Chair: Wei Wang (PhD student, GPBM)
It is all about genetically encoded taste receptors, that you sense sweet, bitter, sour, salty and umami everyday, and tell nutritional or harmful compound by neuronal recognition all the way from taste buds to sensory ganglia, brainstem, thalamus and insula. This session will include a general review on gustatory system and latest breakthroughs in this field.
|Wolfgang Meyerhof (German Institute of Human Nutrition, Germany)
Bitter taste: from molecules to behavior
The sense of taste accomplishes the amazing function of deciding within seconds if a mouthful is safe, of nutritional value and hence, should be swallowed or potentially harmful and should be rejected. Errors could be fatal resulting in malnutrition or acute or chronic intoxication. Each of the five basic tastes fulfills a specific task in this decision-making process. Sweet and umami tastes detect carbohydrates and protein, whereas salty taste recognizes minerals. These sensations are linked to central circuits that mediate attraction and drive intake behavior to supply the body with calories and replenish electrolytes. Sour and bitter tastes indicate the presence of protons and potentially harmful substances derived from plants, animals or food processing and aging. These taste qualities are coupled to neuronal networks mediating aversion preventing ingestion of toxins and unripe or spoiled food. Moreover, in various brain areas gustatory information is integrated with other relevant information regarding intake behavior such as smell and sight of food, postingestive consequences, and metabolic needs to eventually establish dietary patterns. In the oral cavity each basic taste is represented by a dedicated population of epithelial chemosensory cells that are characterized by the presence of special receptor molecules. Salty and sour transduction is based on various ion channels. Umami, sweet and bitter transduction involves G protein coupled receptors of the taste 1 (TAS1R) or taste 2 (TAS2R) family. Whereas the receptor heteromer TAS1R1-TAS1R3 is sensitive to the umami compounds L-amino acids and ribonucleotides, the heteromer TAS1R2-TAS1R3 responds to all sweet compounds. These receptor heteromers respond to their numerous activators by forming various orthosteric and allosteric binding sites.
Bitter taste involves ~25 TAS2Rs in human and ~35 in rodents. They differ widely in their tuning breadth and show functional overlap, but presumably account collectively for the recognition of the countless structurally diverse bitter molecules. TAS2Rs appear to accommodate their diverse bitter agonists in a single ligand binding pocket through contacts with amino acid residues lining a central cavity within the transmembrane domains. Not the entire repertoire of TAS2Rs but rather a selection is coexpressed in the oral chemosensory cells generating subpopulations of functionally distinct bitter sensors. Their abundance varies in the oral chemosensory regions suggesting that different portions of bitter taste are carried by the cranial afferent nerves. The distinct oral bitter sensor population appears to be connected by the afferent nerves with the first order central neurons of the gustatory nucleus in the brain stem in a way that maintains functional diversity in response to bitter stimulation. This variability across bitter responsive gustatory brain stem neurons is associated with avoidance behavior towards bitter substances. The role of the brain stem in establishing aversions will be discussed in the context of taste preference.
|Pekka Lehtonen (Alcohol Control Laboratory, Alko Inc. Finland)
Changes in colour and flavour during wine ageing
Wine ageing contains always three phases: gestation (maturing), full bloom (maturity) and deterioration (decline). Ageing duration is highly variable according to a wine’s origin, type and quality and may vary from one year to decades. Many changes occur in the composition of the wine during this period, accompanied by the development of colour and flavour. The conditions under which wine is stored and handled, as well as the types of containers used, have a very marked effect on these developments, which are close connected with oxidation-reduction phenomena that take place in the wine. To develop well wine should be stored in cold and dark; warm and light cause unwanted changes. Red wines contain a lot of phenolic compounds – mainly tannins and anthocyanins - which protect wine from oxidation. These compounds react with each other in many ways resulting e.g. colour changes in wine. The changes in bottle are very slow after the small amount of dissolved oxygen is used. The amount of some aroma compounds increase in bottle ageing. One of these is the typical kerosene aroma in Riesling wines. During barrel ageing some bitter and spicy compounds appear in wine.