Sandwich Enzyme-Linked Immunosorbent Assay (ELISA) for Detection of Mustard in Foods

Quantification of Soy-Derived Ingredients in Model Bread and Frankfurter Matrices with an Optimized Liquid Chromatography-Tandem Mass Spectrometry External Standard Calibration Workflow

ABSTRACT

The detection and quantification of soy protein is important for food allergen management and identifying the presence of undeclared soy proteins. Heat processing and matrix interactions can affect the accuracy of allergen detection methods. The sensitivity of enzyme-linked immunosorbent assay methods can be compromised if protein epitopes are modified during processing. Therefore, a mass spectrometry (MS)-based method was evaluated for the recovery of total soy protein in incurred matrices. MS-based quantification of total soy protein was assessed by using a combination of external and internal standards. The reproducibility of the standard curves was investigated by comparing within-day and among-day variation. Incurred samples were prepared using bread and frankfurters as model food matrices. Several soy-derived ingredients were used to prepare the matrices with varying levels of soy protein (1, 10, 50, or 100 ppm of total soy protein). A pooled standard curve was used to estimate the total soy protein concentration of the incurred food matrices and the percent total protein recovery. The variation of replicate standard curves between days and among all days was not significant. The differences in slopes obtained from replicate standards run on different days were minimal. The most influential factor on the quantitative protein recovery in incurred samples was the effect of the physical matrix structure on protein extraction. The lowest percent protein recoveries, less than 50%, were calculated for uncooked matrices. The cooked matrices had percentage recoveries between 50 and 150% for all total soy protein levels. Other factors, such as type of ingredient, were determined to be not as impactful on recovery. The MS method described in this study was able to provide sensitive detection and accurate quantification of total soy protein from various soy-derived ingredients present in processed food matrices.

HIGHLIGHTS

First electrochemical immunosensor for the rapid detection of mustard seeds in plant food extracts

This paper describes the first biosensor reported to date for the determination of mustard seed traces. The biosensor consists of an amperometric immunosensing platform able to sensitively and selectively determine Sin a 1 content, the major allergen of yellow mustard and the most abundant protein of these seeds. The immunosensing platform exploits the coupling of magnetic microbeads (MBs) modified with sandwich-type immune complexes, comprising polyclonal and monoclonal antibodies, selective to the target protein for its capturing and detection, respectively. In addition, a HRP-conjugated secondary antibody was used for enzymatic labelling of the monoclonal antibody, and amperometric transduction was made at screen-printed carbon electrodes (SPCEs) using the hydroquinone (HQ)/H2O2 system. The electrochemical immunosensor allows the simple and fast detection (a single 1-h incubation step) of Sin a 1 with a limit of detection of 0.82 ng mL-1 (20.5 pg of protein in 25 μL of sample) with high selectivity against structurally similar non-target allergenic proteins (such as Pin p 1 from pine nut). The developed immunoplatform was successfully used for the analysis of peanut, rapeseed, cashew, pine nut and yellow mustard extracts, giving only positive response for the yellow mustard extract with a Sin a 1 content, in full agreement with that provided by conventional ELISA methodology.

Canola/rapeseed protein - nutritional value, functionality and food application: a review

Plant-based diet and plant proteins specifically are predestined to meet nutritional requirements of growing population of humans and simultaneously reduce negative effects of food production on the environment. While searching for new sources of proteins, special emphasis should be placed on oilseeds of Brassica family comprising varieties of rapeseed and canola as they contain nutritionally valuable proteins, which have potential to be used in food, but are now rarely or not used as food components. The purpose of the present work is to provide a comprehensive review of main canola/rapeseed proteins: cruciferin and napin, with the focus on their nutritional and functional features, putting special emphasis on their possible applications in food. Technological challenges to obtain rapeseed protein products that are free from anti-nutritional factors are also addressed. As molecular structure of cruciferin and napin differs, they exhibit distinct features, such as solubility, emulsifying, foaming or gelling properties. Potential allergenic effect of 2S napin has to be taken under consideration. Overall, rapeseed proteins demonstrate beneficial nutritional value and functional properties and are deemed to play important roles both in food, as well as, non-food and non-feed applications.

Food processing and allergenicity

Food processing can have many beneficial effects. However, processing may also alter the allergenic properties of food proteins. A wide variety of processing methods is available and their use depends largely on the food to be processed. In this review the impact of processing (heat and non-heat treatment) on the allergenic potential of proteins, and on the antigenic (IgG-binding) and allergenic (IgE-binding) properties of proteins has been considered. A variety of allergenic foods (peanuts, tree nuts, cows' milk, hens' eggs, soy, wheat and mustard) have been reviewed. The overall conclusion drawn is that processing does not completely abolish the allergenic potential of allergens. Currently, only fermentation and hydrolysis may have potential to reduce allergenicity to such an extent that symptoms will not be elicited, while other methods might be promising but need more data. Literature on the effect of processing on allergenic potential and the ability to induce sensitisation is scarce. This is an important issue since processing may impact on the ability of proteins to cause the acquisition of allergic sensitisation, and the subject should be a focus of future research. Also, there remains a need to develop robust and integrated methods for the risk assessment of food allergenicity.

