The effect and mechanism of carboxymethylated konjac glucomannan (CMKGM) with different molecular masses (1.57 × 105–7.88 × 105 Da) and degrees of substitution (0–1.63) on stabilizing pea protein dispersion (PPD) were investigated under neutral and acidic (pH 3.5) conditions. The experimental results showed that the critical CMKGM concentration required to stabilize PPD differed depending on its molecular parameters. The influence of the molecular mass on the stability of PPD was greater than that of the degree of substitution (DS). At neutral condition, the viscosity-enhancing effect of CMKGM on the continuous phase played a major role in the stabilization of PPD, whereas at acidic condition the electrostatic repulsion and steric hindrance induced by the electrostatic CMKGM/protein complexes mainly contributed to the stabilization of PPD in addition to increasing the viscosity of the continuous phase.

This study investigated the effect of radio frequency plasma activated water (RF-PAW) treatment on myoglobin color and the color development of cooked ham, and compared the efficacies of sodium nitrite solution and RF-PAW as color fixatives as well as the levels of residual nitrite in hams produced with the color fixatives. The results showed that PAW treatment for up to 6 min did not have significant influence on the color of metmyoglobin (metMb), but caused gradual oxidation of oxygenated myoglobin (oxyMb) into metMb, resulting in color change from bright red to reddish-brown. Naked eye observation showed that both RF-PAW and nitrite solution promoted the color development of ham but the former was more effective than the latter with its active substances causing no adverse effects on ham color. The results of color difference analysis showed that the ham cured with PAW had higher a* and C* values and lower b* values, and it had higher content of nitrosomyoglobin pigment (43.52%), thus showing a deeper red color. The level of residual nitrite in nitrite cured ham was 54.45 mg/kg, and that in PAW cured ham was 52.79 mg/kg, both of which were less than the national standard limit of 70 mg/kg. These findings may provide a theoretical basis and scientific guidance for the application of cold plasma in preservation and curing of meat products.

In order to discover new umami peptides and explore their structure-activity relationship, this study separated and purified umami peptides from the muscle of cultured Takifugu obscurus using 60% aqueous ethanol solution as the extraction solvent, as well as applying ultrafiltration and gel chromatography combined with sensory evaluation. The molecular masses and amino acid compositions of the peptides were further identified by nano-liquid chromatography-quadrupole orbitrap mass spectrometry. The taste characteristics of the peptides synthesized by the solid-phase method were evaluated by sensory evaluation combined with electronic tongue, and their structure-activity relationship was elucidated by molecular docking. The results indicated that seven umami peptides including NWDDMEK, KTGLSPDQF, KTDLNFENL, ASLDGEFKG, ALASLDGEFKG, ALTSLDGEFKG and RLGSSEVEQVQ were identified with a molecular mass in the range of 922.3–1 230.6 Da, and their umami thresholds ranged from 0.38 to 1.04 mmol/L. Glutamic acid (Glu), aspartic acid (Asp) and lysine (Lys) residues in the peptide sequences, and the amino acid residues N69, S276, R151, R277, A302, T149 and N150 in the umami receptor T1R1/T1R3 played important roles in the umami taste of the peptides. This study may guide future studies to elucidate the umami taste of peptides.

This study compared the micromorphology and stability of O/W and W/O/W emulsions with different concentrations of rice bran protein, prepared by double emulsification using rice bran protein as an interfacial stabilizer, and explored the interfacial stability mechanism. The results showed that the stability of the W/O/W emulsion was significantly better than that of the O/W emulsion. The viscosity of the W/O/W emulsion was significantly improved compared with the O/W emulsion at the same protein level. When the concentration of rice bran protein was 0.4 g/100 mL, the stability of the W/O/W emulsion was twice higher than that of the O/W emulsion; besides, there were more W/O droplets inside the W/O/W emulsion, with larger particle size. The emulsion was more stable because it had greater electrostatic repulsion. The rate of protein adsorption to the O/W and W/O/W emulsions were higher than 78% when the concentration of rice bran protein was equal to or greater than 0.4 g/100 mL. This study provides a reference for the application of natural rice bran protein in food-grade emulsions and provides a new idea for the comprehensive utilization of grain by-products.

In order to explore the effect of pH on the interaction of caffeic acid β-phenethyl ester (CAPE) with human serum albumin (HSA), the quenching effect of CAPE on the fluorescence of HSA under different pH (3.0, 5.0 and 7.4) conditions was investigated using fluorescence emission spectroscopy (FES) and synchronous fluorescence spectroscopy (SFS), and the quenching constants, binding constants and thermodynamic parameters were calculated. Meanwhile, the fluorescence quenching mechanism was analyzed, and the binding site was determined by site marker experiment. The fluorescence emission spectra showed that CAPE could quench the intrinsic fluorescence of HSA under all pH conditions tested. The quenching rate was the highest and the binding constant was the largest at physiological pH 7.4. The thermodynamic results suggested that the binding of CAPE to HSA was mainly driven by van der Waals force and hydrogen bonds. SFS indicated that binding to CAPE and the change of pH jointly induced the conformational changes of HSA. The results of site marker experiment showed that the binding site of CAPE to HSA was located near Sudlow’s site I. Altogether, the results revealed that the combination of CAPE with HSA could be promoted by the increase of pH, which can provide a theoretical basis for activity homeostasis maintenance and targeted delivery of CAPE.

In order to protect and even improve the functional properties of pasteurized liquid whole egg, this study investigated the effect of different phosphates (disodium hydrogen phosphate, sodium pyrophosphate, and sodium hexametaphosphate) on the pH, surface hydrophobicity, color, free thiol groups, solubility, foaming properties, emulsifying properties, and gel properties of pasteurized liquid whole egg (LWE). The results showed that each phosphate reduced the surface hydrophobicity and free sulfhydryl content of pasteurized LWE, while relatively high concentrations of disodium hydrogen phosphate (10?and 20?mmol/L) and sodium pyrophosphate (9 and 12 mmol/L) significantly increased the pH. In addition, all phosphates reserved changes in the solubility, foaming properties and emulsifying capacity of LWE caused by pasteurization. Among them, adding 12 mmol/L sodium pyrophosphate was the most effective, resulting in an increase in the emulsifying capacity and foaming capacity of 19.74% and 30.49%, respectively, as well as significantly improved water-holding capacity of heat-induced LWE gels and a 41.41% reduction in the emulsifying stability of LWE. All phosphates increased the yellowness and redness of LWE and therefore could show great application potential. These research findings may provide a theoretical basis for stabilizing the functional properties of pasteurized LWE.

