Professor Roger Lentle from the Institute of Food, Nutrition and Human Health at Massey University has been investigating the qualities of a polysaccharide gum derived from the trunk and fronds of the mamaku or black tree fern. It is strange stuff. Try to stir it, and the harder you stir, the more it will resist; when it flows, it does so as a stretchy, dough-like mass. These 2 qualities – known as shear thickening and extensional flow – baffle the digestive system. (Learn more about shear thickening in the article Non-Newtonian fluids.)
“We know that contractions in the gut are caused by it feeling there is something in there and needing to push it on,” says Professor Lentle. “This extract seems to dupe the sensory nerves in the stomach so they signal that the stuff is flowing when it isn’t and vice versa. This seems to confuse the stomach’s pumping system, causing it to become less effective.”
When the gum reaches the part of the stomach near the intestine, it gives the sensation of satiety. It is a natural suppressant. While it isn’t very digestible, once the stomach acids have acted, it passes harmlessly on through the gut.
A nourishing sweet carbohydrate porridge made from the pith of the mamaku is known to have been an occasional food for pre-European Māori. They used mamaku to treat diarrhoea and other stomach complaints.
Professor Lentle is intrigued by the gum’s possibilities. He believes there is potential for a commercial farming operation. He is keen to talk to anyone, particularly iwi, who may be interested in working with him or can tell him more about the traditional uses of mamaku and its products.
This article deals with the appetite-suppressing effects of gum from a tree fern. In relation to this story, your students may like to try this activity that illustrates how humans can use ferns to survive in the bush.
Using ferns to survive
The mamaku gum is a non-Newtonian fluid. Explore a range of common household substances to determine if they are Newtonian or non-Newtonian fluids.
Slumpy solids or lumpy liquids
Read about Professor Lentle's study in the journal Food & Function: The first of the viscoceuticals? A shear thickening gum induces gastric satiety in rats. What do you think a viscoceutical is?