Question No.  233 :
Why are most types of medicine bitter and others are not?

Bitterness is associated with several distinct classes of chemical substances. The ability to perceive bitterness most likely evolved in order to protect man, and presumably other animals, from the dangers posed by the alkaloids present in many plants. Alkaloids are basic organic compounds having nitrogen in a heterocyclic ring. Nicotine, atropine, and emetine are all alkaloids. Quinine is one of the best known alkaloids in view of its medicinal use. It is also used as a bittering agent in soft drinks such as 'bitter lemon' and 'tonic water'. In natural products, phenolic substances in the form of flavanoids are important sources of bitterness in fruit juices, particularly citrus juices. The best known is naringin which occurs in grapefruit. Another bitter element that can occur in citrus juices in limonin. Bitterness in beer is achieved by adding dried flowers of the hop plant to the sugary extract from the malt. The bittering agents are the organic acids in hops. Many amino acids and oligopeptides have bitter taste. It was found that bitterness is exclusively the property of hydrophobic L-amino acids such as valine, leucine, isoleucine, phenylalanine, tyrosine, and tryptophan. (Hydrophobic means lacking an affinity for or repelling water.) Whether a peptide is bitter or not depends on the average hydrophobicity of its amino acid residues. Drs Chan Lai Wah and Ho Chi Lui, Paul Department of Pharmacy, NUS Question Asked By:

Name: George Siah

Age Group: 13 to 20

Occupation Type: Student

Education Level: N/O Level's