This study was aimed to investigate the effect of solid-state fermented wheat bran (FWB) on the quality of wheat flour and noodles in order to provide a reference for the application of deep processing of wheat bran and the development of relevant functional products. The results showed that solid-state fermentation by Rhizopus oryzae improved the nutritional value of wheat bran by increasing the protein content by 85.44% and the soluble dietary fiber content by 3.71 times. The addition of 5%?15% FWB improved the pasting properties of wheat flour and the textural characteristics of cooked noodles, while FWB had negative effects on the farinographical properties of wheat flour. Using fuzzy mathematics and response surface methodology, the optimized formulation of FWB-incorporated noodles consisted of 7.54% (mass fraction m/m, based on wheat flour) FWB, 8% gluten and 0.5% salt (allboth based on mixed flour). Its physicochemical properties met the industry standard requirements. Finally, the in vitro starch digestibility of FWB-incorporated noodles was studied. It turned out that the starch hydrolysis index and predicted glycemic index were 61.29 ± 3.68 and 73.36 ± 2.01, respectively, which were significantly lower than those of ordinary wheat flour noodles, indicating that FWB could improve the nutritional value of noodles.

This study determined the effect of adding different amounts of propanediol (0%, 0.01%, 0.1%, and 1%) to liquid whole egg (LWE) followed by pasteurization (66 ℃/3.0, 3.5 and 4.0 min) on its physicochemical, foaming, emulsifying and gelation properties, and it also illustrated the underlying mechanism. Results showed that addition of propanediol reduced the aggregation degree of proteins in pasteurized LWE while improving its color. The maximum brightness, redness and yellowness values of 72.28, 17.63 and 75.22 were observed in pasteurized LWE with propanediol compared to 70.26, 13.17 and 57.04 for the control without addition of propanediol or pasteurization, respectively. Moreover, the emulsifying capacity of LWE with 1% propanediol pasteurized for 4.0 min was increased most significantly compared to the control (57.93% versus 44.2%). The best gel properties, namely water-holding capacity (WHC) of 95.95% and hardness of 2 641.02 g, were obtained by pasteurization for 3.0 min plus 0.1% propanediol addition, accompanied by a 1.09-fold and 1.25-fold increase in the elasticity and chewiness, respectively. The emulsion stability of LWE with 1% propanediol addition and pasteurization for 3.5 min was 28.47%, which was 1.71 times higher than that (28.47%) of the control. Therefore, addition of propanediol can effectively protect and even improve the processing characteristics of LWE during pasteurization, which will provide a scientific basis for stabilizing the functional characteristics of LWE.

The effects of different organogelators (beeswax, monoglyceride and ethyl cellulose) on major components, rheological properties, centrifugal oil separation and sensory quality of sesame paste were studied, and the effects of gelation agents acting via different mechanisms on the microstructure of sesame paste were compared. The results showed that the addition of organogelators increased the hardness of sesame paste and reduced the rate of centrifugal oil separation. According to the rheological curves, all sesame paste samples showed pseudoplasticity and uniform flow behavior. The sesame paste added with organogelators had higher modulus of elasticity. The addition of organogelators improved the stability of sesame paste without changing its major components. Sensory evaluation showed that the addition of organogelators increased oil separation in sesame paste and improved its homogeneity without affecting its color. By comparing the effects of different organogelators on the physical properties and sensory characteristics of sesame paste, we found that monoglyceride and ethyl cellulose-beeswax blend imparted good sensory acceptability to sesame paste while maintaining its original properties.

This study explored the effect of modified egg white powder (EWP) on noodle quality to select an EWP that is specially suitable for noodles. The cooking and texture properties of noodles added with nothing (control), raw EWP or one of four commercial modified EWPs were evaluated and they were also characterized by means of low-field nuclear magnetic resonance (LF-NMR), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The results showed that the noodles with modified EWP PHG21 (NPHG21) had the longest optimal cooking time, greatest water absorption index, and lowest breakage and dry matter loss rate. Meanwhile, the optimal cooking time and water absorption index had a significantly positive correlation with the gel strength and chewiness while the breakage rate had a significantly negative correlation with them. In addition, the hardness and chewiness of NPHG21 were high while the adhesion was low. Compared with the control group, the relative content of α-helix in NPHG21 was increased by 91.7% while the relative content of random coil was decreased by 29.6%, indicating significantly increased structural orderliness of gluten proteins. Moreover, the cross-sectional microstructure was tighter with exposure of fewer starch particles. In general, the noodles with PHG21 had better cooking, texture and microstructure as well as higher overall sensory acceptance so that it could be specially used in noodles.

In this study, soybean oil oleogels were developed by using beeswax, rice bran wax or their mixtures (10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 3:7, 1:9, 0:10 m/m) as an oleogelator at concentrations of 5% and 8%, and their physical properties were measured and compared with those of shortening. It was found that the hardness (in the range of 11.9–140.4 g) of oleogels increased first, then decreased, and finally increased slightly with increasing amount of rice bran wax. When the mixing ratio of beeswax and rice bran wax was 8:2, the prepared oleogels had the highest hardness, indicating the synergistic effect of the mixture. Meanwhile, oil separation in oleogels was evaluated by centrifugation. It was found that the oleogels with a low amount of rice bran wax (beeswax : rice bran wax ratio = 5:5) were stable without oil separation. Moreover, oil separation was lower in the oleogels with 8% oleogelator than in shortening. The solid fat content (SFC) of the oleogels (8.5%–4%) was significantly lower than that of shortening (65%–20%) at 10–40 ℃. The melting point of the oleogels (50.2 ℃) measured by differential scanning calorimetry (DSC) was higher than that of shortening (43.1 ℃). The results of X-ray diffraction (XRD) showed the crystalline morphology (β′-type) of the oleogels with 8% beeswax-rice bran wax mixture at an 8:2 ratio was close to that of shortening, both exhibiting fine crystals. It was found that the oleogels provided a good baking performance and resulted in a great reduction in the SFC of baked products and therefore could potentially used to develop healthier products for consumers.

