Influence of baking time and matrix effects on the detection of milk allergens in cookie model food system by ELISA

Validation Procedures for Quantification of Food Allergens by Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assay (ELISA) is a widely used analytical technique for food allergen detection and quantification. Validating ELISA protocols is important for both assay developers and end users as it ensures method reliability. This chapter describes the protocols for validating the sensitivity, specificity, precision, accuracy, robustness, and ruggedness of an ELISA. Example procedures are also provided for sample preparation, allergen extraction, and ELISA operation.

Insights into the Mechanism Underlying the Influence of Glycation with Different Saccharides and Temperatures on the IgG/IgE Binding Ability, Immunodetection, In Vitro Digestibility of Shrimp (Litopenaeus vannamei) Tropomyosin

Tropomyosin (TM) is a heat-stable protein that plays a crucial role as a major pan-allergen in crustacean shellfish. Despite the high thermal stability of the TM structure, its IgG/IgE binding ability, immunodetection, and in vitro digestibility can be negatively influenced by glycation during food processing, and the underlying mechanism remains unclear. In this study, TM was subjected to glycosylation using various sugars and temperatures. The resulting effects on IgG/IgE-binding capacity, immunodetection, and in vitro digestibility were analyzed, meanwhile, the structural alterations and modifications using spectroscopic and LC-MS/MS analysis were determined. Obtained results suggested that the IgG/IgE binding capacity of glycosylated TM, immunodetection recovery, and in vitro digestibility were significantly reduced depending on the degree of glycosylation, with the greatest reduction occurring in Rib-TM. These changes may be attributable to structural alterations and modifications that occur during glycosylation processing, which could mask or shield antigenic epitopes of TM (E3: 61-81, E5b: 142-162, and E5c: 157-183), subsequently reducing the immunodetection recognition and digestive enzyme degradation. Overall, these findings shed light on the detrimental impact of glycation on TMs potential allergenicity and digestibility immunodetection and provide insights into the structural changes and modifications induced by thermal processing.

Filling Analytical Gaps in Allergen Detection─Real-Time PCR for the Detection of Commercially Relevant Cephalopods and Gastropods in Food

Mollusks belong to the group of shellfish, which are considered to be among the elicitors of severe food allergies worldwide. In recent years, numerous PCR detection methods have been developed for other shellfish such as crustaceans. However, cephalopods and gastropods were not considered in the development of these shellfish detection systems. In this study, we have developed highly specific real-time PCR methods for the comprehensive detection of all commercially relevant cephalopod species and the gastropod families Helicidae, Buccinidae, and Muricidae in food matrices. In total, we cross-tested over 100 animal and plant species to show the specificity of our systems. The limit of detection (LOD12) was set at 1 pg of cephalopod and gastropod DNA or 10 ppm (mg/kg) spiked in a vegetarian food product. The robustness of the protocol was confirmed by testing multiple parameters while cooking and autoclaving of samples ensured the practical applicability of the systems.

Effect of thermal processing on the antigenicity of allergenic milk, egg and soy proteins

The detection of allergenic proteins and the influence of processing on the structure and antigenicity of these proteins are relevant topics. Using commercial enzyme-linked immunosorbent assay kits, this study aimed to evaluate the degradation profiles of milk, egg and soy proteins during the processing of semisweet biscuits. The formulations were baked under different conditions according to a complete factorial experiment that included a three-level temperature factor and a six-level time factor. β-lactoglobulin and egg white proteins were severely degraded, the degradation of casein was intermediate, and soy proteins were the most stable. Complete allergen protein degradation was found under only the extreme baking conditions, which resulted in products that were not sensorily acceptable. Residual levels of the proteins were detected after baking, indicating that this thermal processing reduced but did not eliminate the antigenicity of these proteins; thus, baking cannot be considered a strategy to protect allergic consumers.

