Development and validation of a micromethod for fast quantification of 5-n-alkylresorcinols in grains and whole grain products

A 96-well plate micromethod was developed to measure 5-n-alkylresorcinols (5nARs) in cereal grains and food derived products. The 5nARs reacted in alkaline alcoholic medium with Fast Blue RR ½ZnCl2 salt to yield coloured azo-derivatives. The highest sensitivity for 5nARs was obtained at 490 nm with 0.025% ethanolic Fast Blue RR and 5% K2CO3. This reaction showed good linearity for olivetol (0.05–0.20 μg). Contents of 5nARs determined in cereal grains and derived products by the new Fast Blue RR micromethod were highly correlated (R2 = 0.9944) with those obtained by a Fast Blue B method currently used. A Bland–Altman analysis indicated a small positive bias near to zero (R2 = 0.0401), suggesting that the methods can be interchangeably used. The new reaction is completed in 15 min and the coloured products are read within the 15 min after completion. The micromethod offers a fast analysis of 5nARs in cereal grains and derived products with low consumption of reagents and solvents.