Protein and Fe in Wine by Solid Phase Extraction Spectroscopy
3.4.24.
The classical Lowry method was automated in the BI format, and used for protein assay in white wines and beer. In the first step Cu2+ was bound by Superflow NTA resin. The beads charged by Cu2+retained the protein, while the sample solution passed though the beads column. Next, when the Folin-Ciocalteu’s reagent was added, the reduction of FCr takes place and an increase of the color intensity was spectrophotometrically monitored at 500 nm. Before injection, pH of all samples was adjusted to 5.5. No other pre-treatment was required with the exception of the beer sample that was diluted 1/5 with deionized water.
Nitrilotriacetic Acid (NTA) Superflow resin was used as the bead column. The iron (III) ions were retained column by reacting with SCN- producing an intense red color. The change in absorbance was monitored spectrophotometrically at 480 nm.
Left: Flow diagram for BI spectroscopy. Note the innovative approach to keep beads in suspension by peristaltic pumping. Right: a/ Absorbance measurement for total protein content. (a) Protein standard 0.20 g/L prepared in water and in a wine model solution, (b) increase of the absorbance with increasing concentration of BSA.
