Investigation of diversity in wooden barrel soy sauce(KIOKE SHOYU) using component analysis and sensory evaluation

<p>[Objective] The traditional method of fermenting soy sauce in wooden barrels (KIOKE SHOYU) was common until the Edo period. However, wooden barrels(KIOKE) have been largely replaced by FRP and concrete tanks due to cost-effectiveness and the difficulty of stable production from the Meiji era. Recently, KIOKE SHOYU has gained recognition as a high-value product due to its "unique and complex flavors specific to each brewery," though scientific knowledge about its components is limited. This study aims to scientifically investigate the diversity of KIOKE SHOYU as part of KIOKE SHOYU EXPORT FACILITATION CONSORTIUM (referred to as "KIOKE Consortium").</p><p>[Methods] We analyzed 24 types of KIOKE SHOYU from 24 companies (across 17 prefectures) that are members of KIOKE Consortium and 6 types of tank-fermented soy sauce (referred to as "Tank soy sauce") from 5 major manufacturers. The analysis included aroma components using the ultra-fast GC Heracles II, and free amino acids and organic acids using LC-MS. For six distinctive soy sauces, we conducted analytical sensory evaluations and performed principal component analysis (PCA) using the sensory evaluation data correlated with component analysis values. Additionally, we compared the microbial flora between KIOKE and plastic barrels through soy sauce brewing tests.</p><p>[Results] The PCA results indicated that KIOKE SHOYU were positioned farther apart compared to Tank soy sauce, suggesting greater "variety" in terms of component content. The flavor characteristics of KIOKE SHOYU included types with a strong sweet and roasted aroma and those with complex flavors. The brewing tests showed differences in microbial flora between KIOKE and plastic barrels. Electron microscope observations confirmed the presence of numerous microorganisms on the surface of KIOKE, suggesting that these microorganisms contribute to the unique flavors specific to each brewery.</p>