Table of Content

25 January 2023, Volume 44 Issue 2
Food Chemistry
Effect of Oil Phase Structuring on the Formation and Oxidative Stability of Soy Protein-Based Algal Oil Nanoemulsions
YANG Yunyi, CAO Muxi, CHEN Wenrong, WAN Zhili, FANG Suqiong, YANG Xiaoquan
2023, 44(2):  1-8.  doi:10.7506/spkx1002-6630-20220428-363
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In this study, highly stable algal oil-based nanoemulsions stabilized by a combination of soy protein isolate (SPI) and stevioside (STE) were prepared by pre-structuring the oil phase. The microstructure observation, differential scanning calorimetry (DSC) test, and rheological analysis of the algal oil-based oleogels showed that in algal oil with 4% (m/m) beeswax added, a large number of crystals were connected to form a stable network structure, thereby constructing a stable oleogel. The effects of algal oil pre-structuring on the formation and stability of algal oil-based nanoemulsions were investigated. The results showed that the addition of beeswax had no significant effect on nanoemulsion formation. With increasing concentration of beeswax in algal oil (up to 6%), the physical stability of nanoemulsions gradually increased; however, at a higher concentration (8%), more rigid gel network was formed, which destroyed the interfacial layer and in turn led to deterioration of the physical stability of the nanoemulsion. The results of thermal oxidation and photooxidation tests showed that oil phase structuring significantly improved the oxidative stability of the nanoemulsion, and the sample with 6% beeswax added in the oil phase displayed the highest oxidative stability. This study can provide technical support for the preparation of highly stable nanoemulsion-based delivery systems for algal oil in the food industry.
Effect of Number of Freeze-Thaw Cycles on the Properties and Structure of Ultrasonically Modified Corn Starch Gel
HAN Rui, XU Xiuying, HOU Jingyao, QI Jiawei, WU Tianhao, XU Zhilingyun, WU Yuzhu, LIU Jingsheng
2023, 44(2):  9-17.  doi:10.7506/spkx1002-6630-20220430-399
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We investigated the changes of gel characteristics and structure of ultrasonically treated corn starch during freeze-thaw cycles, with a view to providing theoretical guidance for improving the quality of quick-frozen starch-based foods. The effects of the number of freeze-thaw cycles on the dynamic rheological and textural properties of ultrasonically modified corn starch gels were analyzed and their structures were characterized by using a rheometer, a texture analyzer, a low-field nuclear magnetic resonance (NMR) spectrometer, a Fourier transform infrared (FTIR) spectrometer and an X-ray diffractometer (XRD). The results showed that compared with native corn starch, the water separation rate of ultrasonically modified corn starch gels significantly decreased by 5.19% (P < 0.05) at the 4th freeze-thaw cycle, indicating improved freeze-thaw stability; the storage modulus and loss modulus of ultrasonically modified corn starch gels decreased, and the gel strength was weaker; the hardness significantly decreased by 10.83% (P < 0.05), and the amylose content decreased 0.15%. Moreover, the iodine binding force was weakened, the transverse relaxation time distribution curve was shifted to the left, the short-range ordered structure was weakened, and the relative crystallinity was reduced. The gel properties and the structural characterization results indicate that ultrasonic treatment can inhibit water migration and double helix structure formation in the corn starch gel system during freeze-thaw cycles and consequently improve its freeze-thaw stability.
Mechanism of the Influence of Different Gluten Fractions on the Digestibility of Wheat Starch
KUANG Jiwei, ZHANG Chong, HUANG Junrong, PU Huayin, MA Wenhui, MIN Cong, Youling L. XIONG
2023, 44(2):  18-25.  doi:10.7506/spkx1002-6630-20220506-074
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In this study, gluten, glutenin and gliadin were mixed with starch at mass ratio of 14:86. To clarify their effects and mechanism on starch digestibility, the interactions between gluten and its components and starch/α-amylase were investigated by a rheometer, a thermogravimetric analyzer and a confocal laser scanning microscope (CLSM). The results showed that compared with pure wheat starch, the digestibility of starch reduced by 39.93%, 49.48% and 26.61% after 120 min of enzymatic hydrolysis in the presence of gluten, glutenin and gliadin, respectively. Starch could interact with gluten through hydrogen bonds to form a stable complex. Compared with gluten and gliadin, the addition of glutenin formed a denser physical barrier around the starch matrix, which inhibited the enzymatic hydrolysis of starch to a greater extent. In addition, the percentage inhibition of glutenin on α-amylase was the highest (approximately 79%). CLSM observation proved stronger binding between α-amylase and glutenin. The results of this study will help to enrich our understanding of the mechanism of the regulatory effect of typical protein components on starch digestibility in food systems, and provide a theoretical guideline for the development of low-glycemic-index foods.
Effect of Deacetylated Konjac Glucomannan on the Structure and Gel Properties of Pork Myofibrillar Protein
LI Junguang, ZHANG Xuyue, WANG Yu, YU Xiao, PANG Jie, CHEN Lishui, BAI Yanhong
2023, 44(2):  26-31.  doi:10.7506/spkx1002-6630-20220509-109
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In order to investigate the effect and underlying mechanism of deacetylated konjac glucomannan (DKGM) on the structure and gel properties of pork myofibrillar protein (MP), the changes in the gel strength, water retention, water distribution, microstructure, secondary and tertiary structures and gel molecular forces of MP were analyzed after the addition of DKGM at different levels (0%, 0.125%, 0.25%, 0.5% and 1%). The results showed that the gel strength of MP increased with the increase of DKGM addition, reaching the maximum at an addition level of 0.25%, which was 1.55 times higher than that of the control group. The addition of DKGM could retard the flow of water, thus improving the gel water-holding capacity. Cold-field scanning electron microscopy revealed that the addition of DKGM could promote the formation of more uniform and dense network structures in MP gels. The structure and force analysis showed that the addition of an appropriate amount of DKGM could promote the unfolding of MP molecules and the exposure of hydrophobic groups, increase the content of active sulfhydryl groups, induce α-helix-to-β-fold transition, enhance the hydrophobic interactions and disulfide bonds of MP gels, and thus improve the gel strength and water-holding capacity.
Structural Characterization and Pyrolysis Characteristics of Lignin in Traditional Smoked and Roasted Wood
LIN Ju, MA Yangyang, LI Miaoyun, HUANG Haolong, GAO Haoyuan, LIU Shijie, ZHU Yaodi, ZHAO Lijun, LIANG Dong, ZHAO Gaiming
2023, 44(2):  32-38.  doi:10.7506/spkx1002-6630-20211213-141
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In order to explore the effects of different wood types with different chemical compositions and structures on the types and amounts of polycyclic aromatic hydrocarbons produced in traditional smoked meat products, the structural and pyrolysis characteristics of lignin in five kinds of wood commonly used in the production of traditional smoked and roasted meat products, pine, poplar, beech, jujube and apple wood, were investigated by infrared spectroscopy, Raman spectroscopy, thermogravimetry and thermogravimetry coupled with infrared spectroscopy. The results showed that there were differences in the contents of lignin, guaiacyl (G) and syringyl (S) in the five kinds of wood. The pyrolysis process involved three stages, mainly in the range of 200?500 ℃, but the mass loss rate, mass loss temperature, pyrolysis rate and pyrolysis temperature of lignin were different among different kinds of wood, indicating that there are significant differences in the thermal stability of lignin from different wood sources. Differences in lignin content, S/G structure content and side chain structure in smoked and roasted wood could lead to different thermal stability, and different pyrolysis characteristics could in turn affect the formation of harmful substances such as polycyclic aromatic hydrocarbons.
In Situ Characterization and Analysis of Molecular Structure of Gluten Proteins and Moisture Distribution in Dough during Freezing
ZHANG Hua, ZHANG Pu, ZHANG Yuhan, LIU Xingli, ZHANG Yanyan
2023, 44(2):  39-44.  doi:10.7506/spkx1002-6630-20220415-190
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In this experiment, confocal laser Raman spectroscopy and low-field nuclear magnetic resonance imaging were used to in situ characterize and analyze the molecular structure changes of gluten proteins and water migration during the freezing process of dough. The results showed that the disulfide bond configuration of gluten proteins in dough with 45% water content was the most stable, and the relative percentage of the gauche-gauche-gauche (g-g-g) configuration decreased by 4.33% after freezing. During the freezing process, the relatively stable g-g-g configuration was transformed to unstable gauche-gauche-trans (g-g-t) and trans-gauche-trans (t-g-t) configuration. The ratio between the intensities of the absorption peaks at 740 and 1 004 cm-1 (I740/1 004) in the Raman spectrum, which represents the microenvironment around the side chains of amino acids, reached the maximum when 45% water was added to dough, and decreased continuously during freezing. At the end of freeze, there was no significant difference in the relative percentage of α-helix in the secondary structure of gluten proteins with water addition, but the relative percentage of α-helix decreased by 3.63% during the freezing process. The results of water distribution and migration showed that the quality deterioration caused by ice crystal growth appeared earlier with the increase of water addition during the freezing process of dough. The results of this study will help to clarify the mechanism of dough quality deterioration during freezing.
Formation Mechanism of Advanced Glycation End Products in Silver Carp Surimi Products during Freeze-thaw and Heating Treatment
LI Ting, LIAO Zikang, LI Zhen, WU Jinhong, WANG Shaoyun, HUANG Yiqun, WANG Faxiang, LIU Yongle, LI Xianghong
2023, 44(2):  45-53.  doi:10.7506/spkx1002-6630-20220120-208
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Silver carp (Hypophthalmichthys molitrix) surimi was heated after freeze-thaw cycles at different freezing temperatures, and the changes of nonanal, 1-octene-3-alcohol, endogenous fluorescent substances, protein subunits, lysine, α-dicarbonyl compounds (glyoxal, GO and methylglyoxal, MGO), Nε-carboxylmethyl-lysine (CML) as an advanced glycation end product (AGE) and fluorescent AGEs in surimi during freeze-thaw and heating treatment were determined. The results showed that freezing temperature had no significant effect on any of the parameters measured (P > 0.05). As the number of freeze-thaw cycles increased, the levels of nonanal, 1-octene-3-ol, endogenous fluorescent substances, CML and fluorescent AGEs in surimi increased significantly, the content of lysine increased, and the levels of GO and MGO decreased significantly (P < 0.05). The levels of 1-octene-3-ol, GO, MGO, CML and fluorescent AGEs increased significantly during heat processing, the content of lysine increased at first and then decreased, the level of endogenous fluorescent substances decreased significantly (P < 0.05), and the myosin heavy chain was gradually degraded into smaller proteins. The above results showed that freeze-thaw treatment provided a large number of precursors for the formation of AGEs in surimi. Thermal processing promoted fat oxidation and protein degradation, stimulating the formation of AGEs in surimi through various pathways, which could in turn affect the safety of surimi.
Comparison of the Effects of Tea Polyphenols and Epigallocatechin Gallate on Improving Physicochemical Indexes Related to Quality of Air-Dried Golden Pomfret
WANG Rui, WANG Qi, ZHOU Min, YU Bin, ZHANG Xuesha, LIU Zheng
2023, 44(2):  54-63.  doi:10.7506/spkx1002-6630-20220224-207
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In order to comparatively analyze the effects of tea polyphenols and epigallocatechin gallate (EGCG), the major component of tea polyphenols, on the quality-related physicochemical properties during the processing of air-dried golden pomfret, 0.05% tea polyphenols, 0.05% EGCG and 0.02% EGCG were added to the marinade solution (8% salt), separately. The salt content, water-holding capacity (WHC), water migration, thiobarbituric acid reactive substances (TBARS) value and total volatile basic nitrogen (TVB-N) content of fish meat during curing and air drying were detected, and the change of volatile flavor substances during air-dried golden pomfret processing was analyzed by gas chromatography-ion mobility spectrometry (GC-IMS). The results showed that the addition of tea polyphenols and EGCG could effectively inhibit the increase in TVB-N and TBARS values of fish back and abdominal muscles during the curing and air-drying process (P < 0.05), and reduce the loss of immobile water, which in turn could enhance the WHC of fish meat. Among them, the effect of 0.05% tea polyphenols was the most pronounced, followed by 0.05% EGCG, and 0.02% EGCG was least effective. A total of 63 volatile components were identified during the processing of air-dried golden pomfret, among which aldehydes, ketones and esters increased during the curing and air-drying process, contributing to the unique flavor of air-dried golden pomfret. The addition of tea polyphenols and EGCG was conducive to the formation of volatile aldehydes and ketones in air-dried pomfret and reduced the content of offensive odor substances (triethylamine, butyric acid, o-phenol and isopropyl alcohol). It was found that 0.05% tea polyphenols was the most effective in improving the flavor of air-dried pomfret, followed by 0.05% EGCG, and 0.02% EGCG was least effective. This study showed that natural tea polyphenols was more effective in improving the quality of air-dried pomfret during processing than EGCG alone.
Effects of External Proteins on the Structure of Silver Carp Surimi Myofibrillar Protein and Its Capacity to Bind to Characteristic Fishy-Odor Compounds
YAN Hao, WANG Yudong, ZHONG Wu, ZHUANG Yang, YANG Hong
2023, 44(2):  64-70.  doi:10.7506/spkx1002-6630-20220309-115
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In this work, the effects of addition of different amounts (2%, 4% and 6%) of soy protein isolate (SPI), egg white protein (EWP) and whey protein isolate (WPI) on the structure of silver carp surimi myofibrillar protein (MP) and its ability to bind to fishy-odor compounds (hexanal, nonanal, and 1-octen-3-ol) were investigated. The results indicated that adding an appropriate amount of external proteins could promote the unfolding of MP, thus increasing its surface hydrophobicity, turbidity, particle size, and zeta-potential. Moreover, the exposed hydrophobic group enhanced the ability of MP to bind to hexanal and nonanal, and the exposed hydroxyl group enhanced the ability of MP to bind to 1-octen-3-ol. With increasing amount of added EWP and WPI, the capacity of MP to bind to 1-octen-3-ol increased due to the increased hydrophilic groups on the protein surface. In addition, addition of WPI could better enhance the capacity of MP to bind to the three fishy-odor compounds.
Effect of Waxy Corn Starch on the Quality of Dumpling Wrappers
WANG Yuan, LOU Haiwei, ZHAO Renyong
2023, 44(2):  71-78.  doi:10.7506/spkx1002-6630-20220223-198
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In order to explore the effect of waxy corn starch on the quality of dumpling wrappers, the effects of adding different amounts of waxy corn starch on the color, toughness, freezable water content and microstructure of dumpling wrappers and the cooking quality of unfrozen and frozen dumpling wrappers were investigated. The results showed that waxy corn starch addition could significantly improve the brightness (L*) value, toughness and starch binding capacity, and reduce the content of freezable water in dumpling wrappers. Moreover, waxy corn starch addition significantly shortened the cooking time, reduced the cooking loss, increased the shear hardness, and improved the sensory quality of frozen dumpling wrappers. The transparency, cooking loss, shear hardness and chewiness of frozen dumpling wrappers were better than those of unfrozen dumpling wrappers. In summary, the quality of frozen dumpling wrappers can be improved by adding 4%–6% waxy corn starch, which provides a theoretical basis for the development of waxy corn starch in the food industry.
Tremella fuciformis Polysaccharides Inhibited Water Migration and Adhesion in Fresh Wet Noodles
LIU Bingli, FAN Hongxiu, SHAO Tian, WANG Dawei, ZHANG Yanrong, LIU Tingting
2023, 44(2):  79-86.  doi:10.7506/spkx1002-6630-20220516-204
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To investigate the dose-effect relationship of Tremella fuciformis polysaccharides against water migration and adhesion in fresh wet noodles, we evaluated the farinograph and texture properties of fresh wet noodles made with different amounts of T. fuciformis polysaccharides, and we also characterized them by Fourier transform infrared (FTIR) spectroscopy, low field nuclear magnetic resonance (LF-NMR) spectroscopy, dynamic rheological analysis and laser confocal microscopy. The results showed that the fresh wet noodles with T. fuciformis polysaccharides had lower apparent viscosity compared with the control group without the polysaccharides, and the polysaccharides could inhibit the migration of free water, resulting in changes in water distribution. Compared with the control group, the relative α-helix content of fresh wet noodles with T. fuciformis polysaccharides increased by 9.96% and the relative β-turn content decreased by 7.11%. Addition of T. fuciformis polysaccharides in noodles enhanced the structural orderliness of gluten proteins and the microstructural compactness, reduced the exposure of starch granules, and improved the water-holding capacity, which in turn made noodles more stable during storage. The thermal properties and dynamic rheological properties showed that T. fuciformis polysaccharides could promote the formation of a uniform, orderly and stable gluten network structure in fresh wet noodles. Among all concentrations tested, addition of 0.5% T. fuciformis polysaccharides was the most effective in inhibiting water migration and improving adhesion during storage of fresh wet noodles.
Effect of Seaweed Dietary Fiber on Quality of Low-Fat and Low-Salt Chicken Frankfurters
WU Jiuyi, YAO Wenjing, CAO Chuan’ai, WANG Meijuan, KONG Baohua, LIU Qian
2023, 44(2):  87-93.  doi:10.7506/spkx1002-6630-20220325-296
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The present study aimed to investigate the effect of the addition of different concentrations (0.5%, 0.75%, 1%, 1.25%, 1.5% and 1.75%) of seaweed dietary fiber on improving the quality of low-fat and low-salt chicken frankfurters. The results showed that increasing concentration of seaweed dietary fiber could result in a significant decrease in the cooking loss, L* value and b* value of low-fat and low-salt chicken frankfurters (P < 0.05), but a significant increase in the emulsion stability, springiness, resilience, fracturability and sensory evaluation (tightness, juiciness, flavor and overall acceptability) (P < 0.05), and the optimal concentration was 1.5% (P < 0.05). The microstructural observation showed that seaweed dietary fiber could promote the formation of a dense three-dimensional network structure in chicken protein gels. Therefore, seaweed dietary fiber can improve the water-holding capacity and gel properties of low-fat and low-salt chicken meat batters, which in turn can improve the eating quality of the final product. Our results provide a technical guidance for the development of low-fat and low-salt meat products.
