Sandwich immunoassays for the determination of peanut and hazelnut traces in foods

Peanut and hazelnut occurrence as allergens in foodstuffs with precautionary allergen labeling in Canada

Precautionary allergen labeling (PAL) is widely used by food industries. Occurrence studies revealed that few analyzed products contained the allergen(s) present in the statement, but little is known in Canada. To improve manufacturing practices and better manage allergen cross-contamination, occurrence data is needed to determine the exposure of allergic individuals eating those products. Samples were analyzed for peanuts (n = 871) and hazelnuts (n = 863) using ELISA methods. Within samples analyzed for peanuts, 72% had a PAL (n = 628), 1% had peanuts as a minor ingredient (n = 9) and 27% were claimed “peanut-free” (n = 234). Most hazelnut samples had a PAL for tree nuts/hazelnuts (94%; n = 807) with 6% claimed “nut-free” (n = 56). Peanuts and hazelnuts were found in 4% (0.6–28.1 ppm) and 9% (0.4–2167 ppm) of all samples, respectively. Chocolates were mostly impacted; they should be treated apart from other foods and used in risk assessments scenarios to improve manufacturing practices, reducing unnecessary PAL use.

Are current analytical methods suitable to verify VITAL® 2.0/3.0 allergen reference doses for EU allergens in foods?

Food allergy affects up to 6% of Europeans. Allergen identification is important for the risk assessment and management of the inadvertent presence of allergens in foods. The VITAL® initiative for voluntary incidental trace allergen labeling suggests protein reference doses, based on clinical reactivity in food challenge studies, at or below which voluntary labelling is unnecessary. Here, we investigated if current analytical methodology could verify the published VITAL® 2.0 doses, that were available during this analysis, in serving sizes between 5 and 500 g. Available data on published and commercial ELISA, PCR and mass spectrometry methods, especially for the detection of peanuts, soy, hazelnut, wheat, cow's milk and hen's egg were reviewed in detail. Limit of detection, quantitative capability, matrix compatibility, and specificity were assessed. Implications by the recently published VITAL® 3.0 doses were also considered. We conclude that available analytical methods are capable of reasonably robust detection of peanut, soy, hazelnut and wheat allergens for levels at or below the VITAL® 2.0 and also 3.0 doses, with some methods even capable of achieving this in a large 500 g serving size. Cow's milk and hen's egg are more problematic, largely due to matrix/processing incompatibility. An unmet need remains for harmonized reporting units, available reference materials, and method ring-trials to enable validation and the provision of comparable measurement results.

Online immunocapture ICP-MS for the determination of the metalloprotein ceruloplasmin in human serum

Objective

The human copper-protein ceruloplasmin (Cp) is the major copper-containing protein in the human body. The accurate determination of Cp is mandatory for the reliable diagnosis of several diseases. However, the analysis of Cp has proven to be difficult. The aim of our work was a proof of concept for the determination of a metalloprotein-based on online immunocapture ICP-MS. The immuno-affinity step is responsible for the enrichment and isolation of the analyte from serum, whereas the compound-independent quantitation with ICP-MS delivers the sensitivity, precision, and large dynamic range. Off-line ELISA (enzyme-linked immunosorbent assay) was used in parallel to confirm the elution profile of the analyte with a structure-selective method. The total protein elution was observed with the ³²S mass trace. The ICP-MS signals were normalized on a ⁵⁹Co signal.

Results

The human copper-protein Cp could be selectively determined. This was shown with pure Cp and with a sample of human serum. The good correlation with off-line ELISA shows that Cp could be captured and eluted selectively from the anti-Cp affinity column and subsequently determined by the copper signal of ICP-MS.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3324-7) contains supplementary material, which is available to authorized users.

