[P004] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P02-156] EFFECTS OF ORGANIC ACIDS ON KOJI PRODUCTION IN SHOCHU BREWING

○Hieu Minh Dang¹, Yumiko Yoshizaki^1,2, Haoyu Zhu¹, Taiki Futagami^1,2, Hisanori Tamaki^1,2, Kazunori Takamine^1,2 (1. Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan (Japan), 2. United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan (Japan))

Keywords:

shochu,koji,citric acid,acid-stable α-amylase,saccharification,fermentation,fruity aroma

Shochu is a traditional Japanese distilled spirit. Shochu production begins with the koji-making process. Koji is a solid-state culture produced by cultivating koji mold on steamed rice. It contains various enzymes produced by the koji mold, such as α-amylase and glucoamylase, which play essential roles in the fermentation process. Therefore, the quality of koji directly affects the fermentation process and the flavor of shochu. Koji making is conducted under strictly controlled temperature and humidity conditions for approximately 42 hours. In our previous studies, shochu produced from short-time cultivated koji (approximately 19 hours, referred to as 19 h-koji) exhibited a stronger fruity aroma than shochu produced from conventional koji (approximately 42 hours, referred to as 42 h-koji). Thus, the use of 19 h-koji is expected to enhance the fruity aroma of shochu. However, 19 h-koji shows lower enzymatic activity, particularly acid-stable α-amylase and saccharification ability. This results in a prolonged fermentation period and an increased risk of microbial contamination. Therefore, this study aimed to improve the acid-stable α-amylase activity and saccharification ability of 19 h-koji. To achieve this, koji was prepared using rice soaked in an organic acid solution, based on reports that acid-stable α-amylase production by koji mold is induced under acidic conditions during koji making.

Koji mold for shochu (Aspergillus luchuensis mut. kawachii) secretes citric acid, causing the acidity of koji to gradually increase over time, accompanied by increases in acid-stable α-amylase activity and saccharification power. Therefore, citric acid was selected as a reference acid. First, we tried to determine the optimal citric acid concentration. Japonica rice (100 g) was soaked in citric acid solutions at different concentrations (0, 0.064, 0.32, and 0.64% w/w), then steamed and inoculated with spores of koji mold. Koji was cultivated under standard conditions and sampled at 19 and 42 hours. Under this condition, acid-stable α-amylase activity, saccharification ability, and fungal biomass were significantly higher in 19 h-koji treated by 0.32% citric acid (0.005 N) compared to untreated 19 h-koji. Next, we investigated the effect of organic acid types. Citric acid, malic acid, lactic acid, and tartaric acid (0.005 N) were used for the pretreatment of rice. The results indicated that citric acid was the most effective among the organic acids.

Finally, fermentation tests were conducted using untreated 19 h-koji, citric acid-treated 19 h-koji, and 42 h-koji to evaluate fermentation time and aroma characteristics. The results showed that citric acid-treated 19 h-koji significantly shortened the fermentation time compared to untreated 19 h-koji. GC–MS analysis and sensory evaluation revealed that although the concentrations of fruity aroma compounds such as isoamyl acetate, isobutyl acetate, and citronellol in acid-treated 19 h-koji were lower than those in untreated 19 h-koji, they remained higher than those in 42 h-koji.