The aim of this study was to investigate the effects of heat shock-lactic acid stress on the survival of and the expression of related genes in Escherichia coli O26. First, 22 bovine-borne O26 strains were collected and their tolerance to hydrochloric acid and lactic acid were compared. Then, strains with different tolerance to lactic acid were selected to evaluate their survival under heat shock-acid stress conditions. Finally, one representative strain was further selected to examine the differential expression of the general stress response gene rpoS, acid stress response genes (asr, ycfR, gadA), and heat stress response genes (rpoH, dnaK, clpB, and groEL) at 2 and 4 h of acid stress treatment using real-time polymerase chain reaction (real-time PCR). Results showed that the survival of all 22 strains significantly decreased (P < 0.05) after treatment with lactic acid or hydrochloric acid for 2 h. Nevertheless, acid tolerance varied among strains and the tolerance of each strain to lactic and hydrochloric acid was also different. Compared with the control group cultured in normal?tryptic soy broth (TSB), the survival rate of a mixed culture of five O26 strains gradually decreased in the acid stress and heat shock-acid stress groups, being higher in the latter than in the former, indicating that heat shock exerted a cross-protective effect and enhanced the acid resistance of O26. Real-time PCR detection showed that acid stress induced the down-regulation of stress response gene expression, whereas the expression of these genes increased significantly in heat shock-acid stress group compared with the acid stress group, indicating that the cross-protection of heat shock was related to the increased expression of the genes. It is suggested that when the combination of non-lethal heat treatment and acidification is applied in food processing, more attention should be paid to the potential of cross-protection to cause increased food safety risk.

A total of 14 yeast strains were isolated from high-salt liquid-state moromi and identified into four species. Representative strains were selected for physiological and biochemical identification and evaluation of growth characteristics. Moreover, these strains were individually used to ferment soy sauce to explore their effects on flavor soy sauce by gas chromatography-mass spectrometry (GC-MS) detection and sensory evaluation. The results showed that Rhodotorula mucilaginosa and Candida metapsilosis, potential flavor-producing strains, could improve the flavor of soy sauce by producing more 2-phenethyl acetate, 3-methylthio-1-propanol and 2,6-dimethylpyrazine. However, Millerozyma farinose and C. parapsilosis had negative impacts on soy sauce flavor. Notably, M. farinose, forming colonies with a dry and wrinkled surface, could obviously increase the contents of 2-octanone, 2-nonanone and 1,2,3-trimethoxybenzene to produce an intense off-flavor. The findings of this study are meaningful for guiding flavor regulation during soy sauce fermentation.

In the present work, the histidine kinase gene from Rhodococcus ruber SD3 was codon-optimized, and the optimized histidine kinase gene (rhks) was applied to construct a recombinant expression plasmid pGEX-4T-2-rhks. Then, the plasmid was transformed into Escherichia coli BL21 (DE3) for heterologous expression. Under the induction conditions of 25 ℃ and 1 mmol/L IPTG, histidine kinase fusion protein (GST-RHK) was successfully expressed and found to have catalytic activity. GST-RHK was purified electrophoretical homogeneity by glutathione agarose affinity chromatography, with a purification fold of 3.1 and a yield of 19.5%. The protein’s molecular mass was estimated to be 72.75 kDa. Its Km, Vmax and Kcat were 20.92 μmol/L, 0.17 μmol/(L·min) and 1.4 min-1, respectively. The wild-type, rhk enhancement (sdrhkE) and rhk knockdown (sdrhkD) strains were cultured in a medium containing phenol, toluene, chlorobenzene and isooctane individually. sdrhkD grew better than did the wild-type strain, whereas the growth of sdrhkE was inferior than the wild-type strain. This study may pave the way for unveiling the relationship between the signal transduction pathway mediated by histidine kinase and organic solvent tolerance in R. ruber SD3.

In this study, we isolated and identified lactic acid bacterial (LAB) strains from the gut of healthy elderly people in Xiangyang and Enshi, Hubei and then selected Lactobacillus fermentum strains for analysis by multilocus sequence typing (MLST). Results showed that by cultivable methods, 15 species of LAB were obtained belonging to five genera with Lactobacillus being the single dominant genus. In general, L. fermentum and L. salivarius account for about 55% of the total intestinal LAB strains, indicating that the human intestine can be an important source of L. fermentum. MLST analysis based on eight housekeeping genes showed that 25 L. fermentum strains originating from the elderly gut could be divided into 25 sequence types (ST), indicating high genetic diversity. Selection pressure analysis and phi-test showed that the eight housekeeping genes were purified and selected, and among these only the gene rpoB experienced recombination events. In addition, the evolutionary analysis based on Prim’s algorithm and global optimal BURST (goeBURST) algorithm showed that nearly half of the intestinal L. fermentum strains had the tendency to form one single branch, indicating that they had host specificity. This may be due to adaption to the intestinal environment. These strains were likely to undergo an evolutionary process different from that in fermented food habitat in order to adapt to the intestinal environment.

This study aimed to investigate whether and how pgm, fba, and gap overexpression can affect the stress resistance, adhesiveness, and biofilm formation of Lactobacillus plantarum LR-1. Results showed that the overexpression of the pgm and fba genes enhanced the heat, acid and bile salt resistance, biofilm formation and adhesiveness of L. plantarum LR-1. The transcriptional level of the gap gene had no significant effect on the stress resistance, biofilm formation or adhesiveness. The up-regulation of pgm, fba, and gap increased the transcriptional levels of tuf and luxS in this strain with the first two being more effective than the last one. Furthermore, bioinformatic analyses suggested that pgm and fba could be associated with genes related to multiple pathways. These results provide a new understanding of the role of glycolytic pathway-related genes in regulating the stress resistance, adhesiveness, and biofilm formation of L. plantarum.

The effects of two phenolic compounds in lignocellulosic hydrolysate, p-hydroxybenzaldehyde and ferulic acid, on the physicochemical properties of Saccharomyces cerevisiae GGSF16 were studied. Results showed that after treatment with either compound, the glucose metabolism time and alcoholic fermentation time of S. cerevisiae was extended, the contents of extracellular nucleic acid and protein and the content of intracellular trehalose were significantly increased (P < 0.05). Scanning electron microscopic (SEM) images showed that the surface morphology changed from complete and smooth to wrinkled, sticky and cracked. In addition, functional groups of lipids, proteins, nucleic acids were altered as shown by Fourier transform infrared (FTIR) spectra. Collectively, these findings indicated that the p-hydroxybenzaldehyde and ferulic acid can cause damage to S. cerevisiae cell wall and increase cell membrane permeability, thereby resulting in leakage of cell contents, finally causing cell damage.

In order to select a suitable DNA barcode for accurate identification of Dendrobium officinale, 25 samples of D. officinale and 10 samples of other Dendrobium species were subjected to molecular identification using nine commonly used plant DNA barcodes (ITS2, nad1, matK, ycbL, psbK-psbI, trnL-trnF, trnG-trnS, rbcL and trnH-psbA). The results showed that the versatility of the nine DNA barcodes was strong, with high success rates of amplification and sequencing. The maximum genetic distance within species of rbcL and trnH-psbA was greater than the minimum genetic distance between species, which did not meet the basic requirements for barcodes. Instead, the maximum genetic distance within species of the other barcodes was smaller than the minimum genetic distance between species. The decreasing order of interspecific variation was ITS2 > trnL-trnF > trnG-trnS > psbK-psbI > ycf1b > matK > nad1. ITS2 had the fastest evolution rate and the highest mutation rate (25.1%). The identification rates of ITS2 and trnL-trnF for the Dendrobium samples tested were both 90.1%. It is recommended that ITS2 + trnL-trnF be used for the identification of D. officinale germplasm resources. The results of this study are expected to provide a reference and molecular basis for the identification of D.officinale and its closely related species by using DNA barcoding technology.