New Trends in Food Allergens Detection: Toward Biosensing Strategies

Food allergens are a real threat to sensitized individuals. Although food labeling is crucial to provide information to consumers with food allergies, accidental exposure to allergenic proteins may result from undeclared allergenic substances by means of food adulteration, fraud or uncontrolled cross-contamination. Allergens detection in foodstuffs can be a very hard task, due to their presence usually in trace amounts, together with the natural interference of the matrix. Methods for allergens analysis can be mainly divided in two large groups: the immunological assays and the DNA-based ones. Mass spectrometry has also been used as a confirmatory tool. Recently, biosensors appeared as innovative, sensitive, selective, environmentally friendly, cheaper and fast techniques (especially when automated and/or miniaturized), able to effectively replace the classical methodologies. In this review, we present the advances in the field of food allergens detection toward the biosensing strategies and discuss the challenges and future perspectives of this technology.

Development of a sensitive ELISA for the detection of casein-containing fining agents in red and white wines

Fining of wine with proteinogenic fining agents such as casein from cow's milk is a traditional and commonly used technique all over the world. Casein and other proteins from cow's milk are well-known food allergens, which pose a risk for allergic consumers. Temporary regulations exempting the labeling of milk and products thereof in wine expired. Since July 1, 2012, these fining agents have to be declared on the wine label under Regulation (EU) No. 579/2012 in conjunction to article 120g of Regulation (EU) No. 1234/2007 if exceeding the threshold of 0.25 mg/L allergenic protein. The aim of the presented study was to develop sensitive ELISA methods for the detection of casein in white and red wines and to investigate the risk of allergenic residues in fined wines. In this context it was shown that the used substance for calibration is highly relevant. Casein wine fining agents of different commercial producers were investigated by LDS-PAGE and immunoblot. In addition to casein, they contain other milk proteins, which are potentially allergic and therefore have to be incorporated in the development of antibodies for an ELISA method to be set up. An indirect ELISA for the investigation of white wine was developed. The LOD is 0.1 mg/L. For red wine the LOD is 0.2 mg/L in an indirect sandwich ELISA setup. The LOD of the indirect sandwich ELISA for white wine depends on the calibration standard. It is 0.1 mg/L for the fining agent casein and 0.01 mg/L for casein from a chemical trader. It is also shown that the use of different technological procedures during winemaking leads to no detectable amounts of casein in various wine samples.

Analysis to support allergen risk management: Which way to go?

Food allergy represents an important food safety issue because of the potential lethal effects; the only effective treatment is the complete removal of the allergen involved from the diet. However, due to the growing complexity of food formulations and food processing, foods may be unintentionally contaminated via allergen-containing ingredients or cross-contamination. This affects not only consumers' well-being but also food producers and competent authorities involved in inspecting and auditing food companies. To address these issues, the food industry and control agencies rely on available analytical methods to quantify the amount of a particular allergic commodity in a food and thus to decide upon its safety. However, no "gold standard methods" exist for the quantitative detection of food allergens. Nowadays mostly receptor-based methods and in particular commercial kits are used in routine analysis. However, upon evaluation of their performances, commercial assays proved often to be unreliable in processed foods, attributed to the chemical changes in proteins that affect the molecular recognition with the receptor used. Unfortunately, the analytical outcome of other methods, among which are chromatographic combined with mass spectrometric techniques as well as DNA-based methods, seem to be affected in a comparable way by food processing. Several strategies can be employed to improve the quantitative analysis of allergens in foods. Nevertheless, issues related to extractability and matrix effects remain a permanent challenge. In view of the presented results, it is clear that the food industry needs to continue to make extra efforts to provide accurate labeling and to reduce the contamination with allergens to an acceptable level through the use of allergen risk management on a company level, which needs to be supported inevitably by a tailor-validated extraction and detection method.

