Abstract

Objective

Determine whether there is a difference between adults' and children's preferences for sour tastes.

Introduction

Do you know anyone who likes to eat lemons? Or loves really sour candies? Maybe you are one of those people! People have different definitions of what they find palatable (PAH-lih-tuh-bul), which means "good to eat." There are many different factors that go into deciding whether or not something is palatable. One of the biggest parts of that decision is how something tastes. Humans can sense five tastes: sour, salty, bitter, sweet, and umami (oo-MAH-mee), which is the non-salty part of how soy sauce tastes.

Taste is detected by the taste buds that line the tongue and other parts of the mouth. Figure 1 shows a diagram of a taste bud. Although there is some variation from person to person, the human tongue has an average of about 10,000 taste buds. Inside each taste bud are several receptor cells. These cells can sense the five different tastes, and they send that information to the brain.

Figure 1. Each taste bud contains many different taste receptor cells, which help to detect the five different tastes: sour, salty, bitter, sweet, and umami. (Adapted from Selbst Erstellt, 2008.)

In addition to taste, people think about several other factors when deciding if something is acceptable to eat. These include other components of flavor, like how spicy a food is or how it smells, the texture and temperature of a food, and whether the food is something they like eating for cultural or personal reasons. Figure 2 shows a diagram of the different factors people consider when making their food choices.

Figure2. This diagram shows the different factors humans use to determine if a food is acceptable to eat or not. Taste, at the center of the diagram, is one of the most important factors; but other things, including what is typically considered "yummy" in a culture, are also part of the decision.

One job food scientists can have is working at companies to help them design new foods. One of the things they have to do is conduct sensory analysis, which is the scientific process of determining how people react to different foods, and then make decisions about whether or not they like them. Food scientists already know a lot about people's food preferences. For example, they know that babies usually prefer sweet foods, like applesauce and sweet potatoes, over more bitter foods, like broccoli. They also know that Americans and Europeans like mint-flavored toothpastes, while people in China and Japan prefer their toothpastes to be fruit-flavored. But what about sour? There are a lot of sour candies and drinks advertised on TV, in magazines, and in other places that tempt kids, but not many of those advertisements make the foods sound appealing to adults. Is there a difference in the percentage of kids versus adults who like sour-tasting foods? You can find out in this mouth-puckering science fair project by conducting a taste test with four lemonades, each with a different concentration of citric acid. Citric acid is the natural chemical that gives citrus fruits, like limes, lemons, oranges, and grapefruit, their sour taste. Who do you think will like the sourest lemonade the best?

Terms, Concepts, and Questions to Start Background Research

• Palatable
• Umami
• Taste bud
• Receptor cell
• Sensory analysis
• Citric acid
• Citrus fruits
• Concentration
• Stock solution

Questions

• What are some foods that represent the five tastes that humans can detect?
• What factors do people use to decide if they want to eat a certain food?
• Are there any examples of adults and kids having different preferences for certain tastes?

Bibliography

These websites have more information about taste and taste buds:

• Chudler, E. (2008). That's Tasty. Retrieved July 30, 2008, from http://faculty.washington.edu/chudler/tasty.html
• Gavin, M. (2007). What Are Taste Buds? Retrieved July 30, 2008, from http://kidshealth.org/kid/talk/qa/taste_buds.html
• Sohn, E. (2006, August 30). A Sour Taste in Your Mouth. Science News for Kids. Retrieved July 30, 2008, from http://www.sciencenewsforkids.org/articles/20060830/Note3.asp

This website offers help with creating graphs:

• National Center for Education Statistics. (n.d.). Create a Graph. Retrieved July 30, 2008, from http://nces.ed.gov/nceskids/CreateAGraph/default.aspx

Materials and Equipment

• Citric acid, 3 oz (85 grams), used for sprouting or canning foods; can be found as a powder or granules in some grocery stores. Check the spices, baking supplies, or health supplements aisles. Can also be ordered online from some vitamin companies, like LuckyVitamin.com and TheCatalog.com. Caution: only use food-grade citric acid.
• Tablespoon measuring spoon
• Measuring cups
• Mixing spoon
• Water
• Containers that can hold and pour 1 liter of liquid, such as pitchers; thermoses; and empty, clean juice bottles (5)
• Permanent marker
• Masking tape
• Citrus-flavored powdered drink mix, like lemonade flavor, enough to make 4 liters (which is the same as 4 quarts)
• Refrigerator
• Small paper cups (150)
• Helper
• Adult volunteers (15)
• Kid volunteers between the ages of 5 and 11 years old (15)
• Graph paper
• Lab notebook