Preparation and Microrheological Properties of Deaminated Potato Protein Emulsion
LIU Xingli, WEI Yingying, ZHANG Yanyan, WANG Hongwei, FENG Zhiqiang, ZHANG Hua
2023, 44(2):  94-100.  doi:10.7506/spkx1002-6630-20220510-121
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Potato protein deaminated for different durations (0, 0.5, 3, 6 and 12 h) were used to prepare emulsions, and the products obtained were evaluated for droplet size distribution, emulsion stability, microrheological properties and microstructure. The results showed that the droplet volume mean diameter and Turbiscan stability index (TSI) of the emulsion decreased first and then increased with increasing deamidation time. The emulsions with potato protein deaminated for 3 and 6 h exhibited uniform droplet size distribution and good stability, which may be because the increased electrostatic repulsion between the modified protein emulsion droplets prevented their aggregation. The droplet size of the emulsion with potato protein deaminated for 12 h increased and the stability decreased, which may be because of the decreased charge repulsion force and consequent droplet aggregation. The microrheological analysis showed that the emulsion with potato protein deaminated for 6 h had the highest macroscopic viscosity index (MVI) value and the highest viscosity, and the speed of droplet movement was slowed down. There was a strong force between the emulsion droplets, which made the system more stable. This study can provide a reference for further research and development of potato protein products in order to improve the utilization rate of potato protein and expand the application range.
Mechanism and Influential Factors of the Stability of Hydrophobic Starch Pickering Emulsion Gels
GUO Lu, HUANG Liang, ZHANG Bin, FU Xiong, HUANG Qiang
2023, 44(2):  101-108.  doi:10.7506/spkx1002-6630-20220322-263
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This study aimed to investigate the effects of different factors (temperature, pH and ionic strength) on the stability of Pickering emulsion gel stabilized by starch-lipid complexes (SFAC) and uncover the underlying mechanism. The results of observation using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed that SFAC particles could be adsorbed onto the oil-water interface, forming a tight barrier to wrap the dispersed oil droplets, leading to the formation of round emulsion droplets. The close packing of the emulsion droplets resulted in the formation of a stable gel network structure. Optical microscopic observation and analysis of particle size distribution and zeta potential showed that the hydrophobic starch emulsion gel maintained its structure and exhibited good storage stability at pH 3–9 and 0.1–0.9 mol/L ionic strength. In addition, the Pickering emulsion gel was thermally reversible; the particle size increased, the viscosity decreased and the gel melted at high temperatures, and the melted sample gelled again upon cooling. These results showed that hydrophobic starch Pickering emulsion gels are highly stable over a wide range of temperature, pH and ionic strength, and are suitable for the stabilization of different vegetable oils.
Effect of Eugenol on the Structure and Functional Properties of Electrospun Antibacterial Absorbent Pads
YU Dong, FENG Yangyang, CAO Chuan’ai, KONG Baohua, LIAN Junqiang, LIU Qian
2023, 44(2):  109-115.  doi:10.7506/spkx1002-6630-20211205-060
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Our present study investigated the effect of eugenol addition on the characteristics of spinning solution and the physiochemical properties and antibacterial activity of nanofiber absorbent pads. The results showed that the apparent viscosity of the spinning solution decreased with eugenol addition, and the “vesicle” structure in the nanofiber increased. The elongation at break of the absorbent pad decreased with eugenol addition. The tensile strength of the absorbent pad with 15% eugenol was the largest, but the tensile strength showed a significant downward trend with increasing eugenol content above 15%. As the content of eugenol increased, the swelling ratio and water vapor transmission rate of the absorbent pad decreased. The scavenging capacity of the pad with 20% eugenol against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical cation were the strongest with percentage scavenging of 83% and 78%, respectively. Moreover, the nanofiber absorbent pad had a good inhibitory effect on Escherichia coli and Staphylococcus aureus. In summary, the antibacterial absorbent pad can effectively absorb meat exudate, slow down the oxidation rate of meat and inhibit the reproduction of microorganisms.
Quality Changes and Protein Degradation in Edam Yak Cheese during Ripening
WANG Ze, ZHANG Yan, CHEN Lianhong
2023, 44(2):  116-124.  doi:10.7506/spkx1002-6630-20220310-126
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In order to study the ripening mechanism of Edam yak cheese, the sensory, physicochemical and textural properties, and proteolysis and lipolysis indexes of Edam yak cheese were determined after 0, 20, 40, 60 and 80 days of ripening. The degradation of casein was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy, and the correlation between maturation time and quality indices was analyzed by Pearson’s correlation analysis. The results showed that the sensory score decreased at first and then increased with increasing ripening time; the water content and pH decreased; the brightness value (L*) decreased, while the redness value (a*) and yellowness value (b*) increased; the hardness, elasticity and adhesiveness all increased, while the cohesiveness gradually decreased. The storage and loss moduli increased, and the tangent of the loss angle was always less than 1. The ripening time was positively correlated with the total nitrogen content, and the nitrogen content of soluble fractions at pH 4.6 and in 12% trichloracetic acid (TCA) (P < 0.01). The fat content increased firstly and then decreased, and the free fatty acid content and thiobarbituric acid-reactive substances (TBARS) value increased gradually. The results of casein (CN) degradation showed that αs1-CN, αs2-CN, β-CN and κ-CN were degraded continuously during cheese ripening, macromolecular proteins were degraded obviously after 80 days of maturation, and β-sheet and α-helix were gradually transformed to random coil during maturation. The ripening time was positively correlated with the carbonyl content and surface hydrophobicity (P < 0.01), but negatively correlated with the total sulfhydryl content (P < 0.05).
Effects of Four Polysaccharide Prebiotics on Stability of Lactobacillus rhamnosus GG Microcapsules
LIU Jiongna, XU Yuqiao, FAN Fangyu
2023, 44(2):  125-131.  doi:10.7506/spkx1002-6630-20220208-029
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To improve the stability of Lactobacillus rhamnosus GG (LGG), LGG microcapsules were prepared using complex coacervation method. Meanwhile, the effects of four prebiotics, inulin, fructooligosaccharide, pullulan and stachyose on the properties of LGG microcapsules. The microstructure and thermal stability of LGG microcapsules were analyzed by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The results showed that the addition of prebiotics had a positive effect on the performance of LGG microcapsules. After simulated gastrointestinal treatment, the viable count of microcapsules with inulin was the highest, 9.5 (lg(CFU/g)). Stachyose had the strongest protective effect on LGG microcapsules under bile salt concentration and high temperature. The viable count of microcapsules with stachyose was 8.7 (lg(CFU/g)) after treatment at 75 ℃ for 30 min. The storage stability of LGG microcapsules at a water activity of 0.75 was improved by the addition of fructooligosaccharide. DSC analysis showed that the addition of prebiotics improved the thermal stability of LGG microcapsules. The melting temperature of LGG microcapsules with stachyose was 172 ℃, but the addition of fructooligosaccharide reduced the melting temperature of LGG microcapsules. SEM analysis showed that the addition of prebiotics did not affect the structure of LGG microcapsules. This study provides a theoretical basis for future studies on the influence of prebiotics on the performance of LGG microcapsules.
Using Molecular Docking to Investigate the Alpha-amylase Inhibitory Activity of Bitter Peptides RK7 and KQ7 Derived from Yak Cheese
LI Mengyao, LIANG Qi, SONG Xuemei
2023, 44(2):  132-138.  doi:10.7506/spkx1002-6630-20220120-197
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In this study, the physicochemical properties of two bitter peptides derived from yak cheese, RPKHPIK (RK7) and KVLPVPQ (KQ7) were calculated by using online bioinformatics tools such as ExPASy-ProtParam, Innovagen, and Pep-Draw. Molecular docking was used to elucidate the mechanism of the inhibitory effect of the two peptides on α-amylase and their α-amylase inhibitory activity was determined. The results showed that the molecular masses of RK7 and KQ7 were 875.07 and 779.98 Da, and their hydrophobicity were 42.86% and 71.42%, respectively. Molecular docking showed that His305, Glu233, Trp59 and Trp58 in α-amylase played an important role in binding to RK7 and KQ7. Furthermore, Asp197, Glu233 and Asp300 were the key amino acids for the activity of α-amylase. The half maximal inhibitory concentration (IC50) of RK7 and KQ7 against α-amylase were 0.45 and 0.86 mg/mL, respectively. The findings of this study provide new evidence for the study of α-amylase inhibitory peptides.
