Heat-induced alterations in cashew allergen solubility and IgE binding

Quantifying allergenic proteins using antibody-based methods or liquid chromatography-mass spectrometry/mass spectrometry: A review about the influence of food matrix, extraction, and sample preparation

Accurate quantification of allergens in food is crucial for ensuring consumer safety. Pretreatment steps directly affect accuracy and efficiency of allergen quantification. We systematically reviewed the latest advances in pretreatment steps for antibody-based methods and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) protein quantification methods in food. For antibody-based methods, the effects induced by food matrix like decreased allergen solubility, epitope masking, and nonspecific binding are of the upmost importance. To mitigate interference from the matrix, effective and proper extraction can be used to obtain the target allergens with a high protein concentration and necessary epitope exposure. Removal of interfering substances, extraction systems (buffers and additives), assistive technologies, and commercial kits were discussed. About LC-MS/MS quantification, the preparation of the target peptides is the crucial step that significantly affects the efficiency and results obtained from the MS detector. The advantages and limitations of each method for pre-purification, enzymatic digestion, and peptide desalting were compared. Additionally, the application characteristics of microfluidic-based pretreatment devices were illustrated to improve the convenience and efficiency of quantification. A promising research direction is the targeted development of pretreatment methods for complex food matrices, such as lipid-based and carbohydrate-based matrices.

Food Allergens of Plant Origin

This review presents an update on the physical, chemical, and biological properties of food allergens in plant sources, focusing on the few protein families that contribute to multiple food allergens from different species and protein families recently found to contain food allergens. The structures and structural components of the food allergens in the allergen families may provide further directions for discovering new food allergens. Answers as to what makes some food proteins allergens are still elusive. Factors to be considered in mitigating food allergens include the abundance of the protein in a food, the property of short stretches of the sequence of the protein that may constitute linear IgE binding epitopes, the structural properties of the protein, its stability to heat and digestion, the food matrix the protein is in, and the antimicrobial activity to the microbial flora of the human gastrointestinal tract. Additionally, recent data suggest that widely used techniques for mapping linear IgE binding epitopes need to be improved by incorporating positive controls, and methodologies for mapping conformational IgE binding epitopes need to be developed.

Effect of processing treatments on the allergenicity of nuts and legumes: A meta-analysis

The effective food processing to reduce nuts and legumes allergenicity could not be easily and directly concluded from reading a few published reports. Therefore, we conducted a meta-analysis to investigate this issue. A literature search was conducted in eight electronic databases from January 2000 to June 11, 2021. The primary outcome of interest was the allergenicity of processed nuts or legumes determined by enzyme-linked immunosorbent assay from in vitro studies. Data with the standardized mean difference (SMD) of 95% confidence interval (CI) were pooled using a random-effect model by RevMan 5.4 software. Heterogeneity was assessed using Cochran's Q (P_Q ) and I² tests. The search strategy identified 18,793 articles. However, only 61 studies met the inclusion criteria and were included in this meta-analysis. There were 21 and 15 types of respective single and combined food processing treatments analyzed for their effects on reducing allergenicity. In single processing treatment, the extrusion and fermentation had the largest reduction in allergenicity, considering their SMD value, that is, -20.19 (95% CI: -22.22 to -18.17; the certainty of evidence: moderate) and -20.8 (95% CI: -24.10 to -17.50; the certainty of evidence: moderate), respectively. Whereas in the combination, the treatment of fermentation followed by proteolytic hydrolysis showed the most significant reduction (SMD: -53.34; 95% CI: -70.18 to -36.5) and the evidence quality of this treatment was considered moderate. In conclusion, these three food processing methods showed a desirable impact in reducing nuts or legumes allergenicity. PRACTICAL APPLICATION: Nuts and legumes play an essential role as protein sources in food consumption worldwide, but they usually contain allergens. Our study has investigated the food processing methods that effectively reduce their allergenicity by meta-analysis. The result gives valuable information for further laboratory investigation on allergens and can be used by food industries in providing foods from nuts and legumes with lower allergenicity.

