Health and Chemistry

Last Updated on August 8, 2026 by Staff

Eggplant shows up in kitchens across the world, yet many people leave it on the plate. Its flesh can taste bitter, and it often leaves a dry, puckering feeling in the mouth that eaters call astringency.

That matters beyond one dish. Many people, and younger adults in particular, eat fewer vegetables than health advice suggests, and taste tends to drive food choices more than any health message.

Cooks have long known that the way a vegetable is heated changes its taste. A new set of experiments put that idea to a careful test with eggplant, and they help explain why frying so often wins.

Researchers at Osaka Metropolitan University in Japan cooked the same variety of purple eggplant four different ways. Then they asked people to taste the results and describe what they noticed.

Four ways to cook it

The team started with elongated purple eggplants grown in Aichi Prefecture and cut them into cubes about 0.8 inch (20 mm) across.

Each batch was cooked by boiling, steaming, deep frying, or a newer method called superheated steam.

Superheated steam is ordinary steam heated well past the boiling point of water. It cooks food quickly and with very little oxygen in the chamber, which can help protect a vegetable’s color.

The cooking times were matched so that every batch reached a similar softness. Deep frying used hot oil at about 338°F (170°C), while the water-based methods stayed near 212°F (100°C).

Frying won the taste test

Fifty-five untrained tasters, most of them young adults, rated each sample on a nine-point scale from dislike to like. Deep fried eggplant scored clearly higher than the other three, and people agreed with each other more about it.

Boiled, steamed, and superheated-steam eggplant landed close together, with no meaningful gap between them in overall liking. In plain terms, the differences among those three were small enough that they could have come from chance.

Across all the samples, the average score sat well above the midpoint, so people generally liked cooked eggplant. Deep frying simply raised those scores further and made opinions more consistent.

The interesting part was not that frying won. It was the reason it won.

Oil hid the harsh taste

Eggplant is rich in natural plant compounds called polyphenols, which are linked to that dry, astringent feeling. The team measured these compounds and found no real difference among the four cooking methods.

So frying did not strip the astringent compounds out of the eggplant. Yet only about one in nine tasters noticed astringency in the fried samples, compared with nearly a third of tasters for the boiled ones.

Astringency comes from those polyphenols binding to proteins in saliva, which creates the puckering sensation. The oil in fried eggplant may coat the surface and block that contact, so the mouth registers less of it.

Fried eggplant also gained flavors the other methods could not add. Nearly every taster called it oily, and many called it toasty, notes that come from the browning reactions that oil and high heat produce.

Sweeter without more sugar

People called the fried eggplant sweet far more often than the boiled kind, at more than half of tasters against under a third. Yet when the researchers measured the actual sugar-related content, the methods again looked about the same.

The likely explanation is water. Much of the eggplant’s moisture cooked away during frying, leaving the sample far drier than the boiled or steamed versions.

With less water in the flesh, the same amount of sugar tasted more concentrated. The sweetness was a matter of perception, not of extra sugar being created.

The researchers also linked each described trait back to how much people liked the sample. For the water-based methods, more perceived sweetness went with higher liking scores, while more astringency went with lower ones.

Steam kept the color

Superheated steam did not win the taste test, but it stood out in another way. It softened the flesh well while keeping it brighter and keeping the vivid purple of the peel.

That purple comes from a pigment called nasunin, which dissolves in water and breaks down with heat. Most of that pigment leached out during boiling, leaving only about a third of the raw level, while more of it remained after the steam and frying methods.

Every cooking method softened the flesh compared with raw eggplant, and superheated steam and frying produced the softest results. A softer bite changes how a food feels in the mouth, which affects how much people enjoy it.

For a cook who cares how a dish looks, that trade matters. Superheated steam offered a soft texture and strong color without the added oil of deep frying.

What the panel missed

The study has clear limits that shape how far its results reach. The tasting panel was small, at 55 people, and almost all of them were women, so the pattern may not hold for a wider group.

The work also measured taste and liking, not health. Frying improved flavor by adding oil, and the study did not weigh that oil against any nutritional cost.

And a single tasting session cannot say how people would feel about eating these dishes day after day. The researchers call for larger and more balanced panels to confirm what they saw.

Cooking shapes what we taste

The main lesson is that cooking changed enjoyment mostly by changing perception, not by rewriting the eggplant’s chemistry. The polyphenols and sugars stayed roughly steady while people’s experience of eating them changed a lot.

For water-based cooking, a better-liked eggplant means raising perceived sweetness and cutting astringency. For anyone chasing both softness and color, superheated steam looks like a promising middle option.

Source: International Journal of Gastronomy and Food Science.