Changes in dietary fibre, phenolic acids and activity of endogenous enzymes during rye bread-making
The content and composition of dietary fibre (DF), phenolic acids and ferulic acid dehydrodimers as well as the activity of endogenous enzymes were measured in freeze-dried samples of rye wholemeal, dough and bread during the rye bread-making process. Activities of α-amylase, β-xylosidase, α-arabinofuranosidase, and cinnamoyl esterase(s) were found in extracts of wholemeal and in dough after mixing and proofing, whereas activity of endo-xylanase was only found in the wholemeal. As a result of dough mixing, the content of total DF decreased by 21%, which was caused by a decrease in the amount of water-unextractable (WUE) DF. The content of water-extractable (WE) DF was unchanged during the bread-making process, but the relative content of WE DF increased. The content of total ester-bound phenolic acids and ferulic acid dehydrodimers decreased from 1575 µg/g in the wholemeal to 1472 µg/g in rye bread. The most pronounced effect occurred in an imitated sour dough (acidified with lactic and acetic acid instead of by lactic acid bacteria). The observed changes in content and solubility of DF in the dough could be explained by the activity of endogenous enzymes and mechanical disaggregation, whereas the changes observed in the imitated sour dough indicated that some acid hydrolysis might also have taken place.