Richard Willstätter helped explain why carrots are orange

Person: Richard Willstätter
Lived: 1872–1942
Field: Organic chemistry
From: German

The story

In 1905 Richard Willstätter, a young Jewish organic chemist from Karlsruhe, left the University of Munich to become professor of chemistry at the ETH in Zurich. There he and his students set out to understand chlorophyll, the green pigment that lets plants capture sunlight. It was delicate work. Chlorophyll is easily altered, so Willstätter developed careful methods for isolating it from plant material without changing it or introducing impurities.

Good scientists pay attention to what is left over. A preliminary step in the extraction yielded a yellow solution, and on closer study it proved to contain carotenoid pigments, the family of compounds that also colour carrots, tomatoes and egg yolks. These yellow and orange substances had been described before, but Willstätter's work, carried out alongside his chlorophyll research, marked the beginning of a real scientific understanding of them.

Carotenoids, it later emerged, play two key roles in plants. They absorb light energy for photosynthesis, acting as helpers to chlorophyll in the light-harvesting part of the process, and they protect the plant from damage by excess light. More than 1,100 different carotenoids have now been identified, in organisms ranging from algae and fungi to flamingos and salmon.

Willstätter's early progress opened a field that his students carried much further. Richard Kuhn earned his doctorate with Willstätter in Munich in 1922, with a thesis on enzymes, and went on to study carotenoids in depth. In 1938 Kuhn was awarded the Nobel Prize in Chemistry for his work on carotenoids and vitamins, though the Nazi government forbade him to accept it at the time, and he received it only after the Second World War.

Today carotenoids are known to matter for human health too. Some of them, including beta-carotene, have vitamin A activity, meaning the body can convert them into retinol, and some 40 to 50 carotenoids found in fruits and vegetables are part of the human diet. A side observation in a chlorophyll laboratory thus became the starting point for a whole branch of natural product chemistry and nutrition science.

Why it matters

The study of carotenoids that Willstätter helped begin now informs nutrition science, food colouring and efforts to fight vitamin A deficiency around the world.

About Richard Willstätter

Nobel-winning chemist who unravelled chlorophyll and the colours of flowers, refused to convert, resigned his chair in protest at antisemitism and died a refugee in Switzerland.

Read the full profile

Richard Willstätter

1872–1942 · Organic chemistry

View profile →