Tastebud Bamboozle: Chemistry behind flavour deception after brushing

Written by Crystal Jang

Imagine starting your day off by following the usual routine: getting dressed, brushing your teeth, and then pouring yourself a refreshing cup of orange juice, expecting its sweet and tangy flavour to energize you - except it doesn’t. You will most likely recoil in disgust, unable to bear the distinct bitterness of what seemed like a harmless sip. The culprit, as we know, is the toothpaste. But how and why exactly does a phenomenon like this occur?

The tongue

To understand what happens in this unpleasant situation, we first have to understand how the tongue functions in terms of tasting. The tongue is a muscular organ with thousands of papillae, which are tiny bumps on the top surface of the tongue. Papillae’s main function includes providing grip while chewing, and delivering the sense of taste, as they contain taste buds. Taste buds are a type of receptors, simply a bundle of nerve cells that transmit sensory information (sweet, salty, bitter, sour and umami) to the brain. 

The ‘Toothpaste Effect’

The modern day toothpaste contains a mixture of chemicals, such as Fluoride, which strengthens the enamel and prevents cavities; Calcium carbonate and Silica, which removes plaque and food particles mechanically; and Sodium laureth sulfate (SLS), the true underlying cause of taste alteration, which creates foam during brushing by decreasing the surface tension of water and saliva. Apart from generating foam, SLS has an effect of temporarily suppressing the perception of sweetness in general, and intensifying the perception of bitterness. Although the scientific reasoning behind these effects remains imperfectly understood, experimental research established the association between SLS and reduced sweetness perception. Another proposed mechanism explains the increased bitterness perception, and it describes SLS as interacting with a chemical component of saliva, specifically lipids within phospholipids, altering the properties of it. This has an impact of making food taste more bitter, as the normal function of phospholipids - reducing the bitterness of some compounds - is disrupted. 

The reason orange juice tastes especially gross after brushing relates to its two distinct flavour profiles: sweet and sour. Your tongue interprets sweetness less intensively, making the sourness of the drink feel relatively stronger. This combined with the strange post-brushing bitter flavour transforms the familiar zesty flavour into something unpleasant. Despite the precise mechanism behind this phenomenon being elusive, this universal experience could provide us more insight on how chemical reactions influence our perception of taste in unpredictive ways.