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  • Rights: The University of Waikato
    Published 1 February 2007 Referencing Hub media
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    Human digestion1 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?

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    John Monro, Plant & Food Research The in vitro model replicates the main conditions2 that the food encounters when it goes to the gut, which also leads to the blood glucose response. It replicates stomach3 conditions and the conditions in the small intestine4, 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 particle5 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 temperature6 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 enzyme7 called pancreatin, which breaks down the starch. After about 20 minutes of digestion you get the main impact on blood glucose8, 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 reagent9 - 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 validation10.

    1. digestion: The mechanical and chemical breaking down of food into smaller components that can be absorbed into a bloodstream.
    2. condition: An existing state or situation; a mode or state of being.
    3. stomach: An organ of digestion with a sac-like shape located between the oesophagus and the small intestine. It temporarily stores food, mixes and churns it with gastric juice and allows digestion of some of the protein content of food to take place.
    4. small intestine: That part of the gastrointestinal tract that connects the stomach to the large intestine. It consists of three parts: the duodenum, the jejunum and the ileum.
    5. particle: A tiny piece of matter. A particle may refer to an atom, part of an atom, a molecule or an ion.
    6. temperature: A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.
    7. enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
    8. glucose: A simple sugar belonging to the group of carbohydrates called monosaccharides. It is the main form of carbohydrate used by the body.
    9. reagent: A substance used in a laboratory to produce a reaction.
    10. validate: To prove something is accurate. With remote sensing, it is a comparison of data obtained via satellite or other imaging with data collected by conventional means.
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      digestion

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    2. The mechanical and chemical breaking down of food into smaller components that can be absorbed into a bloodstream.

      small intestine

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    4. That part of the gastrointestinal tract that connects the stomach to the large intestine. It consists of three parts: the duodenum, the jejunum and the ileum.

      enzyme

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    6. A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.

      validate

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    8. To prove something is accurate. With remote sensing, it is a comparison of data obtained via satellite or other imaging with data collected by conventional means.

      condition

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    10. An existing state or situation; a mode or state of being.

      particle

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    12. A tiny piece of matter. A particle may refer to an atom, part of an atom, a molecule or an ion.

      glucose

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    14. A simple sugar belonging to the group of carbohydrates called monosaccharides. It is the main form of carbohydrate used by the body.

      stomach

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    16. An organ of digestion with a sac-like shape located between the oesophagus and the small intestine. It temporarily stores food, mixes and churns it with gastric juice and allows digestion of some of the protein content of food to take place.

      temperature

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    18. A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.

      reagent

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    20. A substance used in a laboratory to produce a reaction.