The effects of Lactobacillus plantarum XCT 1-10 at different concentrations (0, 102, 104, 106, 108, and 1010 CFU/mL) on the colony growth and spore germination of Botrytis cinerea and the decay of apples inoculated with B. cinerea were investigated in this study. The results demonstrated that L. plantarum XCT 1-10 at 106 CFU/mL significantly restrained lesion development in apple fruit inoculated with B. cinerea, and distinctly depressed the spore germination and colony growth of B. cinerea. The in vitro test demonstrated that L. plantarum XCT1-10 treatment increased the contents of malondialdehyde (MDA), soluble sugar and soluble proteins, and nucleic acid release, but decreased the relative conductivity of B. cinerea. These findings suggest that L. plantarum XCT 1-10 can suppress the growth of B. cinerea possibly by destroying the cell membrane.

This study sought to analyze the reason why the viscosity of the fermentation broth containing poly-γ-glutamic acid (PGA) can be significantly reduced by adding KCl to the culture medium from the perspective of PGA’s molecular structure. The medium without KCl was used as a control. The molecular structure of PGA obtained from the medium with addition of 15 g/L KCl was characterized systematically by gel permeation chromatography (GPC), chiral chromatography (CC), static light scattering (SLS), circular dichroism (CD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermal analysis and shear viscosity measurement. The results showed that the molecular mass of PGA decreased by 13.9%, the proportion of D-glutamic acid in PGA increased from 47.66% to 53.77%, the PGA was more likely to form an aggregation state in aqueous solution, the conformation changed from single β-sheet to the co-existence of β-sheet and α-helix, and the shear viscosity of PGA aqueous solution decreased by 32.08% when 15 g/L KCl was added to the medium. The decrease of the fermentation broth’s viscosity by KCl may be related to the molecular structural change of PGA. This study provides some new information useful for understanding the mechanism of KCl for reducing the fermentation broth’s viscosity from the perspective of PGA’s molecular structure.

In order to investigate the difference in the storage stability of freeze-dried Lactobacillus plantarum KLDS 1.0328 under different nutritional conditions, the effects of glucose and/or Tween-80 stress on the growth, acid production, morphology and cell membrane fatty acid composition of this strain, the antibacterial activity of bacteriocin produced by it, and the survival rate of its freeze-dried cells during frozen storage were analyzed. It was found that both glucose and Tween-80 stress had different impacts on the growth, acid production and bacteriocin antibacterial activity. Scanning electron microscopic (SEM) results indicated that the bacterial cell shape changed from short rod-like to long rod-like or oval-shaped and that the size also changed when exposed to Tween-80 stress or glucose-Tween-80 stress. The ratio of unsaturated fatty acids to saturated fatty acids in the cell membrane increased under all nutrient stress conditions. In addition, the stability and survival rate of freeze-dried cells stored at ?18 ℃ for up to 42 days were significantly improved by glucose stress.

Objective: In this study, the relationship among methyl-directed mismatch repair (MMR) deficiency, mutation frequency, and the minimal inhibitory concentration (MIC) of ciprofloxacin was investigated to reveal the antimicrobial resistance mechanism of Salmonella hypermutators (SHs). Methods: Ninety SHs were investigated for their susceptibility to ciprofloxacin via agar dilution method. Mutation frequencies were determined by using agar plates containing nalidixic acid and rifampicin. Mutations related to antibiotic resistance were tested by polymerase chain reaction (PCR). The wild-type mutant genes mutS, mutH, mutL, and uvrD were separately transferred into the representative hypermutator 103D2 by electrotransformation. The expression of antibiotic resistance genes in 103D2 and the resulting transformants were tested by real-time PCR so as to determine the effect of MMR gene deficiency on ciprofloxacin resistance. Results: Forty-nine of the 90 SHs (89 of which were ciprofloxacin resistant) were deficient in the MutS (MutS-), and GyrA (67.3%) and ParC (87.8%) mutations were more likely (P = 0.007) to occur in SHs with MutS- compared with the non-MutS wild-type strains. The mutation frequency of the transformants on Luria-Bertani-agar plates with nalidixic acid (20 μg/mL) was significantly (103D2:P-mutS) or extremely significantly (103D2:P-mutL and 103D2:P-uvrD) decreased compared with the original strains. In all transformants, the expression of marA was significantly down-regulated whereas the expression of marR and tolC were significantly upregulated except for 103D2:P-uvrD, leading to deceased ciprofloxacin resistance in 103D2. Conclusion: MMR gene deficiency may be a factor contributing to antibiotic resistance in SHs by affecting the efflux pumps and the expression of marA, tolC, and marR, associated with antibiotic susceptibility.

In order to determine the effects of different starter cultures on the quality of pickled radish, white radish pieces were inoculated with each of six multiple-species starter cultures and fermented for up to 7 days, and the changes in basic physicochemical indexes, texture characteristics, and the contents of nitrite, 17 amino acids and organic acids were analyzed during fermentation. The results showed that the quality of pickled radish inoculated with starter 2 (consisting of Lactobacillus buchneri, Lactobacillus plantarum and Pichia mandshurica) was the best, and it reached maturity on the 4th day. The hardness of fermented radish inoculated with starter 3 (composed of L. plantarum, L. buchneri, unclassified Lactobacillus and P. mandshurica) was slightly higher than that of the other groups after 7 days of fermentation (P > 0.05), and the content of nitrite in the fermentation process was far lower than the national limit standard. In the fermentation process, pickled radish contained a wide variety of amino acids and organic acids. The contents of sweet and umami amino acids in pickled radish fermented with starter 2 were significantly higher than those in the other groups (P < 0.05), with glutamic acid being the most abundant amino acid, (0.18 ± 0.01) mg/g, and the same was observed for organic acids (P < 0.05). The amino and organic acids could impart pickled radish with good flavor quality. Overall, starter 2 can be used a specialized starter culture for the production of premium quality pickled radish.

