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25 July 2021, Volume 42 Issue 14
Food Chemistry
Assembly Behavior and Interaction between Fish Skin Gelatin and Polyphenols
WANG Shuya, ZHAO Jingyun, DAI Yalei, GAO Jin, LIANG Hongshan, LI Shugang, ZHOU Bin
2021, 42(14):  1-8.  doi:10.7506/spkx1002-6630-20200702-033
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In this current work, the interaction and assemble behavior between polyphenols with different structures and fish skin gelatin (GLA) were evaluated, which is expected to provide a scientific basis for the processing of aquatic products, the utilization of by-products and the exploration of novel food ingredients, and to provide a theoretical guidance for the application of polyphenol-protein complexes in food fields. Three kinds of polyphenols with different numbers of pyrogallol groups including tannic acid (TA), epigallocatechin gallate (EGCG) and gallic acid (GA) were selected for this study. The impact of polyphenol concentration and pH on the assembly behavior of GLA-polyphenol systems was evaluated based on turbidity and particle size. Fluorescence spectroscopy and isothermal titration calorimetry (ITC) were used to explore the interaction mechanism between polyphenols and GLA. The results showed that TA and EGCG could be assembled with GLA at a certain concentration to form polyphenol-GLA nanocomposites, whose transmittance could be reversibly tuned by changing the pH. Fluorescence spectroscopic analysis revealed that the formation of GLA-polyphenol complexes could statically quench the endogenous fluorescence of GLA. Isothermal titration calorimetry showed that the main forces of the interaction between TA and GLA were hydrogen bonds and van der Waals forces, while the interaction between EGCG and GLA was mainly driven by electrostatic interaction.
Effect of Heat Treatment on Maillard Reaction Degree and Volatile Components of Milk
YI Shengnan, LU Jing, PANG Xiaoyang, HAO Liyu, ZHANG Shuwen, LÜ Jiaping
2021, 42(14):  9-15.  doi:10.7506/spkx1002-6630-20200622-295
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The Maillard reaction degree of 15 heat-treated milks were evaluated by determining the production of two typical Maillard reaction products, furosine and 5-hydroxymethyl furfural. The change of volatile compounds in the treated samples were investigated by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and electronic nose technology (E-nose). An untreated sample was used as a control. The results showed that greater degree of heat treatment could result in higher degree of Maillard reaction, and the production of furosine and 5-hydroxymethylfurfural increased sharply when the heat treatment temperature was higher than 120 ℃ or the heat treatment time was longer than 15 s. Principal component analysis (PCA) of the E-nose data showed significant odor differences between samples treated at different temperatures for the same duration. GC-MS results showed that the flavor of heat-treated milk at 120 ℃/5 s and 120 ℃/15 s was similar to each other, and as the intensity of heat treatment increased, the number of newly formed flavor substances increased significantly, and the relative contents of aldehydes, ketones and esters increased significantly. On the other hand, the relative contents of some acids significantly dropped. This study corroborated the effect of different heat treatments on the Maillard reaction degree and flavor of milk, which could also provide guidance for milk production.
Screening of Co-pigments to Improve Color Stability of Black Rice Anthocyanins and Underlying Mechanism
ZHAO Lei, PAN Fei, ZHOU Na, ZHANG Yali, HAO Shuai, WANG Chengtao
2021, 42(14):  16-23.  doi:10.7506/spkx1002-6630-20200801-017
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Seven phenolic compounds and organic acids (epicatechin, caffeic acid, rosmarinic acid, chlorogenic acid, oxalic acid, malic acid and clove acid) were evaluated in this study for their effects on the color stability of black rice anthocyanins at pH 3.0 and 5.0. The best co-pigment was selected by virtue of its co-pigmentation and thermal stabilization effects on black rice anthocyanins, and its best concentration was explored at pH 3.0. Afterwards, its underlying mechanism of action was investigated by Fourier transform infrared (FTIR) spectroscopy, molecular docking and molecular simulation. The results showed that all the co-pigments except malic acid had good co-pigmentation effect and could improve the thermal stability of black rice anthocyanins at pH 3.0 and 5.0, among which rosmarinic acid at pH 3.0 had the best effect. The co-pigmentation effect increased with increasing concentration of rosmarinic acid from 0.1 to 4.0 mg/mL. Rosmarinic acid showed the best protective effect on the thermal stability of black rice anthocyanins when used at 2.0 mg/mL. The results of FTIR spectroscopy, molecular docking, and molecular simulation revealed that rosmarinic acid could bind to anthocyanins through hydrogen bonds and π-π stacking interactions, which improved the stability of black rice anthocyanins.
Studying Interactions of Protocatechuic Aldehyde and Ferulic Acid with Bovine Serum Albumin by Molecular Docking and Spectroscopy
LÜ Yanfang, LIANG Qianqian, GUO Yuqing, LI Xuepeng, LIU Xinxin, SHEN Lin, LI Jianrong
2021, 42(14):  24-31.  doi:10.7506/spkx1002-6630-20200618-251
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With the aim of providing an experimental basis for extensive applications of protocatechuic aldehyde (PCA) and ferulic acid (FA) in the field of foods, the interactions and binding capacity of PCA and FA with bovine serum albumin (BSA) were investigated by spectroscopic and molecular docking techniques to uncover the underlying interaction mechanism. The results revealed that PCA and FA spontaneously bound to the active site of BSA by hydrogen bonds and van der Waals force with ΔG < 0. The binding capacity of PCA was much stronger than that of FA. A single binding site was observed for both PCA and FA, which was in the hydrophobic cavity between Domain IIA and Domain IIIA near Trp213 residue, thereby leading to static quenching of the endogenous fluorescence of BSA. The binding constant of PCA to BSA was greater than that of FA at 310 K (9.005 × 105 L/mol versus 2.553 × 105 L/mol). Meanwhile, the molecular docking results corroborated that PCA was closer to the Trp213 residue of BSA than FA (0.512 nm versus 0.518 nm). Therefore, PCA may more easily combine with BSA due to its higher polarity.
Bioengineering
Directional Screening for Reuterin-Producing Lactobacillus reuteri and Its Biological Characteristics
LI Yijuan, SHAO Kaisheng, ZHANG Na, MENG Yingping, TAO Xueying, ZHOU Yingyu, WEI Hua, ZHANG Zhihong
2021, 42(14):  32-38.  doi:10.7506/spkx1002-6630-20201101-003
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Fresh feces from healthy poultry were collected for directional screening for candidate probiotic strains of Lactobacillus reuteri according to their host adaptation characteristics. Through 16S rDNA sequence analysis and pduC gene cluster screening, three reuterin-producing strains of L. reuteri were obtained. Their biological characteristics such as simulated gastrointestinal environment tolerance, antibiotic sensitivity, antibacterial activity of reuterin produced from glycerol by these stains and adhesion capacity to intestinal epithelial cells were evaluated. The results showed that L. reuteri WLRE01, WLRE03, and WLRE04 had strong acid (pH 2.5 and 3.5), bile salt (1.5 g/L) and simulated gastrointestinal juice resistance. After treatment with 1 mmol/L hydrogen peroxide for 6 h, the viable counts of L. reuteri WLRE03 and WLRE04 were almost kept unchanged. The produced reuterin had strong inhibitory effect on Staphylococcus aureus, with a diameter of inhibitory zone of (28.1 ± 1.2) mm. The three strains showed good adhesion capacity to HT-29 cells, and among them WLRE01 had the strongest adhesion capacity. In summary, all three strains from healthy poultry feces deserve further research as candidate probiotic strains.
Processing Properties of Yogurt Affected by the Exopolysaccharide Produced by Lactobacillus plantarum YW11
CAI Miao, HAO Xiaona, LUO Tianqi, CHEN Chao, CAO Yongqiang, YANG Zhennai
2021, 42(14):  39-45.  doi:10.7506/spkx1002-6630-20200511-115
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The effect of the exopolysaccharide (EPS) from Lactobacillus plantarum YW11 on microbial growth, acid production rate and microrheological properties during yogurt fermentation and the texture and flavor characteristics of the final product was studied. The results showed that there was no significant effect of different concentrations (0.05, 0.15 and 0.25 mg/g) of the EPS on the growth of Lactobacillus bulgaricus and Streptococcus thermophilus or acid production rate during the fermentation process. Addition of the EPS had different effects on the elasticity index (EI), microviscosity index (MVI) and fluidity index (FI) of yogurt during fermentation; with increasing addition of the EPS, the EI decreased gradually, the MVI increased, whereas the FI did not change significantly. The water-holding capacity of yoghurt could be improved by adding different amounts of the EPS, reaching the maximum of 57.93% at an EPS concentration of 0.25 mg/g. With increasing addition of EPS, the hardness of yoghurt decreased to the lowest value of 10.08 g, the viscosity increased to the highest value of 9.57 g, while the cohesiveness changed little, varying between 0.45 and 0.48. Addition of EPS enhanced the cross-linked structure of proteins in yoghurt, made the protein particles smaller, and produced larger pores in the network structure. Addition of an appropriate amount of the EPS could promote the formation of flavor compounds such as aldehydes, acids and esters. The results of this study will be helpful for further understanding the effect of L. plantarum EPS on the processing characteristics of yogurt, and the application of the EPS to improve yoghurt quality.