Label free detection of auramine O by G-quadruplex-based fluorescent turn-on strategy

Auramine o (AO) is a synthetic dye used in paper and textile industries. Although it has been an unauthorized food additive in many countries due to its toxic and carcinogenic possibility, its illegal uses have been detected in certain food products such as pasta, semolina and spices and also in pharmaceuticals. The presence of AO in food products should be monitored, therefore, to minimize the negative health effects on consumers. In this study, a simple, highly sensitive and selective label free detection method was investigated for AO by G-quadruplex-based fluorescent turn-on strategy. The optimum fluorescent detection assay was achieved with a specific G-quadruplex DNA sequence, c-myc, at 400 nM in Tris-HCl buffer at pH 7.4. The linearity of fluorescence intensity depending on AO concentration ranged from 0 to 0.07 µM and LOD and LOQ were 3 nM and 10 nM, respectively. The G-quadruplex-based detection assay was highly specific for AO as compared to other two synthetic food colorings and successfully applied to determine AO in pasta, bulgur and curry powder with recoveries in the range from 70.33% to 106.49%. This G-quadruplex-based label free detection assay has a significant potential to be used in the detection of AO in food products.

Selecting processing robust markers using high resolution mass spectrometry for the detection of milk in food products

BACKGROUND

Cow's milk allergy is one of the most reported food allergies in Europe. To help patients suffering from food allergies it is important to be able to detect milk in different foods. An analytical method that is gaining interest in the field of allergen detection is Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry, where the analyte is a target peptide. When these peptide biomarkers are selected the effect of food processing should be taken into account to allow a robust detection method.

OBJECTIVE

This works aims at identifying such processing stable peptide markers for milk for the Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based detection of food allergens in different food products.

METHODS

Milk-incurred food materials that underwent several processing techniques were produced. This was followed by establishing tryptic peptide profiles from each matrix using Ultra-High Performance Liquid Chromatography-High Resolution Mass Spectrometry .

RESULT

A careful comparison of peptide profiles/intensities and the use of specific exclusion criteria resulted in the selection of 8 peptide biomarkers suitable for application in Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based milk detection methods. One of these markers is a α-lactalbumin specific peptide, which has been determined to be stable in different incurred materials for the first time.

CONCLUSION

To our knowledge, this is the first systematic and experimentally based approach for the selection of suitable milk peptide biomarkers robust towards multiple, often applied food processing techniques for milk. Ensuring the exact knowledge of the food processing circumstances by starting from well-defined raw material and using fully controlled settings to produce incurred test material allowed the construction of a peptide database with robust markers. These robust markers can be used for the development of a robust detection method for milk in different food matrices.

Performance of allergen testing in a survey of frozen meals and meals ready-to-eat (MREs)

A 7-plex immunoassay capable of detecting cashew, egg, hazelnut, milk, peanut, shrimp, and soy allergens was used to screen meals ready-to-eat (MREs) and frozen meals that contained meat or poultry. The same food matrices were also evaluated using single individual allergen immunoassays. Multiplex and single allergen test results were compared with the allergen declared on the food label, which was considered the standard. For both the frozen meals (n = 113) and MREs (n = 24) each analytical method failed to detect allergens that were declared on product labels, but only in frozen meals were allergens detected that were not declared on the label. Undeclared allergens were detected for egg in 1.8% (2/113) and for soy in 7.1% (8/113) of frozen meals. Labelled allergens were not detected in 0.9% (1/113) of milk, 4.4% (5/113) of egg, and 15% (17/113) of soy allergens in frozen meals. Assay performance for evaluating allergens in MREs was poor.

Distinction of Signals Generated by Allergens from Cross-Reactivity in Botanicals Used in Dietary Supplements and Spices Using the xMAP Food Allergen Detection Assay

The xMAP Food Allergen Detection Assay (xMAP FADA) is a powerful analytical method by virtue of its ability to simultaneously detect multiple antigenic elements with a repertoire of antibodies targeting 15 food allergens plus gluten. Further, by incorporating multiple levels of redundancy, it can also be used to distinguish between homologous cross-reactive analytes. The power of its analytical capabilities is especially critical when working with botanicals. In this research, 95 botanicals used in dietary supplements and spices were analyzed for cross-reactivity with common food allergens and gluten using the xMAP FADA. Complementary antibody ratios were calculated, and, with most samples, ratios generated by homologous cross-reactive epitopes were easily distinguished from true reactivity. In very few cases, sample ratios were comparable to the ratios generated by the calibration standards, indicating the probable detection of relatively minor quantities of target food allergen. With the xMAP FADA, distinguishing signal indicating target allergen detection from cross-reactivity in botanicals is possible using redundant antibodies and multiple confirmatory end points.

