Matrix effect on food allergen detection – A case study of fish parvalbumin

Insights into effects of processing and food matrices on structure and ELISA detection of sarcoplasmic calcium binding protein

The sandwich ELISA (sELISA) targeting sarcoplasmic calcium binding protein (SCP) is significantly influenced by food matrices, yet the mechanisms are unclear. To clarify the comprehensive effects of environments, matrices, and processing, SCP treated with diverse temperatures, pH, and matrices was subjected to ELISA, electrophoresis, multispectroscopic and molecular simulation assays. Recoveries of sELISA and indirect competitive ELISA (icELISA) were inhibited above 80 °C and 100 °C due to the unfolding of SCP. Under acidic conditions, SCP became more compact improving icELISA while reducing sELISA. The tertiary structure, aggregation state of SCP, and ELISA results were primarily impacted by inorganic salts, carbohydrates, and peanut oil via non-covalent interactions. Slighter impacts of processing on icELISA suggested SCP might preserve epitopes maintaining antibody recognition. These findings elucidated the effects of various factors on SCP structure and the mechanisms behind variations in ELISA results, additionally demonstrating the stronger interference resistance of icELISA.

Development of an indirect competitive ELISA based on the common epitope of fish parvalbumin for its detection

A common epitope (AGSFDHKKFFKACGLSGKST) of parvalbumin from 16 fish species was excavated using bioinformatics tools combined with the characterization of fish parvalbumin binding profile of anti-single epitope antibody in this study. A competitive enzyme-linked immunosorbent assay (ELISA) based on the common epitope was established with a limit of detection of 10.15 ng/mL and a limit of quantification of 49.29 ng/mL. The developed ELISA exhibited a narrow range (71% to 107%) of related cross-reactivity of 15 fish parvalbumin. Besides, the recovery, the coefficient of variations for the intra-assay and the inter-assay were 84.3% to 108.2%, 7.4% to 13.9% and 8.5% to 15.6%. Our findings provide a novel idea for the development of a broad detection method for fish allergens and a practical tool for the detection of parvalbumin of economic fish species in food samples.

Mutation of Disulfide Bond Sites Reduces the Immunoreactivity of Cra a 4 by Changing the Structural Characteristics

Sarcoplasmic calcium-binding protein (Cra a 4) from Crassostrea angulata belongs to the EF-hand superfamily, and understanding of its structure-allergenicity relationship is still insufficient. In this study, chemical denaturants were used to destroy the structure of Cra a 4, showing that disruption of the structure reduced its IgG-/IgE-binding activity. To explore which critical amino acid site affects the allergenicity of Cra a 4, the mutants were obtained by site-directed mutations in the disulfide bonds site (C97), conformational epitopes (I105, D114), or Ca2+-binding region (D106, D110) and their IgG-/IgE-binding activity was reduced significantly using serological tests. Notably, C97A had the lowest immunoreactivity. In addition, two conformational epitopes of Cra 4 were verified. Meanwhile, the increase of the α-helical content, surface hydrophobicity, and surface electrostatic potential of C97A affected its allergenicity. Overall, the understanding of the structure-allergenicity relationship of Cra a 4 allowed the development of a hypoallergenic mutant.

Influence of linoleic acid on the immunodetection of shrimp (Litopenaeus vannamei) tropomyosin and the mechanism investigation via multi-spectroscopic and molecular modeling techniques

The effect of linoleic acid (LA) on the IgG/IgE recognition, in vitro digestibility and immunodetection of shrimp tropomyosin (TM) was investigated. Subsequently, the simultaneous binding of LA-TM was explored using multi-spectroscopic and molecular modeling techniques. Our findings reveled that the addition of LA significantly reduced TM's IgG/IgE immunoreactivity, digestibility, and immunodetection. Further analysis using multi-spectroscopic and molecular modeling techniques indicated that while TM's secondary structure remained largely unchanged, its 3-D structure showed significant alterations such as increased particle size and hydrophobic surface area, and a higher number of buried hydrophobic residues exposed due to the binding of LA to TM. These structural changes rendered it difficult for target antibodies and digestive enzymes to interact with related epitopes and cleavage sites buried inside the molecule. The results obtained in this study provide valuable insights into the molecular mechanism of poor immunodetection caused by food matrix interference.

