Commercial soybean lecithins: a source of hidden allergens?

 Soybeans are known to be allergenic for adults as well as for infants. Processed products derived from soybeans are used in a wide spectrum of foods, drugs and other industrial products. In particular, soybean lecithins are used as stabilizers and emulsifiers and may not be suspected as possible source of allergens. To test this hypothesis, six commercial soy lecithins were investigated for residual allergenicity and compared with extracts from raw and heat-treated soybeans. They were characterized, the protein content was determined by enzyme-linked immunosorbent assay (ELISA) and allergens were analyzed with specific IgE from patients' sera using the enzyme allergosorbent test (EAST), EAST inhibition and protein blotting followed by immunodetection. For further characterization a polyclonal antiserum directed against soybean extract and a monoclonal antibody (mAb 025) directed against the acidic subunit of the soybean storage protein glycinin were used. The EAST studies revealed that three of six sera from patients with allergy to soybeans contained IgE to four soy lecithins (Topcithin 50, Topcithin 300, Emulfluid FD 12, Epikuron 100 P), the same lecithins which were found to contain residual proteins. Two lecithins with a protein content of less than 20 ppb did not bind IgE. EAST inhibition showed that the allergens from soy lecithin were immunologically more closely related to allergens from heat-treated soybeans than to those from raw soybeans. Protein blotting and immunodetection of the protein extract from the lecithins resulted in various allergen bands between 14 kDa and 94 kDa. A heat-stable allergen of 39 kDa was recognized by the monoclonal antibody and thus identified as a subunit of glycinin. The results obtained were confirmed by a mediator release assay based on a rat basophil leukemia cell line. Lecithins that contained residual proteins caused a specific mediator release, suggesting that these products may induce allergic symptoms. Our results show that soybean lecithins are capable of introducing hidden allergens to processed foods and that the IgE binding potential corresponds to the total protein determined by ELISA. Furthermore, it appears to be possible that by monitoring the protein content soy lecithins can be applied which may be safe for the allergic consumer. Received: 22 January 1998     

High-resolution Orbitrap™-based mass spectrometry for rapid detection of peanuts in nuts

Peanut represents one of the most harmful allergenic foods capable of triggering severe and sometimes lethal reactions in allergic consumers upon ingestion of even small amounts. Several proteins capable of inducing allergic reactions that have been recognised by patients’ IgE antibodies have been identified from this nut source. Methods mainly based on ELISA assays have been developed in order to detect peanuts in several food commodities. In addition LC-MS/MS methods based on different mass analysers have also been devised for tracing peanut contamination in different foods achieving low limits of detection. The applicability of a benchtop high-resolution Exactive? mass spectrometer has never been investigated for the rapid screening of peanut contamination in complex food matrices like mixtures of nuts. We report in this paper the design of suitable peanut markers and the development of an high-resolution Orbitrap? mass spectrometer-based method for peanut detection in a mixture of nuts species. With this aim, different types of samples were prepared: (1) nuts-based powder made up of a mixture of hazelnuts, pistachios, almonds and walnuts; and (2) nuts powder fortified with peanuts. Different levels of fortifications were produced and the applicability of the method was tested. Finally, a subset of six peptides fulfilling specific analytical requirements was chosen to check the suitability of the method tailored to the detection of peanuts in nuts-based products, and two of them, peptides VYD and WLG, were selected as quantitative markers. The method proved to be a suitable screening tool to assess the presence of traces of peanuts in other tree nuts with a limit of detection as low as 4 µg of peanuts proteins or 26 µg of peanuts in 1 g of matrix.     