Effects of Whey Protein Isolate Fibrils and Typical Antioxidants on the Survival of Spray-Dried Lactobacillus reuteri TMW 1.656 during Ambient Storage
GUO Qianwan, WANG Qi, YAN Wenli, ZHANG Yunyan, KANG Xu, ZHAO Meng
2023, 44(2):  139-145.  doi:10.7506/spkx1002-6630-20220318-210
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To investigate the protective effects of the novel nanomaterial whey protein isolated fibrils (WPIF) and typical antioxidants against oxidative stress in probiotics during ambient storage, spray-dried probiotic powders were prepared using whey protein isolate (WPI) or WPIF as wall material alone or in combination with different concentrations of epigallocatechin gallate (EGCG) or glutathione (GSH) in this study. The experimental results suggested that the viability of probiotics during ambient storage decreased in the following order: WPIF ≈ WPI > WPI + 0.5 mg/mL EGCG > WPI + 0.5 mg/mL GSH > WPI + 5.0 mg/mL EGCG > WPI + 5.0 mg/mL GSH. There was no significant difference in the probiotic survival between the WPI and WPIF groups, which may be because the high temperature during spray drying allowed the fibrils to break down and aggregate. Interestingly, EGCG and GSH concentration-dependently accelerated the death of probiotics during ambient storage, which might be related to the antimicrobial activity or the cytotoxicity of the oxidative products of EGCG and GSH.
Transcriptomic Analysis of the Dynamic Formation Mechanism of Vibrio parahaemolyticus Biofilm
LI Anqi, SHI Chenglong, QIAN Senhe, WANG Zhou, ZHAO Shiguang, LIU Yan, XUE Zhenglian
2023, 44(2):  146-155.  doi:10.7506/spkx1002-6630-20220224-208
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To investigate the mechanism of biofilm formation in Vibrio parahaemolyticus, its physiological characteristics were examined and the regulation of gene expression during biofilm formation was studied transcriptomic sequencing. Two strains of V. parahaemolyticus (ATCC 17802 and VP-0) that differ in their biofilms were evaluated for their physiological indexes such as extracellular polysaccharides, extracellular proteins, the signaling molecule autoinducer-2 (AI-2), cell permeability, and biofilm microscopic morphology, and the dynamic formation process of biofilm was investigated. The results showed that the biofilm formation process of the tested strains involved reversible adhesion (from 0 to 12 h), irreversible adhesion and micro-colony formation (from 12 to 48 h), maturation (from 48 to 72 h), and dissociation (from 72 to 144 h). The secretion rates of extracellular polysaccharides and proteins at the biofilm maturation stage of ATCC 17802 were 1.67 and 2.3 times higher than those of VP-0, respectively. The difference in signaling molecule content during biofilm formation was not significant (P > 0.05), and laser confocal scanning microscopy (LCSM) showed that ATCC 17802 had a greater degree of aggregation. Based on the results of transcriptomic sequencing, 802, 1 061, and 267 significantly differentially expressed genes were identified in three treatment groups (72 vs 8 h, 48 vs 8 h, and 72 vs 48 h), of which 506, 655 and 96 differentially expressed genes were down-regulated and 296, 406 and 171 differentially expressed genes were up-regulated, respectively. These differences were mainly involved in energy metabolism, flagellar system, transport system, and other aspects related to biofilm formation. The findings obtained in this study provide a theoretical basis for gene expression regulation during the dynamic formation of V. parahaemolyticus biofilm.
Kinetic Modelling of Mixed Culture Fermentation of Oenococcus oeni and Saccharomyces cerevisiae
MAO Yaling, LI Jun’e, YU Jing, YANG Liu, ZHU Xia, YANG Xueshan
2023, 44(2):  156-164.  doi:10.7506/spkx1002-6630-20220211-062
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In order to study the kinetic changes in microbial growth, substrate consumption and product generation during the co-fermentation of Saccharomyces cerevisiae and Oenococcus oeni, indigenous O. oeni ZX-1 and MG-1 were co-inoculated with S. cerevisiae VW and AW into a model grape system, separately, and the viable count of S. cerevisiae, reducing sugar content, alcohol content, O. oeni viable count and L-malic acid content in the fermentation system were measured every day during the fermentation period. The classical Logistic, Boltzmann, SGompertz and DoseResp models were adopted to nonlinearly fit the measured data. The results showed that the Boltzmann model could better describe the growth of S. cerevisiae and the change of alcohol content; the logistic model had the best fitting effect on the change of reducing sugar content. For each of the four co-culture groups, the fitting coefficients R2 of the Boltzmann and DoseResp models for O. oeni growth and L-malic acid content change were consistent, indicating both models could well predict the growth of O. oeni and the trend of L-malic acid content during the co-fermentation process. Taken together, we concluded the tested strains O. oeni have good biocompatibility with S. cerevisiae VW and AW, and the established kinetic models can provide data support and a theoretical basis for the control of mixed culture fermentation for industrial wine production.
Molecular Fingerprinting Analysis of Yeasts Isolated from Traditional Guizhou Xiaoqu, a Traditional Fermentation Starter
WANG Chunxiao, HE Yulin, TANG Jiadai, QIU Shuyi
2023, 44(2):  165-172.  doi:10.7506/spkx1002-6630-20220202-003
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A total of 59 yeast isolates from Xiaoqu from five different regions of Guizhou were identified to belong to six species by sequencing of the D1/D2 domain of the 26S rRNA gene, including Trichosporon asahii (one strain), Saccharomycopsis fibuligera (32 strains), Saccharomycopsis malanga (8 strains), Hyphopichia burtonii (4 strains), Wickerhamomyces anomalus (6 strains), and Saccharomyces cerevisiae (8 strains). The colony characteristics of the six yeast species on WL medium and the restriction fragment length polymorphism patterns of the internal transcribed spacer (ITS) region of the 5.8S rRNA gene of these species were explored in this study in order to provide a basis for their fast identification. Tandem repeat-tRNA (TRtRNA) fingerprinting analysis was applied to discriminate intraspecific diversity, and 17 genotypes were found. Four, three, and eight different genotypes were identified from H. burtonii, W. anomalus, and S. fibuligera, respectively. The genotypes 10, 11, 12, 15, 16 and 17 of S. fibuligera had a close genetic relation, and the other genotypes from H. burtonii, W. anomalus, and S. fibuligera showed a relative far genetic relation at the intraspecific level.
Identification of a Heat-Resistant Strain of Bacillus cereus and Evaluation of Its Efficacy in Alleviating Inflammatory Bowel Disease
XU Yifan, SHENG Kangliang, WANG Yongzhong
2023, 44(2):  173-180.  doi:10.7506/spkx1002-6630-20220316-176
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An unknown laboratory strain was identified and named as Bacillus cereus HMPM18123 based on the 16S rRNA gene and conserved protein-coding gene (gyrA and gyrB) sequences combined with virulence genes (nheA, nheB, nheC, hblA, hblC, hblD, becT, cytK and entFM) and biochemical properties. The tolerance of the strain to different temperatures, pH, simulated gastric and intestinal fluid was evaluated as well as its efficacy in alleviating colitis induced by dextran sulfate sodium (DSS) in mice. The results of growth characteristics showed that the strain had good tolerance to high temperature and simulated gastric and intestinal fluid. In addition, the strain improved DSS-induced colitis symptoms in mice such as body mass loss, colon shortening, increased disease activity index (DAI) score, tissue lesions, and up-regulated expression of inflammatory factors.
Recombinant Expression and Application of Chymotrypsin SplB in Bacillus subtilis
PAN Lijie, WANG Bin, PAN Li
2023, 44(2):  181-188.  doi:10.7506/spkx1002-6630-20220122-224
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In this study, through promoter optimization and host screening, an SplB expression vector with His-tag at the C-terminal was constructed, and SplB was successfully expressed in Bacillus subtilis. The enzymatic properties of the purified recombinant SplB protease were studied, and the application of recombinant SplB protease in the cleavage of recombinant protein Prx with a tag was explored. The results showed that using B. subtilis ATCC6051Δ10 as the host, the recombinant expression activity of SplB mediated by promoter P43 was the highest (10.24 U/mL). The recombinant SplB was purified by affinity chromatography and its enzymatic properties were studied. The optimum temperature was 40 ℃, the optimum pH was 8.5, and the purified SplB had good temperature and pH stability. Low concentrations of Co2+ promoted the activity of SplB, while low concentrations of Mg2+ and K+ did not affect its activity; low concentrations of Cu2+, Zn2+ and Ni+ inhibited the activity of SplB, and sodium dodecyl sulfate (SDS) greatly inhibited the enzyme activity of recombinant SplB. The recombinant SplB protease could concentration-dependently cleave the WELQ peptide tag on the recombinant protein Prx. This study provides support for optimizing the recombinant expression of SplB and its application in the fields of food and medicine.
