Characterization of flavor component in Japanese instant soup stocks 'dashi'

In Japan, many flavors of instant soup stock (dashi) are available and are often chosen on the basis of preference, the type of dish being prepared, and dietary habits of individuals. However, the complete characterization of all flavor components in Japanese instant dashi is unknown. Therefore, in the present study, we characterized the flavor components (free amino acids and 5′-ribonucleotides) of instant dashi and compared these with those of homemade dashi. Moreover, we used sensory evaluation to compare the effects of glutamate (Glu) content on the flavors of both instant and homemade dashi. Instant dashi was prepared using eight powders, seven bags, and one cube in accordance with the manufacturers' directions (generally, 0.67-1.90 g instant dashi/100 mL distilled water). Three homemade types of dashi [bonito, kelp (konbu), and a combination of the two] were conventionally prepared. Free amino acids and 5′-ribonucleotides in these three types were determined with ultra-high-performance liquid chromatography. In dashi containing seasoning (amino acids, etc.), Glu levels were higher (P < 0.05) and aspartate (Asp) and 5′-guanylate levels were lower (P < 0.05) than they were in instant dashi without seasoning. Glu, Asp, serine, threonine, and 5′-inosinate were all found in instant dashi, which contained lower levels of amino acids compared with the bonito-containing homemade dashi. Subsequently, we performed a sensory evaluation of the flavor of high-Glu instant dashi, low-Glu instant dashi, and two low-Glu homemade dashi. We then determined whether Glu levels were related to dashi flavor. The intensities and preferences (saltiness, after taste, and overall flavor) did not differ between high- and low-Glu dashi, suggesting that elevated Glu levels have little impact on flavor in dashi. To add flavor (e.g., saltiness or umami), lower levels of added Glu might be preferable in instant dashi combined with other flavor components.