Effects of different extraction buffers on peanut protein detectability and lateral flow device (LFD) performance

The accidental uptake of peanuts can cause severe health reactions in allergic individuals. Reliable determination of traces of peanuts in food products is required to support correct labelling and therefore minimise consumers' risk. The immunoanalytical detectability of potentially allergenic peanut proteins is dependent on previous heat treatment, the extraction capacity of the applied buffer and the specificity of the antibody. In this study a lateral flow device (LFD) for the detection of peanut protein was developed and the capacity of 30 different buffers to extract proteins from mildly and strongly roasted peanut samples as well as their influence on the test strip performance were investigated. Most of the tested buffers showed good extraction capacity for putative Ara h 1 from mildly roasted peanuts. Protein extraction from dark-roasted samples required denaturing additives, which were proven to be incompatible with LFD performance. High-pH buffers increased the protein yield but inhibited signal generation on the test strip. Overall, the best results were achieved using neutral phosphate buffers but equal detectability of differently altered proteins due to food processing cannot be assured yet for immunoanalytical methods.

Biosensor immunoassay for traces of hazelnut protein in olive oil

The fraudulent addition of hazelnut oil to more expensive olive oil not only causes economical loss but may also result in problems for allergic individuals as they may inadvertently be exposed to potentially allergenic hazelnut proteins. To improve consumer safety, a rapid and sensitive direct biosensor immunoassay, based on a highly specific monoclonal antibody, was developed to detect the presence of hazelnut proteins in olive oils. The sample preparation was easy (extraction with buffer); the assay time was fast (4.5 min only) and the limit of detection was low (0.08 microg/g of hazelnut proteins in olive oil). Recoveries obtained with an olive oil mixed with different amounts of a hazelnut protein containing hazelnut oil varied between 93% and 109%.

Development and validation of a duplex real-time PCR method to simultaneously detect potentially allergenic sesame and hazelnut in food

The paper describes the development and validation of a duplex real-time PCR method allowing the simultaneous detection of traces of potentially allergenic sesame and hazelnut in food. For the detection of sesame and hazelnut, the genes coding for two major allergenic proteins, Ses i 1 and Cor a 1, were selected. The duplex real-time PCR assay did not show any cross-reactivity with 25 common food ingredients from sesame and/or hazelnut containing foods. Analysis of serially diluted sesame/hazelnut DNA resulted in good linearity up to a dilution of 1:10000 (corresponding to 10 pg microL(-1) or 50 pg). Sesame and hazelnut could be detected in blank whole meal cookies which had been spiked with 0.005% sesame and 0.005% hazelnut. The applicability of the real-time PCR assay for determining sesame and hazelnut in different food matrices was investigated by analyzing 30 commercial foodstuffs comprising salty snacks, cookies, chocolates, creams, mueslis and muesli bars.

Development of an electrochemical immunoassay for rapid detection of E. coli using anodic stripping voltammetry based on Cu@Au nanoparticles as antibody labels

A sensitive electrochemical immunoassay for rapid detection of Escherichia coli has been developed by anodic stripping voltammetry (ASV) based on core-shell Cu@Au nanoparticles (NPs) as anti-E. coli antibody labels. The characteristics of Cu@Au NPs before and after binding with antibody were confirmed by transmission electron microscopy (TEM). After Cu@Au-labeled antibody reacted with the immobilized E. coli on Polystyrene (PS)-modified ITO chip, Cu@Au NPs were dissolved by oxidation to the metal ionic forms, and the released Cu(2+) ions were determined at GC/Nafion/Hg modified electrode by ASV. The utilization of GC/Nafion/Hg modified electrode could enhance the sensitivity for Cu(2+) detection with a concentration as low as 9.0 x 10(-12)mol/L. Since Cu@Au NPs labels were only present when antibody reacted with E. coli, the amount of Cu(2+) directly reflected the number of E. coli. The technique could detect E. coli with a detection limit of 30CFU/mL and the overall analysis could be completed in 2h. By introducing a pre-enrichment step, a concentration of 3CFU/10mL E. coli in surface water was detected by the electrochemical immunoassay.

