Protein Taste Interactions

The discussion for protein taste interactions would parallel that of the discussion on carbohydrate taste interactions. One finds literature on sweet proteins and more recently proteins that make sour substances taste sweet. The addition of proteins or a change in type of protein used in a food will influence the taste of that food [35,36]. 

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This volume contains the papers presented in a symposium on carbohydrate-protein interaction. The symposium was devoted to an exploration of protein-glycoconjugate interaction in a wide range of biological phenomena the interaction of enzymes, antibodies, and lectins with complementary carbohydrate molecules the recognition of carbohydrate-containing structures by chemoreceptors such as taste and other plasma membrane proteins and the role of carbohydrates in the organization of connective tissue. 

Hellekant G, Danilova V (1996) Species differences toward sweeteners. Food Chem 56 323 Hobbs JR, Munger SD, Conn GL (2008) Crystal structures of the sweet protein MNEI insights into sweet protein-receptor interactions. In Weerasinghe DK, DuBois GE (eds.) Sweetness and sweeteners. American Chemical Society, Washington Hoon MA, Adler E, Lindemeier J, Battey JF, Ryba NJ, Zuker CS (1999) Putative mammalian taste receptors a class of taste-specific GPCRs with distinct topographic selectivity. Cell 96 541-551... 

Meyer, S., Taste Interactions of Acesulfame Potassium and Other High Intensity Sweeteners with Fruit Flavours in Different Food Proteins, paper presented at 2nd IUPAC International Symposium on Sweeteners (2nd IUPAC-ISS), Hiroshima, Japan, 2001, p. 55. 

Taste receptor cells are organized into taste buds 825 Sensory afferents within three cranial nerves innervate the taste buds 826 Information coding of taste is not strictly according to a labeled line 826 Taste cells have multiple types of ion channels 826 Salts and acids are transduced by direct interaction with ion channels 826 Taste cells contain receptors, G proteins and second-messenger-effector enzymes 827... 

Big molecules of life include the proteins, nucleic acids, polysaccharides, and a few other more exotic constrncts of nature. Generally, it is the interactions between big molecules and small ones that nnderlie really interesting things taste or smeU or the beneficial actions of drugs, for example. 

Food is taken into the buccal cavity, where it is masticated by the teeth and mixed with saliva from three pairs of salivary glands. It moistens the food and dissolves some molecules enabling them to interact with the taste receptors on the tongue. Saliva contains Na% Cl and HCOs ions and a protein, mucin, which is a component of mucus that lubricates the chewed food on its way down the oesophagus. The pH of saliva is about 7.8, which neutralises acid formed by bacteria in the mouth this protects tooth enamel... 

After the saliva has carried the tastants into the taste bud, they interact with the taste receptors on the surface of the cells, or with ion channels, which are pore-like proteins. Salty and sour tastants act through ion channels, and sweet and bitter sensations are mediated by surface receptors. The different taste submodalities rely on specific mechanisms Na+ flux through Na+... 

The astringency of wine tannin fractions appears to be correlated to the content of flavanol units released after thiolysis regardless of their environment in the original mol-ecules. Anthocyanins contributed neither bitterness nor astringency. Whether incorporation of anthocyanin moieties in tannin-derived structures affects their interactions with proteins and taste properties remains to be investigated. 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

The taste cells are situated in the lingual epithelium with the apical membrane exposed to the mucosal surface of the oral cavity and the basal surface in contact with the nerve [interstitial fluid] [FIGURE 10]. Within the basolateral surface are the nerves which respond to the chemestiietic stimulants, i.e. direct nerve stimulation. The microvilli at the apical membrane contain receptor proteins which respond to sweeteners, some bitters and possibly coolants. The olfactory cells are bipolar neurons with dendritic ends containing cilia exposed to the surface and axons linked to the brain, where they synapse in the olfactory bulb. The transfer of information from this initial stimulus-receptor interaction to the brain processing centers involves chentical transduction steps in the membrane and within the receptor cells. The potential chemical interactions at the cell membrane and within the cell are schematically outlined in FIGURE 10. 

FIGURE 10. A) Schematic of taste cell embedded in epithelium. Shown are the apical membrane which contains the microvilli and the basal membrane which synapses with the nerve B) Stimulus can interact with a receptor protein embedded in membrane which activates G-protein, with the membrane or directly with an ion channel protein C) GTP stimulation of phosphatase for formation of cAMP or IP3 and opening of ion channel (Adapted from ref. 2). 

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