Food Allergen Testing

Molecular, Immunochemical and Chromatographic Techniques

George Siragakis, Dimosthenis Kizis, George Siragakis, Dimosthenis Kizis

• Publisher: Wiley-Blackwell
• Year: 2013
• Print ISBN: 9781118519202
• eBook ISBN: 9781118519240
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

An in-depth review of the current scientific knowledge on food allergens testing, covering the major methodologies and techniques used to detect food allergens.

Food allergens are a series of agents, mainly proteins, which cause various unpleasant and sometimes clinical symptoms in humans through consumption of foods.

Perhaps surprisingly, there are no treatments against food allergies which have been found to be 100% effective. The scope for individual difference in terms of how a person reacts to a given allergen is massive, making it incredibly difficult and complex to try and medicate against allergies.

Food Allergens Testing takes a thorough look at modern molecular biology and immunochemical techniques used to detect food allergens. The eleven chapters constitute an in-depth review of the current scientific knowledge on food allergens, covering the major methodologies and techniques used in validated analytical approaches.

The book is aimed at scientists and technical staff in the food industry and analytical laboratories who need an up-to-date treatment of both fundamental and applied research goals on food allergens, as well as a report on the validated methods currently in use for food allergens testing.

1

Introduction

Dimosthenis Kizis¹ and George Siragakis²

¹Food Allergens Laboratory, Larnaca, Cyprus

²Food Allergens Laboratory, Athens, Greece

1.1 Adverse Reactions to Food

Allergy is a disorder of the immune system caused by a variety of substances, in the majority harmless, which are present in the environment (dust, pollen or latex), animals (venom of stinging insects), foods, or medications such as aspirin and antibiotics such as penicillin. Allergic diseases may adversely affect the quality of life of a person, influencing various aspects of his or her physical, psychological, social and economic well-being. For some individuals allergy may be fatal or life threatening, depending on the severity of the adverse reaction. Food allergy has become an important food safety issue worldwide due to the increase of allergic incidents after food consumption. The important health and economic impact of this issue has led to the development of various legislative and technical actions from corresponding official bodies in the last two decades in order to manage food allergy.

An adverse reaction to food is a general term that includes a variety of clinical manifestations induced in an individual by ingestion, inhalation or contact of a food or a food additive. A first attempt to define further the term resulted in a classification of adverse reactions into either food allergy (hypersensitivity) or food intolerance, depending on the involvement or not of an immunological mechanism [1,2]. A modified classification was proposed by the European Academy of Allergology and Clinical Immunology (EAACI) subcommittee, categorizing the adverse reactions to food as either toxic or nontoxic depending on whether the abnormal clinical response relies upon the food itself (provided that the relevant dose is high enough to produce an adverse reaction), or upon the individual's susceptibility to a certain food, respectively [3]. Nontoxic adverse reactions are either immune mediated or non-immune-mediated. The term food allergy (food hypersensitivity) refers specifically to an immunological reaction involving the immunoglobulin E (IgE) mechanism. However, cell-mediated responses related or not to IgE-mediated mechanisms may lead to food allergy. The term food intolerance (nonallergic food hypersensitivity) is used only in non-immune-mediated reactions, describing an abnormal physiological response, of enzymatic, pharmacological, idiosyncratic or undefined nature, of the individual [4–6].

A food allergen is an antigenic molecule, principally of protein nature, that induces an immunologic response [2]. An allergen may exist in multiple forms (isoallergens) in one species. Isoallergens share high amino acid sequence identity and immunological cross-reactivity. If the sequence identity between allergens is greater than 90%, these are referred to as isoforms or variants (polymorphic variants) of the same allergen. The allergen nomenclature has been defined by the Allergen Nomenclature Subcommittee of the World Health Organization and the International Union of Immunological Societies (WHO–IUIS) [7] and revised by the EAACI nomenclature task force [3].

1.2 Manifestation Mechanisms and Symptoms of Food Allergy

Adverse reactions induced by food ingestion, inhalation or contact affect one or more target organs such as the skin, the respiratory and gastrointestinal tracts, and the cardiovascular system [4].