The Global Transcriptional Regulator CodY Promotes Oxidative Stress Resistance in Listeria monocytogenes
YANG Shiyi, LIN Wei, YANG Liyu, ZUO Cheng, LUO Qin
2021, 42(14):  46-53.  doi:10.7506/spkx1002-6630-20200507-072
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Objective: The purpose of this study was to explore the role of the global transcriptional regulator CodY in the oxidative stress response in Listeria monocytogenes. Methods: Oxidative stress tolerance and antioxidant parameters (CAT, SOD and GSH) were compared between the wild-type strain EGDe and the isogenic CodY deletion strain EGDeDcodY at the mid-logarithmic growth stage (OD600 nm= 0.65) under H2O2 stress. Genomic template stability (GTS) of the two strains was compared by random amplified polymorphic DNA (RAPD) method and the transcriptional expression of the genes encoding antioxidants and those involved in SOS response were assessed by real-time PCR. Results: 1) The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of H2O2 against EGDeDcodY were about twice higher than against EGDe, and the diameter of inhibition zone of EGDeDcodY was significantly greater than that of EGDe when the concentration of H2O2 was over 20 mmol/L (P ≤ 0.01); 2) The growth of EGDeDcodY was completely inhibited by 200 mmol/L H2O2, while it just slightly slowed down the growth of EGDe; 3) H2O2-induced oxidative stress decreased CAT activity in both EGDe and EGDeDcodY, but did not significantly alter the transcription level of this enzyme. SOD activity was not changed significantly, but its mRNA expression presented significant differences between the two strains (P ≤ 0.001). Notably, the general trend of transcription and concentration level of GSH in the two strains was almost same, which decreased markedly and then increased slightly with increasing H2O2 exposure time. Moreover, the transcription level of GSH in EGDeDcodY was always lower than that in EGDe (P ≤ 0.01); 4) GTS of EGDe and EGDeDcodY were 93.1% and 80.0%, respectively. In addition, the expressions of recA, lexA, recR, lmo1302, and lmo1975, which are important for SOS response, were significantly inhibited in EGDeDcodY (P ≤ 0.001), while the expressions of recA, lmo1302 and lmo1975 in EGDe were activated. Conclusion: The deletion of CodY can reduce bacterial oxidative stress tolerance, growth rate and GSH content as well as GTS and inhibit SOS response-related gene expressions, corroborating that CodY plays an important role in the oxidative stress response in Listeria monocytogenes.
Growth Heterogeneity of Vibrio parahaemolyticus under Different Oligotrophic Conditions
ZHANG Buke, SHI Jun, PAN Yingjie, ZHAO Yong, LIU Haiquan
2021, 42(14):  54-61.  doi:10.7506/spkx1002-6630-20200509-092
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In order to study the effect of growth heterogeneity of Vibrio parahaemolyticus (Vp) on food safety risk under oligotrophic conditions: different dilutions (100%, 75%, 50% and 25%) of standard TSB+ (3% NaCl) medium, 20 Vp strains isolated from prawns and shrimps were selected. A first-order growth model was fitted for each strain, and second-order growth parameters were analyzed. The results proved that the modified Gompertz first-order model was fitted to the growth data of the Vp strains well, with correlation coefficient R2 of 0.791–0.997. There was no significant difference in the maximum specific growth rate (P > 0.05) under the same nutrient concentration among Vp strains from different sources. The growth parameters of Vp strains were different under different oligotrophic conditions. Through comparison of the present results with those of previous studies, we found that different initial inoculation amounts of Vp strains would also cause the growth heterogeneity of the strains. In summary, Vp strains had great growth heterogeneity under different oligotrophic conditions. The results of this study will contribute to more accurate food safety risk assessment and more scientific prevention and control of foodborne pathogens.
Prediction Model Construction for Aspergillus flavus Growth and Toxin Accumulation in Chili Powder
ZHAO Xue, JIN Xindi, LIU Bin, ZHAO Xubo
2021, 42(14):  62-69.  doi:10.7506/spkx1002-6630-20210127-303
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In order to understand the pattern of growth and aflatoxin production of Aspergillus flavus in chili powder matrix, the growth and toxin accumulation data were obtained under varying conditions of temperature (20, 28, 37 and 45 ℃), water activity (0.85, 0.90, 0.93 and 0.97) and pH (4.5, 5.0 and 5.5). The Baranyi and Roberts model was used to estimate the maximum radial growth rate (μmax, mm/d) of colonies. The modified second-order polynomial model, Arrhenius model and third-order polynomial model were used to describe the combined influence of the environmental factors on μmax. Moreover, a second-order polynomial model was developed depicting the effect of the environmental conditions and culture time on aflatoxin production. The results showed that the modified second-order polynomial model had the highest goodness of fit to determine the growth of A. flavus, with coefficient of determination (R2) larger than 0.99. When comparing observed and predicted values of A. flavus, the bias factor (Bf) and accuracy factor (Af) were found to be 1.077 0 and 1.131 9, respectively. The cumulative amount of aflatoxin was accurately predicted by the proposed model with R2 greater than 0.97. These results can provide basic data for the safe storage and processing of chili powder, and also provide a theoretical basis for extending the shelf life of chili powder.
Artificial Neural Network-Genetic Algorithm-based Optimization of the Formulation of Lyoprotectants to Improve the Freezing Resistance of Lactobacillus reuteri
PAN Haibo, QIN Luqi, HUANG Yanting, LIANG Xiaolin, HUANG Guohong, NIE Menglin, RAO Chuanyan, MEI Lihua, LI Quanyang
2021, 42(14):  70-77.  doi:10.7506/spkx1002-6630-20200323-350
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In order to improve the freezing resistance of Lactobacillus reuteri LTR1318 during freeze-drying, four lyoprotectant ingredients, namely skim milk, glutamic acid, fructo-oligosaccharide and sorbitol were identified as main factors affecting the freeze-drying survival rate of this strain by single factor experiments. The survival rates of freeze-dried cells with different protectant combinations designed by Box-Behnken design were used for training and testing to construct a radial basis function neural network model whose fitting degree was 0.984 4. The genetic algorithm was used to optimize the fitting results of neural network with 50 iterations, and the optimal lyoprotectant composition was obtained as follows: skim milk 10.90%, glutamic acid 1.20%, fructo-oligosaccharide 1.30% and sorbitol 0.80%. The optimized formulation gave a freeze-drying survival rate of (95.74 ± 5.07)%. The activities of lactate dehydrogenase and β-galactosidase in freeze-dried L. reuteri with the lyoprotectant increased by 53.19% and 353% compared to the control without the lyoprotectant, respectively, which accounted for 78.25% and 86.43% of the enzyme activities under normal culture conditions, respectively. In addition, the relative expression of cold shock protein gene was slightly increased by 8.29%. The lyoprotectant developed in this study could be a new promising probiotic lyoprotectant. Our results provide a reference and guidance for the development of freeze-dried preparations of lactic acid bacteria and more extensive applications of vacuum freeze-drying technology.
Prolyl Endopeptidase from Sea Bass (Lateolabrax japonicus): Purification, Characterization and Molecular Cloning
YANG Ruqing, CHEN Shoufeng, XIAO Linlin, CHEN Yulei, SUN Lechang, ZHANG Lingjing, LIU Guangming, CAO Minjie
2021, 42(14):  78-85.  doi:10.7506/spkx1002-6630-20200501-004
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A prolyl endopeptidase (PEP) was purified to homogeneity from the skeletal muscle of sea bass (Lateolabrax japonicus) by ammonium sulfate fractionation followed by column chromatography. By liquid chromatography-tandem mass spectrometry (LC-MS/MS), 43 peptide fragments were obtained highly identical to the sequence of prolyl endopeptidase from Takifugu rubripes, confirming the purified protein to be a prolyl endopeptidase. Using Suc-Gly-Pro-MCA as a substrate, the optimal pH and temperature of the purified enzyme were pH 6.0 and 35 ℃, respectively. Circular dichroism (CD) spectroscopy showed that heating had a significant effect on the secondary structures of PEP, causing irreversible denaturation. The full-length cDNA sequence of PEP was cloned, which contained an open reading frame of 2 226 nucleotides, encoding a protein of 741 amino acid residues with a deduced molecular mass of 84.12 kDa. The molecular structure of PEP was obtained by homologous modeling. PEP exhibited a typical α/β hydrolase folding arrangement. Its catalytic triplets (His-711, Asp-672, and Ser-585) were covered with the central channel of the propeller region formed by β-folding. The stability of the catalytic domain of PEP could be essential for maintaining its activity and its unique structure could be the basis for its substrate specificity.