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Experimental Procedure

Making the Lemonades

1. The first step is to make a stock solution of the citric acid. A stock solution is a mixture that is more concentrated than any of the final mixtures. The stock solution can then be diluted to make all the other drinks. This is easier than measuring out the citric acid for each batch of lemonade because the amounts of citric acid would be too small and hard to measure by volume or weight for some of the less sour batches.
   1. Using the measuring spoon, put 6 tablespoons (Tbsp) of your citric acid in one of your containers.
   2. Add 3 cups of water to the pitcher and mix with a spoon until all the citric acid is dissolved.
   3. This is your stock solution of citric acid. It has twice as much citric acid in it as the most sour batch of lemonade you will make.
   4. Note: You can taste the stock solution if you want, it won't hurt you, but it will be very sour!
2. Using pieces of masking tape and a permanent marker, label each of the four remaining liquid containers with the numbers 1, 2, 3, and 4, which correspond to the information in the table below. Each container will hold a different batch of lemonade.
3. Following the directions on the package of the lemonade mix, add enough of the drink mix to each container to make 1 liter of the drink. Note: The instructions for the drink mix might list quantities in cups or quarts instead of in liters. 1 liter, 1 quart, and 4 cups are all the same amount of liquid.
4. Using the measuring cup and measuring spoon, add the citric acid stock solution and appropriate amount of water to each container. The table below shows how much of each ingredient should be added for each lemonade batch.

   Lemonade Batch #	Level of Sourness	Quantity of Citric Acid Stock Solution to Add to the Drink Mix	Quantity of Water to Add to the Drink Mix
   1	None	None	4 cups
   2	Low; similar to 10% lemon juice	3 Tbsp	4 cups
   3	Medium; similar to 50% lemon juice	2/3 cup	3 and 1/3 cups
   4	High; similar to 100% lemon juice	2 cups and 2 Tbsp	2 cups

5. Use a spoon to mix each lemonade batch until all the drink mix is completely dissolved.
6. Refrigerate the lemonade batches until you are ready to have your volunteers taste-test them.

Conducting the Taste Test

1. You'll need to gather all your volunteers at the same time.
2. With the permanent marker, label 30 paper cups for each lemonade batch. In the end, you'll have a total of 120 paper cups that will hold lemonade: 30 labeled #1, 30 labeled #2, 30 labeled #3, and 30 labeled #4.
3. On a large work surface, with plenty of space to set out all 120 cups, pour the lemonade batches into the appropriately labeled cups. For example, batch #1 (the lemonade without any citric acid added to it) will go in the cups labeled #1. You might want to have a helper move the cups out of the way for you as you pour them. Try to keep each batch grouped closely together.
4. Pour plain water into 30 more cups—these cups don't have to be labeled with anything.
5. Give each volunteer one cup from the first lemonade batch. Note: You can choose to have the volunteers taste the lemonades in any order you want, just make sure that each volunteer follows the same tasting pattern. However, passing them out in numerical order will probably help your volunteers remember which one they liked best and which they liked least.
6. Ask the volunteers to taste the first lemonade. Then pass each person a cup of water and have them take a sip to clear their palettes. Continue to pass out the lemonades, one at a time, asking the volunteers to taste them, and always having the volunteers take a sip of water in between tastings.
7. Once the volunteers have tasted all four batches of lemonade, ask them to tell you which was their favorite, and which was their least favorite. Record the results in a data table, like the one below, in your lab notebook.

Volunteer #	Adult or Kid	Favorite Lemonade Batch #	Least Favorite Lemonade Batch #
1
2
3

Analyzing the Data

1. Make a bar graph illustrating your data.
   1. Make a bar graph showing how many of the volunteers chose each batch of lemonade as their favorite. You can either make two graphs, one for the adults and one for the kids, or one graph with different colored bars for the adult and kid data.
   2. Using the same technique, make a bar graph showing how many of the volunteers chose each batch of lemonade as their least favorite.
   3. You can make the graphs by hand or use a website like Create a Graph to make the graphs on the computer and print them.
2. Look at your graphs. Is there a difference between adults and kids for how many chose the sourest lemonade as their favorite? How about as their least favorite?

Variations

• Do kids and adults have different preferences for other tastes? Design experiments to test preferences for any or all of the other tastes: sweet, salty, bitter, and umami.
• Does being a "picky" eater change how likely a person is to enjoy really sour foods? Ask your volunteers if they are picky, normal, or adventurous eaters. You'll need at least 10 people in each category. Then give them the sour taste test described above. Make bar graphs for each category of eater. Do you see any differences between the categories?

• For more science project ideas in this area of science, see Human Biology & Health Project Ideas.

Credits

Tirza Thebert

Sandra Slutz, PhD, Science Buddies

Last edit date: 2008-10-06 00:00:00