Novel liquid chromatography-mass spectrometry method for sensitive determination of the mustard allergen Sin a 1 in food

Mustard is a condiment added to a variety of foodstuffs and a frequent cause of food allergy. A new strategy for the detection of mustard allergen in food products is presented. The methodology is based on liquid chromatography analysis coupled to mass spectrometry. Mustard allergen Sin a 1 was purified from yellow mustard seeds. Sin a 1 was detected with a total of five peptides showing a linear response (lowest LOD was 5ng). Sin a 1 was detected in mustard sauces and salty biscuit (19±3mg/kg) where mustard content is not specified. Sin a 1, used as an internal standard, allowed quantification of this mustard allergen in foods. A novel LC/MS/MS SRM-based method has been developed to detect and quantify the presence of mustard. This method could help to detect mustard allergen Sin a 1 in processed foods and protect mustard-allergic consumers.

Development and validation of a duplex real-time PCR assay for the simultaneous detection of three mustard species (Sinapis alba, Brassica nigra and Brassica juncea) in food

The paper presents a duplex real-time PCR assay for the simultaneous detection of three potentially allergenic mustard species commonly used in food: white mustard (Sinapis alba), black mustard (Brassica nigra) and brown mustard (Brassica juncea). White mustard is detected in the "green" and black/brown mustard in the "yellow" channel. The duplex real-time PCR assay does not show cross-reactivity with other Brassicaceae species including broccoli, cauliflower, radish and rapeseed. Low cross-reactivities (difference in the Ct value ⩾ 11.91 compared with the positive control) were obtained with cumin, fenugreek, ginger, rye and turmeric. When applying 500 ng DNA per PCR tube, the duplex real-time PCR assay allowed the detection of white, black and brown mustard in brewed model sausages down to a concentration of 5mg/kg in 10 out of 10 replicates. The duplex real-time PCR assay was applied to verify correct labelling of commercial foodstuffs.

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.

Development and validation of a real-time PCR method for the simultaneous detection of black mustard (Brassica nigra) and brown mustard (Brassica juncea) in food

The paper presents a real-time PCR method allowing the simultaneous detection of traces of black mustard (Brassica nigra) and brown mustard (Brassica juncea) in food. The primers and the probe target the B. nigra partial RT gene for reverse transcriptase from gypsy-like retroelement 13G42-26. The real-time PCR method does not show any cross-reactivity with other Brassicaceae species with the exception of white mustard. Low cross-reactivities with cinnamon, cumin, fenugreek, ginger, rye and turmeric can be ignored because in common mustard containing foodstuffs these biological species are present in very low amounts. By analysing serially diluted DNA extracts from black and brown mustard, the DNA of both mustard species could be detected down to 0.1 pg. With 10 ng DNA per PCR tube the real-time PCR method allows the detection of 5 ppm black and brown mustard in brewed sausages.

Food production and processing considerations of allergenic food ingredients: a review

Although most consumers show no adverse symptoms to food allergens, health consequences for sensitized individuals can be very serious. As a result, the Codex General Standard for the Labelling of Prepackaged Foods has specified a series of allergenic ingredients/substances requiring mandatory declaration when present in processed prepackaged food products. Countries adhering to international standards are required to observe this minimum of eight substances, but additional priority allergens are included in the list in some countries. Enforcement agencies have traditionally focused their effort on surveillance of prepackaged goods, but there is a growing need to apply a bottom-up approach to allergen risk management in food manufacturing starting from primary food processing operations in order to minimize the possibility of allergen contamination in finished products. The present paper aims to review food production considerations that impact allergen risk management, and it is directed mainly to food manufacturers and policy makers. Furthermore, a series of food ingredients and the allergenic fractions identified from them, as well as the current methodology used for detection of these allergenic foods, is provided.

Development of a sandwich enzyme-linked immunosorbent assay (ELISA) for detection of buckwheat residues in food