Peanut polyamines may be non‐allergenic

Polyamines such as putrescine, spermidine and spermine have been implicated in preventing food allergies in early life, but they have also been reported to be able to bind to immunoglobulin E (IgE) antibodies in vitro (ie they are possibly allergenic). The objective of this study was to determine if polyamines bind in vitro to IgE antibodies from a pooled serum of five peanut‐allergic individuals. Levels of polyamines were also determined by ion‐exchange chromatography. Indirect and inhibition enzyme immunosorbent assays (ELISAs) were used to determine the IgE binding or allergenic properties of polyamines. Results showed that, of the three polyamines, spermidine was predominant in peanuts. In both indirect and inhibition ELISAs, IgE antibodies did not bind to the polyamines. It was concluded that polyamines from peanuts, unlike peanut proteins, are not allergenic or an additional threat to patients who are allergic to peanuts. Published in 2005 for SCI by John Wiley & Sons, Ltd.     

Allergenicity of roasted peanuts treated with a non-human digestive protease

Peanut allergy is a severe and lifelong type of food allergy triggered by allergenic proteins and peptides in peanuts. This study investigated the effects of ultrasound-assisted alcalase treatment on the concentrations of major allergenic proteins (Ara h 1 and Ara h 2) in roasted peanut kernels and the allergenicity of treated peanut extracts. Peanut kernels were sonicated for 1 h in buffer solution, incubated with different amount of alcalase for various time, then vacuum dried. The variations of Ara h 1 and Ara h 2 contents in soluble and insoluble portions of peanuts treatments were evaluated by sandwich ELISA and SDS-PAGE, respectively. The in vitro IgE-binding capacity of treated peanut extracts was determined by a competitive inhibition ELISA using pooled plasma of 10 peanut allergic patients. Samples with lower in vitro IgE-binding were used for human skin prick tests (SPTs) in peanut allergic individuals. Results indicate that alcalase digestion of sonicated peanuts significantly increased protein solubility while decreasing Ara h 1 and Ara h 2 concentrations in both soluble and insoluble portions of peanuts relative to untreated peanuts. The maximum reductions of Ara h 1 and Ara h 2 levels were obtained following 3 hour digestion with alcalase at concentrations of 4.54 and 6.05 U/100 g. Samples obtained under these conditions showed the lowest in vitro IgE-binding and caused the least allergic response in human SPTs. The current study suggests that the allergenic potential of peanuts could be reduced by postharvest processing such as ultrasound-assisted enzymatic treatment of peanuts kernels.     

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.     

Mycoflora and Aflatoxin Content of Hazelnuts,Walnuts, Peanuts,Almonds and Roasted Chickpeas (LEBLEBI) Sold in Turkey

In this study, 28 hazelnuts, 24 walnuts, 18 peanuts, 13 almonds, and 11 roasted chickpeas (leblebi) were analyzed for aflatoxin contamination using thin layer chromatography (TLC). Aflatoxin was found in 26 of 94 samples (27.66%) at concentrations ranging from 1 to 113 ppb. Detectable levels of aflatoxin were 33.4 ppb in hazelnuts, 22.1 ppb in walnuts, 43.0 ppb in peanuts, 7.4 ppb in almonds, and 1.7 ppb in roasted chickpeas. The highest level of aflatoxin was 113 ppb in a single hazelnut sample. Aspergillus and Penicillium species were frequently determined in all the samples.     

A survey of the bacteriological quality of preroasted peanut, almond, cashew, hazelnut, and brazil nut kernels received into three Australian nut-processing facilities over a period of 3 years

There is little information about bacteriological quality of preroasted kernels available in the public domain. An investigation of the bacteriological quality of preroasted peanut, almond, cashew, hazelnut, and Brazil nut kernels received into three Australian nut-processing facilities was performed over a period of 3 years. A total of 836 samples were analyzed for aerobic plate count, and 921 samples for Salmonella and Escherichia coli. The 921 samples included 653 peanut, 100 cashew, 60 almond, 60 Brazil nut, and 48 hazelnut kernels. There was no E. coli detected in any sample. Salmonella subsp. II (Fremantle) was detected in one raw almond sample. The aerobic plate count percentages of positive samples with counts above the detection level of the plating method used (100 CFU/g) for peanuts, almonds, cashews, hazelnuts, and Brazil nuts were 84, 78, 74, 50, and 45%, respectively. Of the samples containing more than this detection limit, the means were 4.5, 4.4, 3.1, 2.5, and 3.8 log CFU/g respectively. Although roasted kernel quality was not within the scope of this survey, raw microbial bioload would be expected to reduce on roasting. The bacteriological quality of preroasted peanut, almond, cashew, hazelnut, and Brazil nut kernels received into nut-processing facilities in Australia does not appear to suggest a public health concern.     

