. The extract was dehydrated with sodium chloride (NaCl) and anhydrous magnesium sulfate (MgSO4) and purified by dispersive solid phase extraction with N-propyl ethylenediamine (PSA) and graphite carbon (GCB) sorbents. The analytes were detected by tandem mass spectrometry using multiple reaction monitoring (MRM), and quantified by the internal standard method. A good linearity in the concentration range of 0.4–100 μg/L with correlation coefficients (R2) > 0.995 was observed. The limits of quantification (LOQs) for both fipronil and its metabolites were 1 μg/kg. The recoveries of fipronil and its metabolites at four spiked levels (1, 5, 20 and 200 μg/kg) were in the range of 76.72%–96.53% with relative standard deviations (RSDs, n = 6) between 4.76% and 13.07%. The method was found to be simple, sensitive, accurate and suitable for the rapid quantitative analysis of fipronil and its metabolites in tea. Its sensitivity could meet the requirement for the residual limitation of the EU and Japan.
Application of Real-Time PCR Assay in the Identification of Caprinae Meat
SHANG Ke, LIANG Hengxing, ZHANG Biao, DUAN Qingzi, WANG Wei, ZHANG Yu
2020, 41(12):  318-325.  doi:10.7506/spkx1002-6630-20190219-104
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A real-time polymerase chain reaction (real-time PCR) method for the identification of meat from Caprinae (including goats and sheep) was established and optimized based on the inter-species difference of cytochrome b (cyt b) gene. We evaluated the specificity, sensitivity, amplification efficiency, detection limit, reagent consistency and applicability of this method, and we invited five domestic authoritative institutions to validate it. The results showed that this method could be suitable for detecting Caprinae meat products with different substrates because of its good repeatability, wide applicability, high amplification efficiency (> 95%) and accuracy (100%).
Evaluation of Commercial Rapid Test Strips for Detection of Aflatoxin B1 in Edible Oil
ZHANG Wei, ZHANG Wenzhong, GUO Ping, HU Zhongyi, Lü Xiaoli
2020, 41(12):  326-331.  doi:10.7506/spkx1002-6630-20190225-180
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To evaluate and test three rapid aflatoxin B1 (AFB1) test strips from different manufacturers, blind samples were prepared by blank matrix addition, and their uniformity and stability were verified in this study. We investigated the effects of AFB1 concentration and the number of samples on performance indicators of the test strips. The results showed that the sensitivities of the three products were 83%, 100% and 100%, respectively, the specificities were 76.2%, 79.3% and 67.3%, respectively, the false negative rates were 17%, 0% and 0%, respectively, the false positive rates were 23.8%, 20.7% and 32.7%, respectively, and the relative accuracies were 78.9%, 87.6% and 80.6%, respectively. We conducted in-depth discussions on AFB1 concentration setting, stability evaluation and result judgment, and clarified that there were many factors affecting the evaluation of these products. This study is expected to be helpful for the evaluation of rapid test products.