The determination of folic acid in milk and paediatric formulae by optical biosensor assay utilising folate binding protein

An optical biosensor assay for the determination of folate in milk and nutritional dairy products

“…Materials, instrumentation and methods were essentially as described in Indyk (2010), with the following exceptions and additions.…”

“…The spectrophotometric purity of PteGlu and 5-CH 3 H 4 -PteGlu standard materials was established as described previously (Indyk, 2010). Purified bovine FBP was obtained following affinity chromatographic isolation from whey and was a gift from Prof. Peter Nixon (University of Queensland, Brisbane, Australia).…”

“…The nutritional significance of folate in the human diet and the forms in which it can exist in milk have been described in a previous study that formed the basis for the developments currently presented (Indyk, 2010). Although supplementation of foods is currently achieved through the use of synthetic folic acid (pteroylmonoglutamic acid, PteGlu), the recently available (6S)-5-CH 3 H 4 -PteGlu calcium salt may become a more appropriate supplement (Houghton, Sherwood, Pawlosky, Ito, & O'Connor, 2006).…”

“…An SPR protein-binding biosensor assay utilising folate-binding protein (FBP) as biospecific detecting molecule was recently validated for the quantitation of PteGlu in supplemented infant formulae (Indyk, 2010), a method that complemented a previous technique exploiting a monoclonal antibody (mAb) (Boström Caselunghe & Lindeberg, 2000). As the folatedetecting species within an SPR-based assay, FBP offers several advantages relative to an antibody, including innate specificity and monomeric binding stoichiometry (Henderson,1990;Nixon, Jones, & Winzor, 2004), cross-reactivity profile towards folate vitamers (Nygren-Babol, Sternesjö, Jägerstad, & Björck, 2005) and availability from bovine milk (Parodi, 1997;Treloar, Grieve, & Nixon, 2000).…”

“…Given the dominance of endogenous 5-CH 3 H 4 -PteGlu in raw bovine milk, the objective of this study was to extend the scope of the recently reported SPR-biosensor assay for folic acid (Indyk, 2010) to the measurement of folate content in bovine milk products, on the basis that the sum of supplemental PteGlu and endogenous 5-CH 3 H 4 -PteGlu represents a reliable estimate of total folate content in these foods. This aim was accomplished through the incorporation of extraction techniques commonly advocated for the analysis of total folates in foods using conventional analytical platforms, including protection of labile reduced folates during extraction and enzymatic deconjugation of folate polyglutamates, which hitherto have not been evaluated in biosensor immunoassays for the measurement of the folate content of foods.…”