Quantification of Hazelnut Content in Fillings of Cakes and Wafers Using Real-Time Polymerase Chain Reaction

A method for quantification of hazelnuts in fillings of cakes and wafers, using macadamia nuts as an internal standard material, was developed and evaluated. The method was based on quantitative adaptation of the previously developed real-time PCR for identification of hazelnuts. Calibration lines were constructed for two types of fillings, using series of model mixtures. The model mixtures for calibration of cake fillings consisted of hazelnuts and walnuts; the model mixtures for calibration of wafer fillings (pastes) consisted of hazelnuts and peanuts. Linear calibration lines were obtained for both types of matrix, and practical applicability of the developed method was demonstrated on food products from the market. The developed method may be useful for food control laboratories to facilitate analysis of food products with hazelnut filling.     

生物膜干涉法检测花生蛋白与花生过敏患者血清IgE的结合能力

探索基于生物膜干涉技术对花生蛋白与花生过敏患者血清中免疫球蛋白E（immunoglobulin E,IgE）的结合能力进行检测的方法。利用链霉亲和素（streptavidin,SA）标记的传感器、生物素化的羊抗人IgE抗体、花生过敏患者血清池以及花生蛋白建立了一种测定花生蛋白与花生过敏患者血清IgE结合能力的新方法,优化检测条件为抗体1∶100稀释后线下固化20?min,血清1∶10稀释后过夜结合,完成传感器修饰。在线洗基线后用质量浓度为1?mg/mL的花生蛋白与传感器结合3?600?s,解离120?s。利用该法对不同热加工后花生蛋白与患者血清IgE的结合能力进行评估,并与常用的酶联免疫吸附实验（enzyme linked immunosorbent assay,ELISA）检测进行比较。结果表明,本方法可以直接评估过敏原蛋白与血清IgE的结合能力,与ELISA结果相关系数达到0.91。热加工中,油炸处理提高了花生蛋白的IgE结合能力,水煮和烘烤降低了花生蛋白的IgE结合能力,且去壳热加工比带壳热加工花生的蛋白的IgE结合能力更强。     

Relative quantification of walnuts and hazelnuts in bakery products using real-time polymerase chain reaction

Two versions of real-time polymerase chain reaction (PCR) for relative quantification of walnuts and hazelnuts in bakery products were developed. The first method is a duplex real-time PCR with 5′-nuclease (TaqMan) probes labelled with FAM and JOE for walnuts and hazelnuts, respectively. The second method uses two real-time PCR assays for walnuts and hazelnuts with TaqMan probes labelled with FAM, carried out in separate microtubes, with normalisation of the results achieved by adding wheat as an internal standard. The internal standard is quantified in a duplex format using the TaqMan probe labelled with JOE. Both methods produced linear calibration curves (r² = 0.9813 for the former method, r² = 0.9992 for the latter) in the range 10–90% (w/w) for walnut–hazelnut mixtures. Almost identical calibration curves were obtained also for walnut–hazelnut mixtures diluted with inert matrix (oat flakes; the inert matrix accounting for 80 and 96% (w/w), respectively). Practical applicability of the developed methods was demonstrated on bakery products from the market. The developed methods will be useful for food control laboratories to facilitate authentication of bakery products with nut filling.     

