Monoclonal antibody-based ELISA for the quantification of porcine hemoglobin in meat products

High-affinity VNARs targeting human hemoglobin: Screening, stability and binding analysis

Hemoglobin, composed of α- and β-chains, is essential for oxygen transport and is key in diagnosing and treating gastrointestinal and blood disorders. It also aids in detecting blood contamination and estimating transfusion volumes. Immunological methods, based on antigen-antibody interactions, are distinguished by their high sensitivity and accuracy. Consequently, it is necessary to develop hemoglobin-specific antibodies characterized by high specificity and affinity to enhance detection accuracy. The variable domain of the new antigen receptor (VNAR) from sharks, the smallest antigen-binding unit, is ideal for disease diagnosis and treatment due to its small size, stability, and high affinity. In this study, Chiloscyllium plagiosum was immunized with human hemoglobin protein. Nine VNAR immune libraries with sizes ranging from 1 × 108 to 1.82 × 109 colony-forming units (CFU) were constructed and biopanned using phage display, resulting in three hemoglobin-specific VNAR sequences (5-10C, 7-11A, T-12-4D). These sequences were inserted into pTT5-TEV-Fc vectors and transfected into HEK 293F cells. The resulting VNAR-Fc fusion proteins were purified from the cell culture supernatants. Binding activity, cross-reactivity, physicochemical stability, and epitope competition were evaluated using non-competitive enzyme-linked immunosorbent assay (ELISA) and biolayer interferometry (BLI). T-12-4D-Fc exhibited the highest affinity with a KD value of 7.59 nM and superior physicochemical stability. It maintained over 80 % binding activity at 90 °C, over 51 % in extreme pH conditions (pH 2 and 12), and above 65 % in urea concentrations up to 8 mol/L. Its binding activity remained largely unaffected after 6 h of incubation in human plasma-like medium (HPLM). The binding epitope competition results showed that 5-10C-Fc and T-12-4D-Fc targeted the same hemoglobin epitope. Molecular dynamics simulations revealed hydrogen bonds as the primary interaction force between VNARs and hemoglobin. Furthermore, a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) method was established for the detection of human hemoglobin, utilizing T-12-4D-Fc as the coating antibody. This technique demonstrated high accuracy, reproducibility and specificity when applied to human whole blood samples. Hence, the identified VNARs, particularly T-12-4D, demonstrated good stability, specificity, and high affinity, filling the gap of hemoglobin-targeting shark-derived single-domain antibodies and offering a foundation for diagnosing and monitoring hemoglobin-related diseases.

Computerized analysis of haptens for the ultrasensitive and specific detection of Pyriftalid

Pyriftalid (Pyr) is one of the most commonly used herbicides and due to its widespread and improper use, it has led to serious pollution of groundwater, soil and other ecosystems, threatening human health. A rapid method to detect Pyr was urgently needed. A high specific monoclonal antibody (mAb) against Pyr with IC50 values of 4.7 ng/mL was obtained by mAb screening technique and method with enhanced matrix effect. The study firstly proposed colloidal gold immunochromatographic test strips (CGIA) for Pyr, which enables rapid qualitative and quantitative determination of a large number of samples anytime and anywhere, so as to effectively monitor Pyr in environment and grain samples. Based on the properties of the desired Pyr antibody, the hapten Pyr-hapten-4 with high structural similarity to Pyr molecule, similar electrostatic potential distribution, and the ability to expose Pyr functional groups was screened out from five different Pyr haptens, which was consistent with mouse antiserum test. The CGIA quickly analyze the Pyr content in positive samples such as water samples, soil samples, paddy samples, brown rice samples within 10 min, the LOD for Pyr by CGIA as low as 1.84 ng/g, the v LOD value as low as 6 ng/g, and the extinction value as low as 25 ng/g. The content of positive samples detected by CGIA was consistent with the quantitative results of LC-MS/MS, the relative accuracy was within the range of 97-103 %. The recovery rate range for Pyr by CGIA was 92.0-99.7 %, and the coefficient of variation was between 1.30-8.56 %. It indicated Pyr-targeted CGIA test strip was an efficient and fast detection method to detect real environment and food samples.

