Kinetic fluorimetric determination of gliadins in foods.

Kinetic methodology was applied for the first time to the determination of gliadin proteins by using a stopped-flow mixing technique. The method is based on two simultaneous processes: the reaction between gliadins and sodium dodecyl sulfate and the elimination of the quenching caused by this surfactant of the fluorescence of Cresyl Violet. Thus, the increase in fluorescence intensity with time is directly related to gliadin concentration. The use of this oxazine dye allows dynamic fluorescence measurements at long wavelengths, which avoids potential interferences from the sample matrix. The reaction rate is measured within 5 s, so the method is very suitable for the routine determination of gliadins in food samples. The dynamic range of the calibration graph was 0.5-50 micrograms ml-1 and the LOD was 0.25 microgram ml-1. The RSD was 1.6%. The method was applied to different food samples and the analytical recoveries were 88-107%.