Allergic (food hypersensitivity) reactions may be IgE or non-IgE-mediated, or may include both types of mechanism. The IgE-mediated food allergic reactions can be described as generalized (involving anaphylaxis and food-dependent exercise-induced anaphylaxis), cutaneous (such as urticaria and flushing), gastrointestinal (including the oral allergy syndrome (OAS), pollen food allergy syndrome and gastrointestinal anaphylaxis) and respiratory reactions (such as broncho- and laryngo-spasms, or rhinoconjunctivitis) [8–10]. Non-IgE-mediated reactions include contact dermatitis, food-protein-induced enteropathy and celiac disease, whereas examples of mixed-type reactions (IgE and non-IgE-mediated) are atopic dermatitis, gastroenteritis and asthma [10–12].

Food-intolerance adverse reactions can be described as a physiological (nonimmunologic) response of the individual to the ingested food. They can be further classified as toxic or pharmacological (include poisoning–intoxication, e.g. bacterial or heavy metal, and reactions caused by specific food substances, e.g. caffeine or various amines) and nontoxic food intolerance, which includes adverse reactions such as lactase deficiency, gastroesophageal reflux and anorexia nervosa [2,6].

The above types of reaction can be clinically manifested by a plethora of symptoms ranging from moderate (pruritus, urticaria and various types of oedema) and more intense (bronchospasm, abdominal cramps, nausea, vomiting, diarrhoea), to serious and severe symptoms such as asthma, cardiac arrhythmias, hypotension, shock and coma [8–12].

The minimal allergen doses able to elicit an adverse reaction after ingestion, inhalation or contact are difficult to define. Allergen threshold doses below which individuals will not manifest an allergenic response (lowest observed adverse-effect level, LOAEL), may be very low, can show variability from a certain individual to another and could be affected by various factors such as exercise, stress and general health condition [13,14]. The establishment of threshold doses is determined by use of specific food challenges. A food challenge test is a progressive introduction of small amounts of the suspected allergen to the body, through an oral, respiratory or other route. The food challenge used for threshold dose establishment is known as the double-blind placebo-controlled food challenge (DBPCFC). The LOAEL may sometimes be difficult to determine due to the differences in the procedure of DBPCFC followed [15].

Current legislation does not define threshold doses for food allergens; however, future action on this matter is under discussion. The US Food and Drug Administration (FDA) has recently posted an announcement regarding the establishment of threshold doses, requesting information and data on whether threshold doses for major food allergens can be safely established. The relevant questionnaire included points for discussion on matters such as how clinical dose distribution data should be used, what approaches exist for using biological markers or other factors related to the severity of allergic responses, what data and information exist on dietary exposure patterns for individuals on allergen avoidance diets in a threshold risk assessment and what data or other information exists on current levels of exposure associated with the consumption of undeclared major food allergens in packaged foods.

1.3 Diagnosis and Treatment of Food Allergy

Diagnosis of allergic reactions to certain foods beneath physical examination or medical and case history recording is performed with in vitro determination of IgEs, and in vivo specific skin prick tests (SPTs) and positive-controlled oral food challenges (with either fresh or dehydrated food) such as DBPCFC and open food challenges (OFCs) [16]. In vitro diagnostic tests together with SPTs are used to scan for specific IgEs and thus confirm sensitization to a certain food; however, they do not establish the diagnosis of the allergy. The latter is achieved with an oral challenge. OFC is normally used after a negative SPT or in order to establish the end of an elimination diet for a certain food. Oral DBPCFC is considered so far the best type of oral challenge performed, since it introduces double blinding and placebo incorporation (neither the patient nor the medic is aware of the content of the trial), eliminating in this way subjective characterization of the results and bias.

Because the nature of the allergic responses to food is quite complex (immune or cell-dependent mechanisms, immune cross-reactivity (recognition of multiple antigens by antibodies of single specificity) for different allergens, genetic background of the individual), no general treatment for food-allergy cure has been established, yet. Strict exclusion of the offending foods from the individual's diet has proved to be the only effective way to avoid food allergy, together with standard rescue medical treatment (antihistamines, glucocorticoids, epinephrine (adrenaline)) for control of allergic symptoms due to accidental exposure.