Proteomic Analysisof Food Allergens by MALDI TOF/TOF Mass Spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is largely recognized as an important tool in the analysis of many biomolecules such as proteins and peptides. The MS analysis of digested peptides to identify a protein or some of its modifications is a key step in proteomics. MALDI-MS is well suited for the peptide mass fingerprinting (PMF) technique, as well as selected fragmentation of various precursors using collisional-induced dissociation (CID) or post-source decay (PSD).In the last few years, MALDI-MS has played a significant role in food chemistry, especially in the detection of food adulterations, characterization of food allergens, and investigation of protein structural modifications induced by various industrial processes that could be an issue in terms of food quality and safety.Here, we present simple extraction protocols of allergenic proteins in food commodities such as milk, egg, hazelnut , and lupin seeds. Classic bottom-up approaches based on Sodium Dodecyl Sulphate (SDS) gel electrophoresis separation followed by in-gel digestion or direct in-solution digestion of whole samples are described. MALDI-MS and MS /MS analyses are discussed along with a comparison of data obtained by using the most widespread matrices for proteomic studies, namely, α-cyano-4-hydroxy-cinnamic acid (CHCA) and α-cyano-4-chloro-cinnamic acid (CClCA). The choice of the most suitable MALDI matrix is fundamental for high-throughput screening of putative food allergens.

Occurrence of milk and egg allergens in foodstuffs in Canada

Food allergies are life-threatening conditions that allergic individuals can avoid by consulting the food labels before consuming. Precautionary allergen labelling (or PAL), to warn against possible allergen cross-contamination, is widely used by food industries, reducing the food choices for allergic individuals. In Canada, there is limited information on the actual occurrence of allergens in products with a PAL related to the given allergen. This study attempted to fill the data gap by evaluating the occurrence of milk and egg allergens in Canadian products with PAL. A total of 1125 samples were analysed for milk and 840 for eggs, with 23% and 7% of these samples showing positive detection of ≥2.5 mg kg^-1 for milk and ≥0.245 mg kg^-1 for eggs. Chocolate products gave the largest number of positive results. Although the proportion of positive results was low, the levels detected reached 6471 mg kg^-1 in a chocolate sample and were indicative of possible health consequences, if PAL was ignored by allergic consumers. The occurrence data generated is destinated to be used in exposure and risk assessments, to support allergen management linked to cross-contamination, with the possible development of allergen action levels that would be used by food industries, thus improving a risk-based approach for the application of PAL.

A label-free photoelectrochemical immunosensor for detection of the milk allergen β-lactoglobulin based on Ag2S -sensitized spindle-shaped BiVO4/BiOBr heterojunction by an in situ growth method

Food allergies have become a nonnegligible food safety issue, and milk allergies are one of the most common food allergies, that has attracted large consumer attention. In this work, a novel label-free photoelectrochemical (PEC) immunosensor for the detection of the allergen β-lactoglobulin (β-LG) in dairy products was designed that used the specific recognition of allergen β-LG and antibodies in dairy products in combination with biosensing technology. Here, Ag₂S-sensitized spindle-shaped BiVO₄/BiOBr heterojunction was fixed on the surface of the ITO electrode as an excellent photoactive substrate and effectively improved the photocurrent responses and sensitivity. Thioglycolic acid (TGA) was used as a linker to immobilize the β-LG antibody on the surface of the electrode. The photocurrent was detected at different antigen concentrations, which realized the quantitative testing of β-LG. Under the optimal experimental conditions, the PEC immunosensor proved an ideal linear relationship ranging from 10 pg/mL to 100 ng/mL, with a low detection limit of 3.7 pg/mL. The designed immunosensor showed good stability, a wide linear range, high sensitivity and good reproducibility and could be used for the detection of actual samples. The PEC immunosensor had a strong ability to specifically recognize β-LG, which was not affected by other proteins in the milk without pretreatment. Meanwhile, the developed immunosensor provided a promising PEC detection platform and reference idea for the detection of other proteins in milk.