Fermentation Characteristics of Four Indigenous Non-Saccharomyces Wine Yeasts
LIU Peitong, XU Dandan, XU Yinhu, DUAN Changqing, YAN Guoliang
2021, 42(14):  86-93.  doi:10.7506/spkx1002-6630-20200409-121
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The fermentation and aroma production characteristics of four non-Saccharomyces yeast strains (Hanseniaspora uvarum CVE-HU36, H. vineae CVE-HV6, Metschnikowia pulcherrima CVE-MP20 and Issatchenkia terricola CVE-IT8) isolated from three different wine regions of China were evaluated by pure culture fermentation experiments. Saccharomyces cerevisiae BDX was used as a control. The results indicated that CVE-HV6 had the strongest growth capability and the highest fermentation rate, as well as the highest production of glycerol and alcohol. CVE-HU36 and CVE-IT8 produced the most acetic acid and malic acid, respectively, while CVE-MP20 had the lowest alcohol production. A significant difference in the fermentation performance and the ability to produce aromas was observed among non-Saccharomyces strains. CVE-HV6 produced higher contents of phenethyl acetate, phenethyl alcohol and decanoic acid than S. cerevisiae and the other non-Saccharomyce strains. CVE-HV6 produced 3.04 times more phenethyl acetate than S. cerevisiae. CVE-HU36 produced more β-citronellol than S. cerevisiae (2.05 times) and the other non-Saccharomyce yeasts. CVE-MP20 produced the most acetate ester and α-terpineol. The highest concentrations of octanoic acid and 4-ethyl guaiacol were observed in wine fermented by CVE-IT8. Our results showed that the four non-Saccharomyces strains had different fermentation and aroma production characteristics, and CVE-HV6 had better brewing performance with the potential to improve the aroma and quality of wine.
Gene Expression and Activities of Pathogenesis-Related Enzymes in Postharvest Muskmelons Infected with Alternaria alternata
WANG Jin, BAI Yujia, FENG Zuoshan, ZHU Wantong, ZENG Yuruikang, JIANG Liying
2021, 42(14):  94-102.  doi:10.7506/spkx1002-6630-20200228-313
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In this study, Jiashi melons and 86-1 melons were artificially wounded and inoculated with Alternaria alternata to investigate the difference in disease resistance in peel and flesh between the two varieties. The inoculated fruits were stored at (7 ± 1) ℃ and relative humidity (RH) of 85%–90% for up to 30 days. During the storage period, lesion size was measured, lesion microstructure was observed, the expression levels of CmGLU, CmCHT1, CmCHT2 genes were determined by real-time polymerase chain reaction (real-time PCR), and the activities of chitinase (CHT) and β-1,3-glucanase (GLU) were measured. The results revealed that the lesion size in Jiashi melons was smaller than that in 86-1 melons during the whole storage period, and the lesion size in peel was smaller than that in pulp. Moreover, the lesion size in the peel and pulp of 86-1 melons was 1.28 and 1.29 times greater than that in Jiashi melons on day 30. It was also found that the cell structure in the peel of both cultivars was thickened to resist infection by this pathogenic fungus; however, disease resistance of the pulp was weaker than that of the peel. At the late stage of infection, the cell wall in the peel and pulp became stratified and shrunk, and numerous hyphae and spores existed inside the cells. Moreover, some pulp cells were disintegrated so that the cellular structure could not be discerned. The relative expression levels of CHT and GLU genes were higher in Jiashi melons versus 86-1 melons, and in the peel versus the pulp over the entire storage period. The relative expression level of CmCHT1 was higher during the early to middle period, and the relative expression level of CmCHT2 was higher during the middle period, suggesting that infection with A. alternata stimulated the expression of CHT gene. Moreover, the relative expression level of CmGLU was higher during the middle to late period, suggesting that infection with A. alternata stimulated the expression of GLU gene. After infection with A. alternata, the enzyme activities of CHT and GLU in peel and pulp tissues were significantly increased and then decreased with storage time, showing higher values in Jiashi melons relative to 86-1 melons, and in peel relative to pulp. Collectively, these results revealed that Jiashi melons showed stronger disease resistance than 86-1 melons and so did the peel compared with the pulp, which may be closely related with the expression levels and enzyme activities of CHT and GLU.
Immunosuppressive Effect and Mode of Action of Lactobacillus rhamnosus on Tetrodotoxin
YE Jingqin, XIAO Ye, YAN Jun, XU Changhua, WANG Liping, LU Ying
2021, 42(14):  103-109.  doi:10.7506/spkx1002-6630-20200625-340
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In order to explore the mode and possible sites of action of Lactobacillus rhamnosus in reducing the immunologic activity of tetrodotoxin (TTX), activated cells, heat-inactivated cells, broken cell debris, extracellular polysaccharide-deficient cells, protoplasts, cell walls and cell wall peptidoglycans of L. rhamnosus were separately incubated together with TTX standard at 37 ℃ for 1 h, and the changes in the immunologic activity of TTX before and after the treatment were analyzed by competitive enzyme linked immunosorbent assay (C-ELISA). The carboxyl and amino groups on the surface of L. rhamnosus cells were masked by chemical treatment, and Fourier transform infrared spectroscopy (FTIR) was used to analyze changes in the chemical bond vibration and functional groups on the cell surface. The results showed that activated, thermally inactivated and broken L. rhamnosus cells could reduce the immunologic activity of TTX, indicating no correlation between the cell activity and the changes in the immunologic activity of TTX. Extracellular polysaccharide-deficient cells, protoplasts, cell walls and cell wall peptidoglycans could reduce the immunologic activity of TTX by up to 47%. Masking of carboxyl groups on the cell surface of L. rhamnosus significantly decreased the percentage reduction in the immunologic activity of TTX to 18%, while masking of amino groups had no significant effect (P > 0.05). The binding of TTX to carboxyl groups of peptidoglycan in the cell wall of L. rhamnosus probably contributed to the reduction of TTX immunologic activity.
Heterogeneity of Ecological Niche for Fatty Acid Lipidomics in Fermentation Broth during Fermentation Process of Lactic Acid Bacteria
LIU Xin, CHEN Meichun, LIU Yun, ZHENG Xuefang, CHEN Zheng, WANG Jieping, LIU Bo
2021, 42(14):  110-120.  doi:10.7506/spkx1002-6630-20200428-367
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The aim of this study was to explore the heterogeneity of ecological niche for fatty acid lipidomics in the fermentation broth of lactic acid bacteria (LAB) during the fermentation process. Eight LAB species were individually cultured in a mixed medium containing litchi juice and soybean protein. The number of viable bacteria and fatty acid lipidomics were detected during culture and the relationship of ecological niche width and overlap with bacterial growth capability was analyzed. The results showed that a significant difference in growth capability was found among LAB species. The growth capability of Lactobacillus rhamnosus FJAT-13807 was the strongest, while that of Streptococcus thermophilus FJAT-43774 was the weakest. A total of 91 biomarkers of fatty acid lipidomics were detected in the fermentation broths of the eight LAB strains, including 12 biomarkers of straight-chain fatty acids, 70 biomarkers of branched chain fatty acids and 9 biomarkers of complex fatty acids. The order of fatty acid contents was as follows: straight fatty acid > branched chain fatty acid > complex fatty acid. Total fatty acid contents significantly varied in the fermentation broths of different LAB species (P < 0.05), which showed no direct correlation with bacterial growth capability. At the initial stage of fermentation (1 h), there was no significant difference in the ecological niche width of fatty acid lipidomics in the fermentation broths of the eight LAB strains. The ecological niche overlap of fatty acid lipidomics between strains was high, the number of viable bacteria was low, the environmental capacity was large, and the niche width was not correlated with the niche overlap. In the middle of fermentation (24 h), the niche width and overlap of fatty acid lipidomics in the fermentation broth of LAB were significantly differentiated, which affected the growth mode of LAB in the logarithmic growth period. The niche width increased, the growth rate of LAB decreased promptly, and the number of viable bacteria increased in a linear manner. The niche width decreased, the growth rate of LAB increased, and the number of viable bacteria increased in a parabolic manner. The niche width was maintained, the growth rate of LAB was maintained at the original level, and the number of viable bacteria increased in an exponential manner. At the end of fermentation (48 h), the niche width and overlap of fatty acid lipidomics in the fermentation broth of LAB were similarly differentiated. At this time point, LAB were in the stable extinction period, the niche width was big, the growth capacity of LAB decreased, and the number of viable bacteria decreased exponentially. The niche width was small, the growth capability of LAB was enhanced, and the number of viable bacteria changed in a cubic manner. The niche width was maintained, the growth capability of LAB was maintained at the original level, and the number of viable bacteria decreased exponentially. The changes in niche width and overlap of fatty acid lipidomics in the fermentation broth of lactic acid bacteria can be used to evaluate the growth potential and resource utilization of lactic acid bacteria, which will provide a new idea for the ecological study of lactic acid bacteria growth.