With the aim to act on the cause and not just downregulate the symptoms of allergy, allergen immunotherapy has been developed as the alternative approach to deal with the problem [17,18]. The aim is to induce immunologic tolerance to the offending allergen through repeated administration of the allergenic products or other immuno-triggering agents (e.g. monoclonal anti-IgE antibodies) via different oral and cutaneous administrations. Despite the partial efficacy of certain types of food immunotherapy [17,18], still there are various issues to be resolved, including large-scale studies on long-term efficacy, investigation and registry of side effects, as well as discussion of various ethical and regulatory issues, in order to suggest a valid immunotherapy approach for treatment of food allergy.

1.4 Food Allergy Prevalence

The prevalence of adverse food reactions cannot be defined clearly due to the great number of allergic events of minor intensity that happen to individuals and remain undeclared. Food allergy appears to affect nearly 2.0% of the adult population [19], though this percentage is increased in young children less than 3 years old, reaching 6–8% [20]. However, there is a change observed in both the overall and specific food allergy prevalence with respect to age, due to the development of oral tolerance to specific foods from childhood to adulthood, and appearance of specific allergies such as pollinosis, which is most frequent in adults [20]. Other factors, such as the geographical location [13,21,22], the extent of industrialization of a society, the genetic background and the cultural and dietary habits of a population [22,23], play an important role in the determination of the prevalence of specific allergies.

1.5 Allergenic Foods: An Increasing List

Food allergic reactions are induced by a variety of allergens present in foods of either animal or plant origin [5]. The majority of the allergic reactions caused by animal-originated allergens are due to the consumption of certain foods such as milk, eggs, fish, crustaceans (shrimp, lobster, crab and crayfish) and molluscs (clam, scallop, oyster). Main allergens of plant origin are present in certain categories of foods such as legumes including peanut, soybean and lupin, cereals containing gluten such as wheat, rye and barley, a great variety of tree nuts including almond, hazelnut, walnut and many others, various vegetables or vegetable seeds such as celery, mustard or sesame, and fruits such as apple and peach. The phylogenetic conservation and redundancy of various proteins between species, and the stochastic (and in some cases unpredictable) nature of the individual's immunological response to any chemical substance, are two factors that could contribute in the a priori characterization of any food as ‘potentially allergenic’ for an individual. The report of case studies on rare allergic responses to certain food may of course generate an increasing list of food allergens.

The above foods are considered (either as a category or individually) main allergenic foods according to legislations issued from continental (EU, Codex Alimentarius Commission) or country (US, Japan, UK, Australia etc.) legislation bodies, and the majority of them require labelling declaration on food products. However, country legislative adaptations may extend or narrow the list of mandatory declared allergenic foods (e.g. buckwheat in Japan, various types of nut in US and Australia), and compounds present in foods (e.g. sulfur dioxide and sulfites in EU and Canada) [24].

The allergenic proteins contained in the specific foods or food categories described above are categorized in a limited number of protein families. Plant allergens are members of the cupin, prolamin and cystein protease superfamilies as well as of various pathogen-related protein families: profilin, lectin and other protein families. The main allergenic proteins of animal origin are α-lactalbumin ...

Table of contents

• Cover
• Title Page
• Copyright
• List of Contributors
• Chapter 1: Introduction
• Chapter 2: Immunodiagnostics in Food Allergen Testing
• Chapter 3: Molecular Testing for Food Allergens
• Chapter 4: LC–MS/MS Techniques for Food Allergen Testing
• Chapter 5: Detection of Animal Allergens in Foods
• Chapter 6: Detection of Plant Allergens in Foods
• Chapter 7: Gluten Testing in Foods, Pharmaceuticals and Cosmetics
• Chapter 8: Food Allergen Testing in Alcoholic and Other Beverages
• Chapter 9: Allergens in the Food Industry: Customer and Legislation Demands
• Chapter 10: Reference Materials for Food Allergen Testing
• Chapter 11: Proficiency Schemes for Food Allergen Testing
• Index