Healthy substances in curly kale identified

Curly kale is full of healthy substances, and some of them have an inhibiting effect on the growth of cancer cells. Ph.D. student Helle Olsen of the Norwegian food research institute Nofima is now the first to identify a number of polyphenols - a group of health-promoting substances found in curly kale.

This article was last updated more than two years ago.

About curly kale

  • Curly kale belongs to the cabbage family (brassicas).
  • It can be used in soups and stews. It can also be steamed with butter, boiled or fried. Curly kale can also be used as a garnish instead of salad.
  • It has few calories and is rich in vitamins A, K and C. It contains several minerals, and is one of the vegetables that contains the most iron.
  • See for recipes.

Source: Norwegian Fruit and Vegetables Marketing Board (

Inhibits undesirable cell growth

In her research, Olsen has followed the individual polyphenols via heat treatment and storage and seen whether they have an effect on cell growth and cell mortality in cultures of intestinal cancer cells. The effect on cells grown in the laboratory gives an indication of whether the polyphenols have a corresponding effect in the human body.

"We saw reactions in the cells, but we do not yet know exactly what has caused them. We can see that curly kale inhibits undesirable cell growth, and we believe this is due to interaction between the polyphenols, and possibly also other substances," says Olsen.

Raw curly kale is richer in healthy substances than when cooked

Olsen has studied both green and red curly kale grown in Ås in Norway over three seasons. She wanted to find out whether there was any difference in the polyphenol content from year to year, but found no difference. There was however some variation between individual plants.

She compared raw curly kale with kale that had been first blanched and then boiled in a bag. The heat-treated curly kale had a significantly lower polyphenol content than the raw kale, but still had a very high content of these healthy substances.

Vegetable model for advanced methodology

The background to this research was that Nofima was to establish advanced methodology for vegetable analyses, and curly kale proved to be a highly suitable "vegetable model". It has a high content of complex polyphenols, and the chemical structure of these had not previously been studied in detail.

Helle Olsen clarified the chemical structures by using an analysis technique called mass spectrometry, which provides information about the different constituent parts of a molecule. She discovered new complex polyphenols that had never previously been described.

This is important to the international work of establishing information about all types of constituents of food plants.

"New information is being fed into databases all the time and can be used as an extended food product table in the future," Olsen explains.

Helle Olsen defended her doctoral dissertation on 14 September at the University of Oslo. Her supervisors were Dr. Grethe Iren Borge, Dr. Kjersti Aaby and Dr. Stine Grimmer (all from Nofima) and Prof. Elsa Lundanes (Department of Chemistry, University of Oslo). Her thesis is called: “Polyphenols in curly kale (Brassica oleracea L. convar. acephala var. sabellica). Structure elucidation, quantification and biological activity”.

 Food and health  

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