Taste in humans

There is some evidence that camosine supplementation can restore sense of taste in humans. A report from Japan states that polaprezinc (a zinc-carnosine complex) is frequently effective in treating patients experiencing taste disorders (Ikeda et al., 2005). Experiments with zinc-deficient rats showed that polaprezinc was effective in restoration of taste bud proliferation (Hamano et al., 2006). 

FIGURE 1-23 Stereoisomers distinguishable by smell and taste in humans, (a) Two stereoisomers of carvone R) carvone (isolated from spearmint oil) has the characteristic fragrance of spearmint (S)-carvone (from caraway seed oil) smells like caraway, (b) Aspartame, the artificial sweetener sold under the trade name NutraSweet, is easily distinguishable by taste receptors from its bitter-tasting stereoisomer, although the two differ only in the configuration at one of the two chiral carbon atoms. 

Although the above lipid membranes had the ability to sense the taste by responding to many taste substances, information was insufficient to recognize quality of the taste. This weakness was overcome by means of a multichannel sensor, where transducers were composed of lipid membranes immobilized with a polymer [16-23]. We investigated responses of the sensors to various taste solutions. The electrode showed five different response patterns to five primary tastes with small experimental deviations. The patterns looked alike when the applied substance elicited the same taste in humans. 

On the other hand, L-alanine, glycine and L-threonine taste mainly sweet [26]. Only for these amino acids, the potentials of channels 1 and 2 decreased. L-Glutamic acid and L-histidine monohydrochloride, which taste mainly sour, increased each of the potentials of channels 1-5 to almost the same degree. Only monosodium L-aspartate elicits mainly umami taste in humans among amino acids used here the response pattern was different from those of the other amino acids. 

Interestingly, the human TAS1R2/TAS1R3, but not its mouse counterpart, are sensitive to the sweet proteins monellin, thaumatin, and brazzein, and to the artificial sweeteners neo-tame, cyclamate, and aspartame (9-11). This difference provides a molecular explanation for the previous observation that these compounds are sweet for humans but not attractive to rodents (9). The species difference also applies to the inhibitor lactisole that blocks the sweet taste in humans but not in rats, and only inhibits the response of human TAS1R2/TAS1R3 to sweet stimuli (9). 

T Karrer, L Bartoshuk. Effects of capsaicin desensitization on taste in humans. 

What about the sense of smell and taste in humans in the context of communication between individuals What are our natural capacities to emit chemical messages and to receive and interpret them in a reliable way These questions are not recent but they may provide new perspectives on the behavior and on the physiological functions of smell and taste in humans when viewed in the light of studies on mammalian communication. 

The importance of lipophilicity to bitterness has been well established, both directly and indirectly. The importance of partitioning effects in bitterness perception has been stressed by Rubin and coworkers, and Gardner demonstrated that the threshold concentration of bitter amino acids and peptides correlates very well with molecular connectivity (which is generally regarded as a steric parameter, but is correlated with the octanol-water partition coefficient ). Studies on the surface pressure in monolayers of lipids from bovine, circumvallate papillae also indicated that there is a very good correlation between the concentration of a bitter compound that is necessary in order to give an increase in the surface pressure with the taste threshold in humans. These results and the observations of others suggested that the ability of bitter compounds to penetrate cell membranes is an important factor in bitterness perception. 

The aim of our project was to study phloem as a source of fiber and polyphenols, and to develop a method to improve its taste without losing the potentially bioactive polyphenols. In addition, we wanted to investigate the bioavailability, cholesterolemic and antioxidative effects and safety of phloem and its phytonutrients in humans in a randomised double-blind trial. 

P. Overbosch and S. de Jong, A theoretical model for perceived intensity in human taste and smell. Physiol. Behav., 45 (1989) 607-613. 

The balance between excess and insufficient zinc is important. Zinc deficiency occurs in many species of plants and animals, with severe adverse effects on all stages of growth, development, reproduction, and survival. In humans, zinc deficiency is associated with delayed sexual maturation in adolescent males poor growth in children impaired growth of hair, skin, and bones disrupted Vitamin A metabolism and abnormal taste acuity, hormone metabolism, and immune function. Severe zinc deficiency effects in mammals are usually prevented by diets containing >30 mg Zn/kg DW ration. Zinc deficiency effects are reported in aquatic organisms at nominal concentrations between 0.65 and 6.5 pg Zn/L of medium, and in piscine diets at <15 mg Zn/kg FW ration. Avian diets should contain >25 mg Zn/kg DW ration for prevention of zinc deficiency effects, and <178 mg Zn/kg DW for prevention of marginal sublethal effects. 

---