Haruo Oyashiki

Use of Koji prepared with a high citric acid producing mutant of Aspergillus usamii as a raw material for Saké brewing

Abstract There is a possibility of developing a new kind of sake in which the refreshing sour taste of citric acid is introduced. In this study, we bred a new mutant of Aspergillus usamii mut. shiro-usamii that produced much citric acid. The koji prepared with the mutant contained about 20 mg of citric acid per gram of dry koji, twice that of the koji of the parental strain. The activities of a-amylase, glucoamylase, and acidic protease in the koji prepared with the mutant were 82%, 94%, and 95%, respectively, those of the parental strain. Using this koji with the mutant, sake was produced. The levels of citric acid and isoamyl acetate were 5.1 and 1.4 times, respectively, those of sake prepared with koji of A. oryzae. Sensory tests indicated that sake made with koji with the mutant was refreshingly sour, with a good aroma.

Mirin-making at low alcohol concentration with Koji prepared with a new mutant of Aspergillus usamii

Abstract We examined the productivity of mirin-making and the quality if the mirin produced using koji prepared with a new mutant (mutant CA) that originated from Aspergillus usamii mut. shiro-usamii. The koji prepared with the mutant CA contained a large amount of citric acid. Therefore, the concentration of the brewing alcohol added to prevent bacterial contamination of the mash was decreased to 6.0% from the 12.5% needed when the mash was made with koji of the conventional Aspergillus oryzae. A mash containing this low concentration of alcohol was incubated with koji of the mutant CA and enzyme preparations such as α-amylase (6,000 DU/kg mash) from Bacillus subtilis and acidic protease (1,000 PU/kg mash) from Aspergillus niger. The starch and protein in this mash was sufficiently digested. The yield of mirin obtained from this mash was high (96% based on the mash weight), and the resulting mirin contained much citric acid, malic acid, succinic acid, nitrogen compounds, isomaltose, isomaltotriose, and oligosaccarides. The taste of the mirin was refreshingly sour and flavorsome.

Relationship between conditions for steaming rice and productivity in mirin-making

Abstract The relationship between the conditions used to prepare steamed rice and its enzymatic digestion for mirin-making was examined. The degree of gelatinization, G, of the starch in the steamed rice was directly related to the enzymatic digestion, and is represented by Eqs. 1 and 2 for regular and glutinous rice, respectively. G=79.88+(-18.13+0.306 Th) M G=93.08+(-2.69+0.149 Th) M where Th is the temperature of steaming and M is the water content of the soaked rice. Therefore, the degree of gelatinization of starch in steamed rice could be predicted. The water content of regular rice, which was low after soaking, can be estimated by Eq. 3, M=M 0 + exp (0.125 Tw-(10.51-0.00222 t)) where M0 is the water content of rice soaked for 24 h at 20°C and Tw and t are the temperatures and times of soaking, respectively. The optimum water content of soaked regular rice for mirin-making was calculated using Eq. 3. Thus, the design of a system for the steaming process made it possible to obtain steamed rice of the desired degree of gelatinization.

Relationship between enzyme efficiency and alcohol concentration in Mirin mash

Abstract In mirin-making, the influence of alcohol concentration on enzyme activities that originated from koji and from enzyme preparations were analyzed quantitatively in order to determine the optimum concentration for production. The influences were complex. The efficiency of the enzymes in the mash with alcohol could be described by the ratio of the maximum digestibility, Dm, of the components in the raw materials to a constant, tm, which is related to the velocity (Eqs. 1 and 2). D=D m (1- exp (- T 30 t m )) D m t m = lim T 30 →0 d d t (D m (1- exp (- T 30 t m where T30 is the incubation time at 30°C, D is the digestion after T30, and Dm/tm corresponds to the enzyme activity, usually represented as the initial velocities of the enzymes. Analysis of Dm and tm made it possible to achieve maximum productivity in the making of mirin.

Mirin-Making from Koji Prepared with a Mutant Aspergillus oryzae Producing High Activity of Carboxypeptidase☆

Abstract It has been desired to improve the quality of mirin without decreasing the level of productivity. Accordingly, by ultraviolet irradiation to cause mutation, we screened for mutants with high acid carboxypeptidase (ACPase) activity from Aspergillus oryzae IFO 4079 (parental strain). We obtained a mutant with ACPase with the activity of 20,000 units · g −1 of koji , about three times that of the parental strain. In mirin -making, koji prepared with this mutant had the same productivity, but the concentration of amino nitrogen in the mirin obtained with this mutant was 1.2–1.4 times that of the parental strain. Results of sensory tests showed that the mirin prepared with koji of the mutant had a good taste on the whole. The degree of clouding In mirin made with glutinous rice steamed at atmospheric pressure was much less with koji of this mutant than that of the parental strain.

Mirin-making using long-life koji with low water content

Abstract In an attempt to store koji longer than is now possible at room temperature, we investigated ways in which to dry it. Dried koji with a water activity ( Aw ) of 0.77 containing 0.11 g of water/g of solid was prepared from fresh koji with an Aw of 0.88 containing 0.39 g of water/g of solid. Drying was found to be more efficient above 50°C. The most suitable conditions were at 55°C under 760 mm Hg of pressure for 5–6 h (Method I) when fresh koji was prepared with crushed rice. This dried koji had 84% or more of the original enzyme activity. Other methods, such as drying at 55°C under 20 mm Hg of pressure for 6 h (Method II), and drying by mixing fresh koji with dried steamed rice powder at 23°C for 24 h (Method III) were also examined. For retaining enzyme activity after drying, Method III was theoretically the best. In practice, however, Method I was found to be efficient and inexpensive. For dried koji made using Method I, the α-amylase and neutral protease activities were 80% and over 90%, respectively, of the baseline values after 6 months of storage at 30°C. The number of bacteria in the dried koji was small, but the number of thermotolerant bacteria was almost unchanged. For mirin manufactured using dried koji which was stored for 4 months, the yield, properties and sensory qualities of the mirin were essentially the same as those obtained using fresh koji .