A comprehensive overview of emerging processing techniques and detection methods for seafood allergens

Seafood is rich in nutrients and plays a significant role in human health. However, seafood allergy is a worldwide health issue by inducing adverse reactions ranging from mild to life-threatening in seafood-allergic individuals. Seafood consists of fish and shellfish, with the major allergens such as parvalbumin and tropomyosin, respectively. In the food industry, effective processing techniques are applied to seafood allergens to lower the allergenicity of seafood products. Also, sensitive and rapid allergen-detection methods are developed to identify and assess allergenic ingredients at varying times. This review paper provides an overview of recent advances in processing techniques (thermal, nonthermal, combined [hybrid] treatments) and main allergen-detection methods for seafood products. The article starts with the seafood consumption and classification, proceeding with the prevalence and symptoms of seafood allergy, followed by a description of biochemical characteristics of the major seafood allergens. As the topic is multidisciplinary in scope, it is intended to provide information for further research essential for food security and safety.

Proteomic Analysis of Oil-Roasted Cashews Using a Customized Allergen-Focused Protein Database

Cashews are one of the most prevalent causes of tree nut allergies. However, the cashew proteome is far from complete, which limits the quality of peptide identification in mass spectrometric analyses. In this study, bioinformatics tools were utilized to construct a customized cashew protein database and improve sequence quality for proteins of interest, based on a publicly available cashew genome database. As a result, two additional isoforms for cashew 2S albumins and five other isoforms for cashew 11S proteins were identified, along with several other potential allergens. Using the optimized protein database, the protein profiles of cashew nuts subjected to different oil-roasting conditions (139 and 166 °C for 2-10 min) were analyzed using discovery LC-MS/MS analysis. The results showed that the cashew 2S protein is most heat-stable, followed by 11S and 7S proteins, though protein isoforms might be affected differently. Preliminary target peptide selection indicated that out of the 29 potential targets, 18 peptides were derived from the newly developed database. In the evaluation of thermal processing effects on cashew proteins, several Maillard reaction adducts were also identified. The cashew protein database developed in this study allows for comprehensive analyses of cashew proteins and development of high-quality allergen detection methods.

Recent advances in analytical strategies and microsystems for food allergen detection

Food allergies are abnormal immune responses that typically occur within short period after exposure of certain allergenic proteins in food or food-related resources. Currently, the means to treat food allergies is not clearly understood, and the only known prevention method is avoiding the consumption of allergen-containing foods. From the viewpoint of analytical methods, the effective detection of food allergens is hindered by the effects of various treatment processes and food matrices on trace amounts of allergens. The aim of this effort is to provide the reader with a clear and concise view of new advances for the detection of food allergens. Therefore, the present review explored the development status of various biosensors for the real-time, on-site detection of food allergens with high selectivity and sensitivity. The review also described the analytical consideration for the quantification of food allergens, and global development trends and the future availability of these technologies.

Characterization of Anti-Ana o 3 Monoclonal Antibodies and Their Application in Comparing Brazilian Cashew Cultivars

Ana o 3 is an immuno-dominant cashew nut allergen. Four monoclonal antibodies to Ana o 3 (2H5, 6B9C1, 19C9A2, and 5B7F8) were characterized by ELISA and in silico modeling. The 2H5 antibody was the only antibody specific for cashew nut extract. In addition to cashew nut extract, the 6B9C1 and 19C9A2 antibodies recognized pistachio extract, and the 5B7F8 recognized pecan extract. All four antibodies recognized both recombinant Ana o 3.0101 and native Ana o 3. ELISA assays following treatment of purified Ana o 3 with a reducing agent indicated that the 6B9C1 and 19C9A2 antibodies likely recognize conformational epitopes, while the 2H5 and 5B7F8 antibodies likely recognize linear epitopes. In silico modeling predicted distinct epitopes for each of the anti-Ana o 3 antibodies. Screening extracts from 11 Brazilian cashew nut cultivars using all four antibodies showed slight differences in Ana o 3 bindings, demonstrating that these antibodies could identify cultivars with varying allergen content.

