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Effect of the Food Matrix and
Processing on the Allergenic
Activity of Foods
Overview
• Introduction
• Development of Food Processing
• Processing-Induced Modification of Food
Proteins
• Impact of Processing on Food Allergens
Introduction
• Challenging
• Allergic reaction: IgE–binding capacity
• Food allergies are largely caused by protein
molecules
• Food processing affect the way which food
proteins are presented to the immune system
Middleton 8th edition
Epitopes
The sites on a molecule recognized by IgE: epitopes
• Linear epitopes
– short regions of about 8-15 amino acid residues
– mobile
– stable in response to food processing procedures
• Conformational epitopes
– Formed from various segments of a polypeptide by
protein folding
– Food processing procedures can either destroy
conformational epitopes or reveal new epitopes
previously hidden by protein folding
Middleton 8th edition
Introduction
• The effects of thermal processing on
allergenicity of foods is difficult
– Many time-temperature combinations
– Impact of water activity
– Different methods
Middleton 8th edition
Development of Food Processing
• 125,000 years ago, enabled the development of cooking
• Heated stones for boiling, burying food wrapped in
leaves in the hot embers of fires, or baking fish in clay
• Processing procedures: remove inedible tissues
and debris and the use of combined physical,
chemical, and agrochemical treatments that
prevent spoilage by insect pests or fungal and
microbial growth
Middleton 8th edition
Processing-Induced Modification of Food Proteins
Processing-Induced Modification
of Food Proteins
• Food processing
– Destroy linear and conformational IgE-binding
epitopes
– Establish the exposure of formerly hidden
antigenic sites
– Change the susceptibility to digestion
• The presence of other components (fats, sugars)
determine the extent to which proteins are
modified during cooking
Food Processing
• Thermal treatments reduce the size of the milk
fat globule, prevent microbiologic spoilage and
enhance shelf life
– Pasteurization: heating milk to 72 c for 15 sec
– Sterilization
– UHT: heating milk to 140-150 c for a few sec
– Retorting/canning
Middleton 8th edition
• Subjects: 6 mo-21 yr
• Muffin: 350 F x 30 min, Waffle 500 Fx 3 min total milk protein 1.3 g, 4 equal portions over 1 hr, repeat 2 hr later
• Heated milk–reactive subjects: larger SPT, higher specific IgE with sen 100%, NPV 100%
• At 3 months, subjects ingesting heated milk products had significantly smaller SPT, higher casein-IgG4
Nowak-Wegrzyn A, et al. J Allergy Clin Immunol 2008;122:342-7
Food Processing
• Dry processing procedures: roasting and frying
• Freeze-drying such as herbs and spices, for
which preservation of flavor is important
• Proteolysis/hydrolysis in lentils and cow’s milk
– reducing the proteins to such small peptides that
no longer able to trigger an allergic reaction
– either through chemical means (extreme pH) or
food-grade enzymes (often from microbes)
Food Processing
• Bleaching and deodorizing processes involved
in oil refining removes almost all the protein
residues, rendering them almost protein-free
Crevel RWR et al. Food Chem Toxicol 2000;38:385-93 Middleton 8th edition
Food Processing
• Fermentation of the complex food
– Complex mixtures of microbes involves lactic acid
bacteria and yeast
– Cheese, yogurt, preserved meat products;
sausages and salamis, derived soybean product;
miso and soy sauce
Food Processing
• Fermented beverages; beer and wine
– May originate from fish collagen or egg
– Removal of residual yeast particles
– Reported allergic reactions to residual fining
agents
– Safe for most individuals with egg, milk, or fish
allergies
Food Processing
• Maillard reaction: a form of nonenzymatic browning
– a hexose sugar such as glucose with a free amino
group from a protein
– formation an unstable Schiff base that then cyclizes to
form more stable Amadori products (early glycation
products)
• Melanoidins: advanced Maillard reaction products
that confer the brown color of baked, roasted, and
fried foods and the associated toasted flavors
Impact of Processing on Food Allergens
Impact of Processing
on Food Allergens
• Affect the way in which food proteins are
presented to the immune system
• Labile epitopes: Native lgE epitopes lost during
unfolding (especially globular proteins) or
obscured in aggregates
• Neoepitopes: New lgE epitopes revealed during
unfolding
• Stable epitopes: Disordered structures remain
even after unfolding of native proteins
Middleton 8th edition
Cupins
• A number of plant food allergens share the core
β-barrel motif of the cupin superfamily, includes
the vicilin-like 7S seed storage globulins and the
legumin-like 11S seed storage globulins
Middleton 8th edition
Cupins
• Legumes; soybean, peanut, lupin
• Tree nuts; hazelnut, walnut, cashew, pecan,
almond
• Other seeds; sesame, mustard
• Seed storage globulins: prone to aggregate
formation, especially after heating or after
treatment with solutions of extreme pH and low
ionic strength
Cupins
• Boiling the 7S globulin from peanut (Ara h 1)
– aggregates formed
– reduces IgE-binding capacity formation
– Unaltered T cell reactivity
Blanc F, et al. Mol Nutr Food Res 2011;55:1887-94.
