Changes of folates, dietary fiber, and proteins in wheat as affected by germination

Wheat kernels of the cultivar 'Tommi' were germinated for up to 168 h at 15, 20, 25, or 30 degrees C. Samples were taken at different stages of germination and were analyzed for the quantitative protein composition using an extraction/HPLC method, for folate vitamers using a stable isotope dilution assay, and for soluble, insoluble, and total dietary fiber using a gravimetric method. Gluten proteins were substantially degraded during germination. During the first stages of germination the degradation of glutenins was predominant, whereas longer germination times were required to degrade gliadins. The optimal temperature for gliadin degradation was 20 degrees C, and that for glutenin degradation was 25 degrees C. Omega5- and omega1,2-gliadins were less sensitive to proteolytic degradation than alpha- and gamma-gliadins, and LMW subunits of glutenin were less sensitive than HMW subunits. During germination a time- and temperature-dependent increase of total folate occurred. A maximum 3.6-fold concentration was obtained after 102 h of germination at 20 and 25 degrees C including 5-methyltetrafolate as the major vitamer. The concentration of dietary fiber remained constant or decreased during the first 96 h of germination. Prolonged germination times of up to 168 h led to a substantial increase of total dietary fiber and to a strong increase of the soluble dietary fiber by a factor of 3, whereas the insoluble fiber decreased by 50%.