Tree nut allergy

From a botanical point of view, a nut is a kind of dry, closed, unbroken, single-seeded fruit, which has a ligneous pericarp made up of several fruiting bodies surrounded by one free semen. The term “allergy to tree nuts” includes allergies to almonds, Brazil nuts, cashew nuts, hazelnuts, chestnuts, macadamia nuts, pecan nuts, pistachios and walnuts. All tree nuts belong to five orders of plants: Rosaceae, Fagales, Sapindales, Ericales and Proteales. Allergies to tree nuts usually start in childhood, but unlike other food allergies, they rarely fade away and generally persist throughout life. They are one of the main causes of serious allergic reactions ending in death in both children and adults. The epidemiology of allergy to nuts is variable and depends mainly on the geographical zone and eating habits. In northern Europe, hazelnut allergy is prevalent, whereas in the USA the most common is allergy to peanuts and, when taking tree nuts into consideration, to walnuts. The diagnosis of allergies to nuts is difficult and requires the use of the most modern research tools including molecular diagnostic techniques.

Nut Allergenicity: Effect of Food Processing

Nuts are considered healthy foods due to their high content of nutritional compounds with functional properties. However, the list of the most allergenic foods includes tree nuts, and their presence must be indicated on food labels. Most nut allergens are seed storage proteins, pathogenesis-related (PR) proteins, profilins and lipid transfer proteins (LTP). Nut allergenic proteins are characterized by their resistance to denaturation and proteolysis. Food processing has been proposed as the method of choice to alter the allergenicity of foods to ensure their safety and improve their organoleptic properties. The effect of processing on allergenicity is variable by abolishing existing epitopes or generating neoallergens. The alterations depend on the intrinsic characteristics of the protein and the type and duration of treatment. Many studies have evaluated the molecular changes induced by processes such as thermal, pressure or enzymatic treatments. As some processing treatments have been shown to decrease the allergenicity of certain foods, food processing may play an important role in developing hypoallergenic foods and using them for food tolerance induction. This work provides an updated overview of the applications and influence of several processing techniques (thermal, pressure and enzymatic digestion) on nut allergenicity for nuts, namely, hazelnuts, cashews, pistachios, almonds and walnuts.

Detection of Peanut Allergen by Real-Time PCR: Looking for a Suitable Detection Marker as Affected by Processing

Peanut (Arachis hypogaea) contains allergenic proteins, which make it harmful to the sensitised population. The presence of peanut in foods must be indicated on label, to prevent accidental consumption by allergic population. In this work, we use chloroplast markers for specific detection of peanut by real-time PCR (Polymerase Chain Reaction), in order to increase the assay sensitivity. Binary mixtures of raw and processed peanut flour in wheat were performed at concentrations ranging from 100,000 to 0.1 mg/kg. DNA isolation from peanut, mixtures, and other legumes was carried out following three protocols for obtaining genomic and chloroplast-enrich DNA. Quantity and quality of DNA were evaluated, obtaining better results for protocol 2. Specificity and sensitivity of the method has been assayed with specific primers for three chloroplast markers (mat k, rpl16, and trnH-psbA) and Ara h 6 peanut allergen-coding region was selected as nuclear low-copy target and TaqMan probes. Efficiency and linear correlation of calibration curves were within the adequate ranges. Mat k chloroplast marker yielded the most sensitive and efficient detection for peanut. Moreover, detection of mat K in binary mixtures of processed samples was possible for up to 10 mg/kg even after boiling, and autoclave 121 °C 15 min, with acceptable efficiency and linear correlation. Applicability of the method has been assayed in several commercial food products.

Advances on the rapid and multiplex detection methods of food allergens

With the gradually increasing prevalence of food allergy in recent years, food allergy has become a major public health problem worldwide. The clinical symptoms caused by food allergy seriously affect people's quality of life; there are unknown allergen components in novel food and hidden allergens caused by cross contamination in food processing, which pose a serious risk to allergy sufferers. Thus, rapid and multiplex detection methods are required to achieve on-site detection or examination of allergic components, so as to identify the risk of allergy in time. This paper reviews the progress of high-efficiency detection of food allergens, including enhanced traditional detection techniques and emerging detection techniques with the ability high-throughput detection or screening potential food allergen, such as xMAP, biosensors, biochips, etc. focusing on their sensitivity, applicability of each method in food, along with their pretreatment, advantages, limitation in the application of food analysis. This paper also introduces the challenges faced by these high-efficiency detection technologies, as well as the potential of customized allergen screening methods and rapid on-site detection technology as future research directions.

