Key concepts:
Food science
Chemistry
Artificial sweeteners
Sugar
Taste

Introduction
Picture your favorite treats: chocolate fudge cake, vanilla ice cream, pink lemonade… Yum! Can you imagine what these might taste like without the sweet flavor of sugar? Your sweet tooth might be aching without the chemical compound of sucrose that is so appealing. Much of the food we eat contains sucrose or natural sweeteners such as honey. There are of course other sweetening options. Have you ever seen "zero-calorie and sugar-free lemonade" at the store and wondered how it was made? Perhaps you've tried sugar-free candy or diet soda. Scientists have developed artificial sweeteners that provide the taste of "sweet" without the sugar itself. How sweet are they? Get ready to make some of your own artificially sweetened lemonade and find out how it compares with lemonade made with real sugar. Prepare yourself for some sour and sweet scientific discovery!

Background
Artificial sweeteners are a common substitute for sucrose (sugar). Sucrose is a natural substance, a carbohydrate derived from sugar canes that is used by our bodies for energy. Sucralose, the sweetener in Splenda, is a manufactured alteration of the sucrose molecule. The compound cannot be broken down by the body and therefore is calorie-free. Other artificial sweeteners such as saccharin (in Sweet'n Low) work in the same manner, creating the sweet taste without the calories the body gets from sugar. How sweet are these synthetic compounds compared with sugar? You will test just that as you make your own sugar-free lemonade!

Materials

  • Six medium- to large-size lemons (Alternatively, you can buy pure lemon juice at the store.)
  • Pure cane sugar (table sugar)
  • Water: two and one quarter cups
  • Artificial sweetener (Splenda or Sweet'n Low)
  • Three spoons
  • One knife
  • Three drinking cups
  • Strainer
  • Bowl
  • Permanent marker
  • Liquid volume measurer (at least one cup volume)                                          
  • One-quarter teaspoon measuring spoon
  • Volunteer taste testers (optional)
  • Additional cups (three for each volunteer) or large spoons (three for each volunteer)

Preparation

  • To make the lemon juice, slice lemons into four pieces (across the length of the lemon works best) then squeeze the juice into the volume-measuring cup. Squeeze lemons until you have one cup lemon juice.
  • Strain the lemon juice into another plastic cup, and then pour the strained juice back into the liquid volume-measuring cup.

Procedure

  • Using the liquid volume–measuring cup, pour one-quarter cup of lemon juice into three different cups.
  • Use the liquid volume–measuring cup to add three-quarter cup of water to each cup. Stir the contents of the cups with a spoon to mix the juice with water. How do you think the plain lemon-and-water drink will taste?
  • Now it's time to add the sweeteners! Which do you think will make sweeter lemonade—sugar or an artificial sweetener? Why?
  • To the first cup add no sugar or artificial sweetener.
  • To the second cup add one-quarter teaspoon of pure cane sugar (table sugar). Stir with a spoon until the sugar is entirely dissolved, with none left on the bottom.
  • To the third cup add one-quarter teaspoon of artificial sweetener (Splenda or Sweet'n Low). Stir until the sweetener is entirely dissolved, with none left on the bottom.
  • Now it's time for the taste testing! If you have volunteers, you can pour each taste tester a small sample into other cups—or have each person take a large spoonful to taste. Take a small sip of unsweetened lemonade. What does it taste like? What was your reaction?
  • Take a small sip from the lemonade sweetened with sugar. What does it taste like?
  • Now take a small sip of the lemonade sweetened with artificial sweetener. What does this one taste like? How do the two sweetened beverages taste compare with the plain lemon juice? How do they compare with one another?
  • Overall, which cup had the sweetest lemonade? If you had taste testers, does everyone agree? Which beverage do you (and your volunteers) prefer? Why?
  • Extra: Can you make lemonade sweetened by sugar and artificial sweetener equal in sweetness? Start with the one that is bitterer and add more of its sweetening substance, in one-quarter teaspoon increments, until it tastes just as sweet as the other lemonade. How much of the substance did you need to add to make the lemonades equal in sweetness? Were you surprised by how much or how little you needed to add?


Observation and Results

Did you find that the lemonade made with artificial sweetener was sweeter than that made with sugar? Did the original sugar lemonade taste almost as sour and bitter as the pure lemon juice?

Artificial sweeteners are synthetic compounds designed to produce the intense sweet taste you observed in the artificially sweetened lemonade. In fact, the sweetness of artificial sweeteners is many times that of sugar. This means that if you add equal quantities of sugar and an artificial sweetener, the drink with the artificial sweetener will taste sweeter.

If you completed the "Extra" challenge, you may have seen that it took several teaspoons of sugar to equal the sweetness of the artificial sweetener. Splenda is 600 times sweeter than sugar and saccharine, found in Sweet'n Low, is 300 to 500 times sweeter. In the lemonade some of the sweetness is masked by the sourness of the lemon so you will not need to add 100 more teaspoons of sugar to get the same sweetness as one-quarter teaspoon of sweetener.

Although artificial sweetener does not add additional calories to foods and drinks that use it, we don't know exactly how it works inside our bodies after we consume it, so scientists are still looking into health effects.

More to Explore
Comparing the Sweetness of Sugar and Sugar Substitutes, from Science Buddies
Sensory Science: Testing Taste Thresholds, from Scientific American
Artificial Sweeteners May Evict Good Gut Microbes, from Society for Science & the Public
Yeast Reproduction in Sugar Substitutes, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies