[P003] Poster

12:10 PM - 1:00 PM JST(3:10 AM - 4:00 AM UTC)

[P02-179] Reducing koji making time enables the production of imo-shochu enriched with fruits-like aroma

○Haoyu Zhu¹, Yumiko Yoshizaki¹, Mizuki Watanabe¹, Yuta Anan¹, Taiki Futagami¹, Hisanori Tamaki¹, Kazunori Takamine¹ (1. Kagoshima Univ. (Japan))

Keywords:

Imo-shochu,koji making time,enzymatic activity,amino acids,volatile component

This study investigated the influence of different koji cultivation times on the flavor profile of Japanese imo-shochu. Koji prepared at four critical time points of the koji making process, namely Mori (19 h), Naka-shigoto (23 h), Shimai-shigoto (27 h), and De-koji (43 h), were used for fermentation. The first fermentation was initiated by mixing koji with water and Saccharomyces cerevisiae, followed by second fermentation with steamed and mashed sweet potato. Enzymatic activities, including α-amylase, glucoamylase, β-glucosidase, acid protease, and acid carboxypeptidase, were quantified at different fermentation stages. Amino acid concentrations were determined by HPLC with fluorescence detection, while volatile compounds in the distilled imo-shochu were analyzed using GC-MS. Sensory characteristics were evaluated by a trained panel using descriptive analysis.The results showed that Mori koji exhibited significantly lower saccharifying enzyme and protease activities than De-koji, and this reduced enzymatic capacity persisted throughout fermentation, resulting in a slower fermentation rate. However, no significant reduction in ethanol yield was observed, indicating that yeast metabolism remained effective despite limited enzymatic activity. Under these conditions, the concentrations of all amino acids in the moromi using Mori remained relatively low throughout fermentation, yeast likely utilized nearly all available amino acid species. In particular, key amino acids serving as precursors for higher alcohol synthesis, including Val, Leu, Ile, and Phe, showed decreases during the late first and early second fermentation stages, indicating active metabolism via the Ehrlich pathway. In contrast, in the moromi using De-koji, the concentrations of these amino acids increased steadily throughout both fermentation stages. In particular, Arg, Ala, Gln, and Glu accumulated rapidly from the early stage. Arg, Ala, Gln, and Glu serve as preferred nitrogen sources and play essential roles in supporting yeast growth and metabolic activity during imo-shochu fermentation. Such metabolic preference may ultimately influence the formation of higher alcohols and their corresponding esters, thereby shaping the final aroma profile of imo-shochu.GC-MS analysis revealed that isoamyl alcohol, isobutyl alcohol, isoamyl acetate, and isobutyl acetate in the Mori imo-shochu were approximately two-fold higher than those in the De-koji imo-shochu. In contrast, terpene-related compounds such as β-damascenone were most abundant in the De-koji imo-shochu, likely due to the lower pH conditions associated with longer koji cultivation. Sensory evaluation further confirmed that the Mori imo-shochu exhibited significantly enhanced banana-like and apple-like aromas, whereas the De-koji imo-shochu were characterized by stronger sweet and typical imo-shochu notes.Overall, shortening koji cultivation time modulates enzymatic activity and nitrogen metabolism, thereby promoting the efficient conversion of amino acid precursors into higher alcohols and esters. These findings provide new insights into the mechanisms underlying aroma formation and offer a practical strategy for producing imo-shochu with distinctive fruity aroma profiles.