Yajun Wu

Chinese Academy of Inspection and Quarantine, Peping, Beijing, China

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Publications (21)31.45 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: An electrochemical DNA biosensor for the detection of ssDNA sequence related to transgenic maize MON810 was fabricated with an electrochemical reduced graphene (ERG) modified carbon ionic liquid electrode (CILE) as the working electrode and methylene blue (MB) as the hybridization indicator. The probe ssDNA sequence was immobilized on the surface of ERG/CILE through electrostatic adsorption and the presence of ERG increased the adsorption amounts of probe ssDNA sequence on the electrode, which resulted in the corresponding increase of the reduction peak current of MB. Under the optimal conditions differential pulse voltammetric responses of MB were proportional to the concentration of target ssDNA sequences in the range from 1.0 × 10−11 to 1.0 × 10−6 mol/L with the detection limit as 4.52 × 10−12 mol/L (3σ). The sensor was further used for the detection of PCR products of transgenic maize samples with satisfactory results, which exhibited the advantages including simple and rapid procedure with the practical application.
    Sensors and Actuators B Chemical 10/2014; 202:160–166. · 3.84 Impact Factor
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    ABSTRACT: Edible Bird's nests (EBN) have been adulterated with less expensive materials, including white fungus, agar–agar, fried pigskin, egg white and red seaweed, for several years. To protect consumers and regulate the EBN market, it is necessary to establish a robust method for detecting these adulterants in EBN. Herein, we established a TaqMan-based real-time polymerase chain reaction (PCR) assay to specifically detect EBN component and four common adulterants: white fungus, agar, pigskin and egg white. Therefore, five sets of primers and probes were designed for these five components. The assays were specific and reproducible, and the relative detection limits were 0.5% EBN in white fungus, 0.001% white fungus in EBN, 0.5% agar in EBN, 0.001% fried pigskin in EBN and 1% egg white in EBN. These detection levels are capable of effectively detecting the adulterants in commercial samples.
    Food Control 10/2014; 44:220–226. · 2.74 Impact Factor
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    ABSTRACT: Among food allergens, walnut is a frequent cause of adverse food reactions in allergic patients. In this study, the walnut allergen protein 2S albumin precursor (Jug r 1) cDNA was synthesised and cloned into the pGEX-6P-1 expression vector. The recombinant plasmids were transformed into Escherichia coli (E. coli) BL21(DE3) pLys for expression of protein Jug r 1. Polyclonal antibodies were prepared against the expressed purified Jug r 1 protein. An indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of walnut soluble proteins in processed foods was developed using the prepared polyclonal antibodies. The developed ELISA had a high specificity, walnut protein standard solution at 2.2ng/mL [inhibition concentration (IC80) of the competitive test] was clearly identified by the ELISA. The mean recoveries ranged from 86% to 112%. The coefficient of variation (CV) for the 4 model foods was 6.4-8.7%.
    Food Chemistry 03/2014; 147C:106-110. · 3.33 Impact Factor
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    ABSTRACT: A useful procedure for the qualitative determination of edible vegetable oils adulteration has been developed. A CE-SSCP (Capillary Electrophoresis-Single Strand Conformation Polymorphism) method based on PCR (Polymerase-Chain-Reaction) technology was established to distinguish olive, soybean, sunflower, peanut, sesame, maize and corresponding edible oils, which are the most common edible oils in China. Two rbcL (ribulose 1,5-bisphosphate carboxylase large subunit) gene fragments were amplified from these 6 oil plants by 2 pairs of universal primers (uni4 and rbcl1) respectively and the amplicons were identified by CE-SSCP on ABI 3100 automatic sequence analyzer. Six oil plants were successfully differentiated by combined pattern of uni4 and rbcl1. Sensitivity of the method detecting DNA and oil mixture at different ratio was at level as low as 10% (V/V). The method developed was very suitable for the determination of modeled adulterants but it may also reveal an adulteration even if it does not derive from the adulterants employed in this study.
    Food Control. 10/2012; 27(2):322–329.
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    ABSTRACT: To provide accurate and fast method for labeling regulation on fruit juice, conventional PCR, real-time PCR and DHPLC techniques were explored in this study to detect ingredient from 7 fruit species. ITS1-5.8S-ITS2, TrnL-TrnF from chloroplast genome and thaumatin-like protein gene from nucleus genome were targeted. Sensitivity of 6 primer (probe) pairs was determined to be 1–10 pg DNA. Orange and mandarin were universally amplified by the same primer pair and the 8 bp divergence of PCR products could be differentiated by DHPLC analysis. 30 Fruit samples collected from local market were tested and no mislabeling was discovered.
