Is this the protein plant of the future? New study finds ‘sweetness gene’ that makes lupins tastier

Header image: Lupinus albus (altramuces o chochitos), by Calapito via Wikimedia Commons.

Matthew Nelson, CSIRO

If you walk into a bar in Italy, you might be served a dish of salty, nutritious snacks: lupin beans, a legume that has been eaten around the Mediterranean and in parts of the Middle East and Africa for thousands of years.

Lupins are very high in protein and fibre, low in carbs, have a low glycaemic index, and they’re easy to grow in a variety of climates. However, some varieties also contain high levels of unpleasantly bitter alkaloids.

In new research, an international team of researchers has for the first time identified the “sweetness gene” responsible for low alkaloid levels. This discovery may make it easier to reliably produce more palatable plants.

Around 100 years ago, plant breeders in Germany found natural mutations that produced “sweet lupins” with far lower levels of bitter alkaloids. They produced sweet varieties of white lupin (Lupinus albus), narrow-leafed lupin (Lupinus angustifolius, the main type grown in Australia), and the less common yellow lupin (Lupinus luteus).

Over the past 50 years or so, lupins have become more common as food for farm animals. Sweet lupins are good for this, as they don’t require extensive washing to be usable. They are also increasingly eaten by humans – and we are very sensitive to bitterness.

To find the genetic basis for “sweet” lupins, we used a few approaches.

Our colleagues in Denmark studied the biochemistry of the different alkaloids in both bitter and sweet varieties. By looking at the changes in the composition of the alkaloids, we could get an idea of the genes involved.

My own work was on the genetics end. We analysed 227 varieties of white lupin and tested their