Linoleic acid
Quick answer
The polyunsaturated fatty acid that makes up most of the oil in a poppy seed — the substance of the seed’s richness, and the reason its oil does not keep.
What it does
Linoleic acid is the dominant fatty acid of poppy seed oil: 62 to 63 per cent in one cold-pressed oil and its seed, about 71 per cent on average across six Hungarian varieties, with oleic and palmitic acids making up most of the remainder. It is not an aroma compound. What it contributes is the oil itself, and in press-cake flour the oil that remained went with better colour, appearance and feel in the mouth and with more poppy flavour. In the pressed oils a trained panel’s “throat-catching” sensation rose with linoleic acid and with the polyunsaturated total, an association across ten samples and not a demonstrated cause. In sesame it shares the oil with oleic acid: a handbook gives 38 to 49 per cent linoleic and 36 to 54 per cent oleic, in a seed that is 45 to 50 per cent fat.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- low
- Fat solubility
- high
- Water solubility
- low
- Heat stability
- low
An oil this rich in linoleic acid oxidises readily. A cold-pressed poppy seed oil lasted 2.8 hours in an accelerated oxidation test at 120 °C, which its authors put down to the 63 per cent of polyunsaturated fat, more open to oxidation than saturated fat because of its double bonds; they add that oxidation is hastened by high temperature, by poor storage and by damage to the seed, and that pressing itself exposes the oil to oxygen. The seed and oil in that study were sound because they were analysed at once. In the sensory study, the volatiles 2-pentylfuran and hexanal went with lower scores for poppy odour and flavour. For a cook the consequence is about keeping: the seed’s richness is an oil that air and warmth degrade. Neither study roasted or baked the seed.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- Poppy seedMajor component
Most of the seed’s oil, and with it the richness the seed brings; the nutty aroma of toasted seed is a different matter and comes from heating.
- Sesame seedMajor component
One of the two main fatty acids of sesame oil, beside oleic acid, in roughly equal measure.