Effect of Lactic Acid Bacteria Starter Cultures on the Quality of Multigrain Dough and Steamed Bread
XIE Shuiqi, ZHANG Xiaotong, JIN Qiwen, LIU Lijun, MENG Xiangchen
2023, 44(2):  189-194.  doi:10.7506/spkx1002-6630-20220113-129
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In order to study the effect of fermentation with a mixed starter culture of lactic acid bacteria on the quality of multigrain dough and steamed bread, yellow pea flour, naked oat flour, gluten flour and oat β-glucan (OBG) were mixed together to prepare dough and steamed bread with a direct vat set (DVS) mixed starter?culture of lactic acid bacteria. The acidifying capacity of lactic acid bacteria in dough was investigated, and the contents of OBG, resistant starch (RS) and free amino acids and the microstructure of dough were analyzed. Also, the quality and nutritional characteristics of steamed multigrain bread and steamed wheat bread before and after fermentation were compared. The results showed that lactic acid bacteria had strong acidifying capacity in fermented multigrain dough, and the contents of lactic acid and acetic acid were 24.85 and 8.98 mg/mL, respectively, after 24 hours of fermentation. Compared with unfermented multigrain dough, the OBG content in lactic acid bacteria fermented multigrain dough decreased by 32.56%, the RS content increased by 32.88%, the total amount of free amino acids increased by 1.46 times, the amino acid composition pattern was better, proteins and cellulose were partially degraded, and the gluten network was more compact and continuous. In terms of nutrition, the dietary fiber content of steamed multigrain bread was higher than 6% both before and after lactic acid bacteria fermentation, and the protein content was 40.35% and 38.38% in steamed unfermented and fermented multigrain bread, respectively, indicating that steamed multigrain bread is rich in dietary fiber and protein. Its dietary fiber and protein contents were higher than those of steamed wheat bread. Lactic acid bacteria fermented multigrain steamed bread had higher in vitro protein digestibility and specific volume, and the overall sensory score of steamed lactic acid bacteria fermented multigrain bread was significantly higher than that of steamed unfermented multigrain bread, and the overall acceptability was higher.
Effects of Post-Fermentation Temperature on Amino Nitrogen Formation Kinetics and Physicochemical Properties of Bacterial-type Douchi from Different Soybean Varieties
LI Aijun, WANG Di, YANG Gang, SONG Jun, KONG Xiangbing, LIAO Shenglan, KAN Jianquan
2023, 44(2):  195-203.  doi:10.7506/spkx1002-6630-20220309-116
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In order to improve the quality stability of bacterial-type douchi during industrial production, four different varieties of soybean (LS, DBL, DBS and BS) were used to make bacterial-type douchi, and the modified Gompertz equation was used to fit the changes in the amino nitrogen content of bacterial-type douchi at three different post-fermentation temperatures (15, 25 and 40 ℃). Also, the free amino acid content was determined at the end of fermentation. The results showed that the Gompertz equation could well fit the kinetics of amino nitrogen formation (coefficient of determination > 0.96). The predicted fermentation endpoints at post-fermentation temperatures of 25, 15 and 40 ℃were approximately 9, 10, and 4 days, respectively. The maximum production of amino acid nitrogen in the four bacterial-type douchi at post-fermentation temperature of 15 ℃ decreased in the following order: DBL > LS > DBS > BS, while the maximum production of amino nitrogen at 25 and 40 ℃ decreased in the following order: LS > DBL > DBS > BS. The contents of amino nitrogen and free amino acids in black soybean douchi were significantly lower than those in yellow soybean douchi, but there was no significant difference among douchi from different yellow soybean varieties. After post-fermentation, the proportion of umami amino acids in the four bacterial-type douchi increased, and the proportion of bitter amino acids decreased. The proportion of umami amino acids in the four bacterial-type douchi at post-fermentation temperature of 40 ℃ decreased and the proportion of bitter amino acids increased compared with that at 15 ℃. This may be related to consumption of umami amino acids by the Maillard reaction at high temperatures. The correlation analysis of quality indexes shows that the trend of four bacterial-type douchi was similar. The results of this study can provide theoretical guidance for the industrial production of bacterial-type douchi.
Correlation Analysis between Bacterial Community Succession and Changes of Flavor Substances during Whey Wine Fermentation
WANG Hui, WU Xiaoyan, XIA Yanan, WANG Yurong, YANG Yang, WU Youna, SHUANG Quan
2023, 44(2):  204-211.  doi:10.7506/spkx1002-6630-20220210-046
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In this study, gas chromatography-mass spectrometry (GC-MS) was used to analyze the changes of important aroma components in whey wine, and high-throughput sequencing technology was used to analyze the bacterial community changes in whey wine. Moreover, correlation analysis was conducted between aroma components and bacterial community. The results showed that the number of flavor substances generally increased during the fermentation process of whey wine. A total of 102 volatile flavor substances were detected, with ester being the most abundant. Based on their odor activity values (OAV), 15 important aroma substances, such as ethyl benzoate, ethyl acetate and ethyl butyrate were identified in whey wine. Lactobacillus was the absolutely dominant genus at the early stage of fermentation, while Lactobacillus and Lactococcus became the absolute dominant genera as the fermentation process progressed. Bacterial function prediction showed that the major metabolic activities of whey wine were amino acid metabolism and carbohydrate metabolism. Correlation analysis showed that most flavor substances were positively correlated with Lactococcus and Raoultella. The genera Lactococcus and Raoultella showed a significantly positive correlation with ethyl phenyl acetate, ethyl decanoate, ethyl caproate and ethyl acetate. Lactobacillus was positively correlated with citral, caprylic acid, decanoic acid, 4-ethylphenol, ethyl heptanoate, methyl decanoate and ethyl oleate. This study can provide a theoretical basis for the selection of starter cultures for and the flavor control of whey wine.
Fermentation of Yeast Mannoprotein by Intestinal Microorganisms in Vitro and Anti-inflammatory Activity of Its Metabolites
LI Xiang, CHEN Guijie, KANG Yijun, Amirsalar KHANDAN
2023, 44(2):  212-221.  doi:10.7506/spkx1002-6630-20220209-037
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The anaerobic fermentation of yeast mannoprotein (MP) by the gut microbiota in vitro was carried out to evaluate the probiotic activity of MP in this study. The results showed that MP could modulate the structure of the gut microbiota, increasing the relative abundance of Bacteroidetes and decreasing the relative abundances of Firmicutes and Proteobacteria and the ratio of Firmicutes to Bacteroidetes. The concentration of short-chain fatty acids, especially acetic acid and propionic acid, in the fermentation broth were significantly increased by MP. MP showed similar prebiotic activity to inulin. Inulin could stimulate the proliferation of Bifidobacterium, whereas MP could selectively promote the growth of Bacteroides, Veillonella, Clostridium_sensu_srticto, Blautia, Faecalibacterium, Fusicatenibacter and Butyricicoccus. MP had no significant inhibitory effect on lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophages (P > 0.05), whereas the fermentation broth showed anti-inflammatory activity similar to that of inulin, which was superior to that of the blank group. Thus, MP is expected to serve as a functional food ingredient that can offer health benefits by modulating the gut microbiota.
Dissecting the Relationship between Microbial Community Succession and Pyrazine Metabolite Synthesis in Nongxiangxing Daqu
CHEN Yingqi, CHEN Jie, ZHOU Yaojin, LI Zijian, TANG Shichao, ZHAO Yuchuan, LUO Huibo, HUANG Dan
2023, 44(2):  222-230.  doi:10.7506/spkx1002-6630-20220225-224
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The correlation between the stages of pyrazine synthesis and the microbial flora during the making of Nongxiang Daqu was analyzed, and the effect of microbial interactions on the synthesis of pyrazine during Daqu making was explored. Headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and high-throughput sequencing were used for the analysis of the changes in pyrazine contents and the microbial community structure during Daqu making, respectively. Principal component analysis (PCA) and linear discriminant analysis (LDA) were used for finding out differential microorganisms. The correlation between differential microorganisms and pyrazine metabolites was evaluated using Spearman’s correlation coefficient, and a correlation network between these pyrazine metabolism-related microorganisms and the microbial flora of Nongxiangxing Daqu was constructed. The results showed that nine pyrazine metabolites were detected during Nongxiangxing Daqu fermentation, and there were significant differences in the number and types of pyrazine metabolites between the stages of 1–5 and 7–28 days. The microbial community succession could be divided into two stages: A (1–5 days) and B (7–28 days). At stage A, the differential fungi were mainly Kodamae and Candida, and the differential bacteria were mainly Kosakonia, Pantoea and Methylophilus; at stage B, the differential fungi were mainly Thermoascus and Thermomyces, and the differential bacteria were mainly Thermoactinomyces and Saccharopolyspora. The synthesis of pyrazine metabolites during Nongxiangxing Daqu fermentation was positively correlated Cladosporium and Lichtheimia, but negatively correlated with Thermomyces and Fusarium. These pyrazine metabolism-related microorganisms were positively correlated with most other Nongxiangxing Daqu microorganisms, but showed negative correlation with only a few microorganisms, such as Thermomyces. The results of this study provide a theoretical basis for the analysis of the mechanism of microbial synthesis of pyrazine metabolites in Nongxiangxing Daqu.
