Kids, does orange juice taste awfully bitter to you right after brushing your teeth? If so, you are one of about 2/3 of the population who has a taste gene on your tongue that allows you to detect certain bitter compounds. The other 1/3 of you lacks this gene. When one of you who has the gene brushes your teeth with a toothpaste that contains sodium lauryl sulfate (or SLS), you notice this bitterness effect. SLS reduces the sweet taste of sucrose (sugar) and at the same time strengthens the bitterness of citric acid (responsible for the sour and bitter taste of orange juice) by about ten times! If you would like to see if you inherited this gene or not, select a toothpaste that contains SLS in the list of ingredients. Take a sip of orange juice and note the relative strength of the sweet, sour, and bitter tastes. Rinse your mouth with water, then vigorously brush your teeth with the toothpaste. Rinse with water again, then taste the orange juice again. Are the relative intensities of the tastes very different now?
Taste begins with an ion or molecule docking in receptors on the tongue or palate. The substances that trigger sweet and bitter tastes are usually large, complex organic molecules that fit these receptors like keys in a lock. In contrast, salty and sour tastes are triggered by tiny positive ions. SLS is one of the most widely used detergent molecules. It is a large organic molecule found in toothpaste, laundry detergents, and specialty detergents such as Woolite®. The reason why some of you won't notice the taste effect of SLS is because you may be insensitive to the bitter tastes of compounds called phenylthiourea and propylthiouracil, and less sensitive to bitter flavors such as caffeine, potassium chloride, and certain preservatives. These people have failed to inherit a gene from their parents that makes them sensitive to bitter tastes. Some people have inherited the gene from just one parent, and they experience the bitterness effect to a lesser degree.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
December 1995
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Reference: P. DeCristofaro,ChemMatters, published by the American Chemical Society (Washington, DC), 1995, vol. 13, no. 2, pg. 14.