Food allergens: Classification, molecular properties, characterization, and detection in food sources

Food allergy is a large and growing public health problem in many areas of the world. The prevalence of food allergy has increased in the last decades in a very significant way in many world regions, particularly in developed countries. In that respect, the research field of food allergy has experienced an extensive growth and very relevant progress has been made in recent years regarding the characterization of food allergens, the study of their immunological properties, and their detection in food sources. Furthermore, food labeling policies have also been improved decidedly in recent years. For that immense progress made, it is about time to review the latest progress in the field of food allergy. In this review, we intend to carry out an extensive and profound overview regarding the latest scientific advances and knowledge in the field of food allergen detection, characterization, and in the study of the effects of food processing on the physico-chemical properties of food allergens. The advances in food labeling policies, and methodologies for the characterization of food allergens are also thoroughly reviewed in the present overview.

Using molecular descriptors for assisted screening of heterologous competitive antigens to improve the sensitivity of ELISA for detection of enrofloxacin in raw milk

The use of the heterologous competitive strategy has become a vital method to improve the sensitivity of ELISA. In this work, we prepared an anti-enrofloxacin (ENR) mAb with ENR-bovine serum albumin (BSA) as immunogen. The molecular descriptors of quinolones were then used to screen heterologous coating antigens for the detection of ENR based on an ensemble learning method to improve the sensitivity of the ELISA. Results indicated that 6 of the 7 selected heterologous competitive antigens could enhance the sensitivity of ELISA. The ELISA sensitivity for the detection of ENR with sarafloxacin-BSA as heterologous coating antigen was improved 10-fold (in PBS) and 6-fold (in milk) compared with that with ENR-BSA as homologous antigen. The strategy can effectively screen suitable heterologous competitive antigens to improve the sensitivity of ELISA, followed by preparation of mAb with no additional modification to the corresponding immunogen.

Absolute Quantification of Allergen Glb33 in Rice by Liquid Chromatography-Mass Spectrometry using Two Isotope-Labeled Standard Peptides

Allergen Glb33 is an important allergen in rice that can cause allergic reactions such as asthma and atopic dermatitis. However, knowledge of the content in rice is sparse. In the present work, an absolute protein quantification method was established for allergen Glb33 in rice samples using liquid chromatography-tandem mass spectrometry. After extraction of allergen Glb33 from rice grains using salt solution, the isotope-labeled peptide internal standard was added to the extract, followed by enzymatic digestion with trypsin. The signature peptide and its isotope-labeled analogue from the tryptic hydrolysates of allergen Glb33 and the internal standard were detected by liquid chromatography-tandem mass spectrometry. The quantitative bias caused by tryptic efficiency and matrix effect was corrected by using two isotope-labeled standard peptides. The method exhibited good linearity in the range of 1-200 nM, with coefficients of determination of R² > 0.998. A high sensitivity was observed, with a limit of quantification of 0.97 nM. Mean recoveries obtained from different rice matrices ranged from 82.7%-98.1% with precision <8.5% in intraday trials ( n = 6), while mean recoveries were from 75.1%-107.4% with precision <14.6% in interday trials ( n = 14). The developed method was successfully applied to the analysis of allergen Glb33 in 24 different rice cultivars.

The role of incurred materials in method development and validation to account for food processing effects in food allergen analysis

The issue of undeclared allergens represents a matter of great concern, being the subject of many alert notifications by the Rapid Alert System for Food and Feed portal of the European Commission, often leading to food recalls. The availability of reliable analytical approaches able to detect and quantify hidden allergens in processed foods is increasingly requested by the food industry, food safety authorities and regulatory bodies to protect sensitive consumers' health. The present review discusses the fundamental role of incurred materials for method development and analytical performance assessment in a metrology perspective on testing for undeclared allergens in processed foodstuffs. Due to the nature of the analytes and their susceptibility to various processing effects, reliability and comparability of results have posed a great challenge. In this context, the use of incurred samples as reference materials permits simulation of the effects of food processing on target analyte structure affecting analyte extractability and detectability. Graphical abstract ᅟ.

