Improved method to quantitate gluten in purified wheat starch

A method based on gel-permeation high-performance liquid chromatography with fluorescence detection (GP-HPLC-FLD) was developed to quantitate gluten in purified wheat starch (WSt) and detect gliadins and glutenins. Gliadin, glutenin and gluten extracts of GfWSt and the five spiked samples (GfWSt and GfWSt + 16/31/79/157/315 mg gluten/kg) were analyzed by GP-HPLC-FLD. R2 values above 0.995 were obtained for the resulting calibration lines by plotting the peak areas of the FLD against the calculated gliadin, glutenin and gluten contents. Peak area of the unspiked GfWSt matrix was smallest for the gliadin extract and highest for the gluten extract due to some non-gluten proteins located inside the starch granules that were coextracted after starch gelation at 60°C. The gliadin contents of GfWSt1-14 analyzed by GP-HPLC-FLD ranged from below 5.4 mg/kg. Four of the 14 GfWSt contained gliadin below the LOQ. The glutenin contents of GfWSt1-14 were between below 10.2 mg/kg (LOQ of the GP-HPLC-FLD method for glutenin) and 58.9 mg/kg (GfWSt6). Only two of 14 GfWSt had glutenin contents below the LOQ, but one sample had gliadin and glutenin contents below the respective LOQs (GfWSt2). The glia/glut ratios ranged from 0.19 to 0.52, which indicates that gliadins had been removed more efficiently during industrial starch purification than glutenins.