Breeding of Aspergillus luchuensis with high acidic protease production and brewing tests for sweet potato shochu
2020
Setoguchi, S. ((Kagoshima University, Kagoshima (Japan). The United Graduate School of Agricultural Sciences), (Kirishima Shuzou Co., Ltd. Miyakonojo, Miyazaki (Japan))) | Masudome, A. | Oiwa, T. | Futagami, T. | Kawano, K. | Iwai, K. | Tamaki, H.
We previously reported that disruption of the acid protease encoding gene in Aspergillus luchuensis largely affects the flavor formation of sweet potato shochu. Therefore, in this study, we performed the breeding of A. luchuensis J7-2 by the ion beam mutagenesis and halo assay using casein agar plate with a focus on the acid protease activity. We successfully obtained A. luchuensis APH-1 with a high acid protease activity. The acid protease activity and acid carboxypeptidase activity of the rice koji using the APH-1 strain were 4.5- and 2.3-times higher than those of rice koji using the J7-2 strain, respectively. On the other hand, the β-glucosidase activity of the rice koji using the APH-1 strain was as low as 1/4 of the rice koji using the J7-2 strain. In addition, gas chromatography analysis revealed that higher alcohols and esters decreased in the shochu made using APH-1 than in the shochu made using J7-2. Moreover, by using the APH-1 strain, the 1st mash had a lower ethanol concentration, whereas the 2nd mash had a slightly higher ethanol concentration, causing the ethanol yield per ingredient to increase by 6.1 l/t (2.8%). These results indicate that the acid protease activity plays a significantly important role in flavor formation and ethanol production of sweet potato shochu.
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