Immunochromatographic visualization detection platform for bitertanol in foods

As a widely used fungicide in agriculture, bitertanol (BIT) significantly affects hormone regulation leading to imbalance of homeostasis in vivo, which makes it necessary to monitor BIT residues in foods. In this research, a novel hapten derivation scheme was designed by analyzing the chemical structure of BIT to prepare an anti-BIT monoclonal antibody with high affinity, specificity and sensitivity (half inhibitory concentration of 4.78 ng/mL). Subsequently, a visualized gold immunochromatographic assay (GICA) platform was established based on antigen-antibody specific recognition, with a limit of detection of 0.06 mg/kg and 0.18 mg/kg in cucumber and tomato, respectively. GICA has spiked recoveries of 84.3 %-114.1 %, determines results are not significantly different from those of LC-MS/MS, and the complex purification treatments can be reduced during the detection process. Therefore, the developed GICA is a reliable, rapid, and sensitive method for on-site rapid monitoring of BIT in foods.

Immunoassay for the detection of cyproconazole in foods: From hapten synthesis to the establishment of a gold immunochromatographic assay

Cyproconazole (CPZ) is extensively used in agricultural production. However, its overuse can lead to high residue problems in crops. Existing detection methods are still dominated by instrumental methods and the development of rapid, sensitive field detection remains a challenge. In this study, we designed a novel hapten synthetic pathway and prepared a monoclonal antibody (mAb) that could specifically recognize CPZ with high sensitivity (half inhibition rate was 0.27 ng/mL). From this, a gold immunochromatographic assay (GICA) for the detection of CPZ was established by combining the mAb with gold nanoparticles, with limits of detection in rice, tomatoes and grapes of 0.02 mg/kg, 0.01 mg/kg and 0.05 mg/kg, respectively. The spiked recoveries ranged from 86.5 % to 115.1 %, and the results showed that the GICA was not significantly different from detection using LC-MS/MS. Therefore, we have successfully developed a GICA method for the reliable in situ, rapid and sensitive detection of CPZ.

Identification of animal species of origin in meat based on glycopeptide analysis by UPLC-QTOF-MS

Adulteration of meat and meat products causes a concerning threat for consumers. It is necessary to develop novel robust and sensitive methods which can authenticate the origin of meat species to compensate for the drawbacks of existing methods. In the present study, the sarcoplasmic proteins of six meat species, namely, pork, beef, mutton, chicken, duck and turkey, were analyzed by one-dimensional gel electrophoresis. It was found that enolase could be used as a potential biomarker protein to distinguish between livestock and poultry meats. The glycosylation sites and glycans of enolase were analyzed by UPLC-QTOF-MS and a total of 41 glycopeptides were identified, indicating that the enolase N-glycopeptide profiles of different meats were species-specific. The identification models of livestock meat, poultry and mixed animal were established based on the glycopeptide contents, and the explanation degree of the three models was higher than 90%. The model prediction performance and feasibility results showed that the average prediction accuracy of the three models was 75.43%, with the animal-derived meat identification model showing superiority in identifying more closely related species. The obtained results indicated that the developed strategy was promising for application in animal-derived meat species monitoring and the quality supervision of animal-derived food.

Isoelectric point barcode and similarity analysis with the earth mover's distance for identification of species origin of raw meat

In this work, by combining the microcolumn isoelectric focusing (mIEF) and similarity analysis with the earth mover's distance (EMD) metric, we proposed the concept of isoelectric point (pI) barcode for the identification of species origin of raw meat. At first, we used the mIEF to analyze 14 meat species, including 8 species of livestock and 6 species of poultry, to generate 140 electropherograms of myoglobin/hemoglobin (Mb/Hb) markers. Secondly, we binarized the electropherograms and converted them into the pI barcodes that only showed the major Mb/Hb bands for the EMD analysis. Thirdly, we efficiently developed the barcode database of 14 meat species and successfully used the EMD method to identify 9 meat products thanks to the high throughput of mIEF and the simplified format of the barcode for similarity analysis. The developed method had the merits of facility, rapidity and low cost. The developed concept and method had evident potential to the facile identification of meat species.

