What S in the Food We Eat

1

Carbohydrates

As you saw in the PowerPoint slide show, plants use the process of photosynthesis to create carbohydrates. Those carbohydrates are your body’s primary fuel. Your body will burn carbohydrates first, before it burns fat or protein, to make energy.

Photosynthesis works like this:

And, as you saw in the slide show, plants will take some of their simple sugars like glucose and fructose and package them into more complex forms like starch (amylose) and fiber (cellulose). Use the space below to make some drawings:

Based on the symbols used, what seems to be the main difference between simple and complex carbohydrates?

Using the materials at your table, demonstrate that sugar molecules are “small molecules” and starch and fiber molecules are “large molecules”. This simple visual/kinesthetic demonstration will establish memory for understanding a key concept of this unit.

Some Chemical Tests for Carbohydrates

There are three simple chemical tests you can perform to see if a food contains certain kinds of carbohydrates. Unfortunately, we can not perform simple chemical tests to test for all kinds of carbohydrates. For example, there is no fiber test. 

Starch Test: A test to see if an item contains starch.

1. Wear safety glasses and gloves.
2. Place a little of a food item on a spot plate.
3. CAREFULLY Add a few drops of iodine solution.
4. If the item turns a dark purple or black color, the item in question contains starch. (The darker the color, the more starch is present.)
5. If the item is stained orange/brown (the color of the iodine), then there is no starch present in the item.
6. Record your findings on handout page 51.

Simplest Sugar Test: A test to see if an item contains the simplest forms of sugar like glucose, fructose and galactose.

1. Wear safety glasses and gloves.
2. Place a little of a food item in a test tube.
3. CAREFULLY add enough Benedict’s Solution to just cover the item; make sure the test tube is visibly blue.
4. Place the test tube in a beaker of warm water for about three to five minutes.
5. If simplest sugars like glucose or fructose are present, the liquid will turn green, then yellow, then orange. (The greater the change, the more sugar is present.)
6. Solid food items won’t change color in this test – it’s the Benedict’s Solution that will change colors if a simplest sugar is present.
7. Record your findings on handout page 51.

Sucrose Test: There is no direct test to test for sucrose.

However, we have a chemical enzyme called sucrasewhich breaks sucrose into its two components: glucose and fructose. And you CAN test for those simplest forms of sugar.

So…how then could you test a food item to determine if it has sucrose in it? (This is very tricky!

Understanding Carbohydrates on Nutrition Facts Labels

Nutrition Facts labels will tell you about:

Total carbohydrate

Fiber

Sugars

But they don’t tell you how muchSTARCH a food contains.

How can YOU determine

how much starch a food contains?

Carbohydrates on Food Labels

1. Pick a food label to analyze.
2. Determine the amount of sugars, fiber and starch in each food.
3. Record Results on the chart below.

Questions:

Using the ingredients located near the Nutrition Facts box:

For foods high in sugar, what are the primary sources of sugar?

For foods high in starch, what are the primary sources of starch?

For foods high in fiber, what are the primary sources of fiber?

Which of the three forms of carbohydrate seems hardest to find? Easiest to find?