Abstract
Have you ever been to a buffet and found yourself surrounded by a wide variety of taste sensations? People are generally able to discern five basic tastes: sweet, umami (also known as savory), salty, sour, and bitter. How sensitive is a person's tongue for these basic tastes? Is it easier to detect some flavors at low concentrations compared to others? In this human biology science project, you will find out by exploring your taste thresholds for sweetness, saltiness, and sourness. Get ready to find out how low you can go!Summary
Andrew Olson, Ph.D., Science Buddies
- DiBari, 1998. Taste Lab, Troy High School Labs Online, Troy, NY. Retrieved December 1, 2011.
- Dodd, J. and V.F. Castelluci, 1991. Smell and Taste: The Chemical Senses, in Kandel E., J.H. Schwarz and T.M. Jessell. Principles of Neuroscience: Third Edition. Norwalk, CT: Appleton & Lange.
Objective
To determine your threshold of taste for sweetness, sourness and saltiness.
Introduction
Our sensory system for taste, or our taste perception, is remarkably sensitive. Not only can we detect compounds at extremely low concentrations, we can also discriminate between molecular compounds that are closely related. For example, for some molecules we can distinguish between different stereoisomers, which are molecules that are made of exactly the same components, but are mirror images of one another. The artificial sweetener aspartame is an example of this. It tastes sweet to us, but its stereoisomer does not. Our noses are similarly sensitive: one stereoisomer of carvone smells of spearmint while its mirror image smells of carraway (Dodd & Castelluci, 1991).
This amazing sensitivity is made possible by our taste buds. Taste buds are located on small bumps on the tongue called papillae, which are shown in Figure 1, below. Each taste bud is made up of about 50 to 150 taste receptor cells. On the surface of these cells are receptors that bind to small molecules related to flavor. The receptors then relay the taste sensation information to the brain. This entire process allows us to discern the five basic tastes.
Figure 1. The arrows in the picture are pointing to papillae, which are small bumps on the tongue. Taste buds are located on the papillae. (Bladebot, 2006)
In this human biology science project, you will determine your own taste thresholds for sweet, sour, and salty solutions. You will start with a 10% solution, and use the process of serial dilution to make a series of solutions, each 10-fold weaker than the preceding one (i.e., 1%, 0.1%, 0.001%, etc.). If done properly, this is an extremely accurate method.
Terms and Concepts
- Taste perception
- Taste buds
- Papillae
- Serial dilution
Bibliography
For an introduction to the physiology of taste, check out these websites:
- Bowen, R., 2003. Physiology of Taste, Colorado State University. Retrieved January 19, 2006.
- Jacob, T., 2003. Taste-A Brief Tutorial by Tim Jacob, School of Biosciences, Cardiff University. Retrieved January 19, 2006.
Here is an interesting news article about an electronic chemosensor:
- Unattributed news release, 1998. Researchers Taste Success with Electronic Tongue, College of Engineering, University of Texas at Austin. Retrieved December 1, 2011.
Materials and Equipment
- Table salt, or sodium chloride (10 g)
- Granulated sugar, or sucrose (10 g)
- Vinegar (2 mL)
- Water, preferably distilled
- Stirring rod or spoon
- Gram balance, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
- 100 mL graduated cylinder, available from an online supplier such as Carolina Biological catalog #721613.
- 10 mL graduated cylinder, available from an online supplier such as Carolina Biological catalog #721610.
- Cotton swabs (at least 12)
- Paper or plastic cups (at least 12)
- Paper towels (at least 12)
- Volunteers
- Lab notebook
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Experimental Procedure
Working with Human Test Subjects
There are special considerations when designing an experiment involving human subjects. Fairs affiliated with Regeneron International Science and Engineering Fair (ISEF) often require an Informed Consent Form (permission sheet) for every participant who is questioned. Consult the rules and regulations of the science fair that you are entering, prior to performing experiments or surveys. Please refer to the Science Buddies documents Projects Involving Human Subjects and Scientific Review Committee for additional important requirements. If you are working with minors, you must get advance permission from the children's parents or guardians (and teachers if you are performing the test while they are in school) to make sure that it is all right for the children to participate in the science fair project. Here are suggested guidelines for obtaining permission for working with minors:
- Write a clear description of your science fair project, what you are studying, and what you hope to learn. Include how the child will be tested. Include a paragraph where you get a parent's or guardian's and/or teacher's signature.
- Print out as many copies as you need for each child you will be surveying.
- Pass out the permission sheet to the children or to the teachers of the children to give to the parents. You must have permission for all the children in order to be able to use them as test subjects.
- Make a data table in your lab notebook like Table 1, below. Use as many columns as you need to determine your taste threshold for each substance.
| Substance | 10% | 1% | 0.1% | 0.01% | etc. |
| sucrose | |||||
| sodium chloride | |||||
| vinegar |
- Measure 90 ml of distilled water and pour it into a paper or plastic cup. Add 10 grams (g) of granulated sugar. Stir until dissolved. This gives you a 10% (weight/weight, or w/w) sucrose solution.
- Rinse your mouth with plain tap water and wipe your tongue dry with a clean paper towel.
- Dip a clean cotton swab into the 10% sugar solution and smear it all around your tongue. If you can taste the sweetness, put a + in your data table for 10% sucrose. Note any other observations that you make.
- Now measure out 10 ml of the 10% sucrose solution and pour it into a clean paper cup. Add 90 ml of distilled water and stir. (Note: Use a clean stirrer, or else thoroughly rinse and dry the previous stirrer, so that you don't carry over concentrated solution into the dilute solution.) This will give you a 1% sugar solution.
- Repeat step 3. Then dip a clean cotton swab into the 1% sugar solution and smear it all around your tongue. If you can taste the sweetness, put a + in your data table for 1% sucrose. Note any other observations that you make.
- Continue making serial dilutions (by repeating step 5), rinsing and drying your tongue, and testing each new solution with the cotton swab procedure until you no longer taste the sweetness. Record the results in the data table in your lab notebook. The lowest concentration at which you can still taste the sweetness is your approximate taste threshold.
- Repeat steps 2–7 with salt (sodium chloride) and vinegar (main ingredient: acetic acid), separately, instead of using sugar. To make a 10% (volume/volume, or v/v) solution of vinegar, use 2 ml of vinegar and 18 ml of water.
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Analyze your results.
- Were your thresholds the same for all three tastes, or did you have different thresholds? Can you think of reasonable explanations for your results?
- Do sugar solutions that are 10-fold more concentrated taste 10× as sweet? Same question for salt and vinegar solutions.
Ask an Expert
Variations
- Repeat this science project using several volunteers. Compare your results. Do some people generally have lower thresholds than other people? Is there variation in which taste has the lowest threshold for people in the group?
- Is there a difference in taste threshold for iodized vs. non-iodized salt?
- Do background research to find out how many molecules are in 10 g of salt. Calculate the number of salt molecules that were contained in the lowest-concentration solution which you could taste. If you assume that the cotton swab holds 0.1 ml, how many salt molecules were available on the cotton swab for you to detect? Do the same for sugar, and, if you are really enterprising, for vinegar.
- In this experiment you used 10-fold serial dilutions to roughly establish your threshold of taste. Design an experiment to determine your threshold with higher precision.
- Recruit enough volunteers in different age groups to take this threshold of taste test so that you can test the hypothesis that taste threshold changes predictably with age. Do your results support the hypothesis?
Careers
If you like this project, you might enjoy exploring these related careers:
