Flavour and stability of rye grain fractions in relation to their chemical composition

Wholegrain rye is health-beneficial, but intensive and bitter flavour of rye foods, supposedly caused by specific phenolic compounds and small peptides, restricts its use. The aim was to study the stability and sensory quality of rye grain fractions in relation to their chemical composition. In addition to distinctive sensory and chemical properties of wholegrain flour, endosperm-rich fraction and two differently prepared brans, the rye fractions had differences in their stability. The endosperm fraction had the poorest stability and mildest flavour. The rancid flavour was related to free fatty acids. The bran, intense and bitter in flavour, but more stable, had the highest content of phenolic compounds. The high content of phenolic compounds of bran contributing to its bitterness probably also improved its stability by reducing the formation of flavour-active lipid-derived oxidation products. Stability of the rye bran made by an air-classification process was inferior to the bran made by a conventional sieving process, despite similar content of phenolic compounds. Changes in the development rate of rancidity and intensity of flavour were faster in the air-classified than in the sieved bran. This could be due to different microstructure and particle size of the brans, influencing oxidation susceptibility.