Dietary Heme-Containing Proteins: Structures, Applications, and Challenges

Heme-containing proteins, commonly abundant in red meat and blood, are considered promising dietary sources for iron supplementation and fortification with higher bioavailability and less side effects. As the precise structures and accurate bioactivity mechanism of various heme-containing proteins (hemoglobin, myoglobin, cytochrome, etc.) are determined, many methods have been explored for iron fortification. Based on their physicochemical and biological functions, heme-containing proteins and the hydrolyzed peptides have been also widely utilized as food ingredients and antibacterial agents in recent years. In this review, we summarized the structural characterization of hemoglobin, myoglobin, and other heme proteins in detail, and highlighted recent advances in applications of naturally occurring heme-containing proteins as dietary iron sources in the field of food science and nutrition. The regulation of absorption rate, auto-oxidation process, and dietary consumption of heme-containing proteins are then discussed. Future outlooks are also highlighted with the aim to suggest a research line to follow for further studies.

Visual Detection of Chicken Adulteration Based on a Lateral Flow Strip-PCR Strategy

The aim of this study was to develop an accurate, easy-to-use, and cost-effective method for the detection of chicken adulteration based on polymerase chain reaction (PCR) and lateral flow strip (LFS). We compared six DNA extraction methods, namely the cetyltrimethylammonium bromide (CTAB) method, salt method, urea method, SDS method, guanidine isothiocyanate method, and commercial kit method. The chicken cytb gene was used as a target to design specific primers. The specificity and sensitivity of the PCR-LFS system were tested using a self-assembled lateral flow measurement sensor. The results showed that the DNA concentration obtained by salt methods is up to 533 ± 84 ng µL⁻¹, is a suitable replacement for commercial kits. The PCR-LFS method exhibits high specificity at an annealing temperature of 62 °C and does not cross-react with other animal sources. This strategy is also highly sensitive, being able to detect 0.1% of chicken in artificial adulterated meat. The results of the test strips can be observed with the naked eye within 5 min, and this result is consistent with the electrophoresis result, demonstrating its high accuracy. Moreover, the detection system has already been successfully used to detect chicken in commercial samples. Hence, this PCR-LFS strategy provides a potential tool to verify the authenticity of chicken.

Isolation and Characterization of Chicken Serum Albumin (Hen Egg Alpha-Livetin, Gal d 5)

Chicken serum albumin, i.e., hen egg alpha-livetin, is a recognized food allergen in chicken meat and hen eggs. Currently, there is no immunoassay available for its detection from food matrices. The characterization of chicken serum albumin-specific antibodies and the extraction of the target protein are essential for immunoassay development. One monoclonal antibody (mAb), 3H4, was used in this study due to its selectivity to a linear epitope on avian serum albumin. To study the extraction of chicken serum albumin, phosphate-buffered saline (PBS) with two additives, i.e., sodium dodecyl sulfate (SDS) and dithiothreitol (DTT), was used for its extraction from chicken blood plasma and hen egg yolk. SDS and DTT improved the chicken serum albumin’s recovery and enhanced chicken serum albumin’s immunodetection. In addition, chicken serum albumin retained the best solubility and immunoreactivity after heat treatment in a neutral condition. It experienced degradation and aggregation in acidic and alkaline conditions, respectively. Overall, PBS containing 0.1% SDS and 1 mM DTT (pH 7.2) was a better extraction buffer for chicken serum albumin. However, the complexity of the food matrix and elevated temperature could reduce its solubility and immunoreactivity.

