上海海关动植物与食品检验检疫技术中心

In this study,an analytical method based on gas chromatography-mass spectrometry(GC-MS)was developed for the simultaneous determination of 8 common psychoactive substances derived from cathinone compounds in tea.Extraction,clean-up and chromatographic and mass spectrometric conditions were optimized.As a result,an alkaline solution containing methanol was selected as the extraction solvent,and the extract was cleaned up on an HLB solid-phase extraction(SPE)cartridge filled with N-propylethylenediamine(PSA)and separated on a DB-17MS capillary column(30 m × 0.25 mm,0.25 μm).The mass spectrometer was operated using an electrospray ionization(EI)source in the selected ion monitoring(SIM)mode.The calibration curves showed good linearity for the 8 analytes in the concentration range of 0-200 μg/L,with correlation coefficients(R2)higher than 0.998.The limits of detection(LOD,RSN=3)and limits of quantification(LOQ,RSN=10)were 7 and 25 μg/kg,respectively.The recoveries from negative samples spiked at 1 ×,2 × and 10 × LOQ were in the range of 67.2％-117.6％,with relative standard deviations(RSD)of 4.3％-12.3％(n=6).In summary,this method has good stability and high sensitivity,and is suitable for simultaneous determination of the psychoactive substances derived from cathinones in tea.

In this study,the specific fragment of turkey chromosome Z-DNA sequence was selected as the target sequence for turkey-derived material detection.A real-time polymerase chain reaction(real-time PCR)method was established,which had good interspecies specificity and interspecies consistency.The target sequence was cloned into the plasmid pUC57,and after being diluted to different concentrations,the plasmid was tested by real-time PCR.The absolute detection limit of this method was 5 copies/PCR reaction.An international collaborative validation trial was conducted to validate this method.The results showed that the false positive and negative rates of the proposed method were both 0％,and the absolute detection limit was 5 copies/PCR reaction.The results of qualitative analysis of the diluted plasmid showed that the inter-laboratory standard deviation was 0.30,less than the maximum permitted value of 1;at a detection probability of 95％,the absolute detection limit was 3.2 copies/PCR reaction,less than the maximum allowable value of 20 copies/PCR reaction.Based on voting results and reviewers'comments,this method was approved by the International Organization for Standardization(ISO)as an international standard method(ISO/TS 20224-8:2022).

The viable but nonculturable (VBNC) state refers to a state in which bacteria lose their ability to grow and reproduce in conventional media under adverse environmental stress conditions. Bacteria in the VBNC state are usually still metabolically active and remain pathogenic and virulent. Bacteria in the VBNC state can recover and return to a state where they can be cultured normally under certain suitable conditions, posing potential risks to food safety. In this review, the morphological, physiological, biochemical and biomacromolecular characteristics of bacteria, especially foodborne pathogens, in the VBNC state are comprehensively described. Meanwhile, various factors that induce bacteria to enter the VBNC state, including temperature and pH unsuitable for bacteria survival, are summarized. The laboratory conditions for bacterial recovery from the VBNC state are outlined with special reference to adequate nutrition as an indispensable factor for recovery from the VBNC state. Finally, the major methods for the detection of bacteria in the VBNC state are discussed, including molecular biological methods, flow cytometry, and optical microscopy. Molecular biological methods have been widely used in the detection of bacteria in the VBNC state due to their advantages of accuracy, rapidity and high sensitivity. This review provides more ideas for further research on the induction, resuscitation and detection of foodborne pathogens in the VBNC state.

Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae（Xoo） and bacterial leaf streak of rice caused by Xanthomonas oryzae pv. oryzicola（Xoc） are two important bacterial diseases of rice.Identification of Xoo and Xoc belonging to the same species is critical for quarantine and control the diseases.Here, we found that the gene fhuE encoding ferric-rhodotorulic acid/ferric-coprogen receptor in Xoo and Xoc became pseudogenes after partial deletion during evolution. We designed Xoc-specific primers XocFhuE-F（5’-ATCGAACGATGTCACCAGGG-3’） and XocFhuE-R（5’-AGAAACGTGCGGCCAGATAA-3’） targeting the sequences present in the Xoc fhuE pseudogene but absent in the Xoo fhuE pseudogene. Polymerase chain reaction（PCR） amplification produced only a 159 bp DNA fragment from only Xoc strains using the primers XocFhuE-F/XocFhuE-R. Based on the Xoc-specific primers, we developed SYBR Green quantitative real-time PCR（qPCR） and EvaGreen droplet digital PCR（dPCR） methods to detect and identify Xoc. In a 20 μL reaction system with 1 μL of template, the detection limit of qPCR on Xoc was 1.6×10~4 CFU/mL in bacterial suspension and 1.2×10~3 CFU/seed in rice seeds; the detection limit of dPCR on Xoc was 1.6×10~3 CFU/mL in bacterial suspension and 1.2×10~2 CFU/seed in rice seeds. In conclusion, SYBR Green qPCR and EvaGreen dPCR based on the Xoc-specific primers XocFhuE-F/XocFhuE-R provide effective methods for quarantine of Xoc and monitoring of the bacterial leaf streak disease of rice.

Objective To study the rapid identification of freezing-thawing meat by stoichiometry combined with low field nuclear magnetic resonance（LF-NMR）.Methods CPMG sequences were selected by LF-NMR to collect 111 NMR signals from pork tenderloin. Through the inversion of NMR signal data, four principal components were extracted from 12variables by principal component analysis, and the discriminant research model was established.Results According to the analysis of fresh meat, slightly freezing-thawing meat and freezing-thawing meat, the accuracy of the model was 95. 5%verified by back generation method, and it was 94. 6% by cross-verification.Conclusion LF-NMR is simple and rapid, and can be used for discriminant analysis of freezing-thawing meat, which provides a reliable and effective basis for the supervision department.