Changes in Fungal Community Structure in Fermented Grains for Fenjiu, a Traditional Chinese Liquor
WEI Chunhui, ZHEN Pan, ZHANG Lanlan, REN Zhiqiang, HUANG Zhiguo, DENG Jie
2021, 42(14):  121-128.  doi:10.7506/spkx1002-6630-20200408-114
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In this work, the physicochemical properties of fermented grains for Fenjiu sampled at different time points of fermentation were evaluated, and the fungal community structure in it was analyzed by high-throughput sequencing. A comparative analysis was performed between the samples from primary and secondary fermentation. The results showed that the major nutrients and microbial metabolites in fermented grains changed regularly during the fermentation process. Significantly different trends in these compounds were observed between primary and secondary fermentation. Totally 98 fungal operational taxonomic units (OTUs) were obtained from fermented grains, and the diversity of fungi was significantly different between primary and secondary fermentation. The diversity of fungi increased first and then decreased in primary fermentation, while the diversity of fungi gradually decreased in secondary fermentation. The initial fungal communities in primary and secondary fermentation were similar to each other. Pichia was the dominant strain for both fermentation processes. However, the dominant fungi at the later stage of fermentation were quite different between them. Saccharomyces cerevisiae was the most dominant fungus in primary fermentation, and Candida was the most dominant fungus in secondary fermentation. The results from this study are of great significance to further study the metabolic pathway for key flavor substances and to improve the yield and quality of Fenjiu.
Purification and Characterization of Antifungal Chitinase from Penicillium chrysogenum
GAO Zhaojian, DING Feihong, CHEN Huan, GENG Yunlong, ZHAO Yifeng
2021, 42(14):  129-136.  doi:10.7506/spkx1002-6630-20200229-329
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A chitinase (named Chi-Pc76) was isolated and purified from the fermentation broth of Penicillium chrysogenum Xch23 and its application potential was evaluated. The enzyme was purified to homogeneity by consecutive ammonium sulfate precipitation, DEAE-Cellulose A52 ion exchange chromatography and Sephadex G-100 gel filtration chromatography, yielding a 17.1-fold purification with 21.6% recovery and an specific activity of 584.8 U/mg. The molecular mass of Chi-Pc76 was estimated to be 61 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH and temperature for the purified Chi-Pc76 was 6.0 and 55 ℃, respectively. The enzyme showed high stability in the broad pH range of 4.0–10.0 and temperature stability up to 70 ℃. Chi-Pc76 exhibited high activity toward colloidal chitin and moderate activity toward glycol chitin, α-chitin, β-chitin, while it showed no or trace activity toward other tested substrates. Its Km and Vmax values for colloidal chitin were 0.25 mg/mL and 20 μmol/(min·mg), respectively. The activity of the enzyme was stimulated by Ca2+, Ba2+, Mg2+, K+, Na+ ions, but not affected by SDS, Tween 80, Triton X100, PMSF and urea. Mn2+, Co2+, Fe2+, Ag+, Cu2+, Zn2+, Pb2+ and Hg2+ and β-mercaptoethanol, as well as DTT inhibited the enzyme activity. Chi-Pc76 showed antifungal activity toward Aspergillus niger, Aspergillus flavus, Fusarium oxysporum, and P. citrinum. To the best of our knowledge, this is the first report of the antifungal chitinase from P. chrysogenum. In view of its advantages such as simple purification, high thermostability, broad-pH range stability, high-efficiency chitin-degrading ability, and antifungal activity, Chi-Pc76 will have potential applications in the comprehensive utilization of chitin waste, the bioconversion of chitin to pharmacologically active products, food preservation, and the biological control of phytopathogenic fungi and insect larvae.
New Plant-based Carrier for Efficient Delivery and Protection of Lactase
HOU Xinyao, DENG Ziyu, LIANG Hongshan, LI Bin
2021, 42(14):  137-143.  doi:10.7506/spkx1002-6630-20200512-129
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The potency of traditional oral enzyme preparations for treating lactose intolerance can be readily impaired by the strong acidic environment in the stomach. In order to overcome this problem, sun?ower sporopollenin exine capsules (SECs), a new plant-based carrier that can protect lactase from losing its activity, were prepared for use as a carrier for loading and protection of lactase. Loading, encapsulation and release experiments and observation by scanning electron microscopy (SEM) and laser confocal microscopy (LCM) showed that gel microspheres of sodium alginate (5%) and carboxymethylpachymaran (6%) at a mixing ratio of 1:1 (V/V) gave the best release performance in vitro, allowing responsive release of lactase in simulated digestive fluids. The following experiments illustrated that this system also showed the potential as a freeze-drying protective agent for lactase. Based on this, this study successfully demonstrated the feasibility of SECs as an efficient delivery and protection carrier for lactase, which will provide a new idea for the treatment of lactose intolerance.
Component Analysis
Changes of Free and Bound Volatiles in Fresh-cut Pitaya during Cold Storage
ZHANG Qin, ZHOU Dandan, HAN Lu, LONG Jiamei, TU Kang
2021, 42(14):  144-150.  doi:10.7506/spkx1002-6630-20200717-230
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The changes of free and glycosidically-bound volatile compounds were studied from fresh-cut ‘Mibao’ pitaya stored at 4 ℃. Enzymatic hydrolysis was carried out to release bound volatile compounds, and gas chromatography-mass spectrometry (GC-MS) was used for qualitative and quantitative analysis of free and bound volatile compounds in fresh-cut pitaya. The results showed that the compositions and contents of free and bound volatile compounds in pitaya fruit were significantly different from each other. After pitaya fruit were cut open, free volatile compounds sharply increased, and then decreased with storage time. Bound volatile compounds peaked on day 1, then decreased significantly on day 3, and finally remained at a stable level in the late storage period.
Analysis of Differential Non-volatile Chemical Compounds between Green Teas with Refreshing Aroma and Chestnut-like Aroma
WANG Mengqi, ZHU Yin, ZHANG Yue, SHI Jiang, LIN Zhi, LÜ Haipeng
2021, 42(14):  151-158.  doi:10.7506/spkx1002-6630-20200629-373
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The differential non-volatile compounds between green tea with a refreshing aroma and that with a chestnut-like aroma were identified by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). A total of 543 chemical compounds were identified in the two tea samples, 173 of which were found to show significantly different contents between the two samples, including 75 flavonoids, 22 phenolic acids, 1 terpene, 31 lipids, 9 amino acids and their derivatives, 4 alkaloids, 9 nucleotides and their derivatives, 5 organic acids, 5 lignans and coumarins, 1 tannin, and 11 other kinds. Out of the compounds common to both teas, 63 were more abundant and 110 were less abundant in green tea with a refreshing aroma than with a chestnut-like aroma. In addition, a total of 7 compounds, namely α-linolenic acid, palmitoleic acid, vanillin, γ-aminobutyric acid, kaempferol-3-O-rutinoside, cryptochlorogenic acid, and L-methionine were identified as important aroma compounds in green tea. Moreover, cryptochlorogenic acid and L-methionine were found to be prominent in green tea with a refreshing aroma, whilst α-linolenic acid, palmitoleic acid, vanillin, γ-aminobutyric acid, and kaempferol-3-O-rutinoside were dominant in green tea with a chestnut-like aroma.
Authentication of Organic Tomatoes by Nitrogen Stable Isotope Ratio Mass Spectrometry and Liquid Chromatography-High Resolution Mass Spectrometry
WANG Shicheng, LI Guochen, WANG Ying, LI Bo, GAO Ningxuan, SUN Ci, SONG Yang, WANG Yanhong
2021, 42(14):  159-164.  doi:10.7506/spkx1002-6630-20200605-073
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Traditionally, authentication of organic foods requires measuring a variety of parameters before making a comprehensive evaluation, which suffers from the tedious sample preparation and low discrimination accuracy. To address this problem, in this study, a method of identifying organic tomatoes based on stable isotope ratio mass spectrometry (IRMS) and high performance liquid chromatography-high resolution mass spectrometry (HPLC-HRMS) combined with partial least squares discriminant analysis (PLS-DA) was proposed. Specifically, 94 tomatoes were collected, of which 50 were grown organically, while the rest were grown in traditional ways. Each sample was homogenized and freeze-dried before chemical analysis. Nitrogen isotope ratio (δ15N) data and HPLC-HRMS data were acquired. Taken into consideration of all measured factors, a PLS-DA model for discriminating organic tomatoes was established, which was used to select and confirm 13 representative indicators including δ15N, organic acids, and flavonoids. The accuracy of the model was 93.4%, which could meet the requirement for the identification of organic tomatoes. This study provides an advanced approach for discriminating organic tomatoes quickly.
Determination of 10 Elements in Breast Milk by Inductively Coupled Plasma-Mass Spectrometry
WANG Yaling, ZHAO Junying, QIAO Weicang, ZHANG Minghui, LIU Yan, CHEN Lijun
2021, 42(14):  165-169.  doi:10.7506/spkx1002-6630-20200628-358
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A method for simultaneous and quantitative determination of 10 elements including K, Ca, Na, Mg, P, Cu, Mn, Zn, Fe and Se in breast milk was established by inductively coupled-plasma mass spectrometry (ICP-MS). Samples were digested by using a mixture of HNO3 and H2O2 in a closed high pressure vessel before detection by ICP-MS. The mass spectral interferences caused by polyatomic ions were effectively eliminated by using a dynamic reaction cell. The element Rh was used as an internal standard element to correct the matrix effect and signal drift. The external standard calibration method was used for quantification, and relative standard deviation (RSD) was used to examine the method reproducibility. The accuracy of this method was evaluated by using standard reference materials. The correlation coefficients of the linear regression equations for the 10 elements were all above 0.999 0, and the recoveries ranged from 80.00% to 118.19%. The measured values for standard reference materials of milk powder (GBW10017) and defatted milk powder (GBW08509) were in agreement with the certified values, with RSDs below 10.0%. These results showed that this method was precise, accurate and suitable for the determination of mineral elements in massive breast milk samples.
