实时荧光PCR法检测食品和饮料中胡萝卜成分的研究

胡萝卜是一种质脆味美的家常蔬菜,同时也是一种常见的食品过敏原。针对胡萝卜抗冻蛋白基因的保守序列,设计特异性引物和探针,经验证和条件优化,建立胡萝卜成分的实时荧光PCR检测方法。经实验比较,针对胡萝卜抗冻蛋白设计合成的引物和探针具有相对较高的灵敏性,检测限可达1 ng DNA,而且和常见的食物种类无交叉反应,适于胡萝卜成分的检测。该方法的建立,对于加强食品过敏原的标识管理,保护消费者利益、促进进出口贸易具有重要意义。     

食品中杏仁过敏原成分的检测

目的：建立检测食品中桃仁、杏仁过敏原成分的荧光PCR 方法,比较国外3 种ELISA 试剂盒效果。方法：针对杏仁Pru du1 基因设计引物及探针,建立荧光PCR 方法。利用杏仁过敏原参考物质对3 个品牌的ELISA试剂盒的回收率进行比较。结果：建立的荧光PCR 方法,具有很好的特异性;灵敏度为10mg/kg。结论：桃仁及杏仁过敏原成分荧光PCR 检测方法特异性好、灵敏度高,对食品中过敏原的检测有重要的实际意义。     

小麦和榛子过敏原成分检测的实时荧光PCR方法

过敏原风险问题已成为重要的食品安全问题,如何快速准确地检测出食物中的过敏原成为当前亟需解决的关键。目前常用的过敏原检测方法有免疫学检测、质谱及SPR等技术,但这些方法均有一定程度的局限性。通过引入分子生物学鉴定手段,建立小麦、榛子的过敏原基因数据库,并依据数据库寻找特异性序列并设计探针引物,建立一种快速、便捷、高效的过敏原检测方法,并适当调整了方法的检出限,降低了检测误判的风险。通过建立实时荧光PCR方法,可快速筛选样品的过敏原基因,简化了食品中过敏原成分的鉴定,降低了实验成本与技能要求,降低了检测的难度,缩短了实验时间。通过适用性验证与检出限验证实验,该方法用于过敏原成分鉴定可以达到理想的效果,重复性好,准确率高,检出限为1%。     

基于多重连接探针扩增技术的食品中六重过敏原成分检测

基于多重连接探针扩增（multiplex ligation-dependent probe amplification,MLPA）技术建立了一种六重过敏原成分检测方法,可实现食品中大豆、芝麻、花生、杏仁、榛子和核桃6种成分的同时检测。选取多拷贝ITS基因为靶标基因,设计并合成6组特异性杂交探针。探针经杂交、连接和聚合酶链式反应得到扩增片段,经毛细管电泳分析扩增片段大小可明确区分6种过敏原成分。该体系经20余种相关植物、动物及微生物DNA验证显示其特异性良好,经模拟参考样品验证其检出限为5 mg/kg。30份不同种类市售食品MLPA检测结果表明,该方法性能满足实际样品的过敏原的多重检测。因此,本研究建立的基于MLPA技术的六重过敏原检测方法特异性强、灵敏度高,能够为食品过敏原评估、标识管理和风险控制提供技术支撑。     

基于多重连接依赖探针扩增（MLPA）技术检测加工食品中过敏原成分

该研究基于多重连接探针扩增技术（Multiplex Ligation-dependent Probe Amplification,MLPA）同时检测开心果、巴西坚果、芹菜、麸质、夏威夷果、芝麻、榛子、大豆、花生、葵花籽、核桃、腰果、杏仁、芥末等14种植物源性的过敏原成分,针对ITS序列设计特异性杂交探针,样本核酸经95 ℃变性后,与探针进行特异性结合,经连接和PCR扩增反应得到不同大小的目标片段,通过毛细管电泳分析目标片段的有无来判断是否含有待测过敏原成分。利用混合探针体系检测单一模板只能扩增出单一扩增峰,表明探针具有高特异性,检测限结果表明,MLPA扩增最低可检出的DNA质量浓度为1 ng/μL。通过20份实际样本的检测,证明该研究基于MLPA建立的加工食品中过敏原成分的检测方法,具有特异性强,灵敏度高的特点,可以应用于食品安全监管工作。     