    Food Control. 06/2012; 25(2):696–703.
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    ABSTRACT: Species adulteration of vegetable oils has become a main form of adulteration in vegetable oils, severely violating consumer rights and causing disorder in the market. A reliable method of species authentication of vegetable oils is desirable. This paper reports a novel method for identification of seven species of vegetable oils based on suspension bead array. One pair of universal primers and seven species-specific probes were designed targeting rbcl gene of the chloroplast. Each probe was coupled to a unique color-coded microsphere. Biotinylated PCR amplicons of seven oils were hybridized to the complementary probes on microsphere sets. Bound amplicons were detected fluorometrically using a reporter dye, streptavidin-R-phycoeryt hrin (SA-PE). A sample could be analyzed less than 1 h after PCR amplification. With the exception of olive probe, all probes showed no cross-reactivity with other species. Absolute detection limit of the seven probes ranged from 0.01 ng/μL to 0.0001 ng/μL. Detection limit in DNA mixture was from 10% to 5%. Detection of vegetable oils validated the effectiveness of the method. The suspension bead array as a rapid, sensitive, and high-throughput technology has potential to identify more species of vegetable oils with increased species of probes.
    Journal of Agricultural and Food Chemistry 03/2012; 60(9):2362-7. · 3.11 Impact Factor
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    ABSTRACT: Grain purity is of great interest to malting barley trader and beer producer. DNA typing method has been applied for this purpose, but typically, single grain was tested and the procedure was expensive, laborious, and time-consuming. This study first reported fast semi-quantification of cereal seed by DNA test of blended sample. It was helpful for rapid screening of large amount of samples. Particularly, RAPD and 2100 bio-analyzer were combined to determine the purity range of malting barley grain taking advantage of mathematical linear relationship between concentration of marker bands and grain purity. Statistical analysis of 11 independent assays resulted in quantitative parameters for each RAPD marker band. Test of 14 samples using the fast method showed an average of 11% deviation to rated value. Protein profiling method helped to distinguish cultivars which were of identical RAPD pattern. Quantification by protein profile was also explored.
    European Food Research and Technology 01/2012; 234(3). · 1.39 Impact Factor
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    ABSTRACT: Among food allergens, celery is a frequent cause for adverse food reactions in allergic patients. In this study, the celery allergen protein Api g 1.01 RNA was amplified by RT-PCR and cloned into the pET-32a expression vector. The recombinant plasmid was transformed into E.coli BL21(DE3) pLys for the expression of protein Api g 1.01. Monoclonal antibodies were prepared against the expressed purified Api g 1.01 protein. A sandwich enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of celery soluble proteins in processed foods was developed using the prepared monoclonal antibodies. The developed ELISA had a high specificity, although it showed slight cross-reactivity to carrot. The limit of quantification (LOQ) was 0.28 μg/mL (equivalent to 5.6 μg whole celery protein/g food sample). The recovery ranged from 83 to 115%, whereas coefficients of variation were 6.7–8.9%.
    European Food Research and Technology 12/2011; 233(6). · 1.39 Impact Factor
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    ABSTRACT: Food allergies are important food safety issues nowadays. To maintain the safety of people who experience allergic reactions, labeling is required in many countries and efficient and reliable detection methods are necessary. This paper reports a novel method for the rapid identification of food allergens through the use of a silicon-based optical thin-film biosensor chip with which color change results can be perceived by the naked eye without any extra equipment. The whole system can detect eight food allergens including soybean, wheat, peanut, cashew, shrimp, fish, beef, and chicken simultaneously. Sensitive and specific detection of the absolute detection limit of this method was 0.5 pg of cashew DNA, and the practical detection limit of 0.001%. The biosensor chip detection time was about 30 min after PCR amplification. The assay is proposed as a sensitive, specific, high-throughput, and ready-to-use analytical tool to detect the presence or confirm the absence of eight food allergens.