Construction of a Synthetic Microbial Community for Kombucha Fermentation and Analysis of Its Fermentation Characteristics
SONG Xiaoxiao, ZHANG Huixia, LIU Binjie, YANG Minhe, WANG Guohong
2023, 44(2):  231-239.  doi:10.7506/spkx1002-6630-20220209-034
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An artificial microbial consortium was constructed by using four dominant strains isolated from tea fungus. Through comparison of single and mixed cultures, we determined the role of these strains in the fermentation of tea fungus and the formation of biofilm. High performance liquid chromatography (HPLC) and headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) were used to analyze the major biochemical components in the fermentation process of tea fungus. After multiple passages, the stability of the microbial consortium was analyzed using a combination of isolation and metagenomic analysis. The results showed that among the four strains tested, Gluconacetobacter sp. J5 was the core strain producing cellulose and biofilm. The fermentation characteristics of the synthetic microbial consortium was comparable to natural fermentation in terms of cell growth, sugar utilization, pH, total acidity and tea polyphenol content. The microbial consortium was stable and all four strains were dominant in the microbial consortium after six passages. These results suggest that the functional strains isolated from tea fungus can be used to construct a stable artificial starter culture, which will lay the foundation for the standardized industrial production of tea fungus.
Correlation Analysis among Physicochemical Parameters, Flavor Compounds and Microbial Community during Fourth Round of Heap Fermentation of Jiang-Flavor Baijiu
WU Cheng, CHENG Pingyan, XIE Dan, HUANG Wei, FAN Endi, LU Lunwei, HU Feng
2023, 44(2):  240-247.  doi:10.7506/spkx1002-6630-20220401-003
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The composition and change of the microbial community during the fourth round of heap fermentation of Jiang-flavor baijiu were explored using traditional culture-dependent approaches and high-throughput sequencing, and flavor compounds from fermented grains were analyzed by gas chromatography. The correlation among physicochemical parameters, flavor compounds and the microbial community was also analyzed. The results showed that the dominant bacteria were Bacillus amyloliquefaciens, B. licheniformis, uncultured Kroppenstedtia sp., K. eburnea, Sphingobium yanoikuyae and Lactobacillus sp., and the dominant fungi were Pichia kudriavzevii, Kazachstania humilis, Thermomyces languginosus, Byssochlamys spectabilis, Zygosaccharomyces parabilii and Aspergillus sp. The microbial community had a complex relationship with physicochemical parameters and flavor compounds. The water content was positively correlated with yeasts like P. kudriavzevii, negatively correlated with filamentous fungi such as T. lanuginosus, B. spectabilis and A. costiformis, while the starch and reducing sugar contents were positively correlated with Bacillus sp., and negatively correlated with P. kudriavzevii. Meanwhile, yeasts were positively correlated with alcohols such as propanol, isobutanol, isoamyl alcohol and β-phenylethanol (P < 0.01), while filamentous fungi and bacteria were positively correlated with acids and esters, such as acetic acid, propionic acid, isobutyric acid, ethyl lactate, ethyl oleate and butyl caproate (P < 0.01). This study may provide a theoretical basis for further clarifying the mechanism of heap fermentation of Jiang-flavor baijiu.
Effects of Plant Polysaccharides on Intestinal Flora and Metabolism in Patients Investigated Using in Vitro Fermentation Model
JIA Lina, MA Qian, WANG Xinyue, GE Yanyan, WANG Nan, HE Hongpeng, LUO Xuegang, ZHU Liying, JIA Weiguo, HAO Lizhuang, QI Wei
2023, 44(2):  248-261.  doi:10.7506/spkx1002-6630-20220111-102
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This study aims to investigate the effects of five plant polysaccharides from Radix Astragalus, Rhizoma Atractylodis, Radix Scrophulariae, jujubes, Fructus mume on intestinal microorganisms and their metabolites in patients with type 2 diabetes mellitus (T2DM) by using high-throughput sequencing, metabolomic techniques and an in vitro fermentation model. The results showed that plant polysaccharides could significantly improve the structure of the intestinal flora in diabetic patients, and all five polysaccharides could enrich Faecalibacterium and Roseburia and inhibit Escherichia. Plant polysaccharides could regulate the contents of gas medium and short-chain fatty acids, and change the metabolic pathways of amino acids and short-chain fatty acids in the intestinal flora of patients with T2DM. Radix Astragalus, Atractylodis Rhizoma and Radix Scrophularia polysaccharides had significant regulatory effects on the total amount of short-chain fatty acids, and could also regulate the contents of acetic acid, propionic acid, butyric acid, valeric acid, isobutyric acid and isovaleric acid. In addition to these polysaccharides, jujube polysaccharide also increased the content of total gaseous media as well as CO2 and CH4 in patients with T2DM, while Fructus mume polysaccharide could reduce the contents of gas medium and H2S. These results provide a theoretical basis for the screening and utilization of plant polysaccharides and understanding their targeted regulation of intestinal microorganisms.
Analysis of Bacterial Diversity, Free Amino Acids and Fatty Acids in Featured Dry Fermented Dairy Products from Major Pastoral Areas of China
LIU Zhendong, CHENG Xiufeng, Suolangqunpei, XING Shuyuan, LI Liang, ZHANG Jinchao, LUO Zhang
2023, 44(2):  262-270.  doi:10.7506/spkx1002-6630-20220315-164
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This research aimed to study the bacterial community, free amino acid and fatty acid composition in featured dry fermented dairy products from some major pastoral areas of China and to analyze the correlation between bacterial community and free amino acid and fatty acid composition. The V4–V5 region of the bacterial 16S rDNA gene from Suannai Geda from Xinjiang, Qula from Tibet, Naizhazi from Inner Mongolia and milk fan from Yunnan was sequenced by high-throughput sequencing. The contents of fatty acids and free amino acids in these dairy products were determined by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC), respectively. Finally, the correlation of bacterial community with α diversity, fatty acids and free amino acids was evaluated by redundancy analysis (RDA). High-throughput sequencing results showed that a total of 2 421 338 reads were obtained from these dry fermented dairy samples, of which 1 871 524 were clean reads. The bacterial Chao1 and Shannon indexes in milk fan were significantly higher than those in the other three dairy products. The bacterial community compositions in the four dairy products were significantly different, but Firmicutes was dominant in all these products, among which the relative abundance of Firmicutes in Suannai Geda was the highest. The relative abundance of Proteobacteria in Qula was the highest. At the genus level, the bacterial community compositions in the four dairy products were dominated by Lactococcus or Lactobacillus. The contents of 16 fatty acids in milk fan were higher than those in the other three products. A total of 24 free amino acids were detected, among which Suannai Geda contained the largest number (24) of free amino acids, and the contents of most free amino acids in Suannai Geda were higher than those in the other three products. Redundancy analysis showed that alanine was correlated with Acetobacter, Lactobacillus and Streptococcus, and acetic acid and butyric acid were correlated with Acinetobacter. The results of this study may provide a theoretical basis for the industrial production of traditional dry fermented dairy products in different provinces.
Component Analysis
Chemical Composition and Hpyerglycemic Activity of Phenolic Extract from Zanthoxylum bungeanum Pericarps
YANG Chengjun, CHEN Mingshun, LIU Chengmei, ZHOU Wei, LI Jihua, CHEN Jun
2023, 44(2):  271-278.  doi:10.7506/spkx1002-6630-20220224-206
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Crude polyphenols were extracted with ethanol from the pericarps of Zanthoxylum bungeanum and fractionated by sequential solvent extraction with dichloromethane (F1), ethyl acetate (F2), n-butanol (F3) and water (F4). The phenolic composition in these fractions were identified and quantified using ultra-high performance liquid chromatography-electrospray ionization-quadrupole-time of flight-tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS). Their α-glucosidase inhibitory effect and hypoglycemic activity in mice with type II diabetes mellitus were examined. Results demonstrated that 20 phenolic compounds were identified in the pericarps of Z. bungeanum, including nine phenolic acids and their derivatives, and 11 flavonoid compounds. The contents of total phenols, total flavonoids and polyphenols in the four fractions decreased in the following order: F2 > F3 > F4 > F1, indicating that fractional extraction can effectively enrich polyphenols. Polyphenols from Z. bungeanum pericarps had inhibitory effect on α-glucosidase, and F3 gave the highest percentage of inhibition (85.86%). The inhibition of α-glucosidase activity was found to be uncompetitive. The major bioactive components in F3, chlorogenic acid and rutin, were significantly positively correlated with the percentage of α-glucosidase inhibition. Additionally, F3 could reduce fasting blood glucose level and oral glucose tolerance in diabetic mice by 64.2% and 21.42%, respectively, and improve abnormal body mass and diet in diabetic mice. Therefore, polyphenols from Z. bungeanum pericarps have the potential for use as a therapeutic agent for the prevention and treatment of diabetes.
