Gustatory sensation of (L)- and (D)-amino acids in humans.

Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to D-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and L-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, L-serine had mainly sweet and minor umami taste, and D-serine was sweet. We further applied Stevens' psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).

Acute effect of poly-gamma-glutamic acid on calcium absorption in post-menopausal women.

OBJECTIVE: Poly-gamma-glutamic acid (PGA) increases calcium (Ca) solubility in vitro and in vivo, and is associated with reduced bone loss in post-menopausal Japanese women. This study is the first to examine the effect of PGA on Ca absorption in humans. METHODS: A single-blind, randomized, crossover study with a 3-4 week wash-out was performed to determine the effect of PGA (80.6% glutamic acids) on Ca absorption measured by the double stable isotope method. Twenty-four healthy, non-smoking, postmenopausal women (mean age: 56.4 +/- SE 0.9) were given 200 g of orange juice containing 200 mg Ca as Ca-44 enriched CaCO(3), with or without 60 mg of PGA, after an overnight fast. The two tests were separated by 3-4 weeks. An intravenous injection of Ca-42 (CaCl(2) solution) was given 30 min after consuming the drink and a complete urine collection carried out from 24-48 h post-dosing. Ca absorption was calculated from the Ca isotope ratios measured by thermal ionization quadrupole mass spectrometry (TIQMS). RESULTS: Mean Ca absorption with PGA was significantly higher (P < 0.01) than without PGA, 39.1 (SE 1.6) % and 34.6 (SE 1.9) %, respectively. The effect of PGA on increasing Ca absorption was more marked in a sub-group of subjects whose baseline Ca absorption (without PGA) was lower than the population mean value. CONCLUSION: Postmenopausal women who received a single dose of PGA increased their intestinal Ca absorption particularly those individuals with lower basal absorptive capacity.

Taste enhancements between various amino acids and IMP.

It is well known that a strong synergistic interaction of umami occurs between L-alpha-amino acids with an acidic side chain, such as L-Glu or L-Asp, and 5'-mononucleotides, such as inosine 5'-monophosphate (IMP). We tested taste interactions between various L-alpha-amino acids and IMP by the psychophysical method and found that taste enhancement occurred when IMP was added to several sweet amino acids, such as L-Ala, L-Ser and Gly. The enhanced quality of taste was recognized as umami, and was not blocked by the sweetness inhibitor +/-2-(p-methoxyphenoxy)propanoic acid. The total taste intensities of various concentrations of the amino acid and IMP mixtures were measured using magnitude estimation. The results showed that the potentiation ratios were larger than 1 in the cases of L-Ala, L-Ser and Gly. However, the ratio was approximately 1 in the case of D-Ala, which had an enhanced taste of sweetness. Thus the umami taste enhancement of several sweet L-alpha-amino acids by IMP was synergistic rather than additive as that of acidic amino acids.