Nominal effective immunoreaction volume of magnetic beads at single bead level

Immunomagnetic bead (IMB)-based enzyme-linked immunosorbent assay (ELISA) has been the tool frequently used for protein detection in research and clinical laboratories. For most ELISA reactions the recommended dosage of IMBs is usually according to their weight (mg) or mass fraction (w/v) instead of the bead number. Consequently, the processes occurring in the immediate vicinity of the IMBs have always been ignored by researchers and they cannot be revealed in detail during the ELISA reaction. In this paper, we established the relationship between number of IMBs and colorimetric results, and further proposed a new concept of "nominal effective immunoreaction volume (NEIV)" to characterize a single IMB during ELISA reaction. Results showed that the NEIV of a single IMB has a constant value, which is unrelated to the amount of beads and the concentration of antigen. Optimal results of the colorimetric ELISA are achieved when the incubation volume meets each IMB's NEIV and is no longer enhanced by increasing the incubation volume. Thus, the reliable and relatively precise number of IMBs for ELISA detection during practical application could be determined. Most importantly, a study using IMB's NEIV would lay the foundation for a kinetics analysis of IMBs and antigens for future study.

Development of a β-Lactoglobulin Sensor Based on SPR for Milk Allergens Detection

A sensitive and label-free surface plasmon resonance (SPR) based sensor was developed in this work for the detection of milk allergens. β-lactoglobulin (BLG) protein was used as the biomarker for cow milk detection. This is to be used directly in final rinse samples of cleaning in-place (CIP) systems of food manufacturers. The affinity assay was optimised and characterised before a standard curve was performed in pure buffer conditions, giving a detection limit of 0.164 µg mL^-1 as a direct binding assay. The detection limit can be further enhanced through the use of a sandwich assay and amplification with nanomaterials. However, this was not required here, as the detection limit achieved exceeded the required allergen detection levels of 2 µg mL^-1 for β-lactoglobulin. The binding affinities of the polyclonal antibody for BLG, expressed by the dissociation constant (K_D), were equal to 2.59 × 10^-9 M. The developed SPR-based sensor offers several advantages in terms of label-free detection, real-time measurements, potential on-line system and superior sensitivity when compared to ELISA-based techniques. The method is novel for this application and could be applied to wider food allergen risk management decision(s) in food manufacturing.

Effects of the Varietal Diversity and the Thermal Treatment on the Protein Profile of Peanuts and Hazelnuts

Several buffer compositions were compared for their efficiency in protein extraction from both raw and roasted peanut and hazelnut samples, the final goal being to understand the modification of protein solubility upon roasting and maximize the extraction yield. Denaturant conditions provided by urea-TBS buffer resulted in satisfactory extraction yields for both peanut and hazelnut samples, before and after the thermal treatment. In addition, different varieties of peanuts and hazelnuts were characterized to highlight the extent of variability in the protein profile accounted by the varietal factor and eventual differential resistance among cultivars to protein modification induced by the thermal processing. The protein profile was characterized by gel electrophoresis, and specific bands were analyzed by micro-HPLC-MS/MS coupled to software-based protein identification. No significant difference was observed for the investigated hazelnut cultivars, namely, Campana, Romana, and Georgia, whereas interesting features were presented for the peanut varieties Virginia, Zambia, and China. In particular, Zambia variety lacked two bands of approximately 36 and 24 kDa that were visible in Virginia and China varieties, which could suggest a lower allergenic potential of this particular variety which deserves to be further investigated before drawing final conclusions.

Comparison of Laboratory-Developed and Commercial Monoclonal Antibody-Based Sandwich Enzyme-Linked Immunosorbent Assays for Almond (Prunus dulcis) Detection and Quantification

A commercially available monoclonal antibody (mAb)-based direct sandwich enzyme-linked immunosorbent assay (ELISA) kit (BioFront Technologies, Tallahassee, Fla., U.S.A.) was compared with an in-house developed mAb 4C10-based ELISA for almond detection. The assays were comparable in sensitivity (limit of detection < 1 ppm full fat almond, limit of quantification < 5 ppm full fat almond), specificity (no cross-reactivity with 156 tested foods at a concentration of 100000 ppm whole sample), and reproducibility (intra- and interassay variability < 15% CV). The target antigens were stable and detectable in whole almond seeds subjected to autoclaving, blanching, frying, microwaving, and dry roasting. The almond recovery ranges for spiked food matrices were 84.3% to 124.6% for 4C10 ELISA and 81.2% to 127.4% for MonoTrace ELISA. The almond recovery ranges for commercial and laboratory prepared foods with declared/known almond amount were 30.9% to 161.2% for 4C10 ELISA and 38.1% to 207.6% for MonoTrace ELISA. Neither assay registered any false-positive or negative results among the tested commercial and laboratory prepared samples.