Analysis of Taste Compounds in Red Sufu during Fermentation and Discrimination with Electronic Tongue
WANG Peng, WANG Wenping, XU Dandan, ZHANG Xin, GAO Hang, ZHANG Jian, SUN Yong, WANG Fenghuan
2021, 42(14):  170-179.  doi:10.7506/spkx1002-6630-20210304-052
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In order to evaluate the taste compounds and taste characteristics of red sufu during its fermentation process, the samples collected at different fermentation stages were analyzed by ion chromatography, amino acid analyzer, and electronic tongue. The obtained data were analyzed by principal component analysis (PCA) and hierarchical cluster analysis (HCA). Results showed that a total of 17 free amino acids (FAAs), 6 organic acids and 8 taste attributes were identified and quantified in all samples. Total contents of FAAs increased significantly at pre-fermentation and post-fermentation stages, while total contents of organic acids showed a significant increase at the pre-fermentation stage and the middle stage of post-fermentation (P < 0.05). The levels of most FAAs and organic acids increased significantly at the pre-fermentation and post-fermentation stages (P < 0.05). Electronic tongue analysis showed that umami, saltiness, bitterness and richness were major taste attributes. Furthermore, correlation analysis between taste compounds and taste attributes showed that free amino acids (Glu, Asp, Ala, Gly, His, Cys, Phe, Met and Val), organic acids (lactic acid, acetic acid, succinic acid) and some other chemical components (reducing sugar, amino acid nitrogen and NaCl) played an important role in the taste characteristics of red sufu. The results of PCA and HCA showed that the taste compounds and taste attributes could be used to evaluate its maturity extent and that electronic tongue could be a rapid tool for the taste evaluation of red sufu.
Analysis of Differences in Volatile Flavor Compounds between Traditional Industrial Large Wok and Small Wok Stir-Fried Diced Mutton
BAI Shuang, WANG Yongrui, LUO Ruiming
2021, 42(14):  180-186.  doi:10.7506/spkx1002-6630-20200906-071
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This study aimed to determine the changes in the flavor profile during different processing stages of traditional industrial large wok and small wok stir-fried diced mutton. The odor intensity was measured by an electronic nose system and the volatile compounds were quantitatively analyzed by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). The electronic nose could discriminate differences in odor among processing stages. A total of 104 volatile compounds in the diced mutton cooked in large wok and 171 volatile compounds in that cooked in small wok. Aldehydes, alcohols, and ketones were the main volatile compounds of stir-fried diced mutton. Large wok and small wok stir-fried diced mutton could be distinguished by electronic nose combined with GC-MS, which will provide a theoretical basis for the development of a smart stir-frying machine.
Analysis of Alkylresorcinol Homologues in Wheat Flour by GC-MS and LC-MS/MS
HUANG Qinqin, FAN Fengjiao, LI Peng, FAN Yan, ZOU Yanyu, FANG Yong
2021, 42(14):  187-194.  doi:10.7506/spkx1002-6630-20210217-186
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In this study, two methods were established for the determination of the content and homologue composition of alkylresorcinols (ARs) in wheat flour, namely gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample was ultrasonically extracted with ethyl acetate. The extract was derivatized by silanization before GC-MS analysis in the selected ion monitoring (SIM) mode. Quantification was performed the by external standard method. Before LC-MS/MS, the extract was enriched and purified by solid phase extraction (SPE) on a C18 chromatographic column, and the separated analytes were detected in the negative ion scanning mode using multiple reaction monitoring (MRM) and quantified similarly by the external standard method. The results showed that both methods exhibited a good linear relationship in the concentration range of 0.001–5 μg/mL. The detection limit of the GC-MS method was 2.0–6.1 μg/g, and the spiked recoveries were 94.17%–99.15%, with relative standard deviation (RSD) of 2.94%–4.87%. The detection limit of the LC-MS/MS method was 2.0–8.4 μg/g, and the spiked recoveries were 89.05%–99.06%, with RSD of 2.21%–4.17%. These two detection methods, thanks to their good liner relationship, low detection limit, and high sensitivity, could be suitable for the qualitative and quantitative analysis of AR homologues in commercially available wheat flour products, which will provide a technical reference for the quality control and detection of whole-grain wheat products.
Comparative Study on Flavor and Overall Quality of Zanthoxylum bungeanum Seed Oil and Zanthoxylum bungeanum Oil
LIU Yulan, LI Jin, WANG Geping, SUN Guohao
2021, 42(14):  195-201.  doi:10.7506/spkx1002-6630-20200619-269
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Refined oils from Zanthoxylum bungeanum seeds obtained by pressing and leaching, separately were evaluated for volatile flavor components, acid value, peroxide value, amide content and sensory quality. The quality of Z. bungeanum seed oil was compared with that of eight commercial brands of Z. bungeanum oil. The results showed that the acid values of crude pressed and leached oils from fresh Z. bungeanum seeds were 5.94 and 7.37 mg KOH/g, and the peroxide values were 1.13 and 0.59 mmol/kg, respectively, which were significantly better than those from improperly stored seeds. The acid value and peroxide value of refined Z. bungeanum seed oil measured up to the national standard GB/T 22479-2008 for first grade Z. bungeanum seed oil; the amide content was 7.82–9.80 mg/g, which met the requirement (more than or equal to 2.0 mg/g) of the local standard DBS 51/008-2019. The content of amides in commercial Z. bungeanum oil was 7.92–19.11 mg/g. The most dominant in volatile flavor components in Z. bungeanum seed oil and Z. bungeanum oil were alkene compounds, followed by alcohols. The sensory evaluation of both kinds of oil showed an obvious numb and pungent sensation. Freshly pressed Z. bungeanum seed oil had high similarity and consistency with commercial Z. bungeanum oil as a flavor oil or seasoning oil in terms of the contents of amides and volatile flavor components characteristic of Z. bungeanum oil as well as sensory evaluation. Freshly pressed Z. bungeanum seed oil had a strong aroma and numb taste and could be used as an excellent Z. bungeanum flavor oil. The results of this study will be of great significance for the high-value processing and utilization of Z. bungeanum seeds.
Changes in Major Components and Tea Making Suitability of Loquat Leaves during Growth
ZHAO Xiaona, ZHANG Yunyun, WANG Zengbin, SONG Xue, LU Zhoumin
2021, 42(14):  202-208.  doi:10.7506/spkx1002-6630-20200823-305
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In order to find out the pattern of changes in the contents of the major components during the growth of loquat sprouts and its influence on the tea making suitability of loquat leaves, the major components of loquat leaves were determined regularly during two growing seasons: spring and summer, and the tea processing suitability of new leaves of different lengths collected in summer was analyzed comparatively. The results showed that the contents of flavonoids, total phenols and triterpenoid acids in new leaves decreased gradually during both growing seasons, while the content of total soluble sugar increased first and then decreased. In general, the contents of the main components in summer leaves were higher than in spring leaves. The contents of flavonoids, total phenols, triterpenoid acids, phenolic monomers and antioxidant activities of loquat leaves decreased significantly with the increase in leaf length, and so did the contents of vitamin C and free amino acids in the water extract of leaves, whereas the content of soluble total sugar increased first and then decreased. The results showed that loquat leaves can be processed into tea, and the quality of tea made from leaves between 2 and 13 cm long is the best.
Effects of Fixation Methods on the Formation of the Chestnut-like Aroma of Green Tea Analyzed by Infrared-assisted Extraction Coupled to Headspace Solid-phase Microextraction Combined with Gas Chromatography-Mass Spectrometry
WANG Huajie, HUA Jinjie, YU Qinyan, JIANG Yongwen, WANG Jinjin, YANG Yanqin, DENG Yuliang, YUAN Haibo
2021, 42(14):  209-217.  doi:10.7506/spkx1002-6630-20200604-052
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This study was executed in order to explore the effect of different innovative fixation methods: roller-microwave fixation (ROWF), roller-far infrared fixation (ROIF), roller-microwave-far infrared fixation (RWIF) and roller-far infrared-microwave fixation (RIWF) on the formation of chestnut-like aroma in green tea in comparison with roller fixation (ROLF). Sensory evaluation was carried out on the finished tea samples, where a total of 68 aroma compounds were detected by gas chromatography-mass spectrometry (GC-MS). Partial least squares-discriminant analysis (PLS-DA), hierarchical clustering analysis (HCA), odor activity values (OAVs), and significant difference analysis were used to identify the best fixation method for the formation of the chestnut-like aroma of green tea and to find out key components responsible for the chestnut-like aroma. The results showed that fixation with roller-far infrared combinations improved the chestnut-like aroma of green tea. RIWF produced a long-lasting chestnut-like aroma and a refreshing taste, leading to the best overall sensory quality. ROIF, RWIF and RIWF could be beneficial to the formation and transformation of high-boiling alcohols, ketones and aromatic hydrocarbons such as linalool and trans-β-ionone, and RIWF produced significantly larger amounts of these compounds than ROIF and RWIF. PLS-DA and HCA could accurately distinguish and cluster the five fixation methods according to the concentration of chestnut-like aroma. Further according to OAV, trans-β-ionone, linalool, (Z)-hexanoic acid, 3-hexenyl ester, nonanal, geraniol, and phenylacetaldehyde were identified as the key compounds contributing to the chestnut-like odor. The results of this study can provide a theoretical basis and technical guidance for the directed and standardized production of high-quality green tea with chestnut-like aroma.
