Chemical warfare on a stovetop: Swetha Sivakumar on plant defences

Plants don’t want to be eaten. That explains the hard shells, husks, hairs; and why some taste bitter. Here’s the evocative tale of how we bypass it all.

Why do we cook; why have we for so many thousands of years? The reasons, when one gets down to it, are really interesting.

Cooking, of course, kills microbes, making food safer to eat. Heat can also soften fibres and break down starches and proteins, helping the body extract their nutrients more efficiently. But a key reason we cook — the most interesting one to me — is in order to vanquish the defence mechanisms that protect plants.

Plants don’t

The simple act of soaking can make a legume digestible... because it mimics the first stage of growth for a plant. As it prepares to sprout, all the defence mechanisms around the seed start to withdraw. (Adobe Stock)

These chemicals are not essential components of the plant’s basic metabolism; their sole purpose is defence. Which is ironic, of course. Both caffeine and nicotine, for instance, are effective insecticides. And both coffee and tobacco are now grown primarily for consumption.

There are some chemical weapons that do such a good job that we have learnt to leave their plants alone. These include the solanine in green potatoes and the toxic cucurbitacins in some types of bottle gourd, bitter chemicals that signal such high levels of toxicity that they cannot be processed out of the produce.

Now for the third line of defence (and my favourite). This is the “won’t go down without a fight” line of attack. Some plants contain enzyme inhibitors (tannins, trypsin inhibitors, phytates) that prevent them from being broken down in the digestive system. Alpha-amylase inhibitors in legumes attack amylase enzymes and prevent starch digestion. Lectins bind to carbohydrates and disrupt digestion. This is why we cannot eat beans or dals raw. But fermenting, germinating and cooking all reduce or eliminate these anti-nutritional factors.

Even the simple act of soaking can make a legume digestible, and the reason is really a bit moving. Soaking mimics the first stage of growth for the baby plant. As it prepares to sprout, all the defence mechanisms around the seed start to withdraw. Plants being powerful chemists produce other enzymes that break these anti-nutrients down into simpler compounds. As a result, in as little as two hours, some legumes can go from indigestible to edible, even raw, in a salad.

Delicious and nutritious for the human; rather tragic for the plant, which was hoping to sprout and soon have seeds of its own!

(To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com)