Carmen Diaz-Amigo

Eurofins, Germany, Hamburg, Hamburg, Germany

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Publications (10)18.19 Total impact

  • Carmen Diaz-Amigo, Bert Popping
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    ABSTRACT: The determination of prolamin by ELISA and subsequent conversion to gluten appears to be a comparatively simple and straightforward process with which many laboratories have years-long experience. At the end of the process, a value of gluten, typically expressed in mg/kg or ppm is obtained. This value often is the basis for the decision if a product can be labeled gluten-free or not. Based on current scientific information available, the accuracy of the obtained values with commonly used commercial ELISA kits has to be questioned. While recently several ringtrials have been conducted in an attempt to underline and reassure the accuracy of the results, data suggest that it was the precision of these assays, not the accuracy, that was confirmed since some of the underlying assumptions for calculating the gluten content lack scientific data support as well as appropriate reference materials for comparison. This manuscript discusses the issues of gluten determination and quantification with respect to antibody specificity, extraction procedures, reference materials and their commutability.
    Journal of Agricultural and Food Chemistry 05/2013; · 3.11 Impact Factor
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    ABSTRACT: Immunodetection of allergens in dark chocolate is complicated by interference from the chocolate components. The objectives of this study were to establish reference materials for detecting multiple allergens in dark chocolate and to determine the accuracy and precision of allergen detection by enzyme-linked immunosorbent assay (ELISA) before and after chocolate processing. Defatted peanut flour, whole egg powder, and spray-dried milk were added to melted chocolate at seven incurred levels and tempered for 4 h. Allergen concentrations were measured using commercial ELISA kits. Tempering decreased the detection of casein and β-lactoglobulin (BLG), but had no significant effect on the detection of peanut and egg. Total coefficients of variation were higher in tempered than untempered chocolate for casein and BLG, but total and analytical CVs were comparable for peanut and egg. These findings indicate that processing has a greater effect on recovery and variability of casein and BLG than peanut and egg detection in a dark chocolate matrix.
    Journal of Agricultural and Food Chemistry 04/2012; 60(17):4204-11. · 3.11 Impact Factor
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    ABSTRACT: Among the major food allergies, peanut, egg, and milk are the most common. The immunochemical detection of food allergens depends on various factors, such as the food matrix and processing method, which can affect allergen conformation and extractability. This study aimed to (1) develop matrix-specific incurred reference materials for allergen testing, (2) determine whether multiple allergens in the same model food can be simultaneously detected, and (3) establish the effect of processing on reference material stability and allergen detection. Defatted peanut flour, whole egg powder, and spray-dried milk were added to cookie dough at seven incurred levels before baking. Allergens were measured using five commercial enzyme-linked immunosorbent assay (ELISA) kits. All kits showed decreased recovery of all allergens after baking. Analytical coefficients of variation for most kits increased with baking time, but decreased with incurred allergen level. Thus, food processing negatively affects the recovery and variability of peanut, egg, and milk detection in a sugar cookie matrix when using immunochemical methods.
    Journal of Agricultural and Food Chemistry 04/2012; 60(17):4195-203. · 3.11 Impact Factor
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    ABSTRACT: Celiac disease and wheat allergy are the most common adverse reactions triggered by cereal proteins, mainly gluten, which is one of the 14 allergenic food ingredients that must be labeled on food products in the European Union (EU). To meet the requirements of this regulation, reliable analytical methodology for proper quantification of gluten is necessary. However, validation of presently used methods (ELISA and lateral flow device) is limited partly due to the lack of reference methods and incurred reference materials. To solve this problem, the goal of our work was to develop an incurred reference material for the quantification of gluten under the auspices of EU-FP6 funded Network of Excellence MoniQA. During this work, we produced a processed model product (cookie) containing gliadin (major allergenic fraction of gluten) in a defined amount. This paper addresses the development process of this material together with the associated problems (insufficient homogeneity and low recovery) and their solutions. As a result, an incurred food matrix was produced on a laboratory-scale with a potential use as a reference material. The model product was tested by an ELISA method followed by a comparative study of commercially available ELISA kits to investigate the applicability of the product. Preliminary results of this study are also presented.
    Journal of AOAC International 01/2012; 95(2):382-7. · 1.23 Impact Factor
  • Carmen Diaz-Amigo, Bert Popping
    06/2010: pages 175 - 198; , ISBN: 9780470637685
  • Carmen Diaz-Amigo
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    ABSTRACT: There are several enzyme-linked immunosorbent assay (ELISA) kits in the market that have been proven to be useful for the determination of egg in foods. However, inconsistent results that are obtained when different kits are used make the selection of one kit over another very difficult. Two different approaches were used to help understand why results vary among kits. Different kits were used to analyze spiked egg material [NIST reference material (RM) 8445] in wheat flour (raw ingredients) and cookies containing egg as an ingredient baked for different periods of time (processed food). These results were compared with immunoblotting using conjugated antibodies from the commercial kits to determine the antibody specificity and sample extraction efficiency. ELISA results can be difficult to compare because reporting units differ among kits. Results from both ELISA and immunoblotting are in agreement regarding the decreased detection of proteins in baked cookie extracts. Moreover, immunoblotting showed that this reduction is due to reduced protein content in these extracts. However, a properly selected extraction solution may help improve the solubility of certain egg proteins in processed foods. Harmonization of the reporting unit system along with the use of a common reference material is recommended as the path forward in the standardization of detection methods for food allergens. This would assist the end user in making an informed decision regarding the selection of the most appropriate kit for his or her purpose. KeywordsEgg-Allergy-ELISA-Validation-Reference Material
