Bitterness is one of those taste sensations which can either make a food seem highly sophisticated or so repulsive in flavour it is uneatable. This particular type of taste is critical in the acceptance of a food and forms one of the most distinctive sensory aspects. Bitter masking is method of making products more acceptable.
The perception of bitterness has probably evolved to help us recognise toxins and prevent ingestion. It is in this regard an important safety trigger – if its tastes nasty, don’t eat it ! However, there are a few compounds including the isoflavones and flavonoids which have a bitter taste but are associated with positive health benefits (Roland et al., 2013).
A simple definition of taste is that it is a sensory response to chemical stimulation of the taste receptors by molecules called tastants which seems a clumsy term (Chandrashekar et al., 2006). We have five basic tastes:- sweet and sour, salty, bitter, umami and possibly a sixth which is fat. The most complex to understand is bitterness (Behrens et al., 2004).
The latest theory for taste perception is based on the concept that taste buds respond to all stimuli to differing degrees. The taste buds are onion-shaped structure made up of 50 to 100 taste receptor cells. The tastants interact with various surface proteins in these taste receptors as is the case for sweet and bitter sensation, or with pore-like proteins which are ion channels as in the case for sour and salty taste. In both cases there is an electrical change within the taste cells that trigger release of chemical signals which are then transformed into neurotransmission to the brain. The brain than interprets the nerve impulses as a sensation belonging to one or a few of the basic tastes.
There are just over 25 likely bitter receptors which has always meant that finding a single, universal, bitter blocked does not exist.
Typical Bitter Compounds
Flavour companies have built huge businesses offering a wide range of solutions to cover up a bitter molecule. What types of molecule or ingredient for that matter is being covered up ? The ingredients causing bitterness include caffeine, glycerin and even grapefruit juice. We can also add chemical burn from preservatives like sorbic acid and there is a the warmed-over flavour (WOF) in both meats and coffee.
What Taste Masking Techniques Are There ?
- Bitterness can be masked most easily by adding enough a sweetening or strong flavouring agent that it swamps the perception of bitterness. It is extremely simple to employ. The sweeteners are often highly water soluble and dissolve in the saliva to coat the taste bud, which prevents any bitter tastants from interacting with the receptors. They can be combined in ways that modify the sweet sensation. Flavours like menthol for example numb the taste receptors as well so bitterness is masked.
- Compounds which cause bitterness can be complexed in a variety of matrices which reduces their interaction with taste receptors. Complexation is a simple method of fitting a tastant within another molecule like cyclodextrin for example.
- The addition of salt can alter the solubility of some bitterness compounds so they precipitate out of solution.
- Fermentation can remove off-flavours. Lactic acid fermentation often suppresses the formation of off-notes in processed legumes.
Legumes like soy and pea sometimes produce green and beany off-flavours which make the products they are part of, inedible. It is highly restrictive when it comes to considering legumes for product development. In some cases volatile compounds have been added to suppress those compounds causing the off-flavours (Heng et al., 2004). Alternatively, lactic acid fermentation improves pea flavour by reducing off-flavours or masking undesirable green notes (Schindler et al., 2012).
Extracts of Gymnema sylvestre or ziziphins are good for blocking sweet tastes. Lactisole (Na-2,4-methoxyphenoxy-propanoate), a compound that not only blocks sweet taste but has also been shown to reduce umami perception. There are sodium and zinc salts which at certain concentrations suppresses the bitter taste (Breslin and Beauchamp, 1997; Keast and Breslin, 2002; 2005).
Behrens, M. et al. (2004) The human taste receptor hTAS2R14 responds to a variety of different bitter compounds. Biochem. Biophys. Res. Commun. 319: pp. 479–485
Breslin PA and Beauchamp GK. (1997) Salt enhances flavour by suppressing bitterness. Nature. 387(6633): pp. 563.
Chandrashekar, J., Hoon, M. A., Ryba, N. J., & Zuker, C. S. (2006). The receptors and cells for mammalian taste. Nature, 444(7117), pp. 288.
Heng, L., van Koningsveld, G. A., Gruppen, H., van Boekel, M. J. A. S., Vincken, J.-P., Roozen, J. P., and Voragen, A. G. J. 2004. Protein-flavor interactions in relation to development of novel protein foods. Trends Food Sci. Technol. 15 pp. pp. 217-224
Keast, R.S. and Breslin, P.A. (2002) Modifying the bitterness of selected oral pharmaceuticals with cation and anion series of salts. Pharm Res. 19(7) pp. 1019-1026.
Keast, R.S. and Breslin, P.A. (2005) Bitterness suppression with zinc sulfate and Na-cyclamate: a model of combined peripheral and central neural approaches to flavor modification. Pharm Res. 22(11) pp. 1970-7.