Food Biochemistry and Food Processing (2 edition)

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804 Part 8: Food Safety and Food Allegens

allergy is the most commonly occurring food hypersensitivity

with symptoms usually becoming evident in the child’s first year.

Major Egg Allergens

Egg white is more allergenic than the egg yolk. Ovalbumin and

ovocumoid, the two most potent egg allergens together make

up about 65% of the composition of egg white proteins. Oval-

bumin has a MW of 44.5 kDa and contains 385 amino acids.

Using pooled sera from 18 egg-allergic patients, Mine and Rupa

(2003) identified five IgE binding linear epitopes in the primary

structure of the protein. Four of the five epitopes were exposed

at the surface of the protein.

Ovomucoid, the other major allergen, is a 28 kDa MW protein

comprising 186 amino acids. The protein has three structurally

distinct domains (Domain I, II and III), which are cross-linked

by disulfide bonds. Several linear sequences representing aller-

genic epitopes recognised by both IgE and IgG antibodies have

been identified (Zhang and Mine 1998, Mine and Zhang 2002).

Ovomucoid also contains 20–25% carbohydrate moieties. Most

reports indicate that the carbohydrate moieties are not immuno-

genic; however, some studies suggest that the carbohydrate re-

gion in the third domain is immunologically active (Mine and

Rupa 2004). Ovomucoid is relatively stable to digestion, and

heat and allergenic fragments have been detected even after di-

gestion by pepsin.

Other reported egg allergens are ovotransferrin (MW 76 kDa)

and lysozyme (MW 14.3 kDa). Aabin et al. (1996) reported

a higher frequency of reactivity for ovotransferrin (53%) than

for ovomucoid (38%) and ovalbumin (32%), suggesting that it

may be a more important allergen than the latter two. The same

authors reported frequency of reactivity of 15% for lysozyme.

Very few studies have reported on the allergenicity of egg yolk

proteins; however, some of the allergenic proteins identified in

egg yolk include apovitellenin I, apovitellenin VI and phosvitin

(Walsh et al. 1988, 2005).

Thresholds of Clinical Reactivity to Eggs

Reported thresholds of clinical reactivity to eggs range between

0.13 and 6.5 mg of hen’s egg protein (Morisset et al. 2003a,

Taylor et al. 2004). As with other allergens, there are currently

no cures for egg allergy, and the best management tool is the

reading of food labels and avoidance of foods containing egg

or egg-derived ingredients. The use of multiple definitions for

eggs and egg ingredients (e.g. albumin, albumen, conalbumin,

egg nog, egg yolk, egg white, lecithin, livetin, lysozyme, oval-

bumin, ovoglobulin, ovomacroglobulin, ovomucin, ovomucoid,

ovomucin, ovovitellin, ovotransferrin and vitellin) in the past

made egg avoidance challenging. Today, most countries in North

America as well as in Europe require the use of the common

names of priority allergens when they are used as ingredients in

foods or are likely to be present in foods in spite of best efforts

to control their presence. Fortunately, most children outgrow

their egg allergy by school age (Heine et al. 2006). Egg allergy,

however, tends to persist in children with positive skin tests,

multiple allergies and/or who have more severe reactions (e.g.

respiratory symptoms, angiodema and multisystemic reactions)

or other atopic diseases such as asthma (Ford and Taylor 1982,

Mine and Yang 2008).

SOYA BEAN ALLERGENS

Soya bean (Glycine max) is a legume belonging to thefabaceae

family and theglycinegenus. On a dry basis, soya beans contain

35–40% protein, 17–23% lipid, 31% carbohydrate and 4–5%

minerals. Soya bean is considered as one of the most nutritional

plant sources of food providing a well-balanced amino acid

profile and good supplies of omega 3 and omega 6 fatty acids.

The history of the seed dates as far back as 3000–5000 years,

with its origins somewhere in Asia.

Consumption of soya bean and soya bean foods has been

linked to many health benefits. Various studies have reported as-

sociations between soya bean consumption and reduced risk

of cardiovascular disease, cancer, diabetes, bone loss and

menopausal symptoms amongst others (Friedman and Brandon

2001, Hori et al. 2001, Chen et al. 2003, Zhang et al. 2003,

Stephenson et al. 2005, Anderson 2008). These reports have fu-

elled the growth of soya foods in Western countries. In October

1999, the Food and Drug Administration of the United States

approved a health claim linking the consumption of 25 grams

of soya protein a day (as part of a diet low in saturated fatty

acids) to reduced cardiovascular disease risk (FDA 1999). For

manufacturers to make this claim, products must provide at least

6.25 grams of soya protein per serving. Soya flour and soya pro-

tein ingredients are therefore increasingly being used in many

food products.

Unfortunately, soya bean is listed in Canada, the United States,

Australia and the European Union as a priority allergen, requir-

ing labelling when it is used as an ingredient in foods. Symp-

toms of soya bean allergy are similar to the other major allergens

and include cutaneous, respiratory as well as gastrointestinal re-

sponses. Although the majority of allergic responses occur on

ingestion, allergic reactions on inhalation of soya bean and soya

bean byproducts has also been reported (Gonzalez et al. 1992,

1995, Codina et al. 1997).

Major Soya Allergens

Over 17 different allergens have been identified in soya bean.

These include soya bean glycinin (11S),β-conglycinin (7S),

soya bean vacuolar protein (Gly m Bd 30K or P34), the Kunitz

trypsin inhibitor (KTI), Gly m Bd 28K, soya bean profilin

(Gly m 3), soya bean hull proteins (Gly m 1.0101, Gly m

1.0102, Gly m 2) and the pathogensis-related (PR) soya bean

protein SAM22 (Gly m 4) (Wilson et al. 2005, L’Hocine and

Boye 2007, Boye et al. 2010).

Glycinin andβ-conglycinin have been studied extensively

as they are the major soya bean storage proteins and repre-

sent over 70% of the proteins found in soya (Liu 1997). They

are both globulins belonging to the cupin superfamily (Breit-

eneder and Radauer 2004) and have complex quaternary struc-

tures with conserved amino acid sequence homology. Glycinin