In order to explore the function of two-component signal transduction systems (TCSs) in the growth and environmental adaptation of Pseudomonas fluorescens, the dominant?spoilage?organism in aquatic products, the sequence analysis and function prediction of the TCSs in P. fluorescens PF08 were carried out by bioinformatic methods. The results showed that there were 63 histidine kinases (HKs), 84 response regulators (RRs), 39 pairs of TCSs and 25 fusion HKs in P. fluorescens PF08. All HKs in the bacterium possessed the HATPase_c and HisKA domains, and all RRs possessed the REC domain. The phylogenetic analysis suggested that the TCSs with the same domains were clustered in the same cluster, indicating similar functions of these TCSs. The biological functions of 25 pairs of TCSs in P. fluorescens PF08 were successfully predicted, mainly participating in the regulation of nutrient metabolism, material transport, cell differentiation, adaptation to adverse environments, cell resistance and virulence. This study may provide some references for further elucidating the functions of TCSs in the environmental adaptation of P. fluorescens PF08 from aquatic products.

In this work, the differences in the composition and diversity of the bacterial community in environmental samples from each of seven repeated rounds of Maotai-flavor liquor fermentation in 2018 in Maotai town were systematically studied by high-throughput sequencing technology combined with mathematical statistical analysis. The results showed that the diversity and richness of bacterial flora in the fermentation environment were high at each round, but differed with the number of fermentation rounds. The structure and composition of the dominant phyla and genera were similar among rounds, and the dominant bacterial community structure remained stable. Totally 19 phyla and 396 genera were detected from all samples. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the dominant phyla. There were 14 dominant bacterial genera identified, mainly Sphingobacterium, Enterobacter, Pantoea, Pseudomonas, Escherichia-Shigella, Staphylococcus. By partial least squares discriminant analysis (PLS-DA) combined with Adonis and PERMANOVA, we found that the structure of the bacterial community was significantly different at the genus level but not at phylum level among rounds, and the main differential bacterial genera included Lentibacillus, Enterobacter, Escherichia-Shigella, Cronobacter, and Stenotrophomonas. The findings obtained in this study provide scientific evidence for understanding the structure of bacterial microflora in the brewing environment of Maotai-flavor liquor in Maotai town and the brewing mechanism of high-quality Maotai-flavor liquor.

Objective: In order to optimize the fermentation process of apricot wine, improve the comprehensive utilization value of apricot fruit and reduce the resource waste and environmental pollution, apricot juice and pomace were fermented by inoculating two commercial yeast cultures separately, and the effects of different fermentation processes on physicochemical indexes, aroma components and sensory characteristics of apricot wine were compared. Methods: Four fermentation processes were evaluated in this study, namely (1) fermentation of apricot juice with yeast BV818, (2) fermentation of apricot juice with yeast CECA, (3) fermentation of apricot pomace with yeast BV818, and (4) fermentation of apricot pomace with yeast CECA. The aroma components in apricot wine were determined by gas chromatography-mass spectrometry (GC-MS), and sensory evaluation was carried out. Results: In apricot wine, 41 aroma compounds were detected, including 29 esters, five alcohols, two aldehydes and five terpenes. Among these components, the number and amount of ester compounds were the highest, accounting for 72.7% of the total amount of aroma compounds. In wine samples 1–4, the total aroma amounts was 14 765.27, 15 034.37, 12 580.27 and 7 347.61 μg/L, respectively, significantly higher in apricot juice wine than in that made from apricot pomace. Six aroma components with odor activity values (OAV) greater than 1 were found in all wine samples, including ethyl octanoate, ethyl hexanoate, isoamyl acetate, linalool, ethyl decanoate and ethyl butyrate. The results of principal component analysis (PCA) showed that sample 2 was in the same quadrant as the five characteristic aroma components of isoamyl acetate, ethyl butyrate, ethyl hexanoate, ethyl octanoate and linalool, indicating that this sample had the typical aroma characteristics of apricot wine. The results of sensory evaluation showed that apricot wine had fruity aromas like apricot, peach, orange, apple and pear, and floral aroma like Chinese scholar and honeysuckle. Sample 2 had the highest sensory score. Conclusion: Apricot juice wine has high content of aroma substances with fruity and floral aromas, is light-bodied and tastes refreshing, while apricot pomace wine has a high content of total phenol with a complex aroma profile, tastes yeast-like, and is full-bodied. This study provides technical support for optimizing the fermentation of apricot wine, and also provides a theoretical basis for further studies on the formation of aroma components in apricot wine.

In this study, the effect of two exogenous nucleotides, namely, cytidine 5’-monophosphate (5’-CMP) and adenosine 5’-monophosphate (5’-AMP) on the growth of Lactobacillus casei was explored, together with the effects on the biofilm morphology, extracellular polymeric substances and the inhibitory activity of the crude extract from the culture supernatant of L. casei against quorum sensing and the biofilm of foodborne pathogens. The results showed that the two exogenous nucleotides could promote the growth and reproduction of L. casei, and the production of bacterial biofilm and exopolysaccharides (EPS). Moreover, they simulated the quorum sensing inhibitory activity and anti-biofilm activity of the crude extract of L. casei on the biofilm of Shigella spp.. Therefore, the two exogenous nucleotides hold great promise as bacterial growth stimulants in maintaining intestinal health.

In order to study the effect of selenium enrichment on chemical composition of Amaranthus caudatus L. (ACL), we determined and comparatively analyzed the health-benefiting components (polyphenols, flavonoids and minerals) in the roots, stems, leaves and flowers of Se-enriched and non-Se-enriched ACL by metabonomics based on ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that the contents of polyphenols, flavonoids and minerals (except zinc) in Se-enriched ACL were generally higher than those in normal ACL. Among the four plant parts, the leaves of Se-enriched ACL showed the greatest changes in the contents of these components, exhibiting an increase in the contents of polyphenols, flavonoids, calcium, iron, copper, selenium, molybdenum, cobalt and chromium of 65.9%, 95.4%, 39.5%, 16.8%, 297.5%, 1 050.0%, 110.7%, 300.0% and 207.7%, respectively and a 76.4% decrease in the content of zinc compared to the non-Se-enriched ones. The above data showed that selenium enrichment promoted the accumulation of polyphenols, flavonoids and most minerals in different parts of ACL. This study may provide a theoretical basis for the development of health products from Se-enriched ACL.

