Quality characteristics and preparing of solid starter using fungal strains for Takju

In this study, we investigated the effect of fermentation conditions on the amylolytic and proteolytic activities of Aspergillus luchuensis strain 74-5 and Aspergillus oryzae strain 75-2, which are used in the preparation of the starter culture, for Takju (Korean traditional rice wine). The starter culture was optimized using different conditions, such as inoculum size, inoculation temperature, and incubation time. The enzyme activities under each condition were measured. In the A. luchuensis strain 74-5 starter culture, the ${\alpha}-amylase$ and glucoamylase activities increased, however the activity of acidic protease decreased as the diluent to starter culture ratio increased. In the A. oryzae 75-2 starter culture, all enzyme activities were maintained at a higher level even at 5% inoculation ratio. Higher enzyme activities were observed in the middle range of inoculation temperature (35, $40^{\circ}C$), than in the lower range (20, $30^{\circ}C$). Enzyme activity in the starter culture varied with incubation time, however it was the highest at 144 and 120 hr, respectively, for A. luchuensis strain 74-5 and A. oryzae strain 75-2. The spore count of the starter culture was approximately $2{\times}10^7$ during fermentation, out of which contamination by aerobic bacteria was about $3{\times}10^3$. The results suggested that the starter culture of each strain could be used as an inoculum for fermentation. However, we needs to conduct further research for the selection of suitable diluting agents as well as drying methods to reduce the contamination by aerobic bacteria, while retaining the enzyme activity.

탁주용 곰팡이 고체종국 제조 및 품질 특성

본 연구에서는 전분 및 단백질 분해력이 우수한 토착 발효종균 Aspergillus luchuensis 74-5 및 Aspergillus oryzae 75-2로 제조한 고체종국의 품질 특성을 조사하였다. 액체종국 접종량 5%와 10% 접종하였을 때, pH는 각각 5.78 및 3.85 이하로, 적정산도는 2.12와 8.54 이상, 아미노산도는 1.15 및 2.66 이상으로 균주에 따라 차이를 보였다. 효소활성의 변화는 발효종균에 따라 증감 패턴이 특징적으로 나타났고, 액국 접종량에 따라 A. luchuensis 74-5는 접종량이 증가할수록 ${\alpha}-amylase$와 glucoamylase 활성은 증가하나 acidic protease활성은 감소하였고, A. oryzae 75-2는 5% 접종하였을 때 모든 효소활성이 가장 높게 나타났다. 발효온도는 저온보다 중온(35, $40^{\circ}C$)에서 효소활성이 우수한 것으로 나타났고, 발효시간은 종균에 따라 차이는 있지만 각각 144시간과 120시간일 때 효소활성이 높은 것으로 나타났다. 발효조건에 따른 고체종국의 포자수는 약 $2.0{\times}10^7$, 세균의 오염은 약 $3.0{\times}10^3$으로 나타났으며, 세균에 의한 오염도 저감화 및 효소활성을 유지하기 위하여, 구연산, 종국의 건조법 및 부형제 등의 추가적인 연구가 필요하다.