PRACTICAL APPLICATION

Ability to detect and quantify trace amounts of almonds is important for improving safety of almond sensitive consumers. Two monoclonal antibody-based ELISAs were compared for almond detection. The information is useful to food industry, regulatory agencies, scientific community, and almond consumers.

Streamlining the analytical workflow for multiplex MS/MS allergen detection in processed foods

Allergenic ingredients in pre-packaged foods are regulated by EU legislation mandating their inclusion on labels. In order to protect allergic consumers, sensitive analytical methods are required for detect allergen traces in different food products. As a follow-up to our previous investigations, an optimized, sensitive, label-free LC-MS/MS method for multiplex detection of five allergenic ingredients in a processed food matrix is proposed. A cookie base was chosen as a complex food matrix and home-made cookies incurred with whole egg, skimmed milk, soy flour, ground hazelnut and ground peanut were prepared at laboratory scale. In order to improve the analytical workflow both protein extraction and purification protocols were optimized and finally a sensitive streamlined SRM based analytical method for allergens detection in incurred cookies was devised. The effect of baking on the detection of selected markers was also investigated.

Food allergen detection by mass spectrometry: the role of systems biology

Food allergy prevalence is rising worldwide, motivating the development of assays that can sensitively and reliably detect trace amounts of allergens in manufactured food. Mass spectrometry (MS) is a promising alternative to commonly employed antibody-based assays owing to its ability to quantify multiple proteins in complex matrices with high sensitivity. In this review, we discuss a targeted MS workflow for the quantitation of allergenic protein in food products that employs selected reaction monitoring (SRM). We highlight the aspects of SRM method development unique to allergen quantitation and identify opportunities for simplifying the process. One promising avenue identified through a comprehensive survey of published MS literature is the use of proteotypic peptides, which are peptides whose presence appears robust to variations in food matrix, sample preparation protocol, and MS instrumentation. We conclude that proteotypic peptides exist for a subset of allergenic milk, egg, and peanut proteins. For less studied allergens such as soy, wheat, fish, shellfish, and tree nuts, we offer guidance and tools for peptide selection and specificity verification as part of an interactive web database, the Allergen Peptide Browser (http://www.AllergenPeptideBrowser.org). With ongoing improvements in MS instrumentation, analysis software, and strategies for targeted quantitation, we expect an increasing role of MS as an analytical tool for ensuring regulatory compliance.

Advances in ultra-high performance liquid chromatography coupled to tandem mass spectrometry for sensitive detection of several food allergens in complex and processed foodstuffs

Sensitive detection of food allergens is affected by food processing and foodstuff complexity. It is therefore a challenge to detect cross-contamination in food production that could endanger an allergic customer's life. Here we used ultra-high performance liquid chromatography coupled to tandem mass spectrometry for simultaneous detection of traces of milk (casein, whey protein), egg (yolk, white), soybean, and peanut allergens in different complex and/or heat-processed foodstuffs. The method is based on a single protocol (extraction, trypsin digestion, and purification) applicable to the different tested foodstuffs: chocolate, ice cream, tomato sauce, and processed cookies. The determined limits of quantitation, expressed in total milk, egg, peanut, or soy proteins (and not soluble proteins) per kilogram of food, are: 0.5mg/kg for milk (detection of caseins), 5mg/kg for milk (detection of whey), 2.5mg/kg for peanut, 5mg/kg for soy, 3.4mg/kg for egg (detection of egg white), and 30.8mg/kg for egg (detection of egg yolk). The main advantage is the ability of the method to detect four major food allergens simultaneously in processed and complex matrices with very high sensitivity and specificity.