可视化膜芯片技术检测常见食源性过敏原成分

目的 建立包括鱼、虾、鸡、鸭、花生、核桃、小麦以及大豆过敏原成分的基因膜芯片技术, 实现对这几种食源性过敏原的同步可视化检测。方法 针对常见食源性过敏物质的成分特异性基因或者过敏原蛋白基因设计特异性的带生物素标记的引物和探针。采用反向斑点杂交(reversedot blot, RDB)结合多重聚合酶链式反应(multiplex polymerase chain reaction, MPCR)技术, 最终通过化学显色直观显示检测结果, 实现对多种食源性过敏原的同步可视化检测。结果 所建立的可视化基因膜芯片方法准确性强, 通过单目标物以及多目标物特异性实验, 显示本方法仅对鱼、虾、花生、核桃、大豆等靶标食源性过敏原有特异性反应, 非靶标物检测均为阴性; 通过制备不同质量浓度比的模拟样品考核方法的灵敏度, 经检测, 方法检测灵敏度可达0.1%(质量分数)。结论 所建立的方法可达到可视化、快速、准确地鉴别食品中鱼、虾、花生、核桃、大豆等常见食源性过敏原。     

实时定量PCR技术检测食品中花生过敏原Ara h1基因成分

采用Taqman探针PCR技术,建立食品中花生主要过敏原基因Ara h1的检测方法.根据GenBank提供的Ara h1基因(序列号AF432231)中一段DNA序列设计特异性引物与Taqman探针,扩增该目的基因,建立拷贝数-CT标准曲线,可通过标准曲线方程计算食品中含有花生主要过敏原Ara h1基因拷贝数(copies),并用于检测8种食品中是否含有残留的该过敏原基因.此标准曲线在1.5×103copies～1.5×107copies范围内线性关系良好,R2值为0.9759;8种样品检测结果与食物过敏原标注内容相一致.     

质谱方法在过敏原研究中的应用

食品过敏已经成为全球范围内重要的食品安全问题,迫切需要高灵敏度、高特异性的方法对食品中的过敏原进行快速、可靠的检测。检测食品中过敏原最常用的是核酸的方法和酶联免疫的方法,质谱技术的发展,为过敏原的研究提供了新的手段。质谱分析具有灵敏度高、样品用量少、分析速度快等优点,因此,质谱方法逐渐应用于食品过敏原的检测。本文从榛子、花生和牛奶角度,总结质谱技术在过敏原检测中的一些应用。     

食品中马源性成分的实时荧光PCR检测

针对马线粒体DNA细胞色素b基因设计特异性引物和探针,建立食品中马源性成分实时荧光PCR检测方法,并经特异性和灵敏度试验验证其可行性。结果表明:该体系可扩增马DNA片段,长度为127 bp,其他常见畜、禽肉成分均无法正常扩增。该体系的检测灵敏度为1.25 pg马DNA和质量分数0.001%马肉粉。经市售食品的检测验证,表明所建立的马引物探针体系具有特异性好、灵敏度高、快速、高效等优点,可用于对食品中马源性成分的掺假鉴别检测。     

食品过敏原羽扇豆成分的环介导等温扩增 检测方法

目的 建立食品过敏原羽扇豆成分的环介导等温扩增(LAMP)检测方法。方法 根据羽扇豆的ITS基因设计羽扇豆的特异性引物,进行特异性、灵敏度、稳定性测试,建立LAMP检测方法。结果 本文建立的食品过敏原羽扇豆成分LAMP检测方法能有效对羽扇豆成分进行快速检测,具有较强的特异性和稳定性,灵敏度可达0.001%(w/w)羽扇豆粉。结论 该方法特异性强,灵敏度高,可以快速、准确检测食品中过敏原羽扇豆成分。     

荧光定量PCR方法检测榛果过敏原成分

目的建立榛果过敏原成分的荧光定量PCR检测方法,并将此方法与酶联免疫吸附法(enzyme-linked immunosorbent assay,ELISA)方法进行比对实验。方法根据榛果成分oleosin特异性基因设计并筛选合适的引物和探针,优化反应体系和反应条件,建立榛果过敏原成分的荧光定量PCR检测方法,对荧光定量PCR方法与ELISA方法检测结果进行分析。结果建立的榛果过敏原成分荧光定量PCR方法特异性良好,可用于榛果过敏原成分的定量检测,但检测灵敏度低于ELISA检测方法。结论所建立的榛果过敏原成分的荧光定量PCR检测方法特异性好,灵敏度达到10 mg/kg,具有较好的实用性,ELISA检测方法灵敏度高于荧光定量PCR法,但当榛果过敏蛋白被破坏后有可能出现假阴性结果。     

Detection of hazelnut proteins in foods by enzyme immunoassay using egg yolk antibodies

An enzyme immunoassay (EIA) was developed for the detection of hazelnut proteins in foods. This assay used inexpensive chicken egg yolk antibodies in a sandwich EIA format for the immunospecific capture and detection of hazelnut proteins present in a variety of different food matrices. The assay was able to detect less than 1 ppm of hazelnut protein in most of the foods tested and did not exhibit any appreciable cross-reactivity with other nuts or food matrices. This assay will be a useful tool for the food industry and regulatory agencies that wish to test foods for the presence of undeclared hazelnut allergens.     