Epicutaneous immunotherapy protects cashew-sensitized mice from anaphylaxis

Background

The prevalence of tree nut allergy has increased worldwide, and cashew has become one of the most common food allergens. More critically, cashew allergy is frequently associated with severe anaphylaxis. Despite the high medical need, no approved treatment is available and strict avoidance and preparedness for prompt treatment of allergic reactions are considered dual standard of care. In the meantime, Phase III study results suggest investigational epicutaneous immunotherapy (EPIT) may be a relevant and safe treatment for peanut allergy and may improve the quality of life for many peanut allergic children.

Objective

We aimed to evaluate the capacity of EPIT to provide protection against cashew‐induced anaphylaxis in a relevant mouse model.

Methods

The efficacy of EPIT was evaluated by applying patches containing cashew allergens to cashew‐sensitized mice. As negative control, sham mice received patches containing excipient. Following treatment, mice were challenged orally to cashew and anaphylactic symptoms, as well as plasmatic levels of mast‐cell proteases (mMCP)‐1/7, were quantified.

Results

Of 16 weeks of EPIT significantly protects against anaphylaxis by promoting a faster recovery of challenged mice. This protection was characterized by a significant reduction of temperature drop and clinical symptoms, 60 minutes after challenge. This was associated with a decrease in mast‐cell reactivity as attested by the reduction of mMCP‐1/7 in plasma, suggesting that EPIT specifically decrease IgE‐mediated anaphylaxis.

Conclusion

We demonstrate that EPIT markedly reduced IgE‐mediated allergic reactions in a mouse model of cashew allergy, which suggests that EPIT may be a relevant approach to treating cashew allergy.

Microbiological, Physicochemical, and Immunological Analysis of a Commercial Cashew Nut-Based Yogurt

Nut-based milks and yogurts are gaining popularity, but may not offer the same benefits as dairy yogurts to consumers. Cashew nuts often cause severe allergic reactions, and cashew nut allergens are stable to several types of processing. To compare its characteristics to dairy yogurt and characterize the effects of fermentation on the Ana o 1-3 cashew nut allergens, a commercial yogurt made from cashew nuts (Cashewgurt) was evaluated for microbiological, physiochemical, and immunological properties. Average counts for lactobacilli and Streptococcus thermophilus were greater than 10 million colony forming units per milliliter, indicating the capacity to provide a health benefit. Cashewgurt pH and viscosity values were comparable to cow milk yogurts, and it was off white in color. SDS-PAGE analysis indicated a clear reduction in Ana o 1 and 2, and immuno-assay with polyclonal anti-cashew IgG antibody and cashew-allergic IgE indicated an overall reduction in allergen content. In contrast, SDS-PAGE, mass spectrometry, immunoblot, and ELISA all revealed that Ana o 3 was relatively unaffected by the fermentation process. In conclusion, Ana o 1 and Ana o 2 are sensitive to degradation, while Ana o 3 survives lactic acid bacterial fermentation during yogurt production. The analysis presented here indicates that cashew nut yogurt is not suitable for those with cashew nut allergy.

Quantitative allergenicity risk assessment of food products containing yellow mealworm (Tenebrio molitor)

Insect-based foods are starting to enter the EU market, raising concerns about their safety. Allergic consumers might be exposed to even a greater risk, since insects have proven to trigger allergic symptoms, particularly in patients sensitised to crustaceans. Current legislation does not enforce producers to include insects in the list of allergenic ingredients. Food allergenicity risk assessment (FARA) is still at its infancy, and the debate on the need to define allergen thresholds is open. In this paper, we aimed at applying the concepts of stochastic quantitative FARA to describe present and future scenarios of exposure to foods containing Tenebrio molitor, the yellow mealworm. According to our risk characterisation, mealworm-based food products represent a major risk for individuals allergic to crustaceans to develop symptoms after the consumption of a dose lower than a serving size. Moreover, other allergic consumers might be at risk. A correct labelling of insect containing foods would help safeguarding the health of EU allergic consumers. Quantitatively assessing the risk of allergenicity provides a clear description of the problem, facilitating the decisional process of the risk manager, supporting the implementation of effective allergen management procedures and limiting the phenomenon of uninformative precautionary labelling.

