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How does toothpaste make orange juice taste bad?

What is it about toothpaste that transforms the sweet flavour of orange juice into something so bitter? What the cause of this mysterious sensory phenomenon…

In actuality, scientists don’t know for sure why orange juice and toothpaste go so poorly together. This is mostly due to the fact that scientists aren’t entirely certain how taste works. Like smell, full understanding of this sense remains elusive. Still, we have a pretty good idea of what takes place in the process of taste, and based on current observation, researchers have come to a general consensus as to what creates the horrific OJ/toothpaste combo.

The tastes your mouth can perceive are divided into five general categories: sweet, salty, bitter, sour and umami (meaty tastes). While each is separate, they all work together to produce different flavours. Flavour is not the same as taste. In fact, taste is an aspect of flavour, along with temperature, consistency, smell and texture. Each of these factors has an effect on our perception of taste. For example, foods taste sweeter when they’re warmer than they do when they’re colder.

So what’s at the root of the problem?

Currently, scientists believe that flavours are the result of interactions between taste molecules and receptors on your tongue. Molecules of a certain shape will interact with receptors that are shaped to accept them. But these receptors can be manipulated, which is probably the best explanation for why orange juice and toothpaste taste gross together.

The likeliest culprit for the offensive reaction is the foaming agent found in almost all toothpastes. Sodium lauryl sulfate (SLS) is a surfactant – a sudser – added to toothpaste. It creates the froth that toothpaste becomes after you begin brushing by lowering the surface tension of the saliva in your mouth and allowing bubbles to form. While it aids in spreading the toothpaste throughout your mouth, it also creates the impression of cleanliness; a mouthful of foam just feels cleaner.

But SLS has other properties, too. For one, it suppresses your sweet receptors, so it has a dampening effect on the generally sweet taste of orange juice. In addition, SLS destroys phospholipids. These fatty compounds act as inhibitors on your bitter receptors. So by inhibiting sweet receptors and destroying phospholipids, SLS dulls the sweetness and promotes the bitter taste in orange juice.

This is not the only explanation of why orange juice and toothpaste form a bad flavour, but it’s the most widely accepted one. Another explanation, posed by a researcher at the United States Department of Energy, suggests that the horrible taste is the result of interaction between the stannous fluoride in toothpaste and the acetic acid in orange juice.

While research into the science of taste is as intense as minty toothpaste, investigations into the orange juice/toothpaste interaction are actually fairly sparse. The authors of one study, published in the Journal of Sensory Studies in 2005, concluded that it takes at least an hour for the effects of minty toothpaste on the taste of orange juice to dissipate.

But this study examined the effects of only “strongly mentholated toothpaste”. So is the same bad taste created with toothpastes that don’t contain a minty flavour? Any toothpaste with SLS will create the bad taste, says University of California – Davis sensory scientist Dr Hildegarde Heymann. And don’t forget, SLS is present in just about every brand of toothpaste. And Heymann should know, she’s worked as a flavour scientist in the toothpaste industry. Of course, you don’t need a PhD to figure this out. The simple misstep of taking a sip of OJ after brushing your teeth is experiment enough.

This video, from the American Chemical Society’s award-winning Bytesize Science series, explains the phenomenon.



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