Hazelnut Allergens: Molecular Characterization,Detection, and Clinical Relevance

In last few years, special attention has been given to food-induced allergies, in which hazelnut allergy is highlighted. Hazelnut is one of the most commonly consumed tree nuts, being largely used by the food industry in a variety of processed foods. It has been regarded as a food with potential health benefits, but also as a source of allergens capable of inducing mild to severe allergic reactions in sensitized individuals. Considering the great number of reports addressing hazelnut allergens, with an estimated increasing trend, this review intends to assemble all the relevant information available so far on the following main issues: prevalence of tree nut allergy, clinical threshold levels, molecular characterization of hazelnut allergens (Cor a 1, Cor a 2, Cor a 8, Cor a 9, Cor a 10, Cor a 11, Cor a 12, Cor a 14, and Cor a TLP) and their clinical relevance, and methodologies for detection of hazelnut allergens in foods. A comprehensive overview of the current data about the molecular characterization of hazelnut allergens is presented, relating to biochemical classification and biological function with clinical importance. Recent advances in hazelnut allergen detection methodologies are summarized and compared, including all the novel protein-based and DNA-based approaches.     

A food matrix reduces digestion and absorption of food allergens in vivo

Scope: Food allergy is caused by primary (class 1) food allergens, e.g. Bos d 5 (cow's milk) and Cor a 8 (hazelnut) or secondary (class 2) food allergens, e.g. Mal d 1 (apple). The latter cannot sensitize susceptible individuals but can cause allergy due to immunological cross‐reactivity with homologous respiratory allergens. Here, we studied the effects of food matrix on gastrointestinal proteolysis, epithelial transport and in vivo absorption of class 1 and class 2 food allergens. Methods and results: Mal d 1 lost its IgE‐reactivity immediately after simulated gastric digestion whereas Bos d 5 and Cor a 8 did not. Only Cor a 8 maintained IgE‐binding capacity after simulated intestinal proteolysis. The presence of hazelnut and peanut extracts, which served as protein‐rich model food matrices, delayed gastrointestinal degradation and reduced epithelial transport rates of all allergens through CaCo‐2 monolayers. Finally, IgE‐reactive allergens were assessed at different time points in sera from rats fed with all three allergens with or without hazelnut extract. The levels of all allergens peaked 2 h after animals were fed without matrix and increased over 8 h after feeding. Conclusions: A protein‐rich food matrix delays gastrointestinal digestion and epithelial transport of food allergens and thereby may affect their sensitizing capacity and clinical symptoms.     

Peanut and hazelnut traces in cookies and chocolates: Relationship between analytical results and declaration of food allergens on product labels

Accidental exposure to hazelnut or peanut constitutes a real threat to the health of allergic consumers. Correct information regarding food product ingredients is of paramount importance for the consumer, thereby reducing exposure to food allergens. In this study, 569 cookies and chocolates on the European market were purchased. All products were analysed to determine peanut and hazelnut content, allowing a comparison of the analytical results with information provided on the product label. Compared to cookies, chocolates are more likely to contain undeclared allergens, while, in both food categories, hazelnut traces were detected at higher frequencies than peanut. The presence of a precautionary label was found to be related to a higher frequency of positive test results. The majority of chocolates carrying a precautionary label tested positive for hazelnut, whereas peanut traces were not be detected in 75% of the cookies carrying a precautionary label.     

