Modifying the bitterness of rye flour with hydrolytic enzymes
R.-L. Heiniö*, A. Mustranta, L. Lähteenmäki, K. Poutanen, J. Buchert
VTT Biotechnology, Finland
Whole grain rye is an excellent source of fibre and phytochemicals. The use of whole grain rye could be substantially extended if its intensively bitter flavour could be modified. In this work the impact of different hydrolytic enzymes acting on either rye proteins or cell wall polysaccharides on the bitterness of rye was studied.
Five different commercial enzyme mixtures were selected and their activity profiles determined. Rye flour –water suspension was treated with different enzyme dosages and the perceived bitterness was determined.
Only protease treatment increased the perceived bitterness of the suspension as compared to the reference. The partial proteolysis could also be visualized in increased amount of soluble protein in the samples. Concurrently to the perceived increase in bitterness the protease treatment also decreased the fresh odour and rye-like flavour, whereas malty odour, chemical-like flavour and aftertaste intensity was increased. The non-proteolytic enzyme mixtures containing e.g. cellulase, pectinase or amyloglycosidase activities did not affect the bitterness of the rye-water suspensions, despite of the fact that the availability of the phenolic compounds was increased.
Thus, the perceived bitterness seems to be linked at least to certain peptides. It is, however, also possible that some phenolics are covalently bound to proteins and as a result of partial proteolysis their solubility is increased thus contributing to increased bitterness. The effect of added free ferulic acid being the most abundant phenolic acid of rye was also investigated but was not found to increase the bitterness. However, the effect of other phenolic compounds present in rye, such as alk(en)ylrecorsinols and lignans, remains to be investigated. In the next stage of the study the attempt is to block the bitterness in a controlled way by tailored enzymatic treatments.
Key words: Bitterness, rye, enzyme, peptide, phenolic compound