Aroma Perceptual Interactions among Ester Compounds and Their Effects on Sensory Attributes of Huangjiu
YU Haiyan, XIE Jingru, XIE Tong, CHEN Chen, AI Lianzhong, TIAN Huaixiang
2021, 42(14):  218-225.  doi:10.7506/spkx1002-6630-20200527-334
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Gas chromatography-mass spectrometry (GC-MS) coupled with an external standard method was used for the quantification of 20 esters in four typical types of Huangjiu. Gas chromatography-olfactometry (GC-O) was used to determine the odor traits of 14 odor-active esters. Further, four important ester compounds were selected for perceptual interaction investigation by sensory analysis and the S-curve method. Synergistic effects were observed in binary mixtures of ethyl lactate (a) with ethyl acetate (b), and ethyl phenylacetate (c) with ethyl 2-methylbutanoate (d). At 50% correct detection probability, the overall odor thresholds of Huangjiu aromatic reconstitution were reduced from 8.04% (V/V) to 4.32% (V/V), and 11.56% (V/V) to 2.28% (V/V) by these two mixtures (a/b, c/d), respectively. Besides, the a/b (90:10, m/m) and c/d (93:7, m/m) mixtures could obviously enhance the intensity of fruity aroma compared with the single compounds. It was indicated that there was a synergistic aroma enhancing effect between these ester compounds, which affected the fruity aroma of Huangjiu. These results will provide a theoretical foundation for Huangjiu flavor regulation.
Rapid Screening of Radical Scavengers in Essential Oil from Piper longum L. as Food Seasoning
WANG Chan, LI Rong, WU Yang, WANG Ying, TANG Shuhua, TAN Jin, JIANG Zitao
2021, 42(14):  226-231.  doi:10.7506/spkx1002-6630-20200701-016
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In the present work, the chemical components of the essential oil from Piper longum L. (EOPL) were quickly identified with an ultra-fast gas chromatography-based electronic nose (GC-E-nose). The scavenging activities of each component of EOPL against 1,1-dipheny1-2-picrylhydrazyl (DPPH) radicals, 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) cation radicals, and hydroxyl radicals were evaluated by GC-E-nose combined with chemical methods without time-consuming and laborious separation of the monomers. The results showed that the main components of EOPL identified by GC-E-nose were germacrene D (26.04%), caryophyllene (13.57%), cis-anetholel (8.87%), and β-bisabolene (7.32%). Among all identified components, cis-anethol, caryophyllene oxide, and D-limonene had the strongest scavenging capacity against DPPH radicals, ABTS cation radicals, and hydroxyl radicals, with scavenging percentages of 78.1%, 87.0%, and 71.6%, respectively. The results of GC-E-nose for essential oil components were 89.7% consisted with those of gas chromatography-mass chromatography (GC-MS), confirming the feasibility of GC-E-nose.
Effect of Light Fermentation on the Flavor of Beef Jerky
LIU Meng, CHEN Song, ZHANG Shunliang, ZHAO Bing, PAN Xiaoqian, ZHOU Huimin, QIAO Xiaoling, ZANG Mingwu, LI Su, ZHU Ning, WU Qianrong
2021, 42(14):  232-239.  doi:10.7506/spkx1002-6630-20200910-110
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The effect of light fermentation on the flavor of beef jerky was studied by using electronic sensory instruments, gas chromatography-olfactometry-mass spectrometry (GC-O-MS), an amino acid analyzer and sensory evaluation. Beef jerky produced without using a starter was considered as a control. The results demonstrated that light fermentation had a significant impact on the flavor of beef jerky, significantly increasing the contents of volatile compounds and free amino acids compared with the control group. Meanwhile, the electronic nose and electronic tongue could distinguish the two groups clearly, indicating that light fermentation could produce compounds contributing to the flavor of beef jerk. According to volcano plot analysis, relative odor activity values, GC-O-MS analysis and instrumental taste evaluation, glutamic acid was identified as the characteristic taste compound, and 3-methylbutanol, hexanal, octanal, nonanal, trans-2-decennal, trans, trans-2,4-decadienal and 3-methylbutyric acid as the characteristic flavor compounds of light-fermented beef jerky. These findings can provide a theoretical foundation and technical support for the flavor regulation of beef jerky in the future.
Analysis of Physicochemical Characteristics and Flavor Quality of Fermented Beef Jerky during Its Processing
ZHOU Yajun, ZHANG Yu, CHEN Yan, WANG Shujie
2021, 42(14):  240-247.  doi:10.7506/spkx1002-6630-20210204-076
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Fermented beef jerky was made by inoculating and fermenting beef rump with a mixture of Staphylococcus xylosus and Lactobacillus sake. The nutritional components, texture properties, color, free amino acids, fatty acids and volatile flavor compounds of meat samples at the beginning, middle and end of fermentation were determined. Compared with unfermented beef, the pH, water activity, residual nitrite, hardness and chewiness of fermented beef significantly decreased (P < 0.05), while redness value and the contents of free amino acids increased significantly, with umami amino acids accounting for the highest proportion of the total amino acids. Palmitic acid, stearic acid, oleic acid and linoleic acid were the major free fatty acids, oleic acid accounting for the largest proportion of the total fatty acids. Totally 47 volatile compounds were detected in fermented meat, and 42 in the unfermented sample. Fermentation increased the types and relative contents of aldehydes, alcohols, phenols, esters, acids, nitrogen and other compounds in beef jerky. In conclusion, the texture and color of fermented beef jerky were significantly improved, the contents of free amino acids and fatty acids were increased, and the nutritional value, flavor quality and safety of the product were improved in comparison with unfermented beef jerk.
Safety Detection
An Enzyme Inhibition Method for Rapid Multi-residue Determination of β-Lactamase Inhibitors in Milk
LIU Fengyin, LI Ying, WANG Xiaopeng, WU Xiaodan, CHEN Fengyan, LIANG Yue, YUAN Xuewen, MU Hongtao
2021, 42(14):  248-254.  doi:10.7506/spkx1002-6630-20200429-388
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An enzyme inhibition method was established and used for multi-residue detection of β-lactamase inhibitors in milk. For sample preparation, the protein was precipitated with acetonitrile and the fat was removed with n-hexane. The matrix-matched external standard method was used for quantification, which eliminated the interference of the milk matrix. The detection limits of sulbactam, potassium clavulanate, tazobactam and avibactam sodium in milk samples were 42.88, 10.20, 1.68 and 3.48 μg/kg, respectively. The average spiked recoveries were from 80.43% to 115.87% with variation coefficients below 10.14%. When the residue of β-lactamase in milk did not exceed 40 U/mL, the assay results obtained using the developed method were accurate. Good agreement between the results of this method and those of liquid chromatography-tandem mass spectrometry (LC-MS/MS) was obtained for spiked milk samples, with a correlation coefficient (R2) of 0.982. The enzyme inhibition method allowed accurate, rapid, high-throughput and multi-residual detection of β-lactamase inhibitors, and was particularly suitable for on-site screening for β-lactamase inhibitor residues in large numbers of milk samples.
Discrimination of Durian from Different Geographical Origins Based on Mineral Element Fingerprint Characteristics
ZHOU Xiuwen, WU Hao, CHEN Haiquan, YAN Zhi, JIN Baohui, XIE Liqi, ZHAO Yan, ZHAO Chaomin, CHEN Hui, PAN Jiarong
2021, 42(14):  255-262.  doi:10.7506/spkx1002-6630-20200716-218
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Inductively coupled plasma-mass spectrometry was used to determine the contents of 28 mineral elements in the stone and pulp of 73 durian samples from different cultivars grown in Malaysia, Thailand, Cambodia and Vietnam. The data obtained were analyzed by means of analysis of variance (ANOVA), principal component analysis (PCA), Fisher linear discriminant analysis (FLDA) and back propagation artificial neural network (BP-ANN) to develop and validate a model for discriminating durian from different geographical origins. The results showed that the contents of 16 and 13 mineral elements in the stone and pulp of durian significantly varied among growing areas, respectively. In PCA, the cumulative contribution rates of the first six principal components were higher than 85.207%, which could represent the major information about mineral element contents. The significantly differential elements were substituted into Fisher’s stepwise discrimination equation, and the results showed that the discrimination accuracy for single durian stone and pulp was low. However, combinations of mineral elements in durian stone and pulp significantly improved the discrimination accuracy. Through stepwise discrimination analysis, Li, Be, Mg, Mn and Rb in durian stone and Be, Ag and Ba in durian pulp were selected for modeling, and it turned out that the initial validation accuracy of the model was 91.8%, and the cross validation accuracy was 90.4%. The significantly differential elements were substituted into the BP-ANN model. As a result, As, Ag, Al and Rb in durian stone and Ag in pulp were selected as the top five most important elements for artificial neural network; the validation accuracy was 96.1% and 95.5% for the training and test sets, respectively. Our finding proved that it is feasible to distinguish durian from different southeast Asian countries by mineral fingerprint characteristics combined with chemometrics.
