Apple Seeds & Green Potatoes

What they have in common...

When a friend of mine attempted to eat an apple core on a hike a few weekends ago, I stopped him. "Don't you know that apple seeds contain cyanide?" I exclaimed. Though I'm not sure he believed me, the possibility alone was enough to discourage him. Had we had any reception, I'm sure 20 seconds on an iPhone would've settled it right then. Ah, the great outdoors!

It was then that I realized that there must be other seemingly innocuous foods in our diet that could, perhaps under odd circumstances, be potentially harmful to us. This entry is not intended to spook or discourage anyone from eating the following foods. Instead, the hope is to offer a Botany-of-Desire-like perspective to provide an informative look at a few common foods.

Why Plants Make Toxins
Many species of plants produce chemicals that discourage animals from eating them. Although we've domesticated varieties of fruits and vegetables to be edible and tasty, some still contain toxins as a natural form of defense. Below are a few examples:

Cyanide in Apples, Pears, and Citrus Fruits
The seeds of apples, pears and citrus fruits contain cyanide. However, swallowing the seeds whole isn't terribly risky; these seeds have a durable outer coating designed to protect the seed while it passes through an animal's digestive system. The seeds could be dangerous if ingested in large amounts especially when the protective coating is damaged (by chewing for example).

• Avoid by: removing the seeds of apples, pears and citrus fruits, particularly before feeding them through a juice extractor (a juicer that obliterates fruit and vegetables). Also, avoid chewing these seeds.
  

Cyanide in Yuca
Yuca (also known as Cassava, Manioc or Tapioca) is a starchy root that grows in the tropics. The "sweet" varieties sold in the produce section have been bred to contain far less cyanide than the potentially toxic "bitter" variety, but still contain significant amounts concentrated near the skin.

• Avoid by: peeling and then soaking or boiling yuca(cassava) before baking or frying. Luckily, cooking yuca in water makes it healthier but also much tastier.
  

Alkaloids in Potatoes
Alkaloids are a family of compounds that often taste bitter and have an effect on animals. Alkaloids are produced by plants to affect the consciousness of the animals that eat them, effectively distracting the animal and sparing the plant. Though most alkaloids are toxic at high doses, a few common alkaloids that (some) humans utilize include caffeine, morphine, nicotine, theobromine (responsible for increased heartbeat when eating chocolate) and capsaicin (responsible for the spicy burn of hot chili peppers).

Potatoes contain an alkaloid called Solanine that is both bitter and toxic. All potatoes contain small amounts of Solanine, but potatoes exposed to light can have three times the normal amount. Because the potato turns green (for a completely different reason) when exposed to light, green potatoes should be peeled aggressively or, better yet, thrown out.

• Avoid by: storing potatoes in the dark and avoiding potatoes that have turned green. Also, note that the leafy stalks of the potato and its relatives, including the tomato, chili pepper and eggplant, contain even greater amounts of alkaloids and should certainly be avoided, though they supposedly taste terrible anyway.
  

Oxalic Acid in Rhubarb (and, to a Lesser Extent, Spinach)
Oxalic acid is a waste product of plant metabolism that is found notably in spinach, beet greens and rhubarb. Oxalic acid locks onto minerals like calcium and iron, preventing your body from absorbing them.

While the amount of Oxalic acid in spinach and the red portion of rhubarb is safe to eat, the green leaves of rhubarb contain much higher levels making them unsafe.

• Avoid by: never eating the green leafy tops of rhubarb stalks. Cooking spinach will destroy some of its oxalic acid, rendering the calcium and iron more available for absorption by the body.
  

Sources:

* On Food and Cooking - Harold McGee
* The Wellness Encyclopedia of Food and Nutrition - UC Berkeley
* http://www.snopes.com/food/warnings/apples.asp