I recently went to a farmers market and bought two smallish eggplants. They were not quite all purple, but the person selling them said the white streaks on them came from exposure to the sun. I took them home and within a couple of days sliced them, salted them, drained them and sautéed the slices to put in a pasta dish. Before assembling the dish, I took a small taste from one of the slices.
Eggplant should be ripe and (for this variety) have a firm, deep-purple skin.
It was terribly bitter, and though I didn't swallow it, it made my throat burn. It was a very small bite, but it took a long time to get the taste out of my mouth. I threw away the eggplant and we had pasta without. Why were these so bitter? This has never happened to me with eggplant before.
First of all, the problem is that these were probably young eggplants, which have a greater concentration of solanine, which is toxic. (Solanine is also found in the green part of potatoes, under the skin, and it is not good to eat it in this case, either.) Eggplant, as well as potatoes and tomatoes, are members of the nightshade family.
No matter where you are buying eggplant, be sure you are buying a mature, ripe eggplant. The information below is from Wiki Answers:
Heat (as in cooking heat) has no effect on solanine. The best way to avoid this harmful substance is to 1) choose only very ripe
eggplants, 2) soak for a couple of hours in very salty warm water, rinse and soak again in tap water, 3) cook until the eggplant is very well-done (this has nothing to do with exposure to heat but rather to the breakdown in fibers and leeching out of poison this causes). Another precaution, according to Wiki, is to peel the skin.
Connie Sheppard, with the Texas A&M University, suggested that the eggplant also might have stayed in the hot, dry sun on the vine too long. She likes to soak eggplant slices in buttermilk to get rid of any bitterness.
Also, as you noticed the extremely bitter taste when you took a small sample, it is probably a good idea to take a tiny taste first before adding to a dish or serving it to guests!
Also note that eggplant, according to Wikipedia, is richer in nicotine than any other edible plant, with a concentration of 100 ng/g (or 0.01 mg/100g). However, the amount of nicotine from eggplant or any other food is negligible compared to passive smoking. On average, 20 pounds of eggplant contains about the same amount of nicotine as a cigarette.
This is not necessarily a warning about buying produce or anything else at farmers markets. Eggplants, and many other delicious and healthful foods can be purchased there. It is a warning about knowing what you buy and how to prepare it, and what difficulties might be involved — no matter where you purchase it.