Two spectroscopic methods (FT-IR and FT-Raman spectroscopy) were used to determine whether 30-min moisturizing of DF preparations eliminates the structural effects of gluten dehydration. Studies were carried out on model flour that was mixed with non-moisturized and moisturized DF preparations (chokeberry, apple, cranberry, carrot, cacao, carob, flax and oat) in three concentrations: 3%, 6% and 9%. Comparison of the difference spectra concerning secondary structure showed that DF preparations prepared in both ways caused formation of different aggregated structures. Aggregates and pseudo-β-sheets were observed for non-moisturized preparations, while hydrated/extended-β-sheets were formed for moisturized preparations. 3%-addition of both kinds of preparations caused decrease in the amount of disulphide bridges in the g-g-g conformation. It suggests that not only dehydration process but also chemical interactions induced structural changes in gluten. Moreover, the number of S–S bonds in the g-g-g conformation remains constant regardless of increasing DF content for moisturized preparations characterized by high TDF content. Using of the moisturized preparations did not affect tyrosine and tryptophan parameters. The present results indicate that preliminary moisturizing cause different changes in the gluten structure and thus the treatment may improve the quality of the dough and bread supplemented with DF preparations.