Gas Chromatography-Mass Spectrometry Identification of Changes in Odor Characteristics of Live Crassostrea gigas during Different Circulation Stages
LIN Hengzong, LIANG Zhiyuan, QIN Xiaoming, GAO Jialong, FAN Xiuping, HUANG Yanping, CHANG Xiangyang, DENG Jie, WU Weijun
2023, 44(2):  279-287.  doi:10.7506/spkx1002-6630-20220314-150
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This study aimed to reveal the flavor quality changes of live oysters during different steps of circulation, and optimize the management of live oyster transportation in order to improve the survival quality of oysters. The changes in the types and contents of volatile flavor compounds in Crassostrea gigas sequentially subjected to depuration, induced dormancy and simulated waterless live transportation were investigated using solid phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS). Results showed that a total of 49 volatile flavor substances were identified in live C. gigas, including aldehydes, ketones, esters, hydrocarbons, alcohols, nitrogen-containing and sulfur-containing heterocyclic compounds. Post-harvest stress had a significant impact on the flavor quality. The content of pleasant flavor compounds was significantly enhanced while the content of irritating odor substances was evidently reduced, and lipid oxidation was significantly alleviated after 24 h of depuration. Lipid oxidation in oysters was increased with waterless live transportation time, and the total amount of volatile flavor substances was slowly accumulated. Odor activity values (OAVs) showed that heptanal, nonanal, (E)-2-nonenal, 4-ethylbenzaldehyde, hexanal, (E)-2-octenal, undecanal, (E)-2-decenal, decanal, (E,E)-2,4-nonadienal and 2-pentyl furan were the key flavor substances of live C. gigas, which could be used as a reference to reflect the physiological status of live oysters. Principal component analysis (PCA) showed that the cumulative contribution of the first three principal components to total variances was 85.6%, allowing a clear distinction between the different stages of circulation. In conclusion, the vitality and flavor substances of C. gigas reach a new level after post-harvest depuration for 24 h, which is more conducive to long-term low temperature and waterless live oyster preservation. Meanwhile, the analysis of volatile components can be used as a method to identify the vitality during the circulation of live shellfish.
Differences in Volatile Flavor Compounds in Hand-Grab Mutton Frozen at Different Freezing Rates
BI Yongzhao, SHAN Qimei, LUO Ruiming, BAI Shuang, JI Chen, WANG Yongrui
2023, 44(2):  288-295.  doi:10.7506/spkx1002-6630-20220316-192
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To investigate the influence of freezing rate on the volatile flavor compounds in hand-grab mutton, the differences in the volatile flavor compounds among unfrozen samples (control) and those frozen at three different freezing rates, namely 0.26 (?18 ℃), 0.56 (?40 ℃) and 2.00 cm/h (?80 ℃) were analyzed by headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and electronic nose. The results showed that the eutectic point temperature of hand-grab mutton was (?9.66 ± 0.24) ℃. In terms of overall odor perception, the electronic nose could distinguish hand grab mutton frozen at different freezing rates. Totally 44, 40, 49 and 53 volatile substances were identified in the control, ?18 ℃ frozen, ?40 ℃ frozen and ?80 ℃ frozen samples, respectively, among which aldehydes, alcohols and ketones were the major ones. The content of total volatile substances in these frozen samples was 30.78%, 40.79% and 70.75% of that in the control group, respectively. The contents of aldehydes, alcohols, ketones, acids and esters decreased with decreasing freezing rate. For all samples, hexanal, heptanal, octanal, nonanal, (E)-2-octenal, 2,4-decadienal and 1-octen-3-ol were determined as key aroma compounds based on relative odor activity value (ROAV). The higher the freezing rate, the greater the ROAV values of these compounds. The sensory scores of the four samples followed the decreasing order of control > ?80 ℃ > ?40 ℃ > ?18 ℃ (P < 0.05). In summary, we concluded that the freezing of hand-grab mutton can cause losses of a large number of volatile aroma components, but higher freezing rates can reduce the loss of volatile aroma components, maintaining the original flavor to a large extent.
Secondary Metabolite Distribution and Antioxidant Activities of Corn Kernel
ZHAI Xiaotong, HAN Lin, QIAO Congcong, HE Cai’an, LIU Fang, YANG Xiaoji, LI Shan, TAN Bin, WANG Min
2023, 44(2):  296-303.  doi:10.7506/spkx1002-6630-20220418-227
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Layered milling technique combined with targeted metabolomics was applied to analyze the characteristic components including carotenoids and secondary metabolites including phenolic compounds from different parts of corn kernel, and the antioxidant activities of these parts were studied. The results showed carotenoids mainly existed in the aleurone layer and peripheral endosperm of corn kernel, while phenolic compounds existed in the pericarp, seed coat and aleurone layer mostly in a bound form. Totally 17 free phenolic acids were detected in each separated part, with the most abundant ones being vanillin, 4-hydroxybenzoic acid and ferulic acid. The antioxidant activity of each part of corn kernel was positively correlated with the contents of phenolic compounds (P < 0.01), and at individual phenolic acid level, vanillin, 4-hydroxybenzoic acid and syringaldehyde were the major contributors to the antioxidant activity of corn kernel. The antioxidant activity of the inner bran layer was relatively higher than that of the other parts.
Metabolite Composition and Anti-Inflammatory Activity of Ethanol Extract of Camellia oleifera Seed
LIN Xin, LI Yang, ZHAN Miao, FU Xiangjin, ZHONG Haiyan, YAO Wen, LIU Cheng
2023, 44(2):  304-311.  doi:10.7506/spkx1002-6630-20220323-280
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To explore the anti-inflammatory mechanism of Camellia oleifera seed oil, the metabolites in ethanol extracts from 15 batches of C. oleifera seeds were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and the inhibitory activity of the ethanol extracts on enteritis in Drosophila was evaluated by the “Smurf” test. The correlation between small molecular metabolites in the ethanol extracts and their anti-inflammatory activity was investigated and molecular docking with lipoxidase (LOX) was conducted to identify the key metabolites. Finally, the key metabolites were verified by the “Smurf” test. The results showed that the ethanol extract of C. oleifera seeds had good enteritis inhibitory activity, with percentage inhibition of 15.06%–61.71%, and its metabolites mainly included polyphenols, amino acids, organic acids, nucleotides, sugars and lipids. Seven polyphenolic compounds were identified in C. oleifera seeds for the first time. The monomeric compounds with good anti-enteritis activity were preliminarily identified as bruceine B, miltirone, 8-geranyloxypsoralen, cedrelone, wighteone, kaempferitrin and kaempferol-3-O-rutinoside. The anti-inflammatory activity of wighteone was reported for the first time in this study, and at 0.1 mg/mL, the percentage inhibition of enteritis was 64%, much greater than the positive control sulfasalazine (27.99%). This study lays the foundation for further exploring the anti-enteritis activity and mechanism of C. oleifera seed oil in vitro and in vivo.
Isolation, Purification and Structural Identification of Red Pigment from Nuodeng Ham
YANG Zijiang, ZHANG Lihong, LIAO Guozhou, TIAN Mei, LÜ Donglin, HE Ying, GE Changrong, WANG Guiying
2023, 44(2):  312-318.  doi:10.7506/spkx1002-6630-20211203-039
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In order to explore the chemical nature of red pigment in Nuodeng ham, the red pigment was extracted with 75% acetone aqueous solution and purified using a C18 solid phase extraction column, and its chemical structure was characterized by using ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy and ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The UV-Vis spectrum showed a strong absorption peak at 416 nm and two weakly symmetrical absorption peaks at 546 and 584 nm, which are characteristic of metalloporphyrins. When it was excited at 420 nm, the red pigment exhibited a strong fluorescence emission peak at 590 nm and a weak fluorescence emission peak at 644 nm, which highly coincided with those of Zn protoporphyrin IX (ZnPP) standard, indicating that the metal ions in the porphyrin ring were zinc ions. ZnPP was detected by UPLC-MS/MS in both positive (m/z 625.177 9 [M + H]+) and negative ion (m/z 623.161 4 [M-H]–) modes, and the stretching vibrations of characteristic functional groups on the porphyrin ring such as –CH3, –CH2–, C=O, –C–OH in carboxyl groups, C–H on olefin and porphyrin ring C=N were observed in the FTIR spectrum. In addition, the 1H-NMR results of the red pigment were consistent with the structure of the target compound ZnPP. Therefore, the red pigment in Nuodeng ham was identified as ZnPP. The results of this study provide a theoretical basis for the color regulation of Nuodeng ham.
