Scientists discover why linseed oil goes bitter

Scientists from the Technical University of Munich may have discovered why linseed oil becomes bitter when stored — and how manufacturers and flax growers may be able to counteract the problem.

Fresh linseed oil is known for its smooth and nutty flavour profile but this disappears into a stringent, bitter taste when the oil has been stored, a transformation whose mechanics have been unclear for some time.

Food science researchers have now detected the reason for this bitterness and suggest that it is possible to reduce this bitter flavour and preserve the nutty one. This could increase consumer interest in eating linseed oil, which is rich in omega-3 fatty acids.

It had previously been discovered that, in addition to the oxidation of specific fatty acids, peptides known as cyclolinopeptides were the likely culprit for the stored oil’s bitterness.

The scientists used spectroscopic analysis to look at the concentration of these peptides in linseed oil, which enabled them to look at the chemicals causing the bitter taste. The analysis showed that only two of the 25 receptors in the mouth responsible for detecting bitterness were reacting to the peptides in linseed oil — specifically, one kind of peptide that contained methionine sulfoxide was being oxidised and activating taste receptor TAS2R14, leading to the distinct bitter flavour in stored oil. This peptide was not detected in fresh linseed oil.

“This oxidation product therefore seems to be dominantly responsible for the bitter off-flavour compared to others,” said principal investigator Maik Behrens. “Consequently, it would be conceivable to optimise the flavour quality of stored linseed oil by removing or reducing the content of this peptide class in the oil through breeding or technical measures.”

The researchers suggest that it should be possible to genetically modify flax to be less bitter since it’s known which genes encode the different peptides. Alternatively, other flax varieties with lower levels of the peptides exist and could be used to create new breeds that inherently reduce the amount of bitterness.

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