| Research Abstract |
Yellowtail Seriola quinqueradiata meat was extracted and analyzed for free amino acids, organic bases, nucleotides and the related compounds. The taste test performed on the reconstituted extract containing all compounds detected revealed that glutamic acid, histidine, IMP and some other amino compounds as taste-active components. Also, gelatin derived from collagen was found to increase in mildness and flavor strength. Removal of lipid by n-hexane treatment resulted in lacking of smoothness and fish flavor strength, and even in increasing of sourness of yellowtail and red salmon meat extracts.
To demonstrate the role of lipid in taste sensation, immunoreactivity for the putative membrane fatty acid transporter (FAT/CD36) was investigated. The reactivity was specifically localized in the apical part of taste bud cells, possibly gustatory cells, in circumvallate papillae. Peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors, had transcription activation abil
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ity and were induced by fatty acids. The transcriptional control of FAT/CD36 by PPARs in adipocytes and macrophages, which are most active cells in fatty acid metabolism. Long chain fatty acids, especially polyunsaturated fatly acids evoked PPARs activation as ligpnds and the expression of FAT/CD36 and other genes of lipid metabolism, suggesting that these transcriptional mechanism through PPARs might play in lipid taste sensation.
Mechanisms for eliciting umami taste by monosodium glutamate (MSG) and nucleotides such as IMP and GMP were investigated. MSG induced three different responses in mouse taste cells under whole-cell voltage-clamp in Na+ free Ringer solution. The mixture of MSG and IMP induced three different types of responses, similar to MSG alone; the amplitudes of both the transient and sustained inward currents were larger than observed with MSG alone. The electrophysiological tests using several species of umami substances revealed the involvement of the coactivation of mGIuR4 and one or more types of glutamate receptors in umami taste reception Moreover, G protein was found to function in umami transduction and the umami receptor might possibly be a metabotropic glutamate receptor with an IMP-modulated site. Less
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