A cashew specific monoclonal antibody recognizing the small subunit of Ana o 3

Food allergies represent a substantial medical liability and preventing accidental exposure to food allergens requires constant attention. Allergic reaction to cashew nuts is frequently serious, and the small 2S albumin, Ana o 3, is an immuno-dominant cashew allergen. Ana o 3 is composed of five alpha helices, contains 2 subunits linked by cysteine disulfide bonds, and remains soluble even after extensive heating of cashew nuts. The stability and solubility properties of Ana o 3 make it an excellent target for diagnostic and detection methods and tools. In this work, a monoclonal antibody, designated 2H5, aimed at amino acids 39–54 within helices I and II of the small subunit of Ana o 3 was developed that recognizes both recombinant and native Ana o 3 and is cashew specific in ELISA experiments. The K_D against the targeted amino-acid sequence was found to be approximately 7.0 × 10⁻⁶ mg/ml (3.3 nM), while the K_D against the native protein was found to be approximately 1.2 × 10^-3 mg/ml (92 nM). The 2H5 monoclonal anti-Ana o 3 antibody can distinguish between native and recombinant proteins and represents a useful reagent for the study of antibody cashew-allergen interactions and may enable the development of cashew-specific diagnostic tools that can be used to prevent accidental cashew allergen exposures.

Application of real-time PCR for tree nut allergen detection in processed foods

Currently, food allergies are an important health concern worldwide. The presence of undeclared allergenic ingredients or the presence of traces of allergens due to accidental contamination during food processing poses a great health risk to sensitized individuals. Therefore, reliable analytical methods are required to detect and identify allergenic ingredients in food products. Real-time PCR allowed a specific and accurate amplification of allergen sequences. Some processing methods could induce the fragmentation and/or degradation of genomic DNA and some studies have been performed to analyze the effect of processing on the detection of different targets, as thermal treatment, with and without applying pressure. In this review, we give an updated overview of the applications of real-time PCR for the detection of allergens of tree nut in processed food products. The different variables that contribute to the performance of PCR methodology for allergen detection are also review and discussed.

Consumer-friendly food allergen detection: moving towards smartphone-based immunoassays

In this critical review, we provide a comprehensive overview of immunochemical food allergen assays and detectors in the context of their user-friendliness, through their connection to smartphones. Smartphone-based analysis is centered around citizen science, putting analysis into the hands of the consumer. Food allergies represent a significant worldwide health concern and consumers should be able to analyze their foods, whenever and wherever they are, for allergen presence. Owing to the need for a scientific background, traditional laboratory-based detection methods are generally unsuitable for the consumer. Therefore, it is important to develop simple, safe, and rapid assays that can be linked with smartphones as detectors to improve user accessibility. Smartphones make excellent detection systems because of their cameras, embedded flash functions, portability, connectivity, and affordability. Therefore, this review has summarized traditional laboratory-based methods for food allergen detection such as enzyme-linked-immunosorbent assay, flow cytometry, and surface plasmon resonance, and the potential to modernize these methods by interfacing them with a smartphone readout system, based on the aforementioned smartphone characteristics. This is the first review focusing on smartphone-based food-allergen detection methods designed with the intention of being consumer-friendly. Graphical abstract A smartphone-based food allergen detection system in three easy steps (1) sample preparation, (2) allergen detection on a smartphone using antibodies, which then transmits the data wirelessly, (3) analytical results sent straight to smartphone.