In this work, Torulaspora delbrueckii SY-2-2 and Saccharomyces cerevisiae RV002 were used for the fermentation of kiwifruit wine through different inoculation strategies (single, simultaneous and sequential). The volatile aroma compounds of kiwifruit wines were determined by headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that more types of volatile aroma components were obtained by mixed fermentation compared with single fermentation, and the highest number (23) and amount (336.95 mg/L) of aroma components were obtained by the sequential inoculation. In the sequential inoculation, T. delbrueckii contributed to increasing the types and contents of volatile compounds, especially ethyl phenylacetate, ethyl phenylpropionate, phenylethanol, β-damascone, α-terpineol, eucalyptol and etal, which provided kiwifruit wine with a strong flowery and fruity flavor, and enriched its aroma components. The sensory evaluation showed that the sequential inoculation resulted in higher flowery, herbal and sweet aroma, followed by wine-like and fruity aroma, leading to the highest overall sensory score.

A descriptive analysis of the aroma of six samples of Keemum black tea (three grades of Maofeng tea and three grades of Congou tea) was carried out using sensory evaluation, quantitative descriptive analysis (QDA) and flash profile (FP). In QDA, ten trained sensory panelists evaluated 16 aroma attributes, and analysis by PanelCheck and analysis of variance (ANOVA) showed that 10 of the aroma attributes were significantly different among the samples. In FP, 18 untrained consumer panelists established 51 aroma attributes and ranked them in terms of their intensity. Using generalized procrustes analysis (GPA) and agglomerative hierarchical clustering (AHC), we obtained similar results to those using QDA. The FP method could easily and quickly distinguish the differences in aroma between tea samples, but could not provide specific aroma descriptors. The combined use of QDA and FP may provide a more scientific and practical approach for tea sensory evaluation.

The contents of umami amino acids and 5’-nucleotides in the stipe and pileus of Lanmaoa asiatica were analyzed by reversed phase high performance liquid chromatography (RP-HPLC), showing that the contents of umami amino acids and umami nucleotides were distinctly higher in the pileus than in stipe. Three umami peptides from the water extract of the pileus were separated and purified by gel filtration chromatography (GFC), RP-HPLC and Nano ultra-high performance liquid chromatography-tandem mass spectrometry (Nano UPLC-MS/MS), and they were identified as FKDLGEENFK, KMDDFAAFVEK and LVNEVTEFAK. Their molecular masses were 1 225.598, 1 357.622 and 1 148.608 Da, respectively. Through taste dilution analysis, the thresholds for the three peptides were determined to be 9.78, 10.25 and 13.01 mmol/L, respectively.

The odor-active compounds of stewed marinated beef stored for different periods of time (0, 3, 6, 9 and 12 months) were analyzed by purge & trap-thermal desorption-gas chromatography-olfactometry-mass spectrometry (P&T-TDS-GC-O-MS) and odor activity value (OAV), and sensory evaluation was conducted to identify the compounds responsible for the characteristic off-flavor. The results showed that 52 odor-active compounds with OAV ≥ 0.1 were detected. Among them, the number (13) of aldehydes was the highest. Aldehydes and alcohols accounted for a high proportion (34.53%–70.55% and 27.72%–57.91%, respectively) of the total OAV. During storage, the color of stewed marinated beef became darker and its elasticity decreased. At the later storage period, the aroma became weak, and the off-flavor intensively increased, leading to decreased acceptability. Meanwhile, principal component analysis (PCA) showed good separation among samples with different storage periods. The correlation analysis demonstrated that 16 and 12 odor-active compounds were significantly correlated with sensory flavor score and storage time, respectively. According to GC-O identification, 1-octene-3-ol, heptanal, octanal, nonanal, decanal, E,E-2,4-decanodienal, 2-nonanone, and octanoic acid may be the major source of stewed marinated beef off-flavor.

In order to explore the differences in volatile components and aroma profiles between the peel and flesh of tomato fruit, two inbred lines were used for this study, namely, CI1005 (red cherry tomato) with high concentrations of volatile components and TI4001 (green large-fruited tomato) with low concentrations of volatile components. Peel and flesh samples were taken at different maturation stages (mature green, turning, orange, and red stages) to analyze their volatile components as well as odor characteristics and intensity using headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry-olfactometry (GC-MS-O). The results showed that there was little difference in volatile components between the peel and flesh of the same inbred line during fruit ripening. The concentrations of volatile components were significantly higher in the peel than in the flesh of CI1005 at each ripening stage, especially aldehydes, alcohols, esters, acids, and ketones. On the contrary, the concentrations of volatile components were significantly higher in the flesh of TI4001, especially aldehydes, esters, and acids. The aroma intensity was significantly stronger in the peel of CI1005, especially in terms of fatty, malty and green aroma, while the flesh showed stronger sweet taste. The peel and flesh had the strongest grassy and fruity aroma, respectively. During fruit ripening, the aroma of the peel increased more than that of the flesh. The maximum difference occurred at the red mature stage. Aroma intensity was stronger in the flesh than in the peel of TI4001, especially in terms of fatty, mushroom-like and green aroma. The strongest fatty aroma was found in the flesh and the strongest floral aroma in the peel. At the turning stage, both the peel and flesh had the strongest aroma, and the maximum difference occurred at this stage. The concentrations of volatile components and the aroma intensity of CI1005 were significantly higher than those of TI4001. In conclusion, significant differences in volatile components and aroma existed between the peel and flesh of tomatoes.

The characteristic taste compounds of traditional non-fermented and fermented milk cakes were clarified by analyzing free amino acids and free fatty acids using an amino acid analyzer and gas chromatography (GC), respectively as well as calculating taste intensity value (TAV). Furthermore, sensory evaluation was conducted, and the correlation between characteristic taste substances and sensory attributes was analyzed. The results showed that the TAVs of glutamic acid, histidine and kunic acid, lauric acid, myristic acid, oleic acid and linoleic acid in milk cakes were greater than 1, indicating their important contribution to the taste of milk cakes. Significant variation in sensory attributes and taste compounds was found between the two milk cakes. The overall taste intensity of fermented milk cakes was higher than that of traditional yogurt cakes (P < 0.05), and the sensory attributes mainly included sourness, sweetness, bitterness and umami taste. However, traditional milk cakes had an unpleasant odor. Correlation analysis between characteristic taste compounds and sensory attributes using partial least squares (PLS) regression indicated a high correlation between sensory attributes and free amino acids. The saltiness of traditional milk cakes was significantly positively correlated with arginine, and the unpleasant odor was significantly positively correlated with glycine, decanoic acid and palmitoleic acid. Similarly, there was a significant positive correlation between the sourness of fermented milk cakes and stearic acid and linoleic acid, between the sweetness and aspartic acid, threonine, serine, glutamic acid, alanine and linoleic acid, between the bitterness and valine, methionine, isoleucine, amino acid, tyrosine and myristic acid, and between the umaminess and aspartic acid, glutamic acid and alanine (P < 0.05). In conclusion, fermentation improves the taste of milk cakes by promoting the decomposition of protein and fat.