Development of a Biological Assay to Determine the Allergenic Potential of Foods

Food allergies represent a risk for many people in industrialized countries. Unrecognizable allergenic proteins of foodstuffs may be present as ingredients that are not labeled or as unknown cross-contamination. Such hidden allergens can cause severe reactions in allergics, even at minute quantities, sometimes with fatal outcome. For the verification of the presence of allergenic food constituents, analytical methods such as ELISA and PCR have been developed. However, these tests cannot measure allergenic potential. For this reason, a test system that measures the biological activity of allergens has been developed. It is based on the cellular mechanisms of the type I allergy. Rat basophilic leukemia cells (RBL-2H3) were transfected with the genes of the human high affinity receptor for IgE. The resulting cell line expressed the human receptor α-chain and could bind allergenspecific IgE from allergic subjects, in contrast to the parent cell line. After cross-linking of receptor-bound, allergen-specific human IgE by allergens, the cells released measurable inflammatory mediators. These cells were used for the analysis of a variety of allergen extracts, including extracts prepared from foods containing allergenic hazelnut and peanut. The comparative validation with existing ELISA and PCR for hazelnut and peanut demonstrated similar sensitivity and specificity. The established cell line will be a novel tool in the detection of allergens in complex mixtures, especially to address the issue of their allergenic potential, which cannot be accomplished by classical analytical methods. This will add valuable information about the allergenic potential of food constituents to the risk assessment of foods.     

A novel real-time polymerase chain reaction (PCR) method for the detection of hazelnuts in food

A real-time PCR (polymerase chain reaction)-based method for the detection of hazelnuts (nuts of Corylus avellana or C. maxima) in confectionery and bakery products is described. The method consists of DNA isolation by chaotropic solid phase extraction and the subsequent PCR with hazelnut-specific primers and a TaqMan fluorescent probe. The primers and the probe are targeted to the hsp1 gene encoding for a low molecular weight heat-shock protein. The method was positive for five hazelnut varieties approved in Slovakia and negative for all other tested plant materials used in food industry including peanuts, walnuts, almonds, pistachio nuts, cashews and chestnuts. The intrinsic detection limit of the method was 13 pg hazelnut DNA, which corresponds to approximately 27 genome equivalents (1C). Using a series of model pastry samples with defined hazelnut contents, a practical detection limit of 0.01% (w/w) hazelnut was determined. Practical applicability of the PCR method was tested by the analysis of 20 food samples (confectionery and bakery products) along with ELISA. For all of the food samples, identical results were obtained by both methods, which conformed to the labelling. The presented PCR method is useful for sensitive and selective detection of hazelnuts in food samples and can be performed in one working day.     

纳豆芽孢杆菌液态发酵对花生理化指标 及其蛋白在消化过程中致敏性的影响

为探究经发酵后的花生营养价值及其蛋白进入体内后致敏性的变化,更好地将微生物发酵应用于花生制品加工生产中。本实验以花生浆(RPP)为研究对象,依次采用高压蒸汽(121 ℃,20 min)、纳豆芽孢杆菌发酵12~60 h处理后,对其冻干产物进行理化性质检测,同时采用聚丙烯酰胺凝胶电泳(SDS-PAGE)和酶联免疫吸附测定(ELISA)检测其蛋白成分在模拟胃肠消化过程中致敏性的变化。结果表明,RPP经高压蒸汽处理后,其蛋白分子量、致敏性、可溶性蛋白含量降低,水解度和多肽含量增加;经纳豆芽孢杆菌进一步发酵后,随着发酵时间的延长,其蛋白分子量、致敏性降低,水解度增加,多肽和可溶性蛋白含量先增加后降低,且其水解度、多肽和可溶性蛋白含量的增加率最高分别为106.9%(发酵60 h)、339.6%(发酵48 h)、42.8%(发酵36 h)。在模拟消化过程中,花生致敏性的降低主要发生在胃液消化阶段,胃肠液连续作用对花生致敏性的影响比其单一作用效果更明显。结合理化指标及致敏性等因素可知,经纳豆芽孢杆菌发酵36 h的花生浆为最好的发酵花生产品,具有营养价值较高、理化性质较好、致敏性较低等特点。     

