Taste attractiveness of free amino acids and their physicochemical and biological properties (as exemplified by fishes)

Abstract

Using fishes as an example (32 species, II families) the relationship between taste attractiveness of free amino acids (L-isomers) and their physicochemical and biological properties was analyzed. It is shown that the essential amino acids, which are of the highest nutritional requirement for an organism, have lower taste attractiveness in fishes than nonessential ones. Only in 6 species of 32 investigated ones (sun- bleak Leucaspius delineatus, European minnow Phoxinus phoxinus, dace Leuciscus leuciscus, chub Leu- ciscus cephalus, blue gourami Trichopodus trichopterus, pearl gourami Trichopodus leerii) the relation- ship between taste preference and molecular weight of amino acids was confirmed statistically, in all cases being negative. Only in 2 species a statically significant correlation between taste properties of amino acids and the dissociation constant (K₁) was found (positive in stone loach Barbatula barbatula and negative in lake charr Salvelinus namaycush). A positive correlation between taste preference and the value of isoelectric point (pI) of amino acids was found in one species (roach Rutilus rutilus) and negative correlation - in 2 species (brown trout Salmo trutta, Arctic char Salvelinus alpinus erythrinus). A significant correlation between taste attractiveness and solubility of amino acids in water.was found in 2 species (chum salmon Oncorhynchus keta and navaga Eleginus nawaga), negative in both cases. Acidic and polar uncharged amino acids more often possess flavor that stimulates food consumption than basic and non-polar ones, L-isomers of amino acids than D-isomers, amino acids with an amino group in cc-position than in β-position. Amino acids are more attractive than their salts. Aromatic amino acids possess attrac- tive taste much less than sulfur-containing or acyclic ones. Thus, in the majority of fish species the relationship between taste attractiveness of free amino acids and many of their physical, chemical and biolo- gical properties is absent or low, indicating their indirect nature and difficulty of revealing these relation- ships.