Food Biochemistry and Food Processing (2 edition)

BLBS102-c42 BLBS102-Simpson March 21, 2012 14:27 Trim: 276mm X 219mm Printer Name: Yet to Come

812 Part 8: Food Safety and Food Allegens

Table 42.5.Examples of Some Commercially Available Test Kits for Food Allergen Detection

Allergenic Food Target Allergens Test Format and LOD (mg/kg food) Testing Time (min) Manufacturer

Milk Milk protein ELISA (<5) 30 Neogen

Casein ELISA (0.5) 30 R-Biopharm

β-Lactoglobulin ELISA (0.1) 45 ELISA Systems

Eggs Egg-white protein ELISA (0.6) 35 R-Biopharm

Egg-white protein LFA (LOD: not specified) < 10 Tepnel BioSystems

Egg protein ELISA (<5) 30 Neogen

Peanuts Peanut protein LFA (<5) 10 Neogen

Peanut protein LFA (1) < 10 Tepnel BioSystems

Ara h1 LFA (5) 10 R-Biopharm

Nuts Almond protein LFA (1) < 10 Tepnel BioSystems

Hazelnut protein LFA (5) 10 R-Biopharm

Soya beans Soya protein ELISA (<5) 30 Neogen

Crustacean Tropomyosin ELISA (1) 60 ELISA Systems

Cereals Gliadin, secalins, hordeins ELISA (2) 30 R-Biopharm

Gluten Dipstick (10–20) < 15 Hallmark

Gliadin LFA (2.5) 5 R-Biopharm

Molluscs Not specified LFA (5) < 10 Tepnel BioSystems

Source: Adapted from Schubert-Ullrich et al. 2009.

LOD, limit of detection; ppm, milligram of allergenic food/kg of target food sample.

added to an antigen-coated well followed by washing to remove

any unbound material. The higher the concentration of antigen

in the sample, the lower will be the amount of free antibody able

to bind to the antigen in the well. The allergen concentration

in the sample in this assay is therefore inversely proportional

to OD values obtained after adding the substrate. Competitive

ELISA assay is known for its ability to detect relatively small

proteins (Poms et al. 2004). Today, continuous developments in

technology allows the possibility of enzyme labelling of either

the analyte or the analyte-specific antibody.

LFA and Dipstick Tests

Both of these tests are modified versions of ELISA and are

designed to meet the growing need of portable, reliable, user

friendly and cost-effective methods that can detect trace amount

of allergens in suspected foods within a short period of time

(Schubert-Ullrich et al. 2009). Although quantification is pos-

sible in principle by using special strip test readers, commer-

cially available LFA and dipstick test are primarily intended

for qualitative or semi-quantitative purposes (yes or no). Table

42.5 shows some of the commercially available tests based on

ELISA, LFA and dipstick methods.

LFAs or strip tests are immunochromatographic tests with a

mobile phase that allows movement of the allergen–antibody

complex and/or the sample along a test strip. This technique

is based on an immunochromatographic procedure that utilises

antigen–antibody properties and enables rapid detection of the

analyte (Rong-Hwa et al. 2010). For LFAs using a sandwich

ELISA, an allergen-specific detection antibody, deposited on the

membrane, is solubilised upon introduction of a liquid sample

and moves along with the sample until it reaches the zone where

a capture antibody has been immobilised. At that point, the

allergen–antibody complex is trapped. The presence or absence

of allergen is determined with the colour development pattern.

Competitive ELISA format can also be applied in LFA tests.

LFAs results can be obtained within 3–15 minutes after running

the assay (Schubert-Ullrich et al. 2009).

Dipstick tests are also based on a similar principal as LFA but

with no mobile phase. Instead, an incubation phase is required

in the dipstick test. Oliver et al. (2002) used dipstick assay to

detect peanut and hazelnut allergens and reported that results

of the dipstick assays and the corresponding ELISA were in

concordance. Although most dipstick tests are based on sand-

wich ELISA format, application of competitive ELISA has been

reported. Depending on the time needed for incubation, food

allergen detection time, using dipstick test, could vary from

10 minutes to 3 hours (Schubert-Ullrich et al. 2009).

Proteomic Approach

Recently, proteomics has gained much attention especially for

the detection and identification of IgE-binding allergens in com-

plex mixtures. Proteomics is useful for identification and char-

acterisation of proteins, including their post-translational mod-

ifications, protein conformations (native, denatured, folding in-

termediates) and protein–protein interactions (Leadbeater and

Ward 1987, Alomirah et al. 2000).

A proteomic analysis usually consists of sample collection and

preparation, protein separation using electrophoresis or chro-

matography and protein identification and characterisation us-

ing mass spectrometry. Successful identification of proteins de-

pends on many factors such as the sensitivity of the mass spec-

trometer, the completeness of the database, post-translational