Smartphone-based competitive immunoassay for quantitative on-site detection of meat adulteration

Rapid, sensitive, and portable analytical methods for on-site inspection of food fraud are now an urgent requirement to ensure food quality and satisfy the ethnic considerations of consumers. Hence, for the first time, a colorimetric smartphone-based immunoassay was developed for the on-site detection of pork adulteration in meat. In detail, the immunoassay was based on a competitive strategy in which immobilized standard porcine IgG competed with the target porcine IgG extracted in a single step from meat samples. The parameters involved in each step of the immunoassay conception and the digital colorimetric detection were carefully investigated and optimized. Using polystyrene microplates as ready-to-use stable and portable immunoplatforms, TMB as chromogenic substrate, smartphone as signal readout, and Image J software for image processing; the developed immunoassay was able to detect as low as 0.01% of pork in meat mixtures in a total assay time of 30 min. The selectivity of the immunoassay was evaluated for different meat species, and it was shown to selectively respond only to pork. Furthermore, excellent stability of the prepared immunological platform was demonstrated under extreme temperature conditions (50 °C), which confirms its high portability potential for in situ quantification of pork, while being relatively cost effective and non-laborious. The developed method also provides great precision (RSD < 6%) and accuracy (relative error< 6%). Given the universal use of smartphones as portable and affordable devices, such format of immunoassay could be a promising approach for rapid and sensitive real-time monitoring of food fraud.

Non-Specific Binding and Cross-Reaction of ELISA: A Case Study of Porcine Hemoglobin Detection

Different types of enzyme-linked immunosorbent assays (ELISA) have been widely used to control food safety and quality. To develop an accurate and reproducible ELISA, false immunodetection results caused by non-specific binding (NSB) and cross-reaction must be prevented. During the case study of sandwich ELISA development for the detection of porcine hemoglobin (P_Hb), several critical factors leading to NSB and cross-reaction were found. First, to reduce the NSB of the target analyte, the selection of microplate and blocker was discussed. Second, cross-reactions between enzyme-labeled secondary antibodies and sample proteins were demonstrated. In addition, the function of (3-aminopropyl)triethoxysilane (APTES) was evaluated. Overall, this study highlights the essence of both antibody and assay validation to minimize any false-positive/negative immunodetection results.

Immunochromatographic assay based on high-affine monoclonal antibody for the detection of imidocarb in milk

Imidocarb (IM) is an antiprotozoal agent, which is mainly used to treat babesiosis and piroplasmosis for animals. However, overdose or improbable utilization cause IM residues in animal origin products, which would be harmful to human health. Here, a monoclonal antibody (mAb) against IM with extremely sensitive and specific features has been successfully prepared from a novel immunogen synthesized by virtue of the active ester method. The concentration of half-maximal inhibition (IC₅₀ ) of the mAb was 0.074 ng/ml and the affinity constant was 4.58 × 10¹⁰ L/mol. On the basis of this condition, an immunochromatographic strip (ICS) is proposed that could be applied in milk samples to test IM rapidly. For the ICS, the visual detection limit (cut-off value) was 5 ng/ml, IC₅₀ was 0.4 ng/ml, the limit of detection (LOD) was 0.078 ng/ml, the linear detection scope was 0.117 to 1.37 ng/ml. The recovery rates ranged from 88.83% to 91.47% and coefficients of variation (CV) were in the spectrum of 7.31% to 9.43%. In general, the recommended test strip provided an exceedingly simple and reliable detection method for quickly testing the IM. PRACTICAL APPLICATION: In our joint efforts, an extremely sensitive monoclonal antibody against imidocarb was obtained and a test strip for the rapid detection of imidocarb in milk was developed. The developed method could be applied to the field and provided great potential for analytical of imidocarb in other matrixes.

Determination of robenidine in shrimp and chicken samples using the indirect competitive enzyme-linked immunosorbent assay and immunochromatographic strip assay

In this study, the monoclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and an immunochromatographic strip assay were developed for the rapid screening of robenidine hydrochloride (ROBH) in samples.