Iron solubilisation by chicken muscle protein digests

The objective of this work was to compare the solubilisation of iron by in vitro digests of soluble and insoluble protein fractions from chicken muscle. Chicken breast muscle was extracted to provide dilute salt-soluble protein (DSSP) and dilute salt-insoluble protein (DSIP) fractions. These fractions together with casein and ovalbumin were subjected to in vitro digestion in the presence of ferric iron. After proteolytic digestion, soluble iron increased fourfold for DSSP, 20-fold for DSIP, twofold for casein and 0.5-fold for ovalbumin. 64% of the soluble iron in the DSSP digest and 30% of the soluble iron in the DSIP digest were ferrous; in the casein and ovalbumin digests, less than 6% was ferrous. Dialysable iron was less than 5% of the soluble iron for all proteins and was mostly ferric iron. DSIP solubilised twice as much iron as DSSP but much less than casein or ovalbumin digests. It was concluded that muscle proteins solubilise iron by reduction and chelation to mostly large (non-dialysable) peptides resulting from digestion. © 1999 Society of Chemical Industry     

Food allergy—towards predictive testing for novel foods

The risks associated with IgE-mediated food allergy highlight the need for methods to screen for potential food allergens. Clinical and immunological tests are available for the diagnosis of food allergy to known food allergens, but this does not extend to the evaluation, or prediction of allergenicity in novel foods. This category includes foods produced using novel processes, genetically modified (GM) foods, and foods that might be used as alternatives to traditional foods. Through the collation and analysis of the protein sequences of known allergens and their epitopes, it is possible to identify related groups which correlate with observed clinical cross-reactivities. 3-D modelling extends the use of sequence data and can be used to display eptiopes on the surface of a molecule. Experimental models support sequence analysis and 3-D modelling. Observed crossreactivities can be examined by Western blots prepared from native 2-D gels of a whole food preparation (e.g. hazelnut, peanut), and common proteins identified. IgEs to novel proteins can be raised in Brown Norway rat (a high IgE responder strain), and the proteins tested in simulated digest to determine epitope stability. Using the CSL serum bank, epitope binding can be examined through the ability of an allergen to cross-link the high affinity IgE receptor and thereby release mediators using in vitro cell-based models. This range of methods, in combination with data mining, provides a variety of screening options for testing the potential of a novel food to be allergenic, which does not involve prior exposure to the consumer.     

Legumin allergens from peanuts and soybeans: effects of denaturation and aggregation on allergenicity

Legumin proteins Ara h 3 from peanuts and glycinin from soybeans are increasingly described as important allergens. The stability of an allergen's IgE binding capacity towards heating and digestion is considered an important characteristic for food allergens. We investigated the effects of heating and digestion on the IgE binding of Ara h 3 and glycinin. Both proteins are relatively stable to denaturation, having denaturation temperatures ranging from 70 to 92 degrees C, depending on their quaternary structure and the ionic strength. Aggregates were formed upon heating, which were partly soluble for glycinin. Heating slightly decreased the pepsin digestion rate of both allergens. However, heating did not affect the IgE binding capacity of the hydrolyzates, as after only 10 min of hydrolysis no IgE binding could be detected any more in all samples. Peanut allergen Ara h 1, when digested under equal conditions, still showed IgE binding after 2 h of hydrolysis. Our results indicate that the IgE binding capacity of legumin allergens from peanuts and soybeans does not withstand peptic digestion. Consequently, these allergens are likely unable to sensitize via the gastro-intestinal tract and cause systemic food allergy symptoms. These proteins might thus be less important allergens than was previously assumed.     

Angiotensin I-converting enzyme (ACE) inhibitory peptides derived from arachin by simulated gastric digestion

In silico analysis of the sequences of arachin, the major storage protein of peanut suggests that it is laden with antihypertensive peptides. Physiological proteases pepsin, trypsin, chymotrypsin and pancreatin were used to release these peptides. The degree of proteolysis and in vitro angiotensin I-converting enzyme (ACE) inhibition was maximum with pepsin. The ACE inhibitor index of human gastric juice catalysed digestion was similar to pepsin demonstrating that such peptides can be produced in vivo following ingestion of arachin. Three peptides purified from the simulated gastric fluid digests were synthesized. Among them, the pentapeptide, NAQRP was the most potent with an IC₅₀ of 32 ± 2 μM. Molecular docking simulation with human tACE indicate that in addition to a favourable C-terminal Pro residue, the length of the peptides advocate ACE inhibitor potency. These results further potentiate the use of arachin/peanut proteins as functional ingredients in auxiliary therapeutic foods toward blood pressure management.     