The changes of volatile flavor compounds in sea bass muscle during the steaming process were evaluated by gas chromatography-ion mobility spectroscopy (GC-IMS) in this study. The results showed that 43 volatile substances were identified in steamed sea bass muscle by GC-IMS, including aldehydes, ketones, alcohols, acids and ester compounds. There were significant differences in the flavor composition of sea bass muscle with different steaming times. The contents of 3-methylbutanol, dimethyl disulfide and propionic acid were higher in fresh fish, while the contents of octanal, nonanal, 3-methylbutanal, (E,E)-2,4-octandienal, benzaldehyde, 2-heptanone, 2-butanone, 1-octen-3-ol, 1-heptanol and 1-butanol increased significantly after steaming. A total of 11 characteristic indicators with variable importance in the projection (VIP) score greater than 1 were selected by orthogonal partial least squares-discrimination analysis (OPLS-DA). The differences in the volatile flavor of sea bass muscle with different steaming times could be distinguished by heat map clustering analysis. 3-Methylbutanol, 1-heptanol, 2-furanmethanol and (E)-2-heptenal could be used as the characteristic volatile markers to discriminate between raw and cooked sea bass. These results indicated that GC-IMS could effectively distinguish fish samples according to cooking time.

The nutritional composition, physicochemical characteristics and microstructure of tenderloin, rib, hind leg and neck from male Sanfen donkeys were analyzed and compared with each other. The results showed that there were some differences in meat quality and nutritional composition among the four meat cuts. Among these, the hind leg meat had the highest protein content (P < 0.05), the linoleic acid content in the tenderloin meat was the lowest (P < 0.05), while the neck meat contained lower myristic and palmitoleic acid contents and higher arachidonic acid content (P < 0.05). For all cuts, the ratio of unsaturated to saturated fatty acids (UFA/SFA) was greater than 1, and the fatty acid composition was composed mainly of unsaturated fatty acids. The rib and tenderloin meat had higher protein nutritional value, while the tenderloin and hind leg meat had a redder color and smaller fiber diameter (P < 0.05), being more tender. The cross-sectional microstructure of rib and neck muscle tissues showed the presence o lumpy aggregates, while hind leg and tenderloin muscle tissues showed a honeycomb-like structure. The hind leg meat had the highest total sensory score (P < 0.05) and was more popular among consumers. In conclusion, this study shows that there are some differences in the meat quality of different carcass cuts in donkeys, which will provide a theoretical reference for the processing of different grades of donkey meat.

This study selected 11 amino acids that may participate in the Maillard reaction during the processing of Pixian broad-bean paste (PXBP), resulting in the production of the characteristic aroma, to construct Maillard reaction systems consisting of single or combined amino acids and PXBP aqueous extract in order to explore the contribution of exogenous amino acids to the characteristic flavor of PXBP. The results of solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) showed that 17 key aroma compounds were obtained from the Maillard reaction products (MRPs) derived from 11 single amino acids. According to the contribution of the amino acids to the key aroma compounds of PXBP, phenylalanine (Phe), methionine (Met), arginine (Arg), aspartic acid (Asp), lysine (Lys) and leucine (Leu) were selected to construct Maillard reaction systems containing mixed amino acids. Based on sensory evaluation and the number and amount of key compounds, the optimum reaction system consisted of 1.400 g of Asp, 0.720 g of Arg, 0.100 g of Met, 0.740 g of Leu, 0.480 g of Phe and 0.500 g of Lys in every 50 mL of PXBP aqueous extract. The combined addition of amino acids improved the types and contents of key aroma compounds in PXBP, imparting a better-balanced and stronger flavor to the product.

Samples of one bud and two leaves from the tea variety Bixiangzao were collected in summer to prepare black tea using a modified version of the traditional processing technology by introducing piling after the first-drying process. The influence of piling was evaluated on the sensory quality, taste compounds and aroma compounds of black tea. The results showed that compared with the traditional manufacturing technology, piling for 3 h after the first-drying process could significantly improve the quality of black tea, imparting a more mellow and refreshing taste, a bright red orange color and a sweet aroma to the infusion. Moreover, the introduction of piling resulted in significantly increasing the theaflavin content in tea samples from 0.41% to 0.62% (P < 0.05), increasing the relative content of total aroma alcohol compounds from 52.25% to 57.33%, and producing new ketones with fruity aroma including 1,3,7-trimethyl-3,7-dihydro-1H-purine-2,6-dione, 4-[2,2,6-trimethyl-7-oxabicyclo[4.1.0]hept-1-yl]-3-buten-2-one and 6-methyl-5-hepten-2-one. The above results suggest that introducing piling after the first-drying process is feasible to improve the quality of black tea.

In this study, in order to establish a triplex real-time polymerase chain reaction (real-time-PCR) method based on a Taqman probe for the rapid detection of the virulence genes of Vibrio parahaemolyticus, primers and probes were designed targeting V. parahaemolyticus-specific genes and its main virulence genes tlh, tdh and ureR, and the reaction conditions were optimized. Ten strains of V. parahaemolyticus and 22 non-V. parahaemolyticus strains were used to verify the specificity of the designed primers and probes. The results showed that the primers and probes presented high specificity. The optimized primer concentrations were 0.15, 0.15 and 0.80 μmol/L for tdh, tlh and ureR, respectively, and the optimized probe concentrations were 0.50 μmol/L for both HEX and FAM. Even at a high concentration of background bacteria, this method exhibited a good linear relationship between DNA concentration and Ct value, and the lowest detection limit was 1.8 × 102 copies/mL. When the pre-denaturation time was set to 30 min, the amplification result using the intact bacterial cell suspension as the template was comparable to that using genomic DNA (gDNA) (ΔCt < 1). The triplex real-time PCR method can not only allow for rapid and quantitative detection of V. parahaemolyticus, but also effectively distinguish between pathogenic and non-pathogenic V. parahaemolyticus, thus providing a rapid, sensitive and accurate method for risk assessment of pathogenic V. parahaemolyticus.

Herein, a high performance liquid chromatography coupled with diode array detection (HPLC-DAD) method was established for the detection 16 illegally added industrial dyes in foods, including Disperse Red 11, Disperse Yellow 9, Disperse Orange 3, Disperse Orange 11, Disperse Red 1, and Disperse Red 9, Disperse Yellow 54, Disperse Orange 37, Disperse Orange 61, Sudan Red 1, Disperse Yellow 7, Disperse Orange 149, Sudan Red 2, Sudan Red 3, Sudan Red 7B, and Sudan Red 4. The chromatographic separation was achieved on an Agilent ZORBAX SB-C18 column using a mobile phase composed of acetonitrile and water with a flow rate of 0.8 mL/min. For commercial samples of candy, chocolate, tomato ketchup and tomato sauce, the limit of detection (LOD) was 0.26?0.88 mg/kg, and the limit of quantification (LOQ) was 0.82?2.52 mg/kg. The spiked recoveries of the 16 dyes were in the range of 81.0%?110.3% with relative standard deviation (RSD) of 0.3%?7.5%. These results show that the developed method is reliable and stable and can be used for the routine determination and screening of illegally added dyes.