Procedures for the identification and detection of adulteration of fish and meat products

The addition or exchange of cheaper fish species instead of more expensive fish species is a known form of fraud in the food industry. This can take place accidentally due to the lack of expertise or act as a fraud. The interest in detecting animal species in meat products is based on religious demands (halal and kosher) as well as on product adulterations. Authentication of fish and meat products is critical in the food industry. Meat and fish adulteration, mainly for economic pursuit, is widespread and leads to serious public health risks, religious violations, and moral loss. Economically motivated adulteration of food is estimated to create damage of around € 8 to 12 billion per year. Rapid, effective, accurate, and reliable detection technologies are keys to effectively supervising meat and fish adulteration. Various analytical methods often based on protein or DNA measurements are utilized to identify fish and meat species. Although many strategies have been adopted to assure the authenticity of fish and meat and meat a fish products, such as the protected designation of origin, protected geographical indication, certificate of specific characteristics, and so on, the coverage is too small, and it is unrealistic to certify all meat products for protection from adulteration. Therefore, effective supervision is very important for ensuring the suitable development of the meat industry, and rapid, effective, accurate, and reliable detection technologies are fundamental technical support for this goal. Recently, several methods, including DNA analysis, protein analysis, and fat-based analysis, have been effectively employed for the identification of meat and fish species.

Recombinase Polymerase Amplification Based Multiplex Lateral Flow Dipstick for Fast Identification of Duck Ingredient in Adulterated Beef

Simple Summary

The adulteration and authenticity of meat and meat products has become a global social problem. Beef is often intentionally adulterated with cheap meat. In order to ensure the authenticity of meat, and provide technical support to regulatory authorities, we developed a rapid and visual method to detect duck ingredient in adulterated beef. This method is implemented recombinase polymerase amplification (RPA) and multiplex lateral flow dipstick (MLFD) cascade. The whole RPA-MLFD reaction process can be finished within 35 min, and the results can be determined by naked eyes. RPA-MLFD was applied to simultaneously detect duck ingredient and beef ingredient without using additional instruments. An adulteration ratio as low as 5% of duck ingredient in beef can be easily measured. Moreover, we confirmed that our new method held good potential in the detection of commercially processed meat samples. Therefore, this study reports a useful animal derived meat adulteration detection method, which have potential application in future.

Abstract

Meat adulteration has become a global social problem. In order to protect consumers from meat adulteration, several methods have been developed to identify meat species. However, the conventional methods are labor-intensive, time-consuming and require instruments. In the present study, a rapid and visual method based on recombinase polymerase amplification (RPA) and multiplex lateral flow dipstick (MLFD) was developed to detect duck ingredient in adulterated beef. Using recombinase and strand displacement polymerase enable RPA to amplify different double-labeled DNA amplicons at room temperature, which can be further detected by MLFD. The whole reaction process can be finished within 35 min, and the results can be determined by naked eyes. As low as 5% of duck ingredient in adulterated beef can be easily measured. Moreover, we confirmed that our new method held good potential in the detection of commercially processed meat samples. In conclusion, this study reported a useful animal derived meat adulteration detection method, which have potential application in future.

Comparative review and the recent progress in detection technologies of meat product adulteration

Meat adulteration, mainly for the purpose of economic pursuit, is widespread and leads to serious public health risks, religious violations, and moral loss. Rapid, effective, accurate, and reliable detection technologies are keys to effectively supervising meat adulteration. Considering the importance and rapid advances in meat adulteration detection technologies, a comprehensive review to summarize the recent progress in this area and to suggest directions for future progress is beneficial. In this review, destructive meat adulteration technologies based on DNA, protein, and metabolite analyses and nondestructive technologies based on spectroscopy were comparatively analyzed. The advantages and disadvantages, application situations of these technologies were discussed. In the future, determining suitable indicators or markers is particularly important for destructive methods. To improve sensitivity and save time, new interdisciplinary technologies, such as biochips and biosensors, are promising for application in the future. For nondestructive techniques, convenient and effective chemometric models are crucial, and the development of portable devices based on these technologies for onsite monitoring is a future trend. Moreover, omics technologies, especially proteomics, are important methods in laboratory detection because they enable multispecies detection and unknown target screening by using mass spectrometry databases.

