Comparison of Key Aroma Compounds in Five Different Types of Japanese Soy Sauces by Aroma Extract Dilution Analysis (AEDA)

An investigation by the aroma extract dilution analysis (AEDA) technique of the aroma concentrate from five different types of Japanese soy sauces, categorized according to Japan Agricultural Standards as Koikuchi Shoyu (KS), Usukuchi Shoyu (US), Tamari Shoyu (TS), Sai-Shikomi Shoyu (SSS), and Shiro Shoyu (SS), revealed 25 key aroma compounds. Among them, 3-ethyl-1,2-cyclopentanedione and 2'-aminoacetophenone were identified in the soy sauces for the first time. Whereas 3-(methylthio)propanal (methional) and 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) were detected in all of the soy sauce aroma concentrates as having high flavor dilution (FD) factors, 4-ethyl-2-methoxyphenol was detected as having a high FD factor in only four of the soy sauces (KS, US, TS, and SSS). Furthermore, 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone (4-HEMF) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (4-HDMF), which were thought to be the key odorants in KS, were detected in KS, US, TS, and SSS, but the FD factors widely varied among them. The sensory evaluations demonstrated that the aroma descriptions of a cooked potato-like note and a caramel-like/seasoning-like note were evaluated as high scores with no significant differences among the five soy sauces. On the other hand, a burnt/spicy note was evaluated as having high scores in KS, TS, and SSS, but it was evaluated as having a low score in SS. The comparative AEDA experiments and the auxiliary sensory experiments demonstrated that the five different types of Japanese soy sauces varied in their key aroma compounds and aroma characteristics, and the key aroma compounds in KS might not always be highly contributing in the other types of Japanese soy sauces.