Diagnostic tests for detection of allergens in food

ELISA kits can hardly be considered quantitative and LFDs play a key role in the food industry but performance is rarely documented.

Regulatory environment EU Regulation No 1169/2011 specifies fourteen substances or products causing allergens or intolerances for which food labeling is mandatory when they are known ingredients. If there is a risk of a food product being affected by allergen cross-contamination, there should be precautionary ‘may contain’ labeling. However, precautionary allergen labeling should only be used if the risk of allergen cross-contamination is real and cannot be removed. From a food control perspective, it is interesting to note that in the 12-month period prior to September 2019 the Rapid Alert System for Food & Feed (RASFF) shows 204 notifications of products containing undeclared allergens including gluten. This compares with 289 alerts for pesticide residues and 595 alerts for mycotoxins in the same period but nevertheless represents a significant and growing number of rapid alerts for allergens. Additionally, at the national level, there are a large number of product recalls initiated by manufacturers mostly due to incorrect labeling or mislabeling rather than apparently occurring through cross-contact with allergens (cross-contamination). A recent publication has analysed trends in allergen product recalls (Bucchini et al. 2016) and survey work has been reported identifying undeclared allergens in foods on the market, as well as identifying foods where allergens have been labelled as present but were not found (Sefat et al. 2016). Media coverage of recent allergen sufferer fatalities due to failures in providing information about the presence of allergens in takeaway foods and sandwiches have also significantly raised public awareness of this important area, and has been a driver for further regulation. 
Options for food testing In terms of testing for allergens, there is an abundance of commercially available diagnostic test kits available to detect the presence of allergens in foods, probably more so than in any other area of food safety. A recent count showed that ELISA, Lateral Flow Devices (LFDs) and polymer chain reaction (PCR) diagnostic kits are commercially available from at least 16 different suppliers and these cover more than 24 specific food allergens (Senyuva et al. 2019). Indeed, for allergens such as milk and eggs there are even multiple ELISA kits targeted at different specified proteins in both of these two commodities. Whilst on the one hand having such a wide choice of diagnostic kits should be welcomed, unfortunately, method performance data is frequently lacking and comparability of results from different kits for the same matrix sample is not good. Routine allergen testing by the food industry relies upon employing commercial test kits, but frequently the suppliers provide disappointingly little specification detail on the grounds that this is proprietary information. The lack of comparability is understandable when one reflects that ELISA and LFD kits are based on antibodies, which in many cases have been raised against different proteins. In contrast, PCR is based on detection not of an allergenic protein but detection of DNA indicative of the presence of the component which is potentially allergenic but not of the protein itself. PCR is an ultra-sensitive technique, which in areas such as forensic science is a tremendous advantage, but for allergen detection may

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