Saturday, March 30, 2013

Bitterness and Supertasting

Excessive bitterness turns people off consuming those foods. For example, if I eat a food and experience excessive or lingering bitterness from it, I am unlikely to consume the food again. To some people that statement may appear illogical because there are many excessively bitter foods common in the food supply; think about beer or coffee.  An important factor in this discussion is individual differences in perception and what I experience as excessively bitter, a second person may experience little to no bitterness.  In such a situation I reject the food, while the other person finds the food perfectly acceptable. Part of the diversity is due to complex biology underpinning bitter taste – we have at least 25 receptors for bitter taste, some receptors are responsive to multiple compounds, others only one or two compounds. 
Individual differences are the norm, we all have our own flavour worlds and bitter taste is particularly variable among the population. One concept common in discussions about bitterness and individual variation is the ‘supertaster’. The term is applied to a person who is sensitive, or experiences extreme bitterness from the compounds PROP (n-6-propylthiouracil) or PTC (Phenylthiocarbamide); both of these compounds activate the same narrowly tuned bitter taste receptor (meaning only a few compounds activate the receptor).  Some studies have shown that supertasters are more sensitive generally to bitterness of foods, meaning they experience a higher intensity of bitterness not just to PROP or PTC, but all bitterness.  Some studies suggest supertasters are more sensitive to all sensory stimuli.  Operationally this is not true, the term supertaster merely means an individual is more sensitive to a specific bitter compound, and may mean no more than that.  When an individual is generally more sensitive to food chemicals the heightened sensitivity to PROP / PTC may be a defacto marker of increased papillae. Given the thought that more papillae means more taste receptors, and the more receptors the greater the taste signal from the papillae. 
In the same paradigm, people who cannot taste bitterness in PROP / PTC are termed ‘non-tasters’.  This is not because they have no papillae, but because the bitter taste receptor has a minor variation in sequence compared to the receptor in supertasters.  When researchers have looked at supertasters and non-tasters as groups, some differences in food consumption are apparent in some studies – for example supertasters find broccoli and alcohol bitter and consume less of them than non tasters; other studies find no differences in consumption between the groups.
The relevance of sensitivity to PROP / PTC to food consumption is debatable because of the large individual variation to bitterness – just because I am sensitive to PROP or PTC does not mean I am sensitive to the bitterness of caffeine or myriad other bitter chemicals in the food supply. You commonly have the situation where an individual may not eat grapefruit because they find it too bitter, but have no problem consuming black unsweetened coffee. Some others may find both or neither bitter.  It can be confusing, but that is a function of the complex biology and perceptual processes involved.   
Dr John Hayes and I recently published a paper reconceptualising the supertaster terminology (1).