Influence of food processing on the immunochemical stability of celery allergens

Celery roots were processed by microwave heating, cooking, drying, γ-irradiation, ultra high pressure treatment and high voltage impulse treatment. The immunochemical stabilities of the three known allergenic structures of celery were tested with sera from patients who were sensitised to celery. In addition, rabbit antisera were used to detect the allergens profilin and Api g 1 on celery immunoblots. The specificity and reactivity of IgE from the patients' sera were investigated by immunoblotting, by an enzyme allergosorbent test (EAST) and by dose-related IgE inhibition experiments. The results of all three methods agreed closely and indicated high antigenic and allergenic activity in native celery which was reduced by thermal processing. The heat-stability of the known celery allergens decreased in the following order: carbohydrate epitopes> profilin>Api g 1. In contrast, the allergenicity was only mildly reduced by non-thermal processing. The results obtained with human IgE were confirmed by an in vitro mediator-release assay that is based on rat basophil leukemia cells (RBL cells) which were passively sensitised with celery-specific murine IgE. With sera from mice that had been immunised with native celery, the native sample and non-thermal celery preparations elicited the strongest mediator release, whereas a weak response was obtained with samples from heat-processed celery. These results agreed closely with the data obtained in allergic patients whose IgE antibodies were directed against the major protein allergen Api g 1. Our results may be helpful in risk assessment and in selecting food preparations which can be consumed without symptoms by a subgroup of celery-allergic patients with a known sensitisation pattern. ©1997 SCI     

Isolation and characterization of natural Ara h 6: evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat

Peanut allergy is a significant health problem because of its prevalence and the potential severity of the allergic reaction. The characterization of peanut allergens is crucial to the understanding of the mechanism of peanut allergy. Recently, we described cloning of the peanut allergen Ara h 6. The aim of this study was isolation and further characterization of nAra h 6. We purified nAra h 6 from crude peanut extract using gel filtration and anion exchange chromatography. The preparation was further characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) with subsequent immunoblotting. Stability of nAra h 6 was studied by an in vitro digestibility assay as well as by resistance against thermal processing. Sequencing of nAra h 6 identified the N-terminal amino acid sequence as MRRERGRQGDSSS. Further results clearly demonstrated stability of nAra h 6 against pepsin digestion and heating. Immunoglobulin G (IgE) binding analysis and its biological activity shown by RBL 25/30-test of natural Ara h 6 supported the importance of this peanut allergen. Investigation of nAra h 6 revealed evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat.     

基于植物DNA条形码技术对杏仁露中花生源性成分的鉴别研究

杏仁露含有丰富的植物蛋白,深受广大消费者的喜爱,拥有广阔的消费市场,同时其成分与配料表是否相符也备受消费者关心。本研究基于植物DNA条形码技术与PCR技术,设计、筛选同时能对杏仁、花生、核桃、大豆、芝麻和榛子六个物种进行扩增的通用引物,并将其应用于杏仁露中花生源性成分的检测。试验表明引物ITS2-2和trn H-psb A-1分别对六个物种的扩增成功率和测序成功率均较高;通过计算杏仁、花生的基因组DNA提取率,设计掺假模型在提取的杏仁基因组DNA中掺入花生基因组DNA,引物ITS2-2对于掺入85.80%的花生检测结果为杏仁,trn H-psb A-1对于掺入6.94%的花生检测结果为花生。引物ITS2-2和trn H-psb A-1可作为鉴别杏仁露中花生源性成分的植物DNA条形码组合。本研究为该类食品检测提供了新的思路,可作为相关研究的参考。