Influence of different extraction conditions on the detection of glycinin and β-conglycinin in model processed foods by ELISA

ABSTRACT

The presence of undeclared soy proteins in food can cause severe reactions in soy allergic individuals. The extraction of target proteins from processed foods is a crucial step in allergen detection by immunoassays, as only successfully extracted target proteins can be detected by the specific antibodies. The effectiveness was studied of different conditions (type of buffer, temperature and time of incubation) on the extraction of total protein, and concentration of glycinin and β-conglycinin from different food matrices. The yields were determined using a soy protein isolate and three processed foods (sausage, bread and pâté) incurred with soy proteins. The yields were affected by the processing of analysed products and the composition and pH of the extraction buffers. Neutral and alkaline buffers (pH from 7.4 to 10.6) exhibited good protein extraction capacity and detectability of the specific target proteins. Denaturing additives and highly alkaline buffer (pH 12) extracted more crude protein but they were incompatible with the ELISA assay. Overall, the best results were obtained using phosphate (pH 7.4) and Tris/HCl (pH 8.5) buffers in the presence of 0.5 M NaCl. Crude protein yield of food extracts did not correlate with that of glycinin and β-conglycinin, whereas a good relationship was found between the yields of the two proteins.

Graphical Abstract

KEYWORDS:

• Soy allergens
• β-conglycinin
• glycinin
• processed foods
• ELISA
• extraction conditions

Acknowledgments

This work was supported by the Ministerio de Economía y Competitividad (Spain) and by the Fondo Europeo de Desarrollo Regional (European Union) under Grant RTC-2015-3818-2.

Declaration of interest

The authors declare no competing financial interest.

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Additional information

Funding

This work was supported by the Fondo Europeo de Desarrollo Regional (European Union) [RTC-2015-3818-2]; Ministerio de Economía y Competitividad (Spain).