An SPR based sensor for allergens detection

A simple, sensitive and label-free optical sensor method was developed for allergens analysis using α-casein as the biomarker for cow's milk detection, to be used directly in final rinse samples of cleaning in place systems (CIP) of food manufacturers. A Surface Plasmon Resonance (SPR) sensor chip consisting of four sensing arrays enabling the measurement of samples and control binding events simultaneously on the sensor surface was employed in this work. SPR offers several advantages in terms of label free detection, real time measurements and superior sensitivity when compared to ELISA based techniques. The gold sensor chip was used to immobilise α-casein-polyclonal antibody using EDC/NHS coupling procedure. The performance of the assay and the sensor was first optimised and characterised in pure buffer conditions giving a detection limit of 58ngmL^-1 as a direct binding assay. The assay sensitivity can be further improved by using sandwich assay format and amplified with nanoparticles. However, at this stage this is not required as the detection limit achieved exceeded the required allergens detection levels of 2µgmL^-1 for α-S1-casein. The sensor demonstrated good selectivity towards the α-casein as the target analyte and adequate recoveries from CIP final rinse wash samples. The sensor would be useful tool for monitoring allergen levels after cleaning procedures, providing additional data that may better inform upon wider food allergen risk management decision(s) that are made by food manufacturer. In particular, this sensor could potentially help validate or optimise cleaning practices for a given food manufacturing process.

Development of a real-time quantitative PCR assay using a TaqMan minor groove binder probe for the detection of α-lactalbumin in food

Here, we report the development of a real-time PCR assay using a TaqMan minor groove binder (MGB, Genecore, NCBI: AF249896.1, 806-820) probe and primer sets designed to recognize the α-lactalbumin gene from the cow (Bos taurus). We evaluated the efficacy of this assay for detecting and quantifying cow α-lactalbumin in commercial foods. Our results demonstrated that the developed method was highly sensitive and showed high specificity for cow milk, with consistent detection of 0.05 ng of bovine DNA. We tested 42 commercial food samples with or without cow milk listed as an ingredient by using the developed assay. Among the 42 samples, 26 products that listed milk as an ingredient and 3 products might contain milk showed positive signals, whereas the other 9 products that did not contain milk and 4 products that might contain milk tested negative. Therefore, this method could be widely used for the detection of cow milk allergens in food.

Multi-allergen Quantitation and the Impact of Thermal Treatment in Industry-Processed Baked Goods by ELISA and Liquid Chromatography-Tandem Mass Spectrometry

Undeclared food allergens account for 30-40% of food recalls in the United States. Compliance with ingredient labeling regulations and the implementation of effective manufacturing allergen control plans require the use of reliable methods for allergen detection and quantitation in complex food products. The objectives of this work were to (1) produce industry-processed model foods incurred with egg, milk, and peanut allergens, (2) compare analytical method performance for allergen quantitation in thermally processed bakery products, and (3) determine the effects of thermal treatment on allergen detection. Control and allergen-incurred cereal bars and muffins were formulated in a pilot-scale industry processing facility. Quantitation of egg, milk, and peanut in incurred baked goods was compared at various processing stages using commercial enzyme-linked immunosorbent assay (ELISA) kits and a novel multi-allergen liquid chromatography (LC)-tandem mass spectrometry (MS/MS) multiple-reaction monitoring (MRM) method. Thermal processing was determined to negatively affect the recovery and quantitation of egg, milk, and peanut to different extents depending on the allergen, matrix, and analytical test method. The Morinaga ELISA and LC-MS/MS quantitative methods reported the highest recovery across all monitored allergens, whereas the ELISA Systems, Neogen BioKits, Neogen Veratox, and R-Biopharm ELISA Kits underperformed in the determination of allergen content of industry-processed bakery products.