Effects of different ohmic heating treatments on parvalbumin structure and reduction of allergenicity in Japanese eel (Anguilla japonica)

We investigated the effects of ohmic heating (OH) on the structural properties and allergenicity of parvalbumin (PV). Compared to other heating methods (water bath heating (WH), OH combined with WH, and OH combined with air thermostatic heating (AH)), pure OH heating expended the least time and total energy. PV sensitization was reduced by approximately 65% by pure OH heating. SDS-PAGE, tricine-SDS-PAGE, and western blotting analyses revealed a molecular weight of sensitized β-PV of about 12 kDa. Band intensity decreased with increasing OH time, and significant changes were observed in amino acid content, secondary structure, microstructure, and dielectric properties. Reducing PV, allergenicity through protein unfolding and secondary structural changes, thereby possibly reducing the allergenicity of eel, provides a theoretical basis for developing hypoallergenic products.

New Perspectives on Food Matrix Modulation of Food Allergies: Immunomodulation and Component Interactions

Food allergy is a multifactorial interplay process influenced not only by the structure and function of the allergen itself but also by other components of the food matrix. For food, before it is thoroughly digested and absorbed, numerous factors make the food matrix constantly change. This will also lead to changes in the chemistry, biochemical composition, and structure of the various components in the matrix, resulting in multifaceted effects on food allergies. In this review, we reveal the relationship between the food matrix and food allergies and outline the immune role of the components in the food matrix, while highlighting the ways and pathways in which the components in the food matrix interact and their impact on food allergies. The in-depth study of the food matrix will essentially explore the mechanism of food allergies and bring about new ideas and breakthroughs for the prevention and treatment of food allergies.

Characterization, specific recognition, and the performance in fish matrix of a shark-derived single-domain antibody against enrofloxacin

The third generation of genetic engineering antibodies, single-domain antibodies, have been widely reported as potential biomaterials in recognizing small molecular hazards. In this study, a shark-derived single-domain antibody was used as the recognition element for the first time to detect enrofloxacin (ENR), one of the most representative hazards in aquaculture. An ENR-specific clone named 2E6 was isolated by phage display technology. Experimental results proved that 2E6 ssdAb showed high affinity to ENR-PEI complete antigen, with the highest OD₄₅₀ value of 1.348 in binding ELISA. Through icELISA, it was determined that the IC₅₀ of 2E6 ssdAb to ENR was 19.230 ng/mL, while the IC₁₀ was 0.975 ng/mL, with rare recognition to other fluoroquinolones, which showed high sensitivity and specificity to ENR. The 2E6 ssdAb also performed excellently in fish matrix immunoassay. Results showed that the ENR-negative fish matrix did not seriously interfere with the recognition of 2E6 ssdAb to ENR-OVA, with the matrix index between 4.85% and 11.75%, while the results of icELISA in ENR-spiked fish matrix showed that 2E6 ssdAb could recognize the target ENR in different ENR-spiked concentrations of the fish matrix (10-1000 ng/mL), with the recovery between 89.30% and 126.38% and the RSD between 1.95% and 9.83%. This study broadens the application scenario of shark-derived single-domain antibodies as small molecule recognition biomaterials, providing a new recognition element on ENR detection for immunoassay.

Immunodetection of finfish residues on food contact surfaces

Finfish is one of the major allergenic foods, whose declaration is required on packages. Undeclared allergenic residues are mainly derived from allergen cross-contact. Swabbing of food contact surfaces helps to detect allergen cross-contamination. This study aimed to establish a competitive enzyme-linked immunosorbent assay (cELISA) to quantify the major finfish allergen, parvalbumin, from swab samples. First, parvalbumin from four finfish species was purified. Its conformation was investigated under reducing, non-reducing and native conditions. Second, one anti-finfish parvalbumin monoclonal antibody (mAb) was characterized. This mAb had a calcium-dependent epitope which was highly conserved in finfish species. Third, one cELISA was established with a working range between 0.59 ppm and 150 ppm. It showed a good recovery of swab samples on food-grade stainless steel and plastic surfaces. Overall, this cELISA could detect a trace amount of finfish parvalbumins on cross-contact surfaces, which is suitable for allergen surveillance in the food industry.

Development of a sensitive sandwich ELISA with broad species specificity for improved fish allergen detection

A sensitive Enzyme-linked Immunosorbent Assay (ELISA) with improved broad species specificity was developed for the detection of southern hemisphere fish residues in processed foods. The polyclonal antibodies were raised against parvalbumins from 13 fish species representing 7 fish orders selected for their molecular diversity and immunoreactivity profile. The optimized ELISA-2 (based on the rabbit capture antibody (RB#4) - sheep detection antibody (S2#4) pair) displayed an improved detection limit of 0.6 μg/L (3.7 μg of /kg). Our immunoreactivity-directed species selection approach in the strategized antibody production significantly improved the detection of no or weakly immunoreactive fish species previously not detected immunochemically. Of 37 commercially important fish species tested, the ELISA-2 could detect 28 fish species (76%). The optimized sample extraction with a buffer additive achieved good protein recoveries of 87.2 - 117.3% (within the AOAC recommended range). The ELISA-2 was able to detect fish residues in five highly processed food products.

