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Rights: The University of Waikato
Published 1 February 2007
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Human digestion can be replicated in the laboratory. What steps does the food go through in John Monro's digestion model? What advantage does this have over testing in human subjects?

Transcript

John Monro, Plant & Food Research The in vitro model replicates the main conditions that the food encounters when it goes to the gut, which also leads to the blood glucose response. It replicates stomach conditions and the conditions in the small intestine, after the stomach, which is where the digestion of carbohydrates takes place.

Before we put the food into the stomach model, we need to prepare it in the same sort of way it would be prepared by the mouth when you’re eating a food. We have to grind the food so it’s about the same particle size as a chewed food and then we put it into the stomach conditions with a stomach enzyme, called pepsin, which breaks down proteins.

And we have it in a heated block at body temperature and it’s kept moving slowly to make sure it doesn’t settle because in real life your stomach is moving around and your intestines are undergoing peristalsis .

After that’s been going on for half an hour we add an enzyme called pancreatin, which breaks down the starch. After about 20 minutes of digestion you get the main impact on blood glucose, so the measurement we make at 20 minutes is what we take to represent how strongly glycaemic the food is.

At that point we start timing the digestion and taking out samples to measure how much glucose has been released. So we take about half a millilitre and put it into another solution and then we add a colour reagent that reacts specifically with the glucose - it’s called glucose oxidase reagent - and then we measure the colour in a spectrophotometer. And that’s what we use as an indication of what the blood glucose response would be.

We’ve already validated the in vitro test by comparing the amount of glucose released during digestion with the blood glucose responses in subjects. And then we have enough confidence in it to be able to use it on other foods, and so we cut down the cost of clinical validation.