Bitter Taste Perception

The same conclusions were also recorded for vertebrate herbivores. For example rabbits (Cuniculus europaeus) and hares (Lepus europaeus) clearly prefer the sweet plants and leave the bitter plants almost untouched, at least as long as there is an alternative food source. In conclusion, although taste perception in mammals and insects differs in many aspects, there also some similarities both in anatomy and in the function of the bitter taste perception. A comparison of the effects of alkaloids, as well as of other bitter compounds, will be assisted by further advances in the knowledge of the structure of taste genes and receptors. 

Behrens M, Meyerhof W. Bitter taste receptors and human bitter taste perception. Cell. Mol. Life Sci. 2006 63 1501-1509. 

Behrens M, Foerster S, Staehler F, Raguse JD, Meyerhof W (2007) Gustatory expression pattern of the human TAS2R bitter receptor gene family reveals a heterogenous population of bitter responsive taste receptor cells. J Neurosci 27 12630-12640 Behrens M, Meyerhof W (2006) Bitter taste receptors and human bitter taste perception. Cell Mol Life Sci 63 1501-1509... 

Quinine, isolated from cinchona bark in the form of hydrochloride or sulfate, is mainly used in medicine as an antimalarial and antipyretic medication. In sensory analysis it is used as a standard of bitterness and in the food industry for the production of bitter soft drinks, such as bitter lemon and Indian tonic waters, and in some alcoholic beverages (such as the flavoured wine Barolo Chinato in Italy) for its distinctive bitter taste. The taste threshold concentration of bitter taste perception is about 10 mg/1. 

Human perception creates difficulty ia the characterization of flavor people often, if not always, perceive flavors differently due to both psychological and physiological factors. For example, certain aryl thiocarbamates, eg, phenylthiocarbamide, taste exceedingly bitter to some people and are almost tasteless to others (5). This difference is genetically determined, and the frequency of its occurrence differs from one population to another 40% of U.S. Caucasians are nontasters, whereas only 3% of the Korean population caimot perceive the strong bitter taste of the aryl thiocarbamates (6). Similar differences were found ia the sense of smell for compounds such as menthol, carvone, and ethyl butyrate (7). 

Several aspects affect the extent and character of taste and smell. People differ considerably in sensitivity and appreciation of smell and taste, and there is lack of a common language to describe smell and taste experiences. A hereditary or genetic factor may cause a variation between individual reactions, eg, phenylthiourea causes a bitter taste sensation which may not be perceptible to certain people whose general abiUty to distinguish other tastes is not noticeably impaired (17). The variation of pH in saUva, which acts as a buffer and the charge carrier for the depolarization of the taste cell, may influence the perception of acidity differently in people (15,18). Enzymes in saUva can cause rapid chemical changes in basic food ingredients, such as proteins and carbohydrates, with variable effects on the individual. 

Perception of bitter taste can take place via G-proteins the a-subrmit of these G-proteins is know as gustducin and is highly homologous with transducin. The corresponding receptors are just beginning to be characterized (Hohn, 1999). A phosphodiesterase with specificity for cyclic nucleotides and a cyclic nucleotide-gated ion charmel... 

Bitter peptides have been identified in hydrolyzates of casein (12,13), cheese (13a,b), and soy bean (14,15,15a). The bitter taste has been related to the hydrophobic amino acid content (16-20) and to chain length. Ney and Retzlaff (21) established a formula relating the bitterness of peptides to their amino acid composition and chain length. Too large a proportion of hydro-phobic amino acids gives rise to bitterness yet above a certain molecular weight, bitterness is not perceptible even when there are hydrophobic amino acids (21). Peptides that were responsible for bitterness in Cheddar cheese were rich in Pro, which occurred predominantly in the penultimate position (21a). 

Intensive studies on the bitter taste receptor are also in progress, as with the sweet taste receptor.119 In fact, it has been reported that T2R receptors are necessary and sufficient for the detection and perception of bitter... 

There are some hundred different 7TM receptors involved in perception of bitter tastants. The bitter taste receptors also couple through the G protein gustducin yielding the activated Gag-GTP which can thence activate C.AMP/C.GMP phosphodiesterase, thus lowering cAMP and cGMP concentration. Bitter tastant receptors can also act via pertussis... 

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