The effect of chlorophyll on the enzyme-linked immunosorbent assay (ELISA) of procymidone in vegetables and the way to overcome the matrix interference

BACKGROUND

There is now an increasing demand for the immunoassay of procymidone residue in foodstuffs. However, the matrix interference could significantly affect the analysis. Till now there is no detailed information on the source of the interference and the mechanism involved, which greatly limits the real application of these techniques.

RESULTS

Significant matrix effect was observed in the enzyme-linked immunosorbent assay (ELISA) of procymidone in negative vegetable samples (leek, broccoli and cucumber). By the investigation with both vegetable extracts and standard solutions, the chlorophyll was confirmed as an important source of the matrix effect. Therefore, a new strategy was proposed for the pretreatment based on the exploitation of 5-sulfosalicylic acid. It was demonstrated to effectively eliminate chlorophyll and exhibited little effect on procymidone and the competitive indirect ELISA (ci-ELISA) performance. The established technique was validated with different vegetables. With the spiking concentration of procymidone investigated, the recovery rate of ci-ELISA was 71.52-120.37%, and the relative standard deviation was 4.05-17.61%.

CONCLUSION

Chlorophyll was for the first time illuminated as an important source of matrix interference to the immunoassay of procymidone in vegetables. A new pretreatment based on 5-sulfosalicylic acid was established to remove chlorophyll and therefore eliminate the matrix effect. Validated with different vegetable samples, the new technique was demonstrated much better efficiency in comparison to conventional methods, which indicated its promising application for the development of immunoassays of herb-origin samples. © 2021 Society of Chemical Industry.

Detection of Allergenic Proteins in Foodstuffs: Advantages of the Innovative Multiplex Allergen Microarray-Based Immunoassay Compared to Conventional Methods

Several factors can affect the allergen content and profile of a specific food, including processing procedures often leading to a decrease in allergenicity, although no change, or even an increase, have also been reported. Evaluation of the effectiveness of a processing procedure requires the availability of reliable methodologies to assess the variation in molecules able to induce allergic reactions in the analyzed food. Conventional and innovative strategies and methodologies can be exploited to identify allergenic proteins in foodstuffs. However, depending on the specific purposes, different methods can be used. In this review, we have critically reviewed the advantages of an innovative method, the multiplex allergen microarray-based immunoassay, in the detection of allergens in foodstuffs. In particular, we have analyzed some studies reporting the exploitation of an IgE-binding inhibition assay on multiplex allergen biochips, which has not yet been reviewed in the available literature. Unlike the others, this methodology enables the identification of many allergenic proteins, some of which are still unknown, which are recognized by IgE from allergic patients, with a single test. The examined literature suggests that the inhibition test associated with the multiplex allergen immunoassay is a promising methodology exploitable for the detection of IgE-binding proteins in food samples.

Determination of Tropomyosin in Shrimp and Crab by Liquid Chromatography–Tandem Mass Spectrometry Based on Immunoaffinity Purification

A UPLC-MS/MS method was developed for the detection of tropomyosin (TM) in shrimp and crab. After simple extraction, the samples were purified by immunoaffinity column and then digested by trypsin. The obtained sample was separated by Easy-nLC 1000-Q Exactive. The obtained spectrums were analyzed by Thermo Proteome Discoverer 1.4 software and then ANIQLVEK with high sensitivity was selected as the quantitative signature peptide. Isotope-labeled internal standard was used in the quantitative analysis. The method showed good linearity in the range of 5–5,000 μg/L with a limit of quantification (LOQ) of 0.1 mg/kg. The average recoveries were 77.22–95.66% with RSDs ≤ 9.97%, and the matrix effects were between 88.53 and 112.60%. This method could be used for rapid screening and quantitative analysis of TM in shrimp and crab. Thus, it could provide technical support for self-testing of TM by food manufacturers and promote further improvement of allergen labeling in China.

