Tomato Seed | Golden Apples, Pressed for Their Seeds

Golden apples.

In 1554 the Sienese physician Pietro Andrea Mattioli published his great Latin commentary on Dioscorides, printed, as its title page promised, with a great many pictures of plants and animals. In the chapter on the mandrake, after the eggplant, he describes "another kind" that "has begun to be imported". It is flattened like a round apple and ribbed like a melon, "green at first, then, when it has ripened, golden in some plants and red in others." And so, he writes, it is commonly called pomi d'oro, "that is, golden apples". They are eaten, he adds, the same way as the eggplant.^[1]

Italian kept the name. Pomodoro is still the word, half a millennium later, for a fruit Mattioli met as a novelty.

From the Peruvian desert.

The tomato's own story began far from Siena. Two species are thought to be involved in its making: the wild Solanum pimpinellifolium, which grows in the deserts of Peru, and the tomato itself in two forms, a semi-wild cherry tomato and the cultivated fruit. In 2022 a team in Valencia traced its path in the genome. As the wild plant spread slowly north toward the rainforests of Mexico, it became the semi-domesticated cherry tomato, S. lycopersicum var. cerasiforme. Along the way, genes for photosynthesis and flowering time were selected as the plant adapted to new latitudes. The Peruvian and Ecuadorian cherry tomatoes seen today are later hybrids. The team checked the model against where each sample had been collected and against the plants' form, and both supported it.^[2]

A 2020 study added a twist. The semi-wild cherry tomato may be older than domestication itself, and many of the traits that seem typical of a cultivated tomato first arose in South American cherry tomatoes, were lost or weakened as those plants moved north, and were then selected all over again in the common cultivated tomato before it spread around the world.^[3] Its best traits were, in effect, selected twice. The same work points to overlooked wild and semi-wild tomatoes that still carry useful genes for breeders.

Pressed from what juicing leaves behind.

Tomato seed oil has no ancient story, and it makes no pretence of one. It is a by-product. When tomatoes are processed into juice and purée, the seeds and skins are left behind as pomace, and the seeds can be pressed or extracted for oil.

In 2021 a group in Romania and Greece analysed tomato seed oil and peels from industrial processing, from both the "cold break" (65 to 75 °C) and the "hot break" (85 to 95 °C) methods. The oil met the standards of generally accepted edible oils. Linoleic acid, an omega-6, was the main fatty acid, at 61.73 per cent, and syringic acid was one of the two main phenolic acids in the cold-break samples.^[4] A 2023 study from India compared tomato seed oil extracted with water against oil extracted with a solvent. Both came out about 58 per cent polyunsaturated and 24 per cent monounsaturated, with hardly any difference between them. The team also ran four standard tests of how far the oil had oxidised, and measured its antioxidant activity in three different assays.^[5]

What linoleic acid does in skin.

Linoleic acid matters for a reason that has nothing to do with tomatoes. It is the fatty acid the skin threads into its own barrier lipids, the ceramides that hold the outer layer together. The key ones, the ω-O-acylceramides, carry linoleic acid, and without them the barrier fails.

In 2022 a group in Japan showed this sharply in mice. An enzyme, Acsl1, activates linoleic acid for the job. Mice born without it lost those linoleic ceramides and had such severe barrier defects that they did not survive. The skin stores linoleic acid in triglycerides, a reservoir it draws on to build those ceramides, and in these mice the linoleic triglycerides were depleted while the others were not.^[6]

That is the mechanism of the fatty acid, and it holds wherever the linoleic acid comes from. No study has yet tested tomato seed oil itself on skin. What tomato seed oil brings to a blend is a carrier rich in the fatty acid the skin uses for its barrier.

The antioxidants it carries.

A 2022 study from Alicante compared two modern ways of getting oil from tomato seeds: microwave-assisted extraction at about 56 °C, and supercritical CO₂ at about 60 °C and 400 bar. The microwave method gave more oil, 25.3 per cent of the seed against 16.9 per cent. The fatty acids were much the same either way, about 80 per cent unsaturated.^[7]

The oil's antioxidant activity tracked its vitamin E, and the dominant form was γ-tocopherol, at 260.3 milligrams per kilogram, ahead of α-tocopherol.^[7] An oil this rich in linoleic acid needs protecting from air. Its own tocopherols are part of that protection, and so are a fresh supply and a closed bottle. The authors call the seeds a by-product that is "currently underexploited".^[7]

And lycopene, carefully.

Lycopene is the red pigment of the tomato fruit, not of its seed. In the 2021 by-product study it was the main carotenoid in the samples, at 37.43 milligrams per 100 millilitres, and the carotenoids and phenolics shifted with the heat of the processing.^[4] A seed oil can carry some of the fruit's colour with it, depending on how it was made. How much a particular oil holds is a question for its certificate of analysis. Anyone sensitive to tomatoes or other nightshades should patch test first.