Pistachio (Pistacia vera L.) Detection and Quantification Using a Murine Monoclonal Antibody-Based Direct Sandwich Enzyme-Linked Immunosorbent Assay

A commercially available direct sandwich enzyme-linked immunosorbent assay (ELISA) (BioFront Technologies, Tallahassee, FL, USA) using murine anti-pistachio monoclonal antibodies (mAbs) as capture and detection antibodies was evaluated. The assay was sensitive (limit of detection = 0.09 ± 0.02 ppm full fat pistachio, linear detection range = 0.5-36 ppm, 50% maximum signal concentration = 7.9 ± 0.7 ppm), reproducible (intra- and inter-assay variability < 24% CV), and rapid (post-extraction testing time ∼ 1.5 h). The target antigen was stable and detectable in whole pistachio seeds subjected to autoclaving (121 °C, 15 psi, 15, 30 min), blanching (100 °C, 5, 10 min), frying (191 °C, 1 min), microwaving (500, 1000 W, 3 min), and dry roasting (140 °C, 30 min; 168 °C, 12 min). No cross-reactivity was observed in 156 food matrices, each tested at 100,000 ppm, suggesting the ELISA to be pistachio specific. The pistachio recovery ranges for spiked (10 ppm) and incurred (10-50000 ppm) food matrices were 93.1-125.6% and 35.7-112.2%, respectively. The assay did not register any false-positive or -negative results among the tested commercial and laboratory prepared samples.

Fluorescent immunosorbent assay for the detection of alpha lactalbumin in dairy products with monoclonal antibody bioconjugated with CdSe/ZnS quantum dots

In this work, a new method termed competitive fluorescence-linked immunosorbent assay (FLISA) was developed for specifically quantification of bovine α-lactalbumin (α-La) in dairy products. The monoclonal antibodies (mAbs) against α-La were produced through hybridoma technology, and the mAbs were covalently conjugated with the CdSe/ZnS quantum dots (QDs) using the crossing-linking reagents. Moreover, a competitive FLISA based on QD-mAb conjugates was established to detect α-La in dairy products. It was shown that there was a good linear relationship between inhibition efficiency, and logarithm of α-La concentration after the detection parameters were optimised in which the concentration of α-La varied from 0.1 to 1000ng/mL. The value of IC50 was 0.03μg/mL, and the FLISA method exhibited high sensitivity with the LOD at 0.1ng/mL. The developed FLISA has been successfully applied to determine α-La in commercial dairy products, providing more sensitive analysis compared with the ELISA method.

Quantification of allergenic bovine milk α(S1)-casein in baked goods using an intact ¹⁵N-labeled protein internal standard

Intact bovine ¹⁵N-α(S1)-casein was used as an internal standard in a selected reaction monitoring (SRM) assay for milk protein in baked food samples containing fats, sugar, and gums. Effects on SRM results of sample matrix composition in two biscuit recipes containing nonfat dry milk (NFDM) were studied, including samples from a milk allergen ELISA proficiency trial. Following extraction of defatted samples with carbohydrate-degrading enzymes and acid precipitation of casein, the SRM assay exhibited an LOQ of <3 ppm NFDM with 60-80% recovery. NFDM levels measured by the SRM assay were 1.7-2.5 times greater than median levels determined by ELISA. Differences were observed in the α(S1)-casein interpeptide SRM ion abundance profile between recipes and after baking. ¹⁵N-α(S1)-Casein increases SRM analysis accuracy by correcting for extraction recovery but does not eliminate underestimation of allergen concentrations due to baking-related milk protein transformation (modifications).

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.

Affinity and matrix effects in measuring fish plasma vitellogenin using immunosorbent assays: considerations for aquatic toxicologists

Enzyme-linked immunosorbent assays (ELISAs) are important tools in aquatic toxicology and have become crucial in assessing exposure concentrations in the aquatic environment and acute physiological responses in exposed organisms. These assays utilize the inherent properties of antibodies to recognize and selectively bind a target molecule, while largely ignoring other molecules to provide semiquantitative values. A variety of methodologies to measure plasma vitellogenin using ELISAs have generated widely divergent data. Limitations of the ELISA method are known in the wider immunology field, though aquatic toxicologists may be less familiar with these limitations. We evaluated several mechanisms contributing to the divergent vitellogenin data in the literature. Antibody affinities and the matrix in which standard curves are constructed are possible error generators. These errors can be amplified by large sample dilutions necessary to fall within the standard curve. It is important for the aquatic toxicology research community to realize the limitations and understand the pitfalls of absolute plasma vitellogenin data in their studies.