Safety Detection
Non-Destructive Detection of Physical and Chemical Indicators of Salted Duck Eggs during Salting Using Near-Infrared Spectroscopy
TIAN Wenqiang, WANG Qiaohua, XU Buyun, CHEN Yuanzhe, XIAO Shijie, FAN Wei, LIN Weiguo, LIU Shiwei
2023, 44(2):  319-326.  doi:10.7506/spkx1002-6630-20220429-384
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The near-infrared spectral data of salted duck eggs, prepared from Gaoyou Ma duck eggs, were collected during the whole curing period and based on them, a model for nondestructive and rapid detection of the key quality indicators of salted duck eggs (yolk moisture content, yolk sodium chloride concentration and salted egg yolk index). In order to reduce the influence of other external factors on spectrum acquisition, various spectral preprocessing methods such as multiplicative scatter correction and normalization combined with three feature selection algorithms including competitive adaptive reweighted sampling (CARS), successive projections algorithm (SPA) and uninformative variables elimination (UVE) were used to establish partial least squares regression (PLSR) models. Furthermore, CARS or UVE combined with SPA was used to establish a more robust model. It was found that the optimal band selection method for the three quality indicators of salted duck eggs was UVE combined with SPA, which had the best overall performance. Comparative analysis showed that the optimal model structures for egg yolk moisture content, egg yolk sodium chloride concentration, and salted egg yolk index were standardization-UVE + SPA-PLSR, Savitzky-Golay-UVE + SPA-PLSR, and mean centering-UVE + SPA-PLSR, respectively. The correlation coefficients were 0.933 4, 0.897 8 and 0.928 6 for the training set (Rc), and 0.927 6, 0.908 5 and 0.916 3 for the prediction set (Rp), respectively. The spectral model established in this study can allow the non-destructive detection of the physical and chemical indicators of salted duck eggs during the salting period.
Hyperspectral Imaging for Prediction and Distribution Visualization of Total Acidity and Hardness of Red Globe Grapes
GAO Sheng, XU Jianhua
2023, 44(2):  327-336.  doi:10.7506/spkx1002-6630-20220306-078
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In this paper, hyperspectral imaging technology was used for nondestructive detection and distribution visualization of total acidity and firmness of red globe grapes. The hyperspectral information of 360 samples of growing red globe grapes in the wavelength range from 450 to 1 000 nm was collected using a hyperspectral instrument, and the total acidity and firmness of these samples were determined by titration and a texture analyzer, respectively. The Kennard-Stone (KS) algorithm was used to divide the total samples into a training set (270 samples) and a test set (90 samples) in a 3:1 ratio. The collected raw spectral data were preprocessed using various methods such as standard normal variate (SNV), Savitzky-Golay (SG), multivariate scatter correction (MSC), and normalization to determine the best spectral preprocessing method. Then, the feature variables were extracted from the spectral information using six dimensionality reduction algorithms: competitive adaptive reweighted sampling (CARS), successive projections algorithm (SPA), genetic algorithm (GA), uninformative variable elimination (UVE), CARS-SPA, and UVE-SPA. Using partial least squares regression (PLSR), optimal prediction models for total acidity and firmness were developed separately. Finally, the total acidity and hardness for each pixel of the hyperspectral image were calculated according to the proposed optimal prediction models, and a gray scale image was obtained and pseudo-color transformed to visualize the distribution of total acidity and firmness of red globe grapes. The results showed that the optimal prediction model for total acidity was MSC-CARS-SPA-PLSR, with correlation coefficient for the prediction set (Rp), root mean square errors of prediction (RMSEP) and residual predictive deviation (RPD) of 0.985 1, 1.348 2 and 5.664 3, respectively. The optimal prediction model for firmness was SG-CARS-PLSR, with Rp, RMSEP and RPD of 0.929 1, 7.935 4 and 2.510 8, respectively. In summary, hyperspectral imaging provides a new method for the detection and visualization of total acidity and firmness of growing red globe grapes.
Effects of Salt and Sugar Contents on the Migration of Diaminodiphenylmethane Isomers from Laminated Food Packaging Bags
MA Junjie, HU Changying, WANG Zhiwei
2023, 44(2):  337-344.  doi:10.7506/spkx1002-6630-20220117-164
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Liquid chromatography-mass spectrometry (LC-MS) was used to determine the migration of the isomers of diaminotoluene (TDA) and diaminodiphenylmethane (MDA). The migration levels of TDA and MDA from 10 samples of laminated food packaging bags to 4% acetic acid were investigated. In addition, salting-out and sugaring-out assisted liquid-liquid extraction combined with LC-MS was used to explore the effect of sodium chloride and sucrose on the migration of 2,4’-MDA and 2,2’-MDA from laminated food packaging bags to 10% ethanol and water. The results showed that 4,4’-MDA, 2,4’-MDA and 2,2’-MDA were detected in four samples, and the total migration of MDA in one of the samples exceeded 10 μg/kg. The presence of salt and sugar had a significant effect (P < 0.05) on the migration of 2,4’-MDA and 2,2’-MDA to 10% ethanol and water. The migration levels decreased significantly (P < 0.05) with increasing salt and sugar contents in food simulants (2, 5, 10, 15, 20 g/100 mL). Adjustment of food simulants may be needed for packaging material migration tests on foods with high salt or sugar content.
Simultaneous Direct Determination of Glufosinate Ammonium and Its Metabolite Residues in Milk by Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry
ZHANG Lijia, LIU Lijun, WANG Yang, WEN Jing, MO Nan, XIE Ruilong, LÜ Zhiyong, Li Cuizhi
2023, 44(2):  345-350.  doi:10.7506/spkx1002-6630-20220304-054
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Using multi-walled carbon nanotubes (MWCNTs) as a novel sorbent and a new special anionic chromatographic column for pesticide residues, an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous direct determination of glufosinate ammonium and its metabolites 3-methylphosphino-propionic acid and N-acetylglufosinate ammonium in milk. The samples were extracted with methanol, cleaned up using MWCNTs, and degreased by high-speed centrifugation at low temperature. The analytes were separated on an Anionic Polar Pesticide (2.1 mm × 100 mm, 5 μm) column using a mobile phase containing 0.9% formic acid solution (A) and 0.9% formic acid solution-acetonitrile (B). The instrument was operated in the negative ion scanning mode with multiple reaction monitoring. Glufosinate ammonium was quantified by an internal standard method, and its two metabolites by an external standard method. The calibration curves for glufosinate ammonium and its two metabolites were linear in the concentration range of 1–50, 2–50 and 2–50 μg/L with correlation coefficient (R2) greater than 0.99. For these compounds, the limits of detection were 2.5, 5.0 and 5.0 μg/kg, and the limits of quantification were 5.0, 10.0 and 10.0 μg/kg, respectively. The recoveries ranged from 79.35% to 101.80%, with relative standard deviation (RSD) between 1.15% and 8.63%. The proposed method is characterized by simple pretreatment, stable chromatographic conditions, low impurity interference, high sensitivity and good accuracy, and is suitable for the determination of glufosinate ammonium and its metabolite residues in milk.
Determination of Fipronil and Its Metabolites in Tea by Gas Chromatography-Negative Ion Chemical Ionization-Mass Spectrometry
MA Yiying, HAO Yu, ZHANG Peng, LIU Mengmeng, YU Yang, SUN Xinyao, YU Litao
2023, 44(2):  351-356.  doi:10.7506/spkx1002-6630-20220316-172
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In this paper, a gas chromatography-negative ion chemical ionization-mass spectrometry (GC-NICI-MS) method was established for the determination of fipronil and its metabolites fipronil sulfone and fipronil sulfoxide in tea. Fipronil and its metabolites were extracted from samples with acetonitrile, purified by liquid-liquid partition with n-hexane followed by chromatography on a PSA-SPE column, detected by GC-NICI-MS, and quantified by external standard method. The results showed that chromatographic separation was achieved within 16 min. The linear range for the four analytes was 0.002–0.200 μg/mL, with correlation coefficient (R2) larger than 0.999. The detection limit (RSN = 10) was 0.002 mg/kg, and the relative standard deviation (RSD) was less than 5%. At spiked concentration levels of 0.002, 0.010 and 0.020 mg/kg, the recoveries ranged from 96.33% to 102.50%. The developed method has a wide linear range, high accuracy and good repeatability, and allows the rapid and accurate detection of trace amounts of fipronil and its metabolites in commercially available tea.
Determination of Metronidazolem, Dimetridazole and Ronidazole in Honey by On-line Solid-phase Extraction Coupled to Isotope Dilution-Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry
LIN Hao, LIU Chuan, ZHANG Yangyang, XIAO Quanwei, MAO Rui, WAN Yuping, DAI Qin
2023, 44(2):  357-363.  doi:10.7506/spkx1002-6630-20220304-058
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In this study, we established a method for the determination of metronidazolem, dimetridazole and ronidazole in honey by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The analytes were extracted from samples, purified using a cation exchange cartridge, separated on a C18 (3.0 mm × 100 mm, 1.7 μm) chromatographic column, detected in the multiple reaction monitoring (MRM) mode, and quantitated by an internal standard method. Metronidazolem, dimetridazole and ronidazole were separated well and their calibration curves were linear in the concentration range of 1.0–100.0 ng/mL. The relative standard deviation for replicate determinations was 1.6%–3.7% (n = 6), and the average recoveries for spiked samples ranged from 95.0% to 101.4%. This method has the advantages of low matrix interference, simple operation and high accuracy, an is suitable for the determination of the residues of metronidazolem, dimetridazole and ronidazole in honey.