    Food Analytical Methods 01/2010; 3(4):344-350. · 1.97 Impact Factor
  • Carmen Diaz-Amigo, Bert Popping
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    ABSTRACT: Food allergen labeling regulations have been implemented in several countries since 2006. Currently, experts are still discussing the introduction of thresholds or action levels, which should lead to the reduction of the widespread use of advisory statements (e.g., "may contain") for the benefit of the allergic consumer. However, the establishment of threshold requires supporting analytical methodologies to enforce and comply with the regulations. This article discusses the possibilities and limitations of existing and emerging methodologies for the purpose of enabling compliance with and enforcement of allergen action levels.
    Journal of AOAC International 01/2010; 93(2):434-41. · 1.23 Impact Factor
  • Carmen Diaz-Amigo
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    ABSTRACT: Milk and milk derivatives are common ingredients in food products. Undeclared milk is one of the leading causes of recalls in many countries, including the USA, and cases of allergic reactions have been reported due to unexpected exposures. There are commercial enzyme-linked immunosorbent assay (ELISA) kits available to the food industry to comply with the law by ensuring label accuracy and to identify potential sources of cross-contact. These kits are also used by regulatory agencies as part of their compliance programs. However, none of the commercial ELISAs for milk have been validated. Performance of ELISA kits for food allergens is affected by matrix, food processing, and stability and solubility of target proteins, among others factors. The performance of different commercial kits for milk allergens was evaluated by comparing a standard [National Institute of Standards and Technology (NIST) SRM #1549] spiked in wheat flour. We also compared the effect of food processing on detectability of milk proteins from incurred peanut butter cookies baked at various times. Kits differed in their ability to detect heat-treated milk proteins in baked cookies. Immunoblots clearly showed differences in antibody specificities and in their ability to detect proteins in processed foods. Factors such as undefined antibody specificity and differences in sample extraction solutions, materials used for calibrators, and reporting units contribute to variability of results among test kits and, hence, to increased uncertainty regarding the most appropriate use of the kits. Moreover, the use of incurred vs. spiked samples may affect protein recovery and, therefore, jeopardize the quantitative nature of the kit. KeywordsMilk-Food Allergy-ELISA-Validation-Reference Material
    Food Analytical Methods 01/2010; 3(4):351-356. · 1.97 Impact Factor
  • Carmen Diaz-Amigo, Bert Popping
    Journal of AOAC International 95(2):335-6. · 1.23 Impact Factor
  • Carmen Diaz-Amigo, Bert Popping
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    ABSTRACT: Gluten is a commonly used cereal derivative found in bakery products, among other items. In some susceptible individuals, however, it triggers immune responses of different kinds; there is, to a lesser extent, the wheat allergy that is immunoglobulin E (IgE)-mediated and leads to histamine release and typical allergic symptoms. In this case, other water-soluble proteins, like albumins, are also involved. On the other hand, there is, more frequently, celiac disease (CD), where the gluten causes immune reactions in the intestines of certain individuals, leading to degeneration of villi, which typically leads to malabsorption of nutrients and, consequently, malnutrition. The only currently effective health strategy for affected consumers is avoidance of gluten-containing products, based on clear labeling rules. However, despite unanimously accepted Codex definitions by all member jurisdictions, the national implementation of equivalent laws shows significant differences. In the context of CD and in support of the gluten-free statement, regulatory enforcement, as well as manufacturers' quality controls are mostly based on analytical results. However, numerous methods are available, some of which have been validated better than others, and many provide different results on identical samples. Reasons include detection of different gluten components and variability in extraction efficiency due to different buffer compositions, especially from processed foods. Last but not least, the lack of reference materials is hindering the process of generating comparable data across different ELISA kits, as well as other methods. How can such data still be used to support a gluten-free claim? New methodologies, in particular mass spectrometric analysis of gluten derived peptides, are being introduced in numerous laboratories. This methodology is not only capable of detecting gluten derived peptides but can also differentiate between and quantitate wheat, barley, rye, and oat. This paper presents analytical limitations, as well as promising new approaches in support of industry and enforcement activities to ensure compliance with the gluten-free claim under the current regulatory framework.
    Journal of AOAC International 95(2):337-48. · 1.23 Impact Factor

Publication Stats

18 Citations
18.19 Total Impact Points

Institutions

  • 2010
    • Eurofins, Germany
      Hamburg, Hamburg, Germany
    • U.S. Food and Drug Administration
      • Center for Food Safety and Applied Nutrition
      Washington, D. C., DC, United States