Biochemical fluorometric method for the determination of riboflavin in milk.

UNLABELLED: Methods of analysis of vitamin B2 in foods generally consist of the extraction of the sample, followed by enzymatic hydrolysis and quantitative measurement of the analyte, typically through RP-HPLC. The scope of our work here is to present a soft method to measure the free riboflavin content of a nontransparent and nonhomogeneous matrix such as milk, avoiding any extraction and separation of phases that are required in any published method for determination of the free RBF content in foods. We combine the front-face (FF) measurement of the light emission of milk with the ability of the apo-form of the riboflavin-binding protein (RBP) from chicken egg white to quench the riboflavin fluorescence. Thus, we titrate the RBF present in milk by gradually adding a solution of RBP to the milk sample and measuring, upon each addition, the FF residual emission due to uncomplexed RBF. The RBP binding capability has been measured in the same matrix of the analyte. Our results indicate a concentration of free RBF practically co-incident with the certified value for total B2 vitamin content in reference milk CRM 421. KEYWORDS: Front-face fluorescence; riboflavin; apo-riboflavin-binding protein; milk fluorescence.