Origin and Processing Methods Slightly Affect Allergenic Characteristics of Cashew Nuts (Anacardium occidentale)

The protein content and allergen composition was studied of cashews from 8 different origins (Benin, Brazil, Ghana, India, Ivory Coast, Mozambique, Tanzania, Vietnam), subjected to different in-shell heat treatments (steamed, fried, drum-roasted). On 2D electrophoresis, 9 isoforms of Ana o 1, 29 isoforms of Ana o 2 (11 of the acidic subunit, 18 of the basic subunit), and 8 isoforms of the large subunit of Ana o 3 were tentatively identified. Based on 1D and 2D electrophoresis, no difference in allergen content (Ana o 1, 2, 3) was detected between the cashews of different origins (P > 0.5), some small but significant differences were detected in allergen solubility between differently heated cashews. No major differences in N- and C-terminal microheterogeneity of Ana o 3 were detected between cashews of different origins. Between the different heat treatments, no difference was detected in glycation, pepsin digestibility, or IgE binding of the cashew proteins.

Food allergen extracts to diagnose food-induced allergic diseases: How they are made

OBJECTIVE

To review the manufacturing procedures of food allergen extracts and applicable regulatory requirements from government agencies, potential approaches to standardization, and clinical application of these products. The effects of thermal processing on allergenicity of common food allergens are also considered.

DATA SOURCES

A broad literature review was conducted on the natural history of food allergy, the manufacture of allergen extracts, and the allergenicity of heated food. Regulations, guidance documents, and pharmacopoeias related to food allergen extracts from the United States and Europe were also reviewed.

STUDY SELECTIONS

Authoritative and peer-reviewed research articles relevant to the topic were chosen for review. Selected regulations and guidance documents are current and relevant to food allergen extracts.

RESULTS

Preparation of a food allergen extract may require careful selection and identification of source materials, grinding, defatting, extraction, clarification, sterilization, and product testing. Although extractions for all products licensed in the United States are performed using raw source materials, many foods are not consumed in their raw form. Heating foods may change their allergenicity, and doing so before extraction may change their allergenicity and the composition of the final product.

CONCLUSION

The manufacture of food allergen extracts requires many considerations to achieve the maximal quality of the final product. Allergen extracts for a select number of foods may be inconsistent between manufacturers or unreliable in a clinical setting, indicating a potential area for future improvement.

Effects of industrial cashew nut processing on anacardic acid content and allergen recognition by IgE

Cashew nuts are important both nutritionally and industrially, but can also cause food allergies in some individuals. The present study aimed to assess the effect(s) of industrial processing on anacardic acids and allergens present in cashew nuts. Sample analyses were performed using liquid chromatography coupled with mass spectrometry, SDS-PAGE and immunoassay. The anacardic acid concentration ranged from 6.2 to 82.6mg/g during processing, and this variation was attributed to cashew nut shell liquid incorporation during storage and humidification. Dehydrated and selected samples did not significantly differ in anacardic acid content, having values similar to the raw sample. SDS-PAGE and immunoassay analysis with rabbit polyclonal sera and human IgE indicated only minor differences in protein solubility and antibody binding following processing steps. The findings indicate that appreciable amounts of anacardic acid remain in processed nuts, and that changes to cashew allergens during industrial processing may only mildly affect antibody recognition.

Identification and Characterization of Ana o 3 Modifications on Arginine-111 Residue in Heated Cashew Nuts

Raw and roasted cashew nut extracts were evaluated for protein modifications by mass spectrometry. Independent modifications on the Arg-111 residue of Ana o 3 were observed in roasted but not raw cashew nuts. The mass changes of 72.0064 or 53.9529 Da are consistent with the formation of carboxyethyl and hydroimidazolone modifications at the Arg-111 residue. These same modifications were observed in Ana o 3 purified from roasted but not raw cashew nuts, albeit at a relatively low occurrence. Circular dichroism indicated that Ana o 3 purified from raw and roasted cashew nuts had similar secondary structure, and dynamic light scattering analysis indicated there was no observable difference in particle size. The stability of Ana o 3 purified from raw and roasted cashew nuts to trypsin was similar in the absence of or following treatment with a reducing agent. Only minor differences in IgE binding to Ana o 3 were observed by ELISA among a cohort of cashew-allergic patient sera.