Sensitive and Selective Detection of Clenbuterol in Meat Samples by a Graphene Quantum Dot Fluorescent Probe Based on Cationic-Etherified Starch

The use of clenbuterol (CLB) in large quantities in feedstuffs worldwide is illegal and potentially dangerous for human health. In this study, we directly prepared nitrogen-doped graphene quantum dots (N-GQDs) by a one-step method using cationic-etherified starch as raw material without pollution, which has the advantages of simple, green, and rapid synthesis of N-GQDs and high doping efficiency of nitrogen elements, compared with the traditional nitrogen doping method of reacting nitrogen source raw material with quantum dots. The N-GQDs synthesized by cationic etherification starch with different substitution degrees (DSs) exhibit good blue-green photoluminescence, good fluorescence stability, and water solubility. By comparing the fluorescence emission intensity of the two methods, the N-GQDs prepared by this method have higher fluorescence emission intensity and good fluorescence stability. Based on the static quenching mechanism between CLB and N-GQDs, a fluorescent probe was designed to detect CLB, which exhibited a wide linear range in the concentration range of 5 × 10⁻¹⁰~5 × 10⁻⁷ M (R² = 0.9879) with a limit of detection (LOD) of 2.083 × 10⁻¹³ M. More excitingly, the N-GQDs fluorescent probe exhibited a satisfactory high selectivity. Meanwhile, it can be used for the detection of CLB in chicken and beef, and good recoveries were obtained. In summary, the strategic approach in this paper has potential applications in the detection of risky substances in the field of food safety.

Effect of Processing on Fish Protein Antigenicity and Allergenicity

Fish allergy is a life-long food allergy whose prevalence is affected by many demographic factors. Currently, there is no cure for fish allergy, which can only be managed by strict avoidance of fish in the diet. According to the WHO/IUIS Allergen Nomenclature Sub-Committee, 12 fish proteins are recognized as allergens. Different processing (thermal and non-thermal) techniques are applied to fish and fishery products to reduce microorganisms, extend shelf life, and alter organoleptic/nutritional properties. In this concise review, the development of a consistent terminology for studying food protein immunogenicity, antigenicity, and allergenicity is proposed. It also summarizes that food processing may lead to a decrease, no change, or even increase in fish antigenicity and allergenicity due to the change of protein solubility, protein denaturation, and the modification of linear or conformational epitopes. Recent studies investigated the effect of processing on fish antigenicity/allergenicity and were mainly conducted on commonly consumed fish species and major fish allergens using in vitro methods. Future research areas such as novel fish species/allergens and ex vivo/in vivo evaluation methods would convey a comprehensive view of the relationship between processing and fish allergy.

The fabrication of a thiol-modified chitosan magnetic graphene oxide nanocomposite and its adsorption performance towards the illegal drug clenbuterol in pork samples

A novel thiol (provided by (3-mercaptopropyl) trimethoxysilane, MPTS)-modified chitosan magnetic graphene oxide nanocomposite (Fe₃O₄@SiO₂/GO/CS/MPTS) was synthesized and characterized for the first time as an efficient magnetic sorbent for the enrichment and extraction of trace levels of clenbuterol in pork samples (muscle, fat, heart and liver). Various greatly influential parameters were optimized using a Box-Behnken design (BBD) through the response surface methodology (RSM) to obtain more satisfactory recovery. Under optimum conditions, the method detection limits (MDLs) were in the range of 0.054-0.136 ng g^-1. The recoveries of three spiked levels ranged from 84.7% to 101.1%, and the relative standard deviations (RSDs) were lower than 9.3%. The results of the adsorption experiments showed that the maximum adsorption capacity of Fe₃O₄@SiO₂/GO/CS/MPTS for clenbuterol was 214.13 mg g^-1. The adsorption process was most consistent with pseudo second-order kinetics and Langmuir adsorption isotherm, indicating a homogeneous process with a chemisorptive nature. Also, the nanocomposite exhibited high adsorption capability for clenbuterol compared with Fe₃O₄@SiO₂/GO and Fe₃O₄@SiO₂/GO/CS. In addition, regeneration of the nanocomposite was effectively achieved, and it retained about 82% of its initial capacity after four cycles. All these results indicate that the synthetic nanocomposite is a promising efficient adsorbent for the adsorption of clenbuterol with high adsorption capacity and low cost.

Proteomics for understanding pathogenesis, immune modulation and host pathogen interactions in aquaculture

Proteomic analyses techniques are considered strong tools for identifying and quantifying the protein contents in different organisms, organs and secretions. In fish biotechnology, the proteomic analyses have been used for wide range of applications such as identification of immune related proteins during infections and stresses. The proteomic approach has a significant role in understanding pathogen surviving strategies, host defence responses and subsequently, the fish pathogen interactions. Proteomic analyses were employed to highlight the virulence related proteins secreted by the pathogens to invade the fish host's defence barriers and to monitor the kinetics of protein contents of different fish organs in response to infections. The immune related proteins of fish and the virulence related proteins of pathogens are up or down regulated according to their functions in defence or pathogenesis. Therefore, the proteomic analyses are useful in understanding the virulence mechanisms of microorganisms and the fish pathogen interactions thereby supporting the development of new effective therapies. In this review, we focus and summarise the recent proteomic profiling studies exploring pathogen virulence activities and fish immune responses to stressors and infections.