Isolation,cloning, and characterization of the 2S albumin: A new allergen from hazelnut

Scope: 2S albumins are the major allergens involved in severe food allergy to nuts, seeds, and legumes. We aimed to isolate, clone, and express 2S albumin from hazelnut and determine its allergenicity. Methods: 2S albumin from hazelnut extract was purified using size exclusion chromatography and RP‐HPLC. After N‐terminal sequencing, degenerated and poly‐d(T) primers were used to clone the 2S albumin sequence from hazelnut cDNA. After expression in Escherichia coli and affinity purification, IgE reactivity was evaluated by Immunoblot/ImmunoCAP (inhibition) analyses using sera of nut‐allergic patients. Results: N‐terminal sequencing of a ～10 kDa peak from size exclusion chromatography/RP‐HPLC gave two sequences highly homologous to pecan 2S albumin, an 11 amino acid (aa) N‐terminal and a 10aa internal peptide. The obtained clone (441 bp) encoded a 147aa hazelnut 2S albumin consisting of a putative signal peptide (22 aa), a linker peptide (20 aa), and the mature protein sequence (105 aa). The latter was successfully expressed in E. coli. Both recombinant and natural 2S albumin demonstrated similar IgE reactivity in Immunoblot/ImmunoCAP (inhibition) analyses. Conclusion: We confirmed the postulated role of hazelnut 2S albumin as an allergen. The availability of recombinant molecules will allow establishing the importance of hazelnut 2S albumin for hazelnut allergy.     

Cloning of oleosin, a putative new hazelnut allergen, using a hazelnut cDNA library

The clinical presentation of non-pollen related allergy to hazelnut can be severe and systemic. So far, only a limited number of non-pollen related hazelnut allergens have been identified and characterized. The aim of this study was to identify and clone new hazelnut allergens. A lambda ZAP cDNA library of hazelnut was constructed. The library was screened with serum of six hazelnut allergic patients displaying different IgE-binding patterns on hazelnut immunoblot. Rapid amplification of cDNA ends (RACE) protocols were applied to obtain full-length clones. Expression experiments were carried out in Eschericchia coli. Expression was monitored by SDS-PAGE, protein staining and immunoblotting. A hazelnut cDNA library was constructed. IgE screening resulted in the cloning of two isoforms of a novel putative hazelnut allergen. The clones were identified as oleosins, with theoretical molecular masses of 16.7 and 14.7 kDa and pI of 10.5 and 10.0, respectively. The isoforms demonstrated only 37% amino acid sequence identity but contained the typical hydrophobic stretch in the middle of the protein (53% identity) with the characteristic oleosin proline knot region (11/12 amino acids identical). Expression in E. coli of the longer isoform resulted in a clear band on SDS-PAGE. The expressed protein was recognized on an immunodot blot by IgE from serum that was used for screening the cDNA library. Hazelnut contains multiple isoforms of oleosin. IgE binding of a hazelnut-allergic patient to a recombinant version suggest that hazelnut oleosin is an allergen, as has been described for peanut and sesame.     

Optical thin-film biochips for multiplex detection of eight allergens in food

An innovative method for the rapid detection of food allergens is developed and validated. Here we reported the development of silicon-based optical thin-film biochip technology that simultaneously permits visible detection of eight food allergens including celery, almond, oat, sesame, mustard, lupine, walnut and hazelnut on the basis of two tetraplex PCR systems. The biochip detection time was about 30 min after PCR amplification. Briefly, the optical thin-film biochip detects the presence of PCR fragment targets by enzymatically converting the formation of nucleic acid hybrids to molecular thin films. The mass contributed by the thin film alters the interference pattern of light on the biochip surface, resulting in a visible color change on the chip surface. Therefore, this assay permits sensitive, specific and high-throughput detection of allergens in food samples.     

Expression and characterization of three important panallergens from hazelnut

Several hazelnut allergens with different clinical relevance and crossreactive properties have been identified and characterized so far. The aim of this study was to develop protocols for producing relatively large amounts of three recombinant hazelnut allergens Cor a 1.04, Cor a 2, and Cor a 8 in a folded and immunologically active form. The availability of well-characterized, pure recombinant allergens will improve diagnostic in vitro tests for food allergy, by allowing a highly sensitive component resolved diagnosis. Depending on the individual hazelnut allergen, protocols for heterologous production - either as fusion or nonfusion protein - were developed to obtain homogenous protein batches. The resulting proteins were purified by a two-step FPLC method and their IgE antibody reactivity was verified. Identity was verified by N-terminal sequencing and MALDI-TOF-MS analysis. Their secondary and tertiary structure was controlled by circular dichroism (CD)-spectroscopy and NMR analysis. Decisions on the strategies for expression and purification of allergens on a large scale were made on a case by case basis: Preparation of rCor a 1.04 and rCor a 2 as fusion proteins in E. coli from inclusion bodies resulted in approximately 10 mg pure protein per liter whereas rCor a 8 expression in yeast as nonfusion protein yielded 30 mg/L.