A method for the simultaneous determination of residues of 21 siloxane compounds in silicone tableware was established by gas chromatography-tandem mass spectrometry (GC-MS/MS). The analytes were extracted from samples, separated on a ZB-5HT (15 m × 0.25 mm, 0.1 μm) chromatographic column and scanned in the multiple reaction monitoring (MRM) mode using an electron ionization source. The results showed that all analytes were separated well and their calibration curves were linear in the concentration range of 0.05–2.50 mg/L. The minimum detection limit was 0.20 mg/kg for trimethyltriphenylcyclotrisiloxane, tetramethyltetraphenylcyclopentasiloxane and pentamethylpentaphenylcyclopentasiloxane, and 0.05 mg/kg for the other 18 compounds. The recoveries of the spiked analytes were 91.3%–107.8%, with relative standard deviations lower than 5.0%. In conclusion, the method is fast, efficient and has a good linear range. It is suitable for the determination of residues of the 21 siloxane compounds in silicone tableware.

In this work, ultra-high performance liquid chromatography (UPLC) with sample pretreatment by high-throughput automatic purification using immunomagnetic beads was used to accurately determine the content of zearalenone in grains. The reaction time of immunomagnetic beads with zearalenone and the extraction solvent composition were optimized, and the purification effects of immunomagnetic beads on different grain matrices were evaluated. The detection limit and quantitation limit of UPLC were 3.5 and 12.0 μg/kg, respectively. Under the optimized conditions, the recoveries of spiked negative whole wheat and corn flour samples were 99.04%–109.26%, with coefficients of variation not greater than 6.88%. The results of the UPLC method for zearalenone in the national certified reference materials or quality control samples for whole corn flour, whole wheat flour, brown rice flour and wheat flour agreed with the certified values within the extended uncertainty range with coefficients of variation not greater than 3.54%. Analysis by the Bland-Altman method indicated that the difference between immunomagnetic bead purification and immunoaffinity column purification was acceptable. Thus, the two methods could be used interchangeably with each other to purify and enrich zearalenone from grains. The automatic mycotoxin purification system based on immunomagnetic beads, allowing the high-throughput automatic purification of zearalenone from grains, could purify 10–24 samples simultaneously, and it averagely took 2–3 minutes to purify one sample. In conclusion, UPLC has the advantages of rapidity, high sensitivity and high accuracy and can be used for the determination of zearalenone in grains.

In this research, an analytical method for simultaneous determination of thiourea, kojic acid, thiabendazole, thiadiazole and tetracycline in wheat flour by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established. Samples were extracted with 80% ethanol-acetonitrile (1:1, V/V), and then subjected to centrifugation and nitrogen blowing concentration before being quantitatively analyzed by using the multi-reaction monitoring (MRM) mode. The results showed that the developed method exhibited a good linear relationship in the concentration range of 100–5 000 ng/mL for thiourea, kojic acid and tetracycline, 1–50 ng/mL for thiabendazole and 1–50 μg/mL for thiadiazole, with correlation coefficients of higher than 0.999. The limits of detection (LOD) and limits of quantitation (LOQ) were 25 and 50 μg/kg for thiourea, kojic acid and tetracycline; 0.5 and 1 μg/kg for thiabendazole; 0.5 and 1 mg/kg for thiadiazole. The recoveries from spiked samples ranged from 88.6% to 102.2%, and the precision expressed as relative standard deviation (RSD) ranged from 0.7% to 5.6% (n = 6). This method, with simple and rapid pretreatment, can be used for the rapid determination of thiourea, kojic acid, thiabendazole, thiadiazole and tetracycline in wheat flour.

In order to establish a visual detection method for Salmonella using G-guadruplex-generating polymerase chain reaction (PCR), the upstream and downstream primers containing G-quadruplex complementary sequences at the 5’ end were designed according to the Salmonella-specific gene invH, which served as the target gene. Double-stranded DNA contained a large number of G-quadruplexes was obtained after specific amplification of the target sequences by PCR, and bound to hemin after being denaturated to generate DNAzyme with peroxidase-like activity. DNAzyme was able to catalyze the reaction between H2O2 and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, resulting in color change from colorless to green and thus allowing visual detection of Salmonella. Under the optimized detection conditions, there was a good linear relationship between the logarithm of Salmonella genome concentration (y) and absorbance at 421 nm (x), which was fitted to the equation: y = 0.129 9x + 0.217 9 (R2 = 0.994 5) with a linear range of 0.07–771.6 ng/μL, and the sensitivity was 0.07 ng/μL. The specificity analysis showed that this method was suitable for the detection of Salmonella, and could be successfully applied to artificially contaminated milk samples, with a detection limit of 1.2 × 102 CFU/mL. By using this method, 30 commercial samples were tested and the results were consistent with those obtained by the national standard detection method. This study provides a new strategy for the detection of foodborne pathogens.

Based on a detailed understanding of the separation efficiency of eight menthol optical isomers on different chiral and non-chiral capillary columns, a method for the quantitative determination of them was established using gas chromatography-mass spectrometry (GC-MS) after separation on tandem chiral capillary columns. The results showed that four enantiomeric pairs of menthol were separated on DB-5MS, DB-624, DB-ALC1 and DB-INNOWAX capillary columns with non-chiral stationary phase, but the D- and L-enantiomers failed to be separated from each other. The eight menthol optical isomers were successfully separated on tandem CycloSil-B and BGB-175 chiral capillary columns by virtue of the complementarity between them. Being sharp and symmetrical, the chromatographic peaks all met the requirements for separation. The response value and retention time had good stability, and the stationary phase loss was small during the separation process, causing no significant impact on menthol detection. The limit of quantification (LOQ) of the developed method was 23.0–72.9 μg/L, and the recoveries of the spiked analytes ranged from 86.0% to 116.0%. This method was successfully utilized for the separation and quantitative detection of menthol optical isomers in candy and drugs, indicating that the dominant form of menthol in the samples tested was L-menthol, and other menthol isomers were also detected at trace levels in most samples. In addition, menthol types in different samples were distinguished by menthol isomer configuration.