Protein characterisation and immunochemical measurements of residual macadamia nut proteins in foodstuffs
Despite its high nutritional quality, macadamia carries specific proteins that elicit food-induced allergy symptoms in certain individuals. In contrast to other tree nuts, little is known about the way of detecting macadamia allergenic proteins in foods. On the other hand, new labelling regulations require precise detection techniques to trace a specified list of allergenic food residues to the ppm level. In the present study macadamia nuts were extracted using three extraction media i.e. (a) 10% saline, (b) phosphate-buffered saline and (c) Tris buffer at pH 7.5 to find the best solution in order to optimise the extraction condition for a particular protein. In the second part, 2S proteins were isolated and purified from macadamia nuts. Purification was carried out through a multiple stage procedure starting with an ammonium sulfate precipitation in which the concentration of the salt was increased step-by-step from 20 to 90%. The semi-purified protein fraction obtained was further purified using gel filtration chromatography. In the third part, antigen in the form of purified 2S protein from macadamia nuts, were used to produce antibodies in rabbits. Sensitive, specific ELISAs were set up and applied to 12 selected food samples extracted by four different methods of extraction (PBS, urea, PBS followed by acetone and urea followed by acetone). Although the higher total protein yield was not always an indication of an efficient extraction method for individual proteins, however, the results show that immunochemical techniques can reliably detect trace amounts of the nut in food samples. This is the first time that ELISAs for macadamia have been described.
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Document Type: Research Article
Publication date: December 1, 2010