Buckwheat is a pseudocereal (an eudicot with seed qualities and uses similar to those of monocot cereals, family Poaceae) that is consumed in some Asian countries as a staple, and in some western countries as a health food. Allergic reactions to buckwheat are common in some countries. The objective was to develop a specific and sensitive sandwich enzyme-linked immunosorbent assay (ELISA) to detect traces of buckwheat that might inadvertently contaminate other foods in order to assure accurate labeling and consumer protection. Buckwheat-specific antibodies produced in 3 species of animals were tested for specificity and titer by direct ELISA and immunoblot. A sandwich ELISA was developed utilizing pooled rabbit antibuckwheat sera to capture buckwheat proteins and pooled goat antibuckwheat sera, followed by enzyme-labeled rabbit antigoat immunoglobulin G (IgG), to detect bound buckwheat proteins. The lower limit of quantification (LOQ) of the sandwich ELISA was 2 parts per million (ppm) of buckwheat in the presence of complex food matrices. The ELISA is highly specific with no cross-reactivity to any of 80 food ingredients and matrices tested. Validation studies conducted with buckwheat processed into noodles and muffins showed greater than 90% and 60% recovery, respectively. The percent recovery of buckwheat from noodles was similar to that achieved with a commercial buckwheat ELISA kit (ELISA Systems Pty. Ltd., Windsor, Queensland, Australia) at high buckwheat concentrations. However, the sensitivity of this ELISA was greater than the commercial ELISA. This newly developed ELISA is sufficiently specific and sensitive to detect buckwheat residues in processed foods to protect buckwheat-allergic subjects from potential harm. Practical Application: Buckwheat is becoming a common food ingredient in a number of processed foods due to potentially beneficial nutritional properties, without the celiac disease inducing glutenin proteins of wheat and related cereals. However, buckwheat causes allergy in some individuals and must be labeled and tested accurately to protect those with allergy to buckwheat. We describe the development of a new test assay to help food producers ensure that buckwheat is not present in foods that are not intended to contain buckwheat.

Development and validation of a real-time PCR method for the detection of white mustard (Sinapis alba) in foods

This paper presents a real-time PCR method allowing the detection of traces of white mustard ( Sinapis alba ) in complex food matrices. The primers and the probe are targeted at the gene coding for S. alba MADS D. The real-time PCR method was found to be specific for white mustard and did not show any cross-reactivity with 67 biological species, including 12 members of the Brassicaceae family. The limit of detection, determined by analyzing serially diluted white mustard DNA extracts, was 1 pg of white mustard DNA/μL, corresponding to 5 pg of white mustard DNA. In model sausages, the limit of detection was found to be 0.001% white mustard (corresponding to 10 ppm or 10 mg/kg). The real-time PCR method was applied to verify the correct declaration of 20 foodstuffs purchased from Austrian supermarkets. White mustard DNA was detected in one of three samples labeled with "may contain traces of mustard" and in one of seven samples without any information on the presence of mustard.

Detection of mustard, egg, milk, and gluten in salad dressing using enzyme-linked immunosorbent assays (ELISAs)

Enzyme-linked immunosorbent assay (ELISA) is a commonly used method for the detection of trace amounts of potentially allergenic protein residues in foods. However, food matrices and processing conditions can affect the detection of protein residues. The effects of acidity on the detectability of several allergenic proteins commonly found in salad dressing using ELISAs was investigated. First, recovery experiments were performed on salad dressing formulated with 0 to 1000 ppm mustard flour (mustard). The mean percent recovery for mustard from the salad dressing was only 7.7%+/- 1.6%. When the pH of the salad dressing was adjusted to pH 7 prior to spiking with mustard, recovery improved to 94.1%+/- 7.6%. However, if the pH was adjusted to pH 7 after spiking and extraction, the recovery was only 11.1%+/- 1.7%. When vinegar was spiked with mustard flour at pH 3, 3.5, and 4, detectability of mustard was lowest at pH 3. Basic extraction of mustard proteins from salad dressing did not improve the mustard detection. Acidic salad dressing matrices reduced the detectability of mustard by the mustard ELISA probably because of acid precipitation of mustard proteins that renders them insoluble and nonextractable. Commercial salad dressings containing 100 ppm (mg/kg) of egg, milk, or gluten were analyzed every 2 to 4 d for 90 d using 3 commercially available ELISAs. A decrease in the detection of the egg, milk, and gluten in the salad dressing upon storage was observed. Our study highlighted the importance of evaluating the utility of various ELISAs for specific food matrices and the recovery as a function of product storage.

Commercialized rapid immunoanalytical tests for determination of allergenic food proteins: an overview

Food allergies have become an important health issue especially in industrialized countries. Undeclared allergenic ingredients or the presence of "hidden" allergens because of contamination during the food production process pose great health risks to sensitised individuals. The EU directive for food labelling lists allergenic foods that have to be declared on food products by the manufacturers. The list includes gluten-containing cereals, crustaceans, eggs, fish, peanuts, soybeans, milk, various nuts (e.g. almond, hazelnut, and walnut, etc.), celery, mustard, sesame seeds, lupin, and molluscs. Reliable methods for detection and quantification of food allergens are needed that can be applied in a fast and easy-to-use manner, are portable, and need only limited technical equipment. This review focuses on the latest developments in food allergen analysis with special emphasis on fast immunoanalytical methods such as rapid enzyme-linked immunosorbent assays (ELISA), lateral-flow immunochromatographic assays (LFA) and dipstick tests. Emerging technologies such as immunochemical microarrays and biosensors are also discussed and their application to food allergen analysis is reviewed. Finally, a comprehensive overview of rapid immunochemical test kits that are currently available commercially is given in tabular form.