Determination and Pollution Characteristics of 33 Pesticide Residues in Grapes by GC-QqQ-MS/MS with Stable Isotope Internal Standard
ZHONG Haowen, YANG Guoshun, CHEN Wenting, BAI Miao, TAN Jun
2021, 42(14):  263-269.  doi:10.7506/spkx1002-6630-20191119-220
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A gas chromatography-triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS) with multi-reaction monitoring (MRM) was developed for the simultaneous analysis of 33 pesticide residues in grapes, based on the fragmentation mechanism and mass spectrometric behavior of fragment ions from target compounds. The stable isotope dilution method was applied for quantification. The sample pretreatment involved extraction with acetonitrile by homogenization followed by sequential clean-up on C18 solid phase extraction (SPE) cartridge and tandem aminopropyl and activated carbon SPE cartridges. The results indicated that the calibration curves had a good linearity within the concentration range of 0.001 6– 0.320 0 mg/L with correlation coefficients (R) greater than 0.994 7. The limits of detection (LODs) were 0.064–40.000 μg/L and the limits of quantification (LOQs) were 0.000 02–0.013 33 mg/kg. The recoveries ranged from 70.1% to 120.6% for all target pesticides with relative standard deviation (RSD) less than 17.9%, when spiked at three different concentration levels. The developed method was sensitive and accurate for simultaneous and fast determination of trace or ultratrace pesticide residues in grape and other fruit and vegetable samples. Moreover, the characteristics of pollution and distribution of these pesticides in grape samples from different places in Hunan province, China were discussed by partial least square-discriminant analysis (PLS-DA). The results demonstrated that pesticides against grape grey mold or downy mildew, such as iprodione, azoxystrobin and dimethomorph, were found to be major chemical pollutants in grape samples.
Fluorescence Immunoassay Combined with Magnetic Separation Using Upconversion Nanoparticles as Label for the Detection of Tyramine in Food Samples
ZHANG Biao, HUANG Na, ZHANG Wanli, WANG Shuo, SHENG Wei
2021, 42(14):  270-275.  doi:10.7506/spkx1002-6630-20200625-342
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Based on the principle of indirect competitive reaction combined with magnetic separation using up-conversion nanomaterials, a fluorescence immunoassay for the detection of tyramine in meat products, aquatic products and fermented products was established. The optimal working conditions were obtained as follows: 12 μg of the antibody was coupled with NaYF4Yb, Tm up-conversion nanomaterials to prepare signal probes, 70 μg of the coated antigen was coupled with magnetic polystyrene microspheres to prepare capture probes, the addition amounts of signal probes and sensing probes were 70 μL and 100 μL, respectively, and the competitive reaction time was 30 min. The linear range of the developed method was 0.1–100.0 μg/L, with a detection limit of 0.05 μg/L. The method could specifically recognize tyramine without cross-reaction with its structural analogs or other biological amines. The recoveries of tyramine from spiked samples ranged from 86.44% to 101.62%, with coefficient of variation less than 10%. The proposed fluorescence immunoassay can be applied for rapid detection of tyramine in foods.
Determination of 30 Foodborne Stimulant Drug Residues in Pork and Beef Using Ultra-high Performance Liquid Chromatography Coupled with Quadrupole-Time of Flight Mass Spectrometry
MA Junmei, FAN Sufang, LI Qiang, HE Liangna, FAN Lixin, CAO Meirong, SUN Lei, WANG Dong, SUN Wenyi
2021, 42(14):  276-285.  doi:10.7506/spkx1002-6630-20200624-329
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A new rapid method for screening and identification of 30 foodborne stimulant drug residues in pork and beef by ultra-high performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry (UPLC-Q-TOF/MS) was developed. The samples were enzymatically digested for 16 h at 37 ℃ and extracted with acetonitrile (containing 0.10% formic acid, V/V), and the extract was cleaned up using a PriME-HLB cartridge, and then separated on a Waters XBridge BEH C18 column by gradient elution. The analytes were detected by time of flight mass spectrometry-tandem mass spectrometry (TOF/MS) and information dependent acquisition-tandem mass spectrometry (IDA-MS/MS), and they were qualitatively screened and confirmed in one data acquisition cycle. The results showed that the mass accuracy errors of the 30 foodborne stimulant drug residues were lower than 5.0 × 10-6. Good linearity in the range of 0.5–100.0 ng/mL were observed for the analytes, with correlation coefficients greater than 0.998 0. The limits of detection were in the range of 0.1–2.0 μg/kg and the limits of quantitation were in the range of 0.2–4.0 μg/kg. The recoveries of the developed method were in the range of 77.99%–109.2%, with relative standard deviations of 0.29%–9.68% (n = 6). This method proved to efficient and accurate and could have great practical value.
Migration of Mineral Oil Hydrocarbons from Fast Food Wrapping Paper into Solid Food Simulants
ZHANG Yicai, LIN Qinbao, WANG Liang, ZENG Ying, WU Zechun, ZHONG Huaining, CHEN Yanfen, LI Zhong
2021, 42(14):  286-292.  doi:10.7506/spkx1002-6630-20200507-076
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The migration behavior of mineral oil hydrocarbons from 24 kinds of fast food wrapping paper into the solid food simulant Tenax was explored under various conditions (40 ℃/0.5, 1, 2 and 3 h; 40 ℃/10 d; and 70 ℃/2 h), and the factors affecting it were evaluated to evaluate their safety. An n-hexane-ethanol (1:1, V/V) mixed solution was used to extract the mineral oil hydrocarbons in Tenax overnight. Then, the mixed solution was separated and fractionated on silver nitrate solid-phase with mass ratio in 0.3% extraction column into mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH), which were quantified and qualified by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry, respectively. The results showed that the amount of migrated mineral oil hydrocarbons increased as temperature increased. The migration of MOSH from the waxed paper samples was detected at levels of 110.49-615.40 mg/kg, while the migration of MOAH was not detected in any of the samples, indicating that the paraffin layer coated on the waxed paper surface contained MOSH but not MOAH. The migration amounts of MOSH and MOAH from online-purchased traymates and common traymates were approximately 10-400 and 10-70 times higher than the specific limit values (0.6 and 0.5 mg/kg), respectively. However, the migration amounts from traymates with virgin fiber with high-quality printing ink did not exceed the limits. Finally, through source analysis of mineral oil in virgin fiber plate paper with printing ink, it was found that part of the migrated mineral oil may come from the ink. Other sources may include recycled fibers, binders, additives and processing aids.
Development and Application of a Method for Determination of Hexabromobiphenyls in Aquatic Products
ZHANG Longfei, YU Huijuan, TIAN Liangliang, FANG Changling, HUANG Dongmei, QIAO Yipiao, SHI Yongfu
2021, 42(14):  293-300.  doi:10.7506/spkx1002-6630-20191226-322
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An analytical method was established for the determination of trace levels of hexabromobiphenyls (HexaBBs) in aquatic products by gas chromatography (GC) and the accumulation characteristics of HexaBBs in different aquatic products were analyzed. Important operating parameters were optimized, including extraction solvents, ultrasonic treatment time, types of solid-phase extraction (SPE) column and types of capillary column. Satisfactory results were achieved when the sample was ultrasonically extracted with ethyl acetate for 10 minutes, purified on a silica gel SPE cartridge, and detected by GC with an DB-17MS column. The linearity of the calibration curves for five HexaBBs was good in the range of 0.20–10.00 ng/mL, with correlation coefficients R2 greater than 0.998. The limits of detection and quantification of the proposed method were 0.50 and 1.00 μg/kg, respectively. The recoveries ranged from 77.15% to 118.14%, with relative standard deviations (RSD) in the range of 0.56%–13.32% at spiked levels of 1.00 and 5.00 μg/kg. This method could be used for the quantitative analysis of HexaBB residues in aquatic products, and the accumulation characteristics of HexaBBs in aquatic products from different trophic levels were found to be different from each other.