A highly sensitive monoclonal antibody-based paper sensor for simultaneously detecting valnemulin and tiamulin in porcine liver

Valnemulin (VAL) and tiamulin (TIA) are pleuromutilin antibiotics used primarily for treating bacterial infections in swine or other food animals. Furthermore, VAL and TIA are also employed as feed additives to promote animal growth. However, the illegal use of VAL and TIA could cause a series of hazards to consumers. Here, VAL was designed to be conjugated with bovine serum protein to prepare immunogen. A highly sensitive monoclonal antibody that recognized both VAL and TIA has been successfully produced. Moreover, an immunochromatographic strip assay for rapidly screening VAL and TIA in porcine liver was established with visual detection limits (cutoff values) of 50 and 25 ng/g, respectively. The IC₅₀ values calculated from the equation of the standard curve were 6.06 and 3.45 ng/g and the limits of detection were 0.96 and 0.29 ng/g for VAL and TIA. According to the recovery experiment results, the test strip exhibited acceptable accuracy and precision. Generally, the proposed strip provided a practical tool for the detection of VAL and TIA. PRACTICAL APPLICATION: We produced a highly sensitive monoclonal antibody and developed an immunoassay strip for simultaneously monitoring TIA and VAL. Additionally it was preliminarily confirmed that the rapid detection tool was suitable for screening TIA and VAL in porcine liver.

Monoclonal antibody-based sandwich enzyme-linked immunosorbent assay for porcine hemoglobin quantification

The major objective of this study was to establish a monoclonal antibody (mAb)-based sandwich enzyme-linked immunosorbent assay (ELISA) for the quantification of porcine hemoglobin (P_Hb) in raw meat products. Before assay development, two mAbs immunoreactive to P_Hb β subunit with different epitopes were characterized. The optimized immunoassay was specific to P_Hb and had a wide P_Hb working range from 15.6 µg/mL to 3,000 µg/mL and high reproducibility with low coefficient of variations (CV < 20%). Through this assay, the estimated P_Hb residuals in pork loin and shoulder meats were 0.4 mg/g and 1.1 mg/g, respectively. In addition, this immunoassay could effectively quantify P_Hb in laboratory-spiked meats (pork loin, pork shoulder, and turkey breast) with acceptable recovery. Overall, this is the first mAb-based sandwich ELISA that is suitable for the government, food industry, and third-party authority to monitor P_Hb residuals or porcine blood adulteration in raw pork and pork-free meat products.

A novel non-enzymatic sensing platform for determination of 5'-guanosine monophosphate in meat

Graphitic carbon nitride (g-C₃N₄) doped carboxylated MWCNTs nanocomposite was synthesized using a simple method. The composite films containing 45 wt%, 50 wt%, 56 wt%, 67 wt% fraction of the carboxylated MWCNTs doped into g-C₃N₄ were fabricated and characterized. An electrochemical non-enzymatic sensor for determination of 5'-guanosine monophosphate (GMP) based on the nanocomposite was developed. The results indicate that the g-C₃N₄-carboxylated MWCNTs nanocomposite has highly electrocatalytic activity, good conductivity and biocompatibility, which plays an essential role in the determination of GMP. Under the optimum conditions, the linear fitting equation was I (µA) = -0.0022c (μg·mL^-1) + 0.3560 (R² = 0.9982). The linear range was from 0.5 to 100 μg·mL^-1 and the detection limit (LOD, S/N = 3) was 0.109 μg·mL^-1. This non-enzymatic sensor can offer a better alternative to other methods for the analysis of GMP because of cheap cost, low detection limit and good anti-jamming capability in meat quality evaluation.