Roasted peanuts
• Hydrolysis of both Ara h 1 and Ara h 2/6
• Ara h 1
– Decreased the IgE-binding capacity
– Increased the capacity to elicit mediator
release
• Ara h 2/6: decreased both the IgE-binding
capacity and degranulation capacity
Vissers YM, et al. Clin Exp Allergy 2011;4: 1631-42
Vissers YM, et al. PLoS One 2011;6:e23998
Frying or boiling compared with roasted
peanuts
• Less Ara h 1, reduction of IgE-binding intensity
• Lee IgE binding to Ara h 2 and Ara h 3
• Similar protein amounts
• Explain the difference in prevalence of peanut allergy observed in the 2 countries
Beyer K, et al. J Allergy Clin Immunol 2001;107:1077-81
USA Roasting: 170c, 20 min Frying in pure vegetable oil 5-10 min Boiling: 100 c, 20 min
Middleton 8th edition
Cupins
• Not as well characterized in other legume
allergens
• Boiling lentils
– Lost allergenic globulin and destroy most of
the IgE-binding activity
– Some resistant fragments do remain
Prolamin superfamily
• Sensitization to seed storage prolamins is
associated with conditions such as atopic
dermatitis and exercise-induced
anaphylaxis
• 3 groups of proteins that share a
conserved skeleton of cysteine residues in
a three-dimensional structure
Prolamin superfamily
• Containing 5 α-helices arranged in a right-
handed superhelix
1. 2S albumins: low-molecular-weight seed
proteins, some of which act as storage
proteins
2. Lipid-transfer proteins (LTPs); disulfide
bonds allows lipids to bind
3. Cereal α-amylase inhibitors
Prolamin superfamily
• Lipid-transfer proteins (LTPs)
– Expression in fresh fruits and vegetables
changes during ripening and storage
– Located in the outer layer of fruits and
seeds, and removal of these outer layers,
such as by peeling, significantly reduces
the potential for an allergic reaction
Middleton 8th edition
Prolamin superfamily
• The level of LTP allergen from apple;
Apple, Mal d 3
• Increased when mature, the rate was dependent
on cultivar and tree position
• Decreased during postharvest storage
• Cox’s orange pippin, Jonagored, and Gala
Sancho AI, et al. J Agric Food Chem 2006;54: 5098-104
Middleton 8th edition
Prolamin superfamily
• 2S albumin and LTP allergens appear to be more thermostable than many other types of allergens
• Peanuts, tree nuts, Brazil nuts, and sesame seeds heated to temperatures >110° C, the 2S albumin begins to unfold
• Peach LTP, Pru p 3 retain its allergenic activity in commercial juices and after ultrafiltration
Johnson PE, et al. Mol Nutr Food Res 2010;54: 1701-10
Brenna O, et al. J Agric Food Chem 2004;8:493-7
Prolamin superfamily
• Severe heat treatment (100C, 2 hr)
– Minor changes in protein structure
– Decrease in IgE-binding and biological activity
• Glycation had a protective effect
• The presence of sugars in fruits may contribute to the
thermostability of the allergenic activity of LTP in heat-
processed foods
Sancho AI, et al. Allergy 2005;60: 1262-8
BET V 1 Superfamily
• Group of proteins with a shared β-barrel
structure that possess a central lipid-binding
tunnel, belongs to PR group 10 proteins
• Initially sensitized to Bet v 1 from birch pollen
and related proteins from other pollens
• IgE-binding epitopes on Bet v 1 sites on the
native proteins on fresh fruits and vegetables
Pollen-fruit
Middleton 8th edition
BET V 1 Superfamily
• Generally thermolabile
• Purified protein is stable after heating to 90 c
• Processed fruits and vegetables lost the native
structure
• Can consume cooked fruits and vegetables
• Apples
– Preparing an apple for a fresh fruit salad can
be enough to prevent it from eliciting intense
oral itching
Middleton 8th edition
BET V 1 Superfamily
Celery
• Celery remains allergenic even after extended
thermal treatment (76.07 min,100 C)
• Celery spice is allergenic for patients with an
allergy to raw celery
Ballmer-Weber BK, et al. Allergy 2002;57:228-35
Tropomyosin
• Crustacean and molluscan shellfish species
• α-helical structural protein
• Found in both muscle and nonmuscle cells
• The greasy back shrimp (Met e 1): heat-stable
• Boiling may enhance the allergenicity of shrimp for
certain individuals
• Boiled extracts induced larger wheals than raw extracts
Carnes J, et alAnn Allergy Asthma Immunol 2007;98:349-54
Parvalbumins
• White muscle of fish
• Thermal processing usually reduces but does
not abolish the allergenic activity of fish
• Enhance the allergenic activity in a few people
• Severe thermal processing; canning reduces its
allergenic activity more extensively than boiling
Bernhisel-Broadbent J, et al. J Allergy Clin Immunol 1992;90:622-9