Analysis of Acetanilide Herbicide Residues in Adzuki Beans (Vigna angularis) by Aqueous Two-Phase Extraction Coupled with High Performance Liquid Chromatography
ZHANG Liyuan, ZHANG Yue, YU Runzhong, WANG Changyuan, ZHANG Dongjie
2021, 42(14):  301-307.  doi:10.7506/spkx1002-6630-20200430-394
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A method for the determination of four acetanilide herbicides including acetochlor, butachlor, propanil, and metolachlor in adzuki beans was established using ammonium sulfate-ethanol-based aqueous two-phase extraction combined with high performance liquid chromatography. In the aqueous two-phase extraction, the polarity of the alcohol-rich upper phase was more similar to that of the herbicides in the same organic solvent. The salt solution of the lower phase could effectively precipitate protein and fat. Based on the recoveries of the herbicides, the optimal pretreatment conditions were determined as follows: aqueous two-phase system containing 25% ethanol and 28% ammonium sulfate, and ultrasonic extraction for 1 min at 35 ℃. Avoiding the use of toxic organic solvents, the current method was environmentally friendly. The detection limits for acetochlor, butachlor, propanil, and metolachlor were 3.5, 7.1, 4.6 and 5.8 μg/kg, respectively. The average recoveries at spiked concentrations of 10 and 100 μg/kg ranged from 86.1% to 95.9%, with relative standard deviation equal to or lower than 4.5%.
Determination of Fipronil and Its Metabolites in Aquatic Products from Paddy Field by QuEChERS Combined with High Performance Liquid Chromatography-Tandem Mass Spectrometry
MA Lisha, XIE Wenping, YIN Yi, SHAN Qi, LIU Shugui, LI Lichun, ZHAO Cheng, ZHENG Guangming
2021, 42(14):  308-314.  doi:10.7506/spkx1002-6630-20200622-286
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A method was developed for the determination of fipronil and its metabolites including fluorocarbonitrile, fipronil sulfone and fipronil sulfide in paddy field-cultured aquatic products by quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Samples were extracted using acetonitrile (containing 0.10% formic acid, V/V) as the extraction solvent with vortex shaking using a ceramic homogenizer, and purified by 0.15 g of primary secondary amine (PSA) sorbent. The target compounds were separated on an Agilent ZORBAX Extend-C18 column (2.1 mm × 100.0 mm, 1.8 μm), and was detected by using an electrospray ionization (ESI) source in the negative ion mode with multiple reaction monitoring (MRM). The analytes were quantified with external standard using the matrix-matched standard calibration curve method. The results indicated that the average spiked recoveries of fipronil, fluorocarbonitrile, fipronil sulfone and fipronil sulfide in paddy field-cultured aquatic products were 85.2%–112.6% with relative standard deviations (RSDs) of 1.2%–12.4%. Good linearity was obtained in the concentration range of 0.5–100.0 ng/mL, with correlation coefficients higher than 0.999. The limit of detection (LODs) were 1.0–1.5 μg/kg, and the limit of quantitation (LOQs) were 3.0–5.0 μg/kg, which were both lower than the maximum residue limit (10 μg/kg) for fipronil in poultry meat stipulated by the national standard GB 2763–2019 Maximum Residue Limits for Pesticides in Food. The developed method was simple, sensitive and accurate, and could be used for routine analysis of fipronil and its three metabolite residues in paddy field-cultured aquatic products.
Residual Dynamics and Risk Assessment of Dietary Exposure to Prochloraz and Its Metabolite 2,4,6-Trichlorophenol in Kumquats (Fortunella japonica Swingle) Treated with Prochloraz during Storage
SU Desen, ZHENG Yunyun, CHEN Ziqiang, WU Jianyan, HUANG Chongyao
2021, 42(14):  315-319.  doi:10.7506/spkx1002-6630-20200627-345
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A gas chromatography-tandem mass spectrometry method was established for the simultaneous determination of the residues of prochloraz and its metabolite 2,4,6-trichlorophenol in kumquats dipped in prochloraz solution. The residual dynamics of prochloraz and 2,4,6-trichlorophenol in kumquats during storage and the risk of dietary exposure to the pesticide through the consumption of kumquats were evaluated in this study. The limits of detection (LODs), average spiked recoveries, and repeatability (expressed as relative standard deviation, RSD) for prochloraz and 2,4,6-trichlorophenol were 1.70 and 0.68 μg/kg, 95.7% and 98.1%, and 5.14% and 3.89%, respectively. The results indicated that the residual levels of prochloraz and 2,4,6-trichlorophenol were increased with increasing concentration of prochloraz and dipping time. The prochloraz concentration in kumquats was increased until a peak on the third day, and then decreased gradually. However, the residual amount of 2,4,6-trichlorophenol in kumquats kept increasing until day 21. The residual concentrations of prochloraz and 2,4,6-trichlorophenol in kumquats dipped in 450 mg/L prochloraz solution for 2 min were 8.180 and 0.069 mg/kg on day 14, respectively. The residual concentration of prochloraz in kumquats dipped in 900 and 2 700 mg/L prochloraz solutions exceeded the maximum residue limit for prochloraz in citrus fruits even after storage for 21 days. The risk of chronic dietary exposure to prochloraz from kumquats after 14 days was within an acceptable range, while the risk of acute dietary risk exposure was larger than 100%, which is not accepted.
Rapid Determination of 62 Pesticide Residues in Chicken Eggs by Enhanced Matrix Removal of Lipids Combined with Gas Chromatography-Tandem Mass Spectrometry
SHU Xiao, CHU Nengming, ZHANG Xuemei, MENG Xia, LI Dianyan, HUANG Chenglan, XIANG Jia, YANG Junying
2021, 42(14):  320-327.  doi:10.7506/spkx1002-6630-20191211-121
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A multi-residue method for the simultaneous determination of 62 pesticide residues in chicken eggs was developed using gas chromatography-tandem mass spectrometry (GC-MS/MS) after clean-up by enhanced matrix removal of lipids (EMR-Lipid). The sample was extracted with a mixture of 10 mL of 1% acetic acid-acetonitrile and 5 mL of H2O and then salted out by adding sodium chlorid. Finally, 5 mL of the extracted organic phase was transferred to an EMR-Lipid tube for cleanup and high-speed centrifugation, and the analytes were detected by GC-MS/MS and quantified by the external standard method. Good linearity was shown for the 62 analytes with correlation coefficients exceeding 0.95. The limit of detection (LOD) and the limit of quantitation (LOQ) for 59 of the pesticides in eggs were 0.5–5.0 μg/kg and 1.0–20.0 μg/kg, respectively. The recoveries and repeatability for the 62 pesticides in eggs obtained using EMR-Lipid were both better than those obtained directly using a solid-phase extraction tube. The average recoveries at a spiked level of 100 μg/kg were 70.7%–117.2% for 61 of the pesticides, with relative standard deviations (RSD) between 0.3% and 10.9%. Only 20 of the pesticides showed weak matrix effects, and the test results for them should be corrected using matrix standard solutions. This method has been applied to actual sample analysis successfully.
Determination of Cu2+ by Stripping Voltammetry with Electrodes Modified with Methanobactin-Functionalized Gold Nanoparticles
XUE Ye, WANG Yan, ZHAO Ning, DOU Boxin, XIN Jiaying, HAN Ye
2021, 42(14):  328-332.  doi:10.7506/spkx1002-6630-20200502-009
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Methanobactin-functionalized gold nanoparticles (Mb-AuNPs) were prepared based on the ability of Mb to capture copper ions in the environment and the signal amplifying function of AuNPs. Stripping voltammetry with an Mb-AuNPs-modified electrode could specifically detect Cu2+. Under the optimal conditions, the peak current response showed a good linear relationship with logarithmic copper ion concentration in the range of 10 nmol/L–100 μmol/L with a correlation coefficient of 0.960 09 and the detection limit was 1.15 nmol/L at a signal-to-noise ratio of 3. Accordingly, the new electrochemical method established in this study had high sensitivity and stability, which will provide theoretical basis for the detection of copper irons in foods in the future.
Determination of Fipronil and Its Metabolites in Vegetables by Gas Chromatography-Negative Ion Chemical Ionization-Mass Spectrometry
GAO Xia, CHEN Hui, TAN Min, LI Yuxiu, HE Honglin
2021, 42(14):  333-338.  doi:10.7506/spkx1002-6630-20200714-180
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A method was developed for the determination of fipronil and its three metabolites including fluorocarbonitrile, fipronil sulfone and fipronil sulfide in vegetables by gas chromatography-negative ion chemical ionization-mass spectrometry (GC-NCI/MS). The target compounds were extracted from samples with acetonitrile, and then purified by the QuEChERS method before analysis. Quantification was performed using a matrix-matched calibration curve with external standards. The results indicated that the linearity of the method was good in the concentration range between 0.2 and 10.0 μg/L, and the average recoveries were 88.9%–105.8% with relative standard deviations (RSDs) of 2.2%–7.6% at three spiked levels (1.0, 5.0 and 10.0 μg/kg). The limits of detection (LODs) were 0.2–0.3 μg/kg,and the limit of quantification (LOQ) was 1.0 μg/kg. The developed method was simple, sensitive and accurate, and could be used for the routine analysis of the residues of fipronil and its three metabolites in vegetables.