令和8年度 研究成果

HORI Ryotaro, OSAFUNE Yukio, IKEDA Yuriko, MUKAI Nobuhiko, and ISOGAI Atsuko

Recently, sake aged for several years to decades, called long-term aged sake, has attracted some attention. Aged liquors also exist in other countries, such as Chinese rice wine (Huangjiu) and fortified wines (Sherry, Madeira, Port). To understand the characteristics of long-term aged sake among the typical aged liquors worldwide, we analyzed and compared the flavor components and sensory characteristics of aged sake, Huangjiu, and fortified wines. Accordingly, flavor component analysis revealed a common trend toward increases in sotolon, aldehydes, polysulfides, ethyl esters, and decreases in acetate esters with age. However, the increases in aldehydes and polysulfides were more significant in sake and Huangjiu, whereas the increases in ethyl esters were more significant in fortified wines. Moreover, the concentrations and variances of acetate esters in sake were highest among the five liquor categories. Sensory evaluation revealed that sake and Huangjiu presented stronger sulfur aroma and bitter taste, whereas fortified wines presented stronger dried fruit, honey aroma and sweet taste. Furthermore, sake samples showed a larger variance in the intensity of caramel, burnt, and soy sauce aroma than did the other liquor categories. These results indicate that the compositional and sensory characteristics of the aged liquors can be grouped into sake/Huangjiu and fortified wines and that sake is featured by extensive variations in the levels of age-related components and sensory attributes.

LEE Lin-Jie, SATO Yuki, JOYO Midori, TAKAHASHI Kei, OKUDA Masaki

The influence of the genetic background of rice on its suitability for brewing shochu and sake (Japanese alcoholic beverages) has not been clarified. This study investigates the effects of starch biosynthesis-related genes (Wx and Alk) on the water absorption capacity of commercially available rice samples and thus examines the possibility of using rice genotype as a predictor of suitability for shochu and sake brewing. The 24 examined rice samples were classified into four genotypes: Alk/Wx^a, alk/Wx^a, alk/Wx^b, and alk/wx. No significant differences were observed among these genotypes in terms of nonstarch properties such as grain morphology, as well as the water absorption ratio during the initial absorption phase. However, after 1 h of absorption, significant differences in terms of this ratio were observed (Alk/Wx^a < alk/Wx^a < alk/Wx^b < alk/wx). Starch structural analysis revealed that amylose content increased in the order of alk/wx < alk/Wx^b < alk/Wx^a ≈ Alk/Wx^a and the proportion of short amylopectin chains increased in the order of Alk/Wx^a < alk/Wx^a ≈ alk/Wx^b. Correlation analysis revealed a significant negative correlation between the water absorption ratio at 20-120 min and amylose content. The Wx genotype, through its influence on amylose content, was found to play a major role in determining short-term and steamed-rice water absorption ratios regardless of rice type, thus being a promising descriptor of rice suitability for shochu and sake brewing. Thus, our work provides fundamental insights for cultivar breeding and developing brewing methods tailored to specific rice varieties.

OKUDA Masaki, AKAMATSU Fumikazu, HIRAO Ryo, JOYO Midori, MUKAI Nobuhiko

Sake, a traditional Japanese alcoholic beverage, is produced from rice and water throughout (and increasingly outside of) Japan. Hence, methods of identifying the geographic origin of sake are urgently required. Herein, we characterized a series of sakes and the corresponding raw materials (brewing water and rice) in terms of their oxygen stable isotopic compositions (δ¹⁸O values) and contents of 22 elements, aiming to identify brewing water–specific elements suitable for determining the geographic origin of sake. Based on the results of small-scale brewing tests and correlation analyses, eight brewing water–specific elements (Li, Na, Mg, Si, Ca, V, Sr, and Ba) were identified. The contents of these elements in sake and its δ¹⁸O values showed significant positive correlations with the corresponding parameters of brewing water but not rice. Preliminary principal component analysis, multinomial logistic regression analysis, partial least squares discriminant analysis, and sparse partial least squares discriminant analysis were conducted using the contents of these eight elements in sake. For three sake production areas in Japan, the scores of discrimination analyses obtained for the eight water-specific elements were separated, and model accuracies were high. The results suggested that these contents may be used to discriminate between sake production areas and improve the accuracy of existing methods for determining the geographic origin of Japanese sake.

MATSUOKA Taro, ODA Ken, IWASHITA Kazuhiro, WATANABE Jun

The thermostable proteases present in soy sauce can degrade proteins in processed foods, such as boiled eggs and fish cakes, leading to undesirable textural changes in the product. In this study, we identified DeuA, a deuterolysin-like metalloprotease from Aspergillus oryzae, as the major contributor to thermostable protease activity during soy sauce fermentation. Using CRISPR/Cas9-based genome co-editing, we generated deuA-knockout mutants and mutants of the related gene deuB, which encodes a deuterolysin-like metalloprotease, and evaluated their enzymatic activity levels under solid-state culture conditions mimicking soy sauce koji fermentation. The ΔpyrGΔdeuA strain exhibited a marked reduction in thermostable protease activity, with residual activity barely detectable in both the koji extracts and the final soy sauce, whereas knockout of deuB had no significant effect. These results indicate that DeuA is the predominant contributor to thermostable protease activity in soy sauce. The knockout of deuA did not affect other key brewing parameters such as the nitrogen or sugar contents, indicating the potential of this gene as a target for strain improvement. Our findings establish DeuA as an essential thermostable protease in soy sauce and provide a foundation for the development of brewing strains with improved industrial applicability that will not affect the textural stability of processed foods.