There are currently a range of methods for detection of allergens in food in place in countries around the world, but they are not without their problems. In response to this, a researcher based at the National Institute of Health Sciences in Japan is investigating ways of improving
food allergen detection methods. Dr Shinobu Sakai, Section Chief of Division of Environmental Chemistry at the Institute, is hoping to address some specific knowledge gaps in the field. 'A labelling system for food allergenic ingredients was established in Japan in April 2002. To monitor the
labelling, the Japanese government announced official methods for detecting allergens in processed foods in November 2002,' explains Sakai. 'The official methods consist of quantitative screening tests using enzyme-linked immunosorbent assays (ELISAs) and qualitative confirmation tests using
Western blotting or polymerase chain reactions (PCR). These official methods are carried out in laboratory sites by scientists.' Throughout the course of his studies, Sakai has already achieved notable progress, including the development of an onsite detection system by magnetic beads-binding
enzyme-linked immunosorbent assays (ELISA). 'While immunoprecipitation reaction using gel carriers such as sepharose and agarose is already widely used for protein isolation and purification, the reaction is caused by nonspecific adsorption due to the surface area size,' he outlines. 'In addition,
there are many problems such as high detection background due to contaminants during incubation. Then there is the fact that each step involves complicated operations such as high-speed centrifugal separation and washing, and therefore sample loss and residual insoluble matter are problems.'
However, because the micro magnetic beads he has developed accumulate support using magnetic force, there is no need for centrifugal operation, and the risk of sample loss, etc. can be reduced. 'The primary antibody is bound to the hydrophilic magnetic microbead and added to the antigen solution
(food extract) to capture the antigen. Next, a secondary antibody labeled with colloidal gold particles is allowed to react to perform a coloring reaction,' explains Sakai. 'Taking the convenience of detection into consideration, by mixing the food allergen extract and the lyophilised gold
colloid labeled IgG probe in the same tube and accumulating the antigen-labeled antibody complex at the magnet part, it is possible to perform the detection step with one pot.' 'Moreover, by using monodisperse polystyrene microspheres incorporating various dyes inside the particles instead
of colloidal gold particles, it is possible to apply the technology to the sandwich type of magnetic beads, food allergen protein and dye beads,' Sakai continues. This enables multiple detection by color tones such as red for egg (anti-ovalbumin antibody-labeled beads), blue for milk (anti-lactoglobulin
antibody-labeled beads), and green for wheat (anti-gliadin antibody-labeled beads). In this particular detection method, he has developed, all steps - excluding food allergen extraction - are completed within the target time of two minutes.
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