Digesting starches (V0293)
Some starches release glucose more quickly into your blood than others. Scientists at Crop & Food Research (now called Plant & Food Research) explain why some starches are digested differently.
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Why might vegetable starch be better than wheat starch in some foods?
Alison Wallace (Plant & Food Research): We think that carbohydrates are quite a simple food, but they are actually quite complex. This is where glycaemic load comes in. It takes into account not only the type of carbohydrate but also the amount, because both things will have an effect on blood glucose.
Kevin Sutton (Plant & Food Research): Carbohydrates are a class of chemical compound which are made up of carbon, hydrogen and oxygen. They start in the simplest case as sugars - things like glucose, which is found in a lot of plants; fructose which is found in fruits; and sucrose, which is the common sugar that you put in your tea or coffee, which comes from sugar cane.
From there you can actually join those sugars together and many plants do this as a way of storing sugars into much more complicated molecules. Starch is the most complicated.
Lyall Simmons (Plant & Food Research): There is one starch, but all starches have two components. They are made up of two polymers. A polymer is a chain of repeating chemical groups that is repeated a number of times. All starches have these two polymers.
They are called amylose, and amylopectin. One is a very linear molecule. It’s just a long straight chain - that’s amylase. The other one has lots of branches on it, so it’s like a tree, as opposed to perhaps a telephone pole.
The reason they are important is the ratio of the two components of the starches varies according to the source of the starch. So potato starch is different from wheat starch; wheat starch is different from bean starch.
The reason that’s important is that one of the forms of starch, the amylopectin, is more easily digested than the amylose. The greater the amount of amylopectin that you have, the easier the starch is to digest, and the higher the glycaemic index.
- 01 February 2007
- The University of Waikato