(Bio)technological approach to understand the bitterness of whole grain rye

R.-L. Heiniö (1), P. Lehtinen (1), O. Myllymäki (1), E. Selinheimo (1), J.-M. Pihlava (2), A. Kaukovirta-Norja (1), K. Poutanen (1, 3), J. Buchert (1)
1 VTT Technical Research Centre of Finland,  Finland ,
2 MTT Agrifood Research Finland, Finland,
3 University of Kuopio, Food and Health Research Centre, Department of Public Health and Clinical Nutrition, Finland
 raija-liisa.heiniovtt.fi

Rye is considered as an exceptionally health-beneficial cereal grain containing abundant amounts of dietary fibre and bioactive compounds. However, the obvious bitterness of rye may limit its extensive consumption.

As we earlier have shown, the flavour components are unevenly distributed in the rye grain, the endospermic inner part of rye grain being mild-tasting and the outermost bran fraction bitter. Bioactive phenolic compounds are mainly concentrated to the outer fractions. The contribution of certain non-volatile phenolic compounds on the perceived bitterness of rye has been suggested, but the impact of selected peptides on the bitterness remains still to be proved.

In this work the location of the perceived bitterness in rye grain was studied more closely. The main aim of the study is to understand the overall impact of non-volatile compounds (phenolic compounds and peptides) on the bitter taste of rye.

Rye flours produced by different milling fractionation techniques were studied as water extractions and flour-water suspensions, aiming in progressive enrichment of bitterness. The conditions for water extractions were carefully optimised to maximise the bitterness. Furthermore, bitterness was even enhanced enzymatically (protease, hemicellulase-ferulic acid esterase) aiming to produce maximum bitterness for the next stage of the research. Sensory assessment (difference to control, descriptive profiling) and chemical analysis (soluble proteins, phenolic compounds, reducing sugars) were performed to analyse the rye samples. The increase in perceived bitterness correlated well with the amounts of soluble proteins and phenolic compounds. With these results the main aim of the study, blocking the bitterness in a controlled way by tailored enzymatic treatments and other biotechnological tools, is expected to be reached.