    Journal of Agricultural and Food Chemistry 06/2011; 59(13):6889-94. · 3.11 Impact Factor
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    ABSTRACT: Olive oil adulteration with other cheap oil species has long been upsetting the industry, consumer, and authority around the world. In this article, we first reported the application of PCR-CE-SSCP method to detect other oil species in olive oil. The method was proved to be fast, accurate, reproducible, and interpretation easy. SSCP profiles of 7 oil species were all characterized by single amplicon peak which differentiate olive and the other plants distinctly. The method detection limit was less than 10% of other plant DNA blended with olive DNA. The practical limit for oil was 30–50% refined soybean oil in olive oil. KeywordsPCR-CE-SSCP–Other oil–Olive oil–Detect
    European Food Research and Technology 01/2011; 233(2):313-324. · 1.39 Impact Factor
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    ABSTRACT: Celery was found to provoke human allergenic response in some countries. Labeling of celery ingredients was required by the European Union, and the threshold set at 10 mg/kg (0.001%). In our study, a celery mannitol transporter (Mat3) gene-based detection method was established by means of SYBR Green real-time PCR technique. No cross-reactivity was found between celery and the other food materials. Absolute detection limit (LODa), relative detection limit (LODr), and practical detection limit (LODp) of the method were determined through experiments on pure celery DNA, DNA mix, and spiked food samples. The method was able to detect 0.001% raw food sample and 0.01% heated food sample. The utility of the method was confirmed by the investigation of 13 commercial foods.
    Journal of AOAC International 01/2010; 93(5):1530-6. · 1.23 Impact Factor
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    ABSTRACT: Edible bird's nest (EBN) as a special kind of food tonic has been highly esteemed in Chinese cuisine and medicinal culture. Particularly with the discovery of its healthy function by modern science, consumption of EBN food gained greater popularity within Chinese community and outside. Authentication of this precious and expensive food material became an urgent task facing the increasing occurrence of adulteration in the market. Herein we reported the combination of DNA based PCR and protein based two dimensional gel electrophoresis (2DGE) methods for rapid and reliable identification of genuine EBN product. Fourteen EBN samples from different countries were studied. PCR method was proved to be able to differentiate EBN and the other biological materials and it could detect EBN ingredient from 0.5% EBN/Tremella fungus mixture. 2DGE method was proved to be feasible and versatile in EBN identification because of the simple and unique protein pattern of EBN. The method could detect 10% Tremella fungus from EBN.
    Food Research International. 01/2010; 43(8):2020-2026.
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    ABSTRACT: A real-time PCR method aimed at the gene sequence of the walnut vicilin-like seed storage protein was established for the detection of the allergen walnut in food. The primers and probe were designed based on published methods. The method provided positive results for walnut and negative results for other tested agricultural plant materials including pecan. The intrinsic detection limit of the method was 0.00125 ng of walnut DNA, and the practical detection limit was 0.001% (wt/wt) walnut content in wheat; both of these values are lower than that of previously published methods. Therefore, this real-time PCR method is sufficiently specific and sensitive for the detection of walnut component in food.
    Journal of food protection 11/2009; 72(11):2433-5. · 1.83 Impact Factor
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    ABSTRACT: Lycoriella pleuroti is a pest of edible fungi, commonly cultured on a cottonseed shell–based medium. L. pleuroti larvae were reared on culture media containing variety CRI30 (transgenic Bacillus thuringiensis [Bt]) cottonseed, variety CRI16 (nontransgenic) cottonseed, Bt (CryIAc) protein, gossypol, tannin, and quercetin. The mortality of larvae reared on media with CRI30 cottonseed was significantly higher than that of larvae reared on media with CRI16 cottonseed, and mortality increased with increasing CRI30 and CRI16 cottonseed content. Media containing Bt protein, gossypol, tannin, and quercetin negatively influenced survival of L. pleuroti larvae. Of the four ingredients, the negative effects of gossypol and tannin were the largest. The suppression caused by the Bt protein was not as great and did not increase with increasing dose. The presence of quercetin also increased larval mortality over the control, but mortality decreased with increasing quercetin content.
    Environmental Entomology 10/2009; · 1.31 Impact Factor
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    ABSTRACT: Multiplex PCR–CE–SSCP approach was used to identify foodborne pathogens. 16srRNA system including three target fragments localized at different position of 16srRNA gene and gyrB system including two target fragments at gyrB gene were established. SSCP profile was analyzed in a similar way as RAPD and the identity of each peak was determined by relative position to inner standard. Twenty-five reference bacteria strains representing 2 classes, 12 genus and 19 species were tested. All bacteria could be distinctly determined at genus level by 16srRNA system. GyrB system improved discriminating resolution of some bacterial at species level. Phylogenetic analysis showed that 16srRNA based phylogenetic relationship was consistent with traditional classification of these organisms. Good reproducibility and resolution make multiplex PCR–CE–SSCP protocol a promising approach for fast screening of foodborne pathogens.