Development of a real-time PCR method to detect potentially allergenic sesame (Sesamum indicum) in food

Recent papers indicate that the prevalence of allergic reactions to sesame (Sesamum indicum) is increasing in European countries. This paper describes the development of a selective real-time PCR method for the detection of sesame in food. The assay did not show any cross-reactivity with 17 common food ingredients. The real-time PCR method was applied to determine sesame in several crackers, salty snacks, biscuits, tahina sesame paste and sesame oil. With the exception of sesame oil, in all of the samples where sesame was declared, sesame was detected by the real-time PCR assay (Ct value<35). In the samples which might contain sesame or where sesame was not listed, sesame could not be detected (Ct value>35).

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.

Identification of hidden allergens: Detection of pistachio traces in mortadella

An analytical method based on the detection of specific DNA was developed and applied to mortadella samples with and without pistachio (Pistacia vera). The method is proposed for the detection of traces of pistachio deriving from previous processes or from accidental contamination, since in predisposed individuals pistachios can cause allergic reactions leading to anaphylactic shock. Three pairs of primers were identified and tested by polymerase chain reaction (PCR) on mortadella samples prepared with pistachio. Accidental contamination was also simulated. The optimized PCR was able to detect the presence of pistachio, even at low concentrations. The primers pair PSTC 1-2 is suggested for unambiguous identification of pistachio in mortadella. The limit of detection for this primers pair was 100 mg kg-1. No interference was observed from other spices or ingredients utilized in the formulation of the mortadella. The method enabled the identification of possible traces of pistachio remaining in the production plant after less than thorough washing.

Determination of no-observed-adverse-effect levels and eliciting doses in a representative group of peanut-sensitized children

BACKGROUND

Current labeling practices for allergenic foods like peanut can be inadequate. For future regulatory and industry guidelines, information on no-observed-adverse-effect levels (NOAELs) and eliciting doses (EDs) for allergenic foods is necessary.

OBJECTIVE

To determine NOAEL and ED in a representative group of peanut-sensitized children, relate these data to history and sensitization, and evaluate the outcome of dietary management.

METHODS

From an overall eligible group of 96 peanut-sensitized children, a representative group of 27 was evaluated by questionnaires, skin prick test, determination of specific IgE, and double-blind placebo-controlled food challenge (DBPCFC) with peanut according to the international consensus protocol, with 9 doses ranging from 10 microg to 3 g peanut flour. Dietary management was evaluated over a 12-month period.

RESULTS

Twenty-two children (81%) had a positive DBPCFC. The NOAEL in this group was 1 mg peanut flour, corresponding to 2 mg whole peanut. The ED for subjective symptoms (10 mg to 3 g) was significantly lower than for objective symptoms (100 mg to 3 g; P = .002). Severe reactions occurred only at high doses. EDs were not correlated to previous reactions by history, skin prick test, or specific IgE levels. All patients with a positive DBPCFC were advised to follow a strict diet. During the follow-up period, 10 patients had a less strict diet likely containing traces of peanut. In 3 cases, a mild reaction occurred with food products labeled "may contain peanut."

CONCLUSION

The NOAEL in a representative group of children with peanut allergy was 2 mg. Dietary compliance in half of this group was inadequate.

Microplate-based screening methods for the efficient development of sandwich immunoassays

The selection of suitable antibodies is a critical step in immunoassay development, since the final assay performance is predetermined by this decision to a large extent. Particularly, the screening for matching pairs in sandwich immunoassays is difficult, if both antibodies are derived from one species or when monoclonal antibodies are only available as cell supernatants. Several microplate-based approaches for in situ labeling of detection antibodies were tested, in order to avoid time consuming purification of antibodies for enzyme conjugate synthesis. We investigated labeling with anti-species antibodies and Fab fragments thereof, labeling with protein G and biotinylation of cell supernatants without prior purification. Antibodies against peanut proteins were used as a model and signal-to-blank ratios were used in all cases as a measure of the antibody pair performance. Amongst the investigated approaches, preincubation of the detection antibody with labeled anti-species antibody turned out to be most suitable under our conditions. Diagrams, showing the performance of all possible antibody combinations, were generated with this method and were compared to results obtained with covalently labeled detection antibodies. Finally, a flowchart is presented, suggesting an efficient strategy for the development of highly sensitive sandwich immunoassays.