    European Food Research and Technology 01/2009; 228(4):511-518. · 1.39 Impact Factor
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    ABSTRACT: Differentiating pasteurized milk and reconsti-tuted milk by scientific approach was necessary to defend consumer from economic fraud of wrong labeling. In this paper 2DGE (2 Dimen-sional Gel Electrophoresis)-coomassie brilliant blue staining method was employed and sig-nificant color intensity changing was observed among raw milk, pasteurized milk, UHT milk and reconstituted milk. For example, the intensity of 10 protein spots including casein and lac-toglobulin reduced more than two folds from pasteurized milk to reconstituted milk. However, DIGE (Differential Gel Electrophoresis) assay showed that the majority protein remained simi-lar level from pasteurized milk to reconstituted milk. Therefore the color fading of coomassie brilliant blue stained 2D gels may be due to other biochemical reaction, such as Maillard reaction, instead of protein degradation. Stability of 2DGE pattern was confirmed by running six gels of the same sample in parallel and software analysis showed that all proteins were at similar level. Two commercialized pasteurized milk samples and one reconstituted milk sample were tested by 2DGE-coomassie blue staining method and re-constituted milk could be easily identified.
    01/2009; 1:146-151.
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    ABSTRACT: A real-time qualitative and quantitative polymerase chain reaction method (cer-194) using the fluorescence dye EvaGreen and aimed at the cytochrome b sequence was established for detection of cervidae DNA in feedstuff. Eight meat meal samples derived from deer, bovine, ovine, camel, pig, rabbit, fish, and chicken and 17 cervidae hair samples covering 2 subfamilies, 4 genera, and 7 species were tested to prove the specificity of the cer-194 system and its universality within the cervidae family. Detection limit of 0.1% deer meat in fish meal, blood powder, and feather powder matrixes was confirmed.
    Journal of AOAC International 01/2009; 92(1):175-80. · 1.23 Impact Factor
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    ABSTRACT: A sensitive real-time PCR method using the novel fluorescence stain Evagreen was established for detection of olive oil. First, a comparative study was made of two different methods for the recovery of high quality DNA from oil samples. Thereby, the Promega wizard DPSF kit proved to be the most suitable for recovery of DNA from oil samples. Second, an olive-specific pair of primers was designed based on the sequence of an olive plasma intrinsic protein cDNA sequence. Experiments with 13 samples including olive, soybean, sesame, sunflower seed, pumpkinseed, walnut, rapeseed, rice, peanut, maize, pig, chicken and fish confirmed that this pair of primers is highly specific for olive. Additional experiments indicated that the absolute detection limit of our test is 0.07ng olive DNA and that 0.5% olive DNA can be detected against background of 2ng/μl sesame DNA.
    European Food Research and Technology 08/2008; 227(4):1117-1124. · 1.39 Impact Factor
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    ABSTRACT: There were differences of peroxidase isozyme patterns between the tissues of Pleurotus ostreatus cultured with non-transgenic cottonseeds and transgenic cottonseeds, but differences also existed among the tissue of P. ostreatus cultured with different varieties and amount of cottonseeds, and among the tissue from varieties of P. ostreatus. Differences of peroxidase isozyme between tissues cultured with non-transgenic cottonseeds and those cultured with transgenic cottonseeds were similar to the differences between tissues cultured with different varieties and amounts of cottonseed, and not larger than the differences between the tissues from different varieties of P. ostreatus. The results suggest that the effect of transgenic cottonseed on the peroxidase isozyme of P. ostreatus were not larger than the effects of different varieties of cottonseed and different varieties of P. ostreatus.
    Food Control. 01/2007; 18(4):281-286.
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    ABSTRACT: So far royal jelly (RJ) has been widely used as a kind of popular and traditional food for health promotion. However, the quality of RJ is vulnerable to improper storage conditions. In order to prohibit the low quality RJ products entering the market and consequently affect the health of humans, it is necessary to define the quality parameters and establish corresponding detection methods for the freshness of RJ. In this research, we applied two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight mass spectrometry to research major royal jelly proteins (MRJPs) changes under different storage conditions after 6-month storage, looking for a stable and reliable protein marker which was also feasible to detect the freshness of RJ. Further research with the help of Western blotting analysis (WB) confirmed that, under room temperature, MRJP5 began to hydrolyze within 30 days and would completely degrade within 75 days, indicating that MRJP5 can be adapted as a freshness marker for RJ products. Moreover, the assessment results of the freshness of 12 commercial RJ products with WB showed that MRJP5 was present in twelve RJ samples at different abundance levels which further confirmed the detection of MRJP5 could be a feasible method to assess the quality and freshness